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# On a certain transatlantic crossing, 20 percent of a ship's

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Math Expert
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On a certain transatlantic crossing, 20 percent of a ship's [#permalink]

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09 Mar 2014, 15:17
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The Official Guide For GMAT® Quantitative Review, 2ND Edition

On a certain transatlantic crossing, 20 percent of a ship's passengers held round-trip tickets and also took their cars aboard the ship. If 60 percent of the passengers with round-trip tickets did not take their cars aboard the ship, what percent of the ship's passengers held round-trip tickets?

(A) 33 1/3%
(B) 40%
(C) 50%
(D) 60%
(E) 66 2/3%

Problem Solving
Question: 146
Category: Arithmetic Percents
Page: 81
Difficulty: 600

GMAT Club is introducing a new project: The Official Guide For GMAT® Quantitative Review, 2ND Edition - Quantitative Questions Project

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Re: On a certain transatlantic crossing, 20 percent of a ship's [#permalink]

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09 Mar 2014, 15:17
1
5
SOLUTION

On a certain transatlantic crossing, 20 percent of a ship's passengers held round-trip tickets and also took their cars aboard the ship. If 60 percent of the passengers with round-trip tickets did not take their cars aboard the ship, what percent of the ship's passengers held round-trip tickets?

(A) 33 1/3%
(B) 40%
(C) 50%
(D) 60%
(E) 66 2/3%

Let the total # of passengers be 100.

Now, 20 passengers held round-trip tickets AND cars.

As 60% of the passengers with round-trip tickets did not take their cars then 40% of the passengers with round-trip tickets did take their cars, so # of passengers with round-trip tickets AND cars is 40% of the passengers with round-trip tickets.

If we take # of the passengers with round trip tickets to be $$x$$ then we'll have $$0.4x=20$$ --> $$x=50$$.

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Re: On a certain transatlantic crossing, 20 percent of a ship's [#permalink]

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09 Mar 2014, 18:18
Assume total passengers = 100,

So people with round ticket and having cars = 20

These 20 people = 40% of total round ticket holders. So total round ticket holders = 60
% of Round Ticket holders = 60/100 = 60%
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Re: On a certain transatlantic crossing, 20 percent of a ship's [#permalink]

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09 Mar 2014, 19:59
2

Lets say total passengers = 100

Passengers with round ticket & cars = 20

If 60 percent of the passengers with round-trip tickets did not take their cars aboard the ship which means 40% with round trip tickets took cars

40x/100 = 20

x = 50

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tik.jpg [ 23.4 KiB | Viewed 7943 times ]

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Re: On a certain transatlantic crossing, 20 percent of a ship's [#permalink]

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09 Mar 2014, 20:14
2
20% of the passengers were RT passengers with cars aboard. 60% of RT passengers did not bring cars. Thus, 20% of all passengers corresponds to 40% of RT passengers.

r = RT
t = total

2r/5 = t/5

r = 5t/10

= t/2

= 50%

OR 40% = 2(20%). 10% of all passengers are 20% of RT, so 100% of RT are 50% of passengers.
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Re: On a certain transatlantic crossing, 20 percent of a ship's [#permalink]

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09 Mar 2014, 21:09
1
Total Passengers = 100
Both RT and Cars = 20

RT*(1-.6) = 20
RT = 50
RT/Passengers = 50/100

C
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Re: On a certain transatlantic crossing, 20 percent of a ship's [#permalink]

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09 Mar 2014, 21:37
As there are only percents involve here and no numbers, we can assume some comfortable numbers.

Total = 100
Passenger with round trip+ cars = 20% of Total = 20
Passenger with round trip+no car = 60% of round trip

Hence,
20 = 100% of round trip - 60% of round trip = 40% of round trip
Therefore,
roundtrip = 50
which is 50% of Total

Difficulty level 650 (It took me complete 2 mins which I think makes this problem lengthy)
Time Taken 2:00
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Re: On a certain transatlantic crossing, 20 percent of a ship's [#permalink]

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10 Mar 2014, 00:28
1
Option C.
If 60% of passengers with round-trip do not have cars,40% of passengers with round-trip tickets will have their cars on board.
40% of total=20
=50
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On a certain transatlantic crossing, 20 percent of a ship's [#permalink]

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15 Jun 2015, 11:07
1
1
We can solve this problem using Double matrix. Unknown NUmber is here the number of pasengers with round trip tickets - let it be X, then 60% of X = 0,6X
Let the Total be 100, then people with Round Trip Tickets and Cars = 20% of 100 = 20

See the attached screenshot and then solve.

20 + 0,6X = X
X = 50
Attachments

Temp.JPG [ 12.22 KiB | Viewed 5954 times ]

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On a certain transatlantic crossing, 20 percent of a ship's [#permalink]

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05 Jun 2016, 13:59
pepo wrote:
On a certain boat, 20 % of the passengers have round-trip tickets and are trasporting cars. if 60% of the passengers who have round-trip tickets are not transporting cars, what percent of all the passengers have round-trip ticketsOn a certain boat, 20 % of the passengers have round-trip tickets and are trasporting cars. if 60% of the passengers who have round-trip tickets are not transporting cars, what percent of all the passengers have round-trip tickets?

A 40%
B 50%
C 60%
D 70%
E 80%

Let's suppose total customers are 100 and customers who have round-trip tickets are r

if 60% of the passengers who have round-trip tickets are not transporting cars or 40% who have round trips are transporting cars.

i.e. .6r are not transporting cars and .4r are transporting cars.

Its given that 20 % of the passengers have round-trip tickets and are transporting cars (20 out of 100)

.4r=20
r=50%

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Re: On a certain transatlantic crossing, 20 percent of a ship's [#permalink]

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10 Aug 2016, 12:37
1
I have a slight difficulty in understanding the question:
1.On a certain transatlantic crossing, 20 percent of a ship's passengers held round-trip tickets and also took their cars aboard the ship.
2.If 60 percent of the passengers with round-trip tickets did not take their cars aboard the ship, what percent of the ship's passengers held round-trip tickets?

>> So 2nd statement means that 40% have Round trip ticket and also took car.

But in the first sentence it said that percentage of such people who have round trip ticket and brought their cars is 20% ?

How did you guys understand this question ?
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On a certain transatlantic crossing, 20 percent of a ship's [#permalink]

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04 Apr 2018, 04:55
Bunuel wrote:
The Official Guide For GMAT® Quantitative Review, 2ND Edition

On a certain transatlantic crossing, 20 percent of a ship's passengers held round-trip tickets and also took their cars aboard the ship. If 60 percent of the passengers with round-trip tickets did not take their cars aboard the ship, what percent of the ship's passengers held round-trip tickets?

(A) 33 1/3%
(B) 40%
(C) 50%
(D) 60%
(E) 66 2/3%

Problem Solving
Question: 146
Category: Arithmetic Percents
Page: 81
Difficulty: 600

GMAT Club is introducing a new project: The Official Guide For GMAT® Quantitative Review, 2ND Edition - Quantitative Questions Project

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generis, pushpitkc,

do you guys have any tips for overlapping sets ? i need some methodologic approach to solve these type of questions

i dont understand whats wrong with my solution

the only thing I would change in my diagram x-20 into 20-x
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On a certain transatlantic crossing, 20 percent of a ship's [#permalink]

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04 Apr 2018, 06:55
1
dave13 wrote:
Bunuel wrote:
The Official Guide For GMAT® Quantitative Review, 2ND Edition

On a certain transatlantic crossing, 20 percent of a ship's passengers held round-trip tickets and also took their cars aboard the ship. If 60 percent of the passengers with round-trip tickets did not take their cars aboard the ship, what percent of the ship's passengers held round-trip tickets?

(A) 33 1/3%
(B) 40%
(C) 50%
(D) 60%
(E) 66 2/3%

Problem Solving
Question: 146
Category: Arithmetic Percents
Page: 81
Difficulty: 600

GMAT Club is introducing a new project: The Official Guide For GMAT® Quantitative Review, 2ND Edition - Quantitative Questions Project

Each week we'll be posting several questions from The Official Guide For GMAT® Quantitative Review, 2ND Edition and then after couple of days we'll provide Official Answer (OA) to them along with a slution.

We'll be glad if you participate in development of this project:
2. Please vote for the best solutions by pressing Kudos button;
3. Please vote for the questions themselves by pressing Kudos button;
4. Please share your views on difficulty level of the questions, so that we have most precise evaluation.

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generis, pushpitkc,

do you guys have any tips for overlapping sets ? i need some methodologic approach to solve these type of questions

i dont understand whats wrong with my solution

the only thing I would change in my diagram x-20 into 20-x

Hi dave13

Let the ship's passengers who hold round-trip tickets be x
P(Hold round-trip tickets) = x

We are told that 60% of this number did not take their cars
P(Only hold round-trip tickets) = 0.6x
Also, P(Both) = 20%.

If total number of people is 100, P(Both) = 20
P(Hold round-trip ticket) = P(Only hold round-trip tickets) + P(Both)

$$x = 0.6x + 20$$ -> $$x - 0.6x = 20$$ -> $$0.4x = 20$$ -> $$x = \frac{20}{0.4} = 50$$
Therefore, the percentage of ship's passengers who hold round trip tickets is $$\frac{50}{100} = 50$$% (Option C)

Hope this helps you.
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Re: On a certain transatlantic crossing, 20 percent of a ship's [#permalink]

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04 Apr 2018, 12:29
pushpitkc wrote:
dave13 wrote:
Bunuel wrote:
The Official Guide For GMAT® Quantitative Review, 2ND Edition

On a certain transatlantic crossing, 20 percent of a ship's passengers held round-trip tickets and also took their cars aboard the ship. If 60 percent of the passengers with round-trip tickets did not take their cars aboard the ship, what percent of the ship's passengers held round-trip tickets?

(A) 33 1/3%
(B) 40%
(C) 50%
(D) 60%
(E) 66 2/3%

Problem Solving
Question: 146
Category: Arithmetic Percents
Page: 81
Difficulty: 600

GMAT Club is introducing a new project: The Official Guide For GMAT® Quantitative Review, 2ND Edition - Quantitative Questions Project

Each week we'll be posting several questions from The Official Guide For GMAT® Quantitative Review, 2ND Edition and then after couple of days we'll provide Official Answer (OA) to them along with a slution.

We'll be glad if you participate in development of this project:
2. Please vote for the best solutions by pressing Kudos button;
3. Please vote for the questions themselves by pressing Kudos button;
4. Please share your views on difficulty level of the questions, so that we have most precise evaluation.

Thank you!

generis, pushpitkc,

do you guys have any tips for overlapping sets ? i need some methodologic approach to solve these type of questions

i dont understand whats wrong with my solution

the only thing I would change in my diagram x-20 into 20-x

Hi dave13

Let the ship's passengers who hold round-trip tickets be x
P(Hold round-trip tickets) = x

We are told that 60% of this number did not take their cars
P(Only hold round-trip tickets) = 0.6x
Also, P(Both) = 20%.

If total number of people is 100, P(Both) = 20
P(Hold round-trip ticket) = P(Only hold round-trip tickets) + P(Both)

$$x = 0.6x + 20$$ -> $$x - 0.6x = 20$$ -> $$0.4x = 20$$ -> $$x = \frac{20}{0.4} = 50$$
Therefore, the percentage of ship's passengers who hold round trip tickets is $$\frac{50}{100} = 50$$% (Option C)

Hope this helps you.

hi pushpitkc, thanks!

here $$x = 0.6x + 20$$ why do you denote 20 as number and not percent ? 60 and 20 are both percentages ?

do you mind correcting my diagram so as i can see visually what i did wrong ?
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Re: On a certain transatlantic crossing, 20 percent of a ship's [#permalink]

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04 Apr 2018, 23:35
1
dave13 wrote:

hi pushpitkc, thanks!

here $$x = 0.6x + 20$$ why do you denote 20 as number and not percent ? 60 and 20 are both percentages ?

do you mind correcting my diagram so as i can see visually what i did wrong ?

Hey dave13

Attachment:

Diagram.png [ 4.61 KiB | Viewed 919 times ]

Here, we are assuming the total number of passengers to be 100.
However, we have no clarity about the total number of passengers with round-trip tickets(which we are assuming to be x)

60% of the passengers who hold round-trip tickets do not take their cars.
Therefore, the total number of passengers who only have round-trip tickets are 60% of x or $$\frac{60}{100}*x = 0.6x$$

In the diagram, it is clear why P(Hold round-trip ticket) = P(Only hold round-trip tickets) + P(Both)

So, we arrive at the equation x=0.6x+20

Hope that it's clear now!
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Re: On a certain transatlantic crossing, 20 percent of a ship's [#permalink]

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06 Apr 2018, 08:46
1
Bunuel wrote:

On a certain transatlantic crossing, 20 percent of a ship's passengers held round-trip tickets and also took their cars aboard the ship. If 60 percent of the passengers with round-trip tickets did not take their cars aboard the ship, what percent of the ship's passengers held round-trip tickets?

(A) 33 1/3%
(B) 40%
(C) 50%
(D) 60%
(E) 66 2/3%

We can let the number of passengers = 100.

Thus, 20 passengers held round trip tickets and took their cars aboard the ship. Since we are given that 60 percent of the passengers with round-trip tickets did not take their cars aboard the ship, the 20 passengers who held round trip tickets and took their cars aboard the ship represent 40 percent of the passengers with round-trip tickets. If n = the number of passengers with round-trip tickets, we have:

20 = 0.4n

n = 20/0.4 = 200/4 = 50

Thus, 50/100 = 50% of the ship’s passengers held round-trip tickets.

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Re: On a certain transatlantic crossing, 20 percent of a ship's   [#permalink] 06 Apr 2018, 08:46
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Paper ID: 1034 Title: On the Sample Complexity of Subspace Learning
Reviews

Submitted by Assigned_Reviewer_5

Q1: Comments to author(s). First provide a summary of the paper, and then address the following criteria: Quality, clarity, originality and significance. (For detailed reviewing guidelines, see http://nips.cc/PaperInformation/ReviewerInstructions)
Paper Summary:
Authors deal with a fundamental problem of deriving PAC-style rates for subspace estimation using samples. The key result shows for n samples drawn from some underlying distribution, the quality of subspace estimation improves at a rate O(n^-r), where r related to the decay rate of the spectrum of the underlying distribution.

Review:
I am not familiar with the previous literature on PAC-style analysis of subspace learning, or if properties of the spectrum of the covariance was previously considered for subspace learning; so assuming that the work is novel, I believe authors have done a good job in relating these concepts.

I do have a few suggestions that the authors should consider adding to the current text:

Although authors have focused on the theoretical aspects of subspace learning, it would be nice to see how well the condition of ‘polynomial decay’ holds on real world data. This would help with the significance of this work to the larger machine learning audience.

Going a step further, it would be very instructive to see what the rates look like when the covariance C is unknown. That is, is it possible to give the error rate in terms of _observed_ covariance C_n and an empirical decay rate ‘r_n’ (instead of the true covariance C and decay rate r)? This would certainly be helpful when dealing with real data where one only has access to a sample from some underlying measure. I would encourage the authors to at least add a brief discussion on this.

Theorem 3.1 in its current form seems to be for a fixed value of k, again for practical purposes, k is often chosen based on the samples, so perhaps a uniform bound on k would be more useful?

Why suppress the dependence on \delta in Corollary 4.1 and 4.2? I believe it would be more instructive to see the explicit dependence O( log(n/delta)/n ^ …). I would suggest to move the generic rate to the introduction, and give explicit rate with all the constants in the corollaries.

I have to admit that given the short review period, I did not have a chance to check the proofs.

Quality:
This is a theoretical paper, with main proof using concepts from operator theory. Given the short review period, I did not have a chance to verify the proof.

Clarity:
The paper is written clearly.

Originality:
I am not familiar with the past literature, and cannot comment on the originality of this work.

Significance:
Given the ubiquity of subspace finding methods, I believe work is very significant as it provides the finite sample rates for subspace learning.
Although I didn't have chance to check the proofs, if the proofs check out, I believe this work would be a nice paper for the theoretically inclined audience. I do encourage the authors to consider the suggestions made in the review.

Submitted by Assigned_Reviewer_6

Q1: Comments to author(s). First provide a summary of the paper, and then address the following criteria: Quality, clarity, originality and significance. (For detailed reviewing guidelines, see http://nips.cc/PaperInformation/ReviewerInstructions)
The paper derives error estimates for subspace learning under spectral assumptions on covariance operators.

The paper makes a solid impression -- though you have minor things like missing words, inner product symbols, missing axes labels etc which should be corrected.

The problem addressed by the authors is certainly of relevance. And they have a number of findings that seem useful:

- they derive convergence rates for the (truncated) PCA which guarantee with a high probability that the support of the measure is retrieved with an error of ~ n^-(1-1/r) and -r is the exponent of the decay of the eigenvalues of the associated covariance operator

- for support estimation they gain a factor of 3 in the exponent

- they state that their bound is a better predictor for the decay rate c for the expected distance from samples to the inferred sub space estimate.

- they find an estimate from which on the distance of inferred subspace to the real one does not shrink significantly

- would be good to specify the support M in the unit ball B exactly. I guess this just means that rho(H\B) negligible

- or better what is the support M? Should that be like the smallest measurable set M such that H\M is negligible. Does such a set exist or only up to measure zero; I mean nothing big here but would be nice to have an exact definition as M is your main object of investigation.

- eq (2): I would like a bit of an discussion of the parameters alpha and p. Also is there a case beside 1/2,2 that is of relevance, and why?

- directly after eq 2: I guess you mean here closed subspaces so that the projectors are well defined;

- eq (3): here a discussion of the norm/the constant seems needed. The issue is that you don't converge to zero in your leading term but to sigma_k so the constants are not unimportant.

- Thm 3.2: didn't check the details but I'm wondering if this is for a specific k or uniform over all k; I guess the former and it would be good to point this out. Something like "given k" ...

- Cor 3.3 * -> k

A solid paper which derives error rates for subspace learning which improve over state of the art rates.

Submitted by Assigned_Reviewer_9

Q1: Comments to author(s). First provide a summary of the paper, and then address the following criteria: Quality, clarity, originality and significance. (For detailed reviewing guidelines, see http://nips.cc/PaperInformation/ReviewerInstructions)
This paper deals with estimating the subspace on which an unknown sampling distribution is supported. I found the exact problem statement somewhat unclear. Quoting the 2nd paragraph:
<<
Given a measure rho from which independent samples are drawn, we aim to estimate the smallest subspace S_rho that contains the support of rho. In some cases, the support may lie on, or close to, a subspace of lower dimension than the embedding space, and it may be of interest to learn such a subspace S_rho in order to replace the original samples by their local encoding with respect to S_rho.
>>

What I find confusing here is that the support of rho can never be smaller than the sample support. Certainly, the sample points may lie on a strict subspace of the embedding space, but this is trivially discovered (via PCA, for example). What (lossless) dimensionality reduction is possible beyond that? Perhaps you intend to recover an "approximate" support, or an "effective" support, but this needs to be clearly stated early on.

The English is mostly fine but occasionally incorrect usage leads to comprehension problems. In particular, the authors tend to write "it is" instead of "we have that, "it is the case that" or some similar expression. [E.g., lines 084, 158, 233.]

The result are technical and I did not have time to verify their correctness, but they seem plausible. However, the motivation and intuitive explanation is sorely lacking. What is the significance of the particular distance metric you chose? What about the eigenvalue decay condition? Do such conditions hold in practice?
The paper should be rewritten with an eye to clarity, motivation, intuition, grammar.

Submitted by Meta_Reviewer_2

Q1: Comments to author(s). First provide a summary of the paper, and then address the following criteria: Quality, clarity, originality and significance. (For detailed reviewing guidelines, see http://nips.cc/PaperInformation/ReviewerInstructions)
The paper deals with the problem of linear subspace estimation from samples, which appears in many applications such as PCA, kernel PCA and support estimation. The main contribution of the paper is that it provides a general formulation for the problem of subspace estimation and provides learning rates assuming certain decay behaviour for the eigenvalues of the covariance operator associated with the data distribution. As special cases, learning rates are provided for PCA and support estimation improving upon the existing results.

Clarity: While the paper is technically interesting, the motivation presented in Section 1 is not clear. The paper is more of a technical exercise and lacks intuitive explanation. A better approach would have been to introduce the PCA problem (as discussed in Section 4.1) in Section 2 or may be even elaborate it in Section 1 so that the reader is introduced to the operator theoretic interpretation of PCA. With this motivation, one can generalize this notion as it is done in Section 2. I think this will improve the readability of the paper. As a minor comment, there are few typos, e.g., usage of "it is", which need to be fixed.

Originality and Significance: The paper is technically interesting and is mathematically correct.

1. In the paragraph below Eq. 2, it is mentioned that d_{\alpha,p} is a metric for 0\le\alpha\le 1/2 and 1\le p\le\infty. However, in Proposition D.1 says that it is also a metric for 1/2\le \alpha\le 1. Its not clear why this restriction to 0\le\alpha\le 1/2? I dont see that such a restriction is needed at least at this point.

2. In the proof of Proposition D.1, it is mentioned that S_\rho=Ran C. Isn't it the closure of Ran C by Proposition D.3?

3. As mentioned above, it will be better to motivate the work through PCA and use proposition D.4 to motivate Eq. 2. While one might wonder are there any interesting values of \alpha and p other than 1/2 and 2, then you can present the application of set estimation where \alpha and p take values other than these.

4. In theorem 3.2, corollary 3.3 and remark 3.4, it is not mentioned that \alpha > 1/(rp). Without this condition, the estimator will not be consistent. This means for a fixed \alpha, p > 1/(r\alpha) which means the results do not hold for all 0\le p\le \infty as mentioned in the statements. Similar is the case with $\alpha$ where for a fixed p, the results hold only for \alpha > 1/(rp), or it should be assumed that r > max(1,1/(p\alpha))

5. Line 126: postponed to "Section 7"

6. The discussion about the non-requirement of regularizer from a statistical view point is not clear. Can you please elaborate what is making the difference compared to [11], that the proposed formulation does not require a regularizer even from statistical point of view. It is clear that some regularizer is needed for numerical stability but the lack of it is surprising from statistical sense.

7. While the proof technique is interesting and non-trivial, it appears that one can just do the entire analysis with p=2, i.e., Hilbert-Schmidt norm. Since the Schatten p-norm is a p-norm of the sequence of singular values (which can be countable in number as the operators considered are compact), it easy to check that ||A||_q\le ||A||_p for any 0 < p < q\le infty (because of the inclusion of l^p space in l^q). This means the analysis can simply by carried out using p=2 for any while bouding ||A||_p for any p\ge 2. This means classical Bernstein's inequality in Hilbert spaces can be used without needing sophisticated tools like Theorem B.1. Similarly for the case with 1\le p\le 2, one can bound ||A||_p by ||A||_1 in deriving from (14) onwards where one can use Holder and convert the analysis into bounding HS norms of certain operators.

While I do not find anything wrong the current analysis and it is indeed nice, I am just wondering whether one needs the approach used in the paper to get sharp rates or one can still get such rates using the above mentioned analysis using HS norms. If one really needs the approach used in the paper to get sharp rates, this has to be highlighted along with a possible reason showing where HS approach fails.
A general formulation for the problem of learning subspace from samples is proposed along with learning rates under certain conditions on the spectrum of the covariance operator associated with the data distribution. The paper is theoretically interesting, mathematically correct and provides sharper learning rates for PCA and spectral support estimation. However, the clarity and organization of the paper has to be improved along with providing intuitive explanation of the theoretical results.
Author Feedback

Q1:Author rebuttal: Please respond to any concerns raised in the reviews. There are no constraints on how you want to argue your case, except for the fact that your text should be limited to a maximum of 6000 characters. Note however that reviewers and area chairs are very busy and may not read long vague rebuttals. It is in your own interest to be concise and to the point.
* "I am wondering whether one needs the approach used in the paper to get sharp rates or one can still get such rates [...]

using classical Bernstein's inequality[...] without sophisticated tools like Theorem B.1"

While this approach would simplify the analysis, it produces looser bounds.
In particular, for p=2, alpha=1/2, and a decay rate r=2 (as in the example in the paper), it would be:

d_{1/2,2}(S_ρ,S_n) = O(n^{-1/4}) (using Theorem B.1)
d_{1/2,2}(S_ρ,S_n) = O(n^{-1/6}) (using Bernstein inequalities)

By using classical Bernstein inequalities in Hilbert spaces (e.g. Pinelis),
Lemma 7.2 would result in a range for t of q n^{-r/(r+1)} <= t <= ||C||,
implying k* = O(n^{1/(r+1)}) (instead of O(n^{1/r})), and thus Theorem 3.2 for k>=k* would become
d_{\alpha,p}(S_ρ,S^k_n) = O(n^{-alpha*r/(r+1) + 1/(p*(r+1))}) (compared with the sharper O(n^{-\alpha + 1/rp}) of Thm 3.2).

* "In theorem 3.2, corollary 3.3 and remark 3.4, it is not mentioned that \alpha > 1/(rp). Otherwise, the estimator wont be consistent."

This is an important observation that will be clarified in the text.
We note that this condition is not a restriction on the validity of the bound,
but is necessary for the subspace-learning problem to be feasible

(indeed, if \alpha <= 1/(rp) then |C^\alpha|_p = infty, and thus d_{\alpha,p}(S_ρ,S_n) = |(P - P^k_n)C^\alpha|_p = infty).

* "Can you please elaborate what is making the difference compared to [11], that the proposed formulation does not require a regularizer even from statistical point of view."

The work of [11] proves a U-shaped upper bound for d_{(r-1)/(2r),\infty}.
The bound's minimum converges to 0 (with n->\infty), but its value at k=n does not converge to 0.
Therefore, a form of regularization is needed to ensure consistency.
Our bound is instead L-shaped (no trade-off), and consistency is ensured for k=n whenever \alpha > 1/(rp).

* "Th. 3.1 in its current form seems to be for a fixed value of k[...], so perhaps a uniform bound on k would be more useful?"

As pointed out by the reviewer, one may in practice choose k based on the data, and a bound reflecting such a choice may be useful. We address this next.

* "[...]is it possible to give the error rate in terms of _observed_ covariance C_n and an empirical decay rate 'r_n'?"

The reviewer suggests an extension to the work in which the bound depends only on information that can be obtained from the sample data.
Our preliminary work in this direction indicates that it does seem to be possible to produce such a bound.

* One of the reviewers suggests moving some of the descriptions currently in section 4.1 earlier to sections 1 and 2, in order to further clarify the motivation

format: plain


text:
HAL will be down for maintenance from Friday, June 10 at 4pm through Monday, June 13 at 9am. More information

# Efficient Learning in Games

1 MAIA - Autonomous intelligent machine
INRIA Lorraine, LORIA - Laboratoire Lorrain de Recherche en Informatique et ses Applications
Abstract : We consider the problem of learning strategy selection in games. The theoretical solution to this problem is a distribution over strategies that responds to a Nash equilibrium of the game. When the payoff function of the game is not known to the participants, such a distribution must be approximated directly through repeated play. Full knowledge of the payoff function, on the other hand, restricts agents to be strictly rational. In this classical approach, agents are bound to a Nash equilibrium, even when a globally better solution is obtainable. In this paper, we present an algorithm that allows agents to capitalize on their very lack of information about the payoff structure. The principle we propose is that agents resort to the manipulation of their own payoffs, during the course of learning, to find a game'' that gives them a higher payoff than when no manipulation occurs. In essence, the payoffs are considered an extension of the strategy set. At all times, agents remain rational vis-à-vis the information available. In self-play, the algorithm affords a globally efficient payoff (if it exists).
Keywords :
Document type :
Conference papers
Complete list of metadata

Cited literature [11 references]

https://hal.inria.fr/inria-00102188
Contributor : Alain Dutech Connect in order to contact the contributor
Submitted on : Friday, September 29, 2006 - 1:49:16 PM
Last modification on : Wednesday, February 2, 2022 - 3:51:42 PM
Long-term archiving on: : Tuesday, April 6, 2010 - 1:17:27 AM

### Identifiers

• HAL Id : inria-00102188, version 1

### Citation

Raghav Aras, Alain Dutech, François Charpillet. Efficient Learning in Games. Conférence Francophone sur l'Apprentissage Automatique - CAP 2006, 2006, Trégastel, France. ⟨inria-00102188⟩

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text:
## April 1st special: The War of the Worlds

Conrad Barski has posted a sneak peak from his upcoming Lisp textbook/comic: Land of Lisp.

The first slides may seem unrelated, but boy does the message sting when you reach the ending...

FPers will be quick to note, of course, that this being April Fools' Day the whole thing is a joke and we can all go back to Haskell...

## Comment viewing options

### Purity, where is thy sting?

I can't help noticing that the comic's observations about purity miss the point. A better accusation against the defendants would be "guilty of having undeclared side effects". Which of course Haskell also allows, with unsafePerformIO.

As a number of Haskellers have observed, Haskell makes a fine imperative language — "the world's finest imperative language", according to Erik Meijer. It only asks that, ideally, you annotate the type of imperative functions - confess their sins, as it were. (Please, no yellow sleeve patches in future comics.) This would seem to satisfy the wizard's desire that "We just believe that everyone should have the right to cause side effects if they really want them."

Of course, the classic complaint is that combining purity with a fully static type system introduces the dreaded (to a Lisper) B&D style of programming. But defending undeclared side effects seems like the harder sell. At the end of that road is ninja patching.

### True enough. At various

True enough. At various points I thought that the target is going to be Ada (the language most often accused of being a B&D language), even though I knew better.

### This Comic has been Interpreted...

...as more critical of Haskell than I intended- The Lisp guys in the cartoon are pretty bumbling and their offhanded complaints of "why box yourself in with Haskell" isn't really a meaningful critique of Haskell. Note that they are responsible for creating a propaganda movie of Haskell and that their use of unsafe coding techniques apparently killed the cat at the end of the cartoon :)

A serious critique of the Monadic approach of Haskell is possible but I agree my comic doesn't contain it.

### But hey, wasn't Haskell an

But hey, wasn't Haskell an elaborate prank all along?!

### Actually...

Actually, this is how I interpreted the comic, but I was sort of afraid to say so...

In any case, a world divided between Lisp and Haskell would be a big step forward. :)

### Maybe voters prefer bumblers?

I was really responding to Ehud's point about the message stinging, but that was based on an assumption about the bit that stung.

I did notice the propaganda-film within propaganda-comic aspect, but to me the bumbling obviousness of the wizard appears more benign than the portrayed totalitarianism of the other side. The wizard's approach may kill the odd cat, but he means well and isn't really scary. That might explain the interpretations you've seen.

### I was just making sure

I was just making sure people read through to the end.

### Good point

It may also explain why people persist in preferring Lisp. ;)

### Not scary?

Check out this little Scheme program by Matthias Felleisen. It's got mutually-recursive self-modifying higher-order procedures that use call-cc! That is totally wicked cool, but "isn't really scary" is not how I'd describe it. :)

### Nice! But call/cc isn't

Nice!

But call/cc isn't scary. What I find scary in Scheme are type errors that manifest themselves late in the life cycle...

### Category mismatch

I was talking about the behavior of the characters in the comic! Any resemblance to real programming languages appears to be entirely coincidental.

[P.S. Besides, a true Scheme wizard would not be nearly as blasÃ© about side effects as the comic's wizard.]

### "the world's finest imperative language"

Going off on a tangent here... Haskell people often say this bit about it being the finest imperative language, but as much as I love Haskell, I'm not sure I agree with it.

Monads are cool and important for a lot of reasons, but the way they are used in Haskell to model effects doesn't seem to be ideal to me. As long as your code does only one kind of effect, everything is fine. But what if you want to use state and IO in the same function? Ok, you use monad transformers, but this already feels somewhat clumsy and awkward. If there are more than two effects, well, good luck, it's going to be a fun ride.

So ok, you can say that you should never use more than two effects in the same function, and avoid to use more than one. I don't know if this is reasonable. Also, having to lift all your functions to work in monads is a bit boring too.

I don't like invisible side-effect very much, like in ML languages that you can "hide" a side-effect inside what seems like a pure function, but the current Haskell way of using monads may not be the end of the story. I hope it's not, at least.

### You need a type system that

You need a type system that handles effects. (For some reason this became clear to me the other day in the shower when I was adjusting the water temperature and reaching for the soap at the same time...)

### I think there are advantages

I think there are advantages to a functional encoding of effects (e.g. with monads) over building the effects into your logic/type system (recently Disciple or Separation Logic). It makes the core of your language simpler and is generally more powerful (at least seems so to me - how do you use an effect system to implement software transactional memory?)

I agree with Andrei that Haskell is presently far from ideal as an imperative language, and the (relative) ease with which you can do some hard things (e.g. custom interpretation of monads) is often overshadowed by the difficulty of doing things that would be simple in a conventional imperative language. (EDIT: The newtype deriving stuff Derek concurrently posted about does make the situation much better - but it's still far from ideal IMO)

### STM is a language change

How do you use monads to implement STM? The language has to change, in Haskell they used monads as a notational device for STM but the semantics of the language was extended. Of course you can implement STM in Haskell without changing the semantics of the language, it is turing complete, but the same can be done in (turing complete) languages with effect systems. Other thing to notice is that monads are a device available to any programming language, it's just a data type and the do-notation is just syntatic sugar. For example, Disciple can have a Monad class and use return and >= instead, with a special main that interprets the built monad and builds the effects. If the given monad uses control effects it will require additional interpretation (IIUC Disciple only tracks state-like effects, not things like shift/reset or retry from STM).

### IIRC, monad is a term like

IIRC, monad is a term like group that is abused by convention. That is, it formally refers to a mathematical structure consisting of a set and some operations, but is often used to refer to just the set. That the monadic structure is explicitly identified with a typeclass in Haskell is irrelevant to most everything we're discussing here.

The relevant bit is that the operations on e.g. IO are not presented as side-effects to special functions that need a special type (effect) system to describe, but rather are presented in terms of the functional behavior of your code (i.e. the types of the continuations you pass in).

Whether or not STM requires a change to the underlying semantics of your language depends on what language you're talking about. If you already have state and some basic concurrency primitives, then you should be able to roll it yourself I think.

### Semantics semantics

Maybe pedantic, but I also think you have to be careful to define 'semantics' to be able to say that you require a semantic change to implement e.g. concurrency. A language will have an 'internal semantics' that merely maps programs to their functional behavior without assigning any external meaning to IO, producing values polymorphic in runtime interpretation. This semantics doesn't require change.

### Bathtub insights...

A very Archimedean moment!

If you want to use more than two effects you simply use monad transformers again. Nowadays with GHC's newtype deriving and the MonadState/MonadReader/etc. classes, it's pretty much free to do this however many effects you want. For example, from XMonad we have,

newtype X a = X (ReaderT XConf (StateT XState IO) a)

This demonstrates using three "effects" at a time (in a particularly common arrangement no less). This automatically does all the lifting of functions except for the IO ones since they are not parameterized; however, liftIO is automatically created so you can lift an IO computation into an X one without needing to know how many layers there are.

If another monad "layer" was added, absolutely nothing would need to change except the "runX" function, though you'd probably add MonadFoo to the deriving clause.

Using more than two effects is not at all uncommon and, nowadays, is exactly as difficult as using two, which not at all hard. One of my earliest Haskell programs used a monad "stack" four or five levels deep (and this was way before newtype deriving).

In a nutshell, nowadays, monad transformers are no harder to use than monads themselves and are handled in a way that have rather good software engineering properties. Are there better ways of handling effects (in an explicit manner)? Possibly, probably even. Could even Haskell's usage of monads be improved? Yes, but it is very clear that this has been thought about and dealt with with the weight of years of experience.

Ok, you use monad transformers, but this already feels somewhat clumsy and awkward.

I am new to Haskell, but my experience with Monad Transformers was so far smooth. I too found the "lift" count a horrible way to denote which monad in the stack I want to use, and the MonadIO and other such classes quite ad-hoc.

My monad stack was for GUI code, and had a "ReaderT" for the GUI's environment, a StateT for the GUI state, and a StateT to represent the model the gui is editing.

I had: liftModel, liftGuiState and liftEnvironment (actually I only had getEnv because that's the only thing I'd do with the environment).

This makes the code very reasonable, e.g: liftGuiState State.modify modifier...

It does mean that each monad transformer comes with a short boilerplate (specifying the lifters, and a MonadTrans instance), but so far it does not seem like a big deal. Perhaps some new syntax or otherwise novel approach can get rid of that boilerplate too.

### This comic is offensive to

This comic is offensive to Haskell and must be taken down. I have started a petition to remove the insulting comic and I hope you will support freedom by signing it.

### Chronological discrepancy

Should I adjust the timestamp on your comment for those of us east of Pacific time? ;)

### great comic!

That was actually funny! And with a surprise ending!
That's all

### Zap

It was neat to see Flakey Foont and Mr. Natural on a programming adventure, but Crumb's really let his crosshatching go.

### every day

every day is april 1, from now on, until conditions change.

### I don't believe you

I don't believe you-- your post was clearly time-stamped 2008-04-02, which according to you is April 1st. Also, this statement is false. That is all.

### truth is

i've realized i do actually love big brother. (2+2=5 if you look at it right).

One must keep in mind that monad transformers simply lack
expressiveness and fundamentally inefficient. First of all, the order
of effects may matter: when adding transformers for the state and the
backtracking effects, the order matters a great deal. Sometimes we
need both persistent and backtrackable state, so we need two instances
of StateT. We distinguish them via the number of 'lift' operations --
using unary notation. This is error prone, inconvenient let
alone just ridiculous. One should also keep in mind that each layer
present even in the code that does not use that particular
effect. Please contrast with OCaml: a code that does not use mutation
or backtracking can be compiled without any knowledge of mutations and
backtracking. In contrast, a monadic code that does no State or
backtracking operation still has to thread the state throughout, even
if that piece of code does nothing with the state.

The most serious problem with monad transformers is that they simply
lack expressiveness. Monad transformers impose a fixed ordering of
effects, which is not sufficient in practice. Our paper on Delimited
Dynamic Binding (ICFP06) discusses the issue and points to Haskell
code. That lack of expressiveness was quite surprising to us when we
realized it. Incidentally, this result helps explain the popularity of
powerful flat monads, such as IO.

I think there are advantages to a functional encoding of effects
system (recently Disciple or Separation Logic). It makes the core of
your language simpler and is generally more powerful

The more powerful claim is provably false. Please see the works of
Filinski and Wadler, Thiemann. In general, type-and-effect systems are
transformers, you provably lose power.

As to simplicity, it seems that the unending stream of monad tutorials
explaining once again what is essentially a functional composition (or
the A-normal form, to be more precise) points out that perhaps the
concept of a Monad isn't at all a good match for a programming
language practice. Monads may be deeply rooted in Category Theory --
but then Peano numerals are too have the clearest mathematical
foundations and yet nobody seriously proposes to use them for
practical numerical computations.

I'm extremely delighted to see the work by Ben Lippmeier. Finally
someone answers the call Filinski made back in 1994, in his paper
especially the paragraph starting with the phrase But surely there
is more to "functional programming with escape and state" than monadic
effects. After all, monads provide only the lowest-level framework for
sequencing computations.'' I'm anxiously looking forward to the
further development of The Disciplined Disciple Compiler.

how do you use an effect system to implement software
transactional memory?

Very easily: the function atomically takes a thunk whose type dictates
that the thunk may not do any observable effect. If the thunk needs to
access or modify a global variable, it has to ask (using
continuations, for example) the operating system', the central
arbiter. The arbiter decides on the appropriate policy, be it
optimistic or pessimistic. Please see the Zipper File System, which is
transactional naturally.

### Thanks for the detailed

Thanks for the detailed reply, Oleg. I'm actually aware of much of the work you cite, including (some of) Wadler and Filinski's work and your own IFCP06 paper. I deliberately advocated a 'functional encoding (e.g. monads)' so as not to limit my meaning to what Haskell currently does (I even made reference to the current situation in Haskell being far from ideal elsewhere in this thread).

One must keep in mind that monad transformers simply lack
expressiveness and fundamentally inefficient.

I think there are two separate issues here:
1. How effectful capabilities are presented? Are effects modeled in terms of their functional behavior, or are they treated specially as something outside of the language?
2. How are they implemented? e.g. Is state implemented by threading values along?

The implementation issue is clear cut. You can't simulate state or multi-processing without gross inefficiency. And it doesn't even make sense to simulate effects like IO with pure functions when the effects are the entire purpose.

The more powerful claim [comparing a functional encoding to an effect system] is provably false...

Well, certainly if you get to choose what I meant by powerful ;).

how do you use an effect system to implement software
transactional memory?

Very easily: the function atomically takes a thunk whose type dictates
that the thunk may not do any observable effect. If the thunk needs to
access or modify a global variable, it has to ask (using
continuations, for example) the operating system', the central
arbiter.

In other words, you go back to a functional interface for this part? Suppose you have a system that was written with very modest atomicity requirements - it just had to verify that atomic blocks were in fact atomic. So it was written in an effectful style, with 'beginAtomic' and 'endAtomic' producing effects that just manipulated counters in memory. How do you now provide implementations of 'beginAtomic' and 'endAtomic' that implement STM without changing their interfaces?

I don't see how to do that with effects. This is the sense in which I suspect monadic style to be more powerful - it's more resilient to reinterpretation.

### Drawbacks may be overstated

One must keep in mind that monad transformers simply lack
expressiveness and fundamentally inefficient. First of all, the order
of effects may matter: when adding transformers for the state and the
backtracking effects, the order matters a great deal. Sometimes we
need both persistent and backtrackable state, so we need two instances
of StateT.

Picking the ordering certainly takes a little getting used to, though I've found a suitable intuition that I'm quite happy with[1]. The example of two instances of StateT strikes me as a feature rather than a bug though: I have no desire to be limited to only one form of state, or to hand-fuse its implementation with the rest of my side-effects!

We distinguish them via the number of 'lift' operations --
using unary notation.

I have to admit that this irritated me the first time I built a monad out of a number of transformers. After writing multiply-lifted versions of a few functions I decided it might just be an idea to name the layers on the stack and write accessor functions equal to an appropriate number of composed lifts - it's never been a problem since.

One should also keep in mind that each layer
present even in the code that does not use that particular
effect. Please contrast with OCaml: a code that does not use mutation
or backtracking can be compiled without any knowledge of mutations and
backtracking. In contrast, a monadic code that does no State or
backtracking operation still has to thread the state throughout, even
if that piece of code does nothing with the state.

This is certainly the case given a typical implementation and naive compilation (though it can be argued that OCaml compilation is always aware of mutation!), and I have to admit that at present I don't entirely trust GHC to optimise it appropriately. That said, we are talking about highly stylised code and it should definitely be possible to eliminate much of the overhead. Indeed, it can be argued that the basic idea behind Boquist's GRIN is to implement a lazy language by building a (restricted) lazy monad on top of a (restricted) strict monad, then inlining the lazy monad away and letting rip on the resulting code.

The most serious problem with monad transformers is that they simply
lack expressiveness. Monad transformers impose a fixed ordering of
effects, which is not sufficient in practice. Our paper on Delimited
Dynamic Binding (ICFP06) discusses the issue and points to Haskell
code. That lack of expressiveness was quite surprising to us when we
realized it. Incidentally, this result helps explain the popularity of
powerful flat monads, such as IO.

It really shouldn't be a surprise - the issue is simply that you have two effects whose interaction in each others' presence is non-trivial and needs to be specified in terms of the other effect. As such, a full specification of the effects is mutually recursive! It then follows that we can't build them individually without the use of a letrec-like construct or an appropriate combinator to put them together - the only reason it is surprising is that our (yes, mine included) thinking about effects and constructs such as monads is still partly-formed and otherwise obvious things are therefore hidden from our view.

This isn't an issue with monad transformers at all - it's an issue with combining effects under an open-world assumption where new effects can be defined by a user. To put it another way, the issue comes not from the encoding but from the problem domain! It's not, however, an actual loss of expression so long as a monad transformer can be written offering the appropriate combination of effects. Rather, it's a net gain on the flat monad - an effect's extent is delimited by the function running its corresponding monad transformer.

As the paper points out, the effects could still be encoded as a stack of transformers - one per delimiter - though a static stack is not sufficient. This raises a question: can we maintain a suitable dynamic stack (whether of monad transformers or something merely related) and present it as one transformer from the outside while handing out references to layers on the inside?

I think there are advantages to a functional encoding of effects
system (recently Disciple or Separation Logic). It makes the core of
your language simpler and is generally more powerful

The more powerful claim is provably false. Please see the works of
Filinski and Wadler, Thiemann. In general, type-and-effect systems are
transformers, you provably lose power.

You haven't shown a loss of power above - is there a result I'm unaware of?

As to simplicity, it seems that the unending stream of monad tutorials explaining once again what is essentially a functional composition (or the A-normal form, to be more precise) points out that perhaps the concept of a Monad isn't at all a good match for a programming language practice. Monads may be deeply rooted in Category Theory -- but then Peano numerals are too have the clearest mathematical foundations and yet nobody seriously proposes to use them for practical numerical computations.

That wasn't the value of simplicity being used in the comment quoted.

I'm extremely delighted to see the work by Ben Lippmeier.

I'm definitely looking forward to playing with it some - though I'm looking to use such a language as an underlying metalanguage rather than directly managing all my effects in it.

[1] Imagine you're playing, say, a board game. There are many rules, and on occasion as stated they may conflict (this is equivalent to effect interaction). As a means of resolving the conflict, they have been numbered - lower numbered rules take priority.

The monad transformer stack is a collection of rules, and the monad on the bottom of it is item 0 (this is why there's no IOT - however powerful your language, it can't produce programs that override the laws of physics!).


text:
A debt of $4500 due in 3 years and$6000 due in 5 years is to be repaid by a single payment of $1... 1 answer below » A debt of$4500 due in 3 years and $6000 due in 5 years is to be repaid by a single payment of$1000 now and two equal payments that are due each consecutive years from now. If the interested rate is 6% compounded annually how much are each of the equal payments?

A single payment is of \$_______


text:
fiftyone.core.odm.sample¶

Backing document classes for fiftyone.core.sample.Sample instances.

Class hierarchy:

SerializableDocument
├── NoDatasetSampleDocument
└── DatasetSampleDocument
├── my_custom_dataset
├── another_dataset
└── ...

Implementation details

When a new fiftyone.core.sample.Sample is created, its _doc attribute is an instance of NoDatasetSampleDocument:

import fiftyone as fo

sample = fo.Sample()
sample._doc  # NoDatasetSampleDocument

When a new fiftyone.core.dataset.Dataset is created, its _sample_doc_cls attribute holds a dynamically created subclass of DatasetSampleDocument whose name is the name of the dataset’s sample collection:

dataset = fo.Dataset(name="my_dataset")
dataset._sample_doc_cls  # my_dataset(DatasetSampleDocument)

When a sample is added to a dataset, its _doc attribute is changed from type NoDatasetSampleDocument to type dataset._sample_doc_cls:

dataset.add_sample(sample)
sample._doc  # my_dataset(DatasetSampleDocument)

Classes:

 DatasetSampleDocument(*args, **values) Base class for sample documents backing samples in datasets. NoDatasetSampleDocument(**kwargs) Backing document for samples that have not been added to a dataset.
class fiftyone.core.odm.sample.DatasetSampleDocument(*args, **values)

Base class for sample documents backing samples in datasets.

All fiftyone.core.dataset.Dataset._sample_doc_cls classes inherit from this class.

Attributes:

 STRICT collection_name field_names filepath A unicode string field. id An Object ID field. in_db Whether the document has been inserted into the database. media_type metadata A field that stores instances of a given type of fiftyone.core.odm.BaseEmbeddedDocument object. pk Get the primary key. tags A list field that wraps a standard Field, allowing multiple instances of the field to be stored as a list in the database.

Methods:

 add_field(path, ftype[, embedded_doc_type, …]) Adds a new field or embedded field to the document, if necessary. add_implied_field(path, value[, …]) Adds the field or embedded field to the document, if necessary, inferring the field type from the provided value. cascade_save(**kwargs) Recursively save any references and generic references on the document. Hook for doing document level data cleaning (usually validation or assignment) before validation is run. clear_field(field_name) Compares the indexes defined in MongoEngine with the ones existing in the database. Returns a deep copy of the document. create_index(keys[, background]) Creates the given indexes if required. delete([signal_kwargs]) Delete the Document from the database. Drops the entire collection associated with this Document type from the database. ensure_index(key_or_list[, background]) Ensure that the given indexes are in place. Checks the document meta data and ensures all the indexes exist. fancy_repr([class_name, select_fields, …]) Generates a customizable string representation of the document. field_to_mongo(field_name) field_to_python(field_name, value) from_dict(d[, extended]) Loads the document from a BSON/JSON dictionary. Loads the document from a JSON string. get_field(field_name) get_field_schema([ftype, embedded_doc_type, …]) Returns a schema dictionary describing the fields of this document. Get text score from text query has_field(field_name) Returns an iterator over the (name, value) pairs of the public fields of the document. Lists all indexes that should be created for the Document collection. merge(doc[, merge_lists, merge_dicts, overwrite]) Merges the contents of the given document into this document. merge_field_schema(schema[, expand_schema, …]) Merges the field schema into this document. modify([query]) Perform an atomic update of the document in the database and reload the document object using updated version. register_delete_rule(document_cls, …) This method registers the delete rules to apply when removing this object. reload(*fields, **kwargs) Reloads all attributes from the database. save([validate, clean, safe]) Saves the document to the database. select_related([max_depth]) Handles dereferencing of DBRef objects to a maximum depth in order to cut down the number queries to mongodb. set_field(field_name, value[, create, …]) switch_collection(collection_name[, …]) Temporarily switch the collection for a document instance. switch_db(db_alias[, keep_created]) Temporarily switch the database for a document instance. Returns an instance of DBRef useful in __raw__ queries. to_dict([extended]) Serializes this document to a BSON/JSON dictionary. to_json([pretty_print]) Serializes the document to a JSON string. to_mongo(*args, **kwargs) Return as SON data ready for use with MongoDB. update(**kwargs) Performs an update on the Document A convenience wrapper to update(). validate([clean]) Ensure that all fields’ values are valid and that required fields are present.

Classes:

 my_metaclass alias of mongoengine.base.metaclasses.TopLevelDocumentMetaclass
id

An Object ID field.

Parameters
• description (None) – an optional description

• info (None) – an optional info dict

filepath

A unicode string field.

Parameters
• description (None) – an optional description

• info (None) – an optional info dict

tags

A list field that wraps a standard Field, allowing multiple instances of the field to be stored as a list in the database.

If this field is not set, its default value is [].

Parameters
• field (None) – an optional Field instance describing the type of the list elements

• description (None) – an optional description

• info (None) – an optional info dict

metadata

A field that stores instances of a given type of fiftyone.core.odm.BaseEmbeddedDocument object.

Parameters
• document_type – the fiftyone.core.odm.BaseEmbeddedDocument type stored in this field

• description (None) – an optional description

• info (None) – an optional info dict

property media_type
STRICT = False
classmethod add_field(path, ftype, embedded_doc_type=None, subfield=None, fields=None, description=None, info=None, expand_schema=True, recursive=True, validate=True, **kwargs)

Adds a new field or embedded field to the document, if necessary.

Parameters
Returns

True/False whether one or more fields or embedded fields were added to the document or its children

Raises

ValueError – if a field in the schema is not compliant with an existing field of the same name

classmethod add_implied_field(path, value, expand_schema=True, dynamic=False, recursive=True, validate=True)

Adds the field or embedded field to the document, if necessary, inferring the field type from the provided value.

Parameters
• path – the field name or embedded.field.name

• value – the field value

• expand_schema (True) – whether to add new fields to the schema (True) or simply validate that the field already exists with a consistent type (False)

• dynamic (False) – whether to declare dynamic embedded document fields

• recursive (True) – whether to recursively add embedded document fields

• validate (True) – whether to validate the field against an existing field at the same path

Returns

True/False whether one or more fields or embedded fields were added to the document or its children

Raises

ValueError – if a field in the schema is not compliant with an existing field of the same name

cascade_save(**kwargs)

Recursively save any references and generic references on the document.

clean()

Hook for doing document level data cleaning (usually validation or assignment) before validation is run.

Any ValidationError raised by this method will not be associated with a particular field; it will have a special-case association with the field defined by NON_FIELD_ERRORS.

clear_field(field_name)
property collection_name
classmethod compare_indexes()

Compares the indexes defined in MongoEngine with the ones existing in the database. Returns any missing/extra indexes.

copy()

Returns a deep copy of the document.

Returns

a SerializableDocument

classmethod create_index(keys, background=False, **kwargs)

Creates the given indexes if required.

Parameters
• keys – a single index key or a list of index keys (to construct a multi-field index); keys may be prefixed with a + or a - to determine the index ordering

• background – Allows index creation in the background

delete(signal_kwargs=None, **write_concern)

Delete the Document from the database. This will only take effect if the document has been previously saved.

Parameters
• signal_kwargs – (optional) kwargs dictionary to be passed to the signal calls.

• write_concern – Extra keyword arguments are passed down which will be used as options for the resultant getLastError command. For example, save(..., w: 2, fsync: True) will wait until at least two servers have recorded the write and will force an fsync on the primary server.

classmethod drop_collection()

Drops the entire collection associated with this Document type from the database.

Raises OperationError if the document has no collection set (i.g. if it is abstract)

classmethod ensure_index(key_or_list, background=False, **kwargs)

Ensure that the given indexes are in place. Deprecated in favour of create_index.

Parameters
• key_or_list – a single index key or a list of index keys (to construct a multi-field index); keys may be prefixed with a + or a - to determine the index ordering

• background – Allows index creation in the background

classmethod ensure_indexes()

Checks the document meta data and ensures all the indexes exist.

Global defaults can be set in the meta - see Defining documents

By default, this will get called automatically upon first interaction with the Document collection (query, save, etc) so unless you disabled auto_create_index, you shouldn’t have to call this manually.

Note

You can disable automatic index creation by setting auto_create_index to False in the documents meta data

fancy_repr(class_name=None, select_fields=None, exclude_fields=None, **kwargs)

Generates a customizable string representation of the document.

Parameters
• class_name (None) – optional class name to use

• select_fields (None) – iterable of field names to restrict to

• exclude_fields (None) – iterable of field names to exclude

• **kwargs – additional key-value pairs to include in the string representation

Returns

a string representation of the document

property field_names
field_to_mongo(field_name)
field_to_python(field_name, value)
classmethod from_dict(d, extended=False)

Loads the document from a BSON/JSON dictionary.

Parameters
• d – a dictionary

• extended (False) – whether the input dictionary may contain serialized extended JSON constructs

Returns

a SerializableDocument

classmethod from_json(s)

Loads the document from a JSON string.

Returns

a SerializableDocument

get_field(field_name)
classmethod get_field_schema(ftype=None, embedded_doc_type=None, include_private=False)

Returns a schema dictionary describing the fields of this document.

If the document belongs to a dataset, the schema will apply to all documents in the collection.

Parameters
• ftype (None) – an optional field type to which to restrict the returned schema. Must be a subclass of fiftyone.core.fields.Field

• embedded_doc_type (None) – an optional embedded document type to which to restrict the returned schema. Must be a subclass of fiftyone.core.odm.BaseEmbeddedDocument

• include_private (False) – whether to include fields that start with _ in the returned schema

Returns

a dictionary mapping field names to field types

get_text_score()

Get text score from text query

has_field(field_name)
property in_db

Whether the document has been inserted into the database.

iter_fields()

Returns an iterator over the (name, value) pairs of the public fields of the document.

Returns

an iterator that emits (name, value) tuples

classmethod list_indexes()

Lists all indexes that should be created for the Document collection. It includes all the indexes from super- and sub-classes.

Note that it will only return the indexes’ fields, not the indexes’ options

merge(doc, merge_lists=True, merge_dicts=True, overwrite=True)

Merges the contents of the given document into this document.

Parameters
• doc – a SerializableDocument of same type as this document

• merge_lists (True) – whether to merge the elements of top-level list fields rather than treating the list as a single value

• merge_dicts (True) – whether to recursively merge the contents of top-level dict fields rather than treating the dict as a single value

• overwrite (True) – whether to overwrite (True) or skip (False) existing fields

classmethod merge_field_schema(schema, expand_schema=True, recursive=True, validate=True)

Merges the field schema into this document.

Parameters
• schema – a dictionary mapping field names or embedded.field.namesto fiftyone.core.fields.Field instances

• expand_schema (True) – whether to add new fields to the schema (True) or simply validate that fields already exist with consistent types (False)

• recursive (True) – whether to recursively merge embedded document fields

• validate (True) – whether to validate the field against an existing field at the same path

Returns

True/False whether any new fields were added

Raises

ValueError – if a field in the schema is not compliant with an existing field of the same name or a new field is found but expand_schema == False

modify(query=None, **update)

Perform an atomic update of the document in the database and reload the document object using updated version.

Returns True if the document has been updated or False if the document in the database doesn’t match the query.

Note

All unsaved changes that have been made to the document are rejected if the method returns True.

Parameters
• query – the update will be performed only if the document in the database matches the query

• update – Django-style update keyword arguments

my_metaclass

alias of mongoengine.base.metaclasses.TopLevelDocumentMetaclass Methods:

 get_auto_id_names(new_class) Find a name for the automatic ID field for the given new class. mro Return a type’s method resolution order.
property pk

Get the primary key.

classmethod register_delete_rule(document_cls, field_name, rule)

This method registers the delete rules to apply when removing this object.

reload(*fields, **kwargs)

Reloads all attributes from the database.

Parameters
• fields – (optional) args list of fields to reload

• max_depth – (optional) depth of dereferencing to follow

save(validate=True, clean=True, safe=False, **kwargs)

Saves the document to the database.

If the document already exists, it will be updated, otherwise it will be created.

Parameters
• validate (True) – whether to validate the document

• clean (True) – whether to call the document’s clean() method. Only applicable when validate is True

• safe (False) – whether to reload() the document before raising any validation errors

Returns

self

Handles dereferencing of DBRef objects to a maximum depth in order to cut down the number queries to mongodb.

set_field(field_name, value, create=True, validate=True, dynamic=False)
switch_collection(collection_name, keep_created=True)

Temporarily switch the collection for a document instance.

Only really useful for archiving off data and calling save():

user = User.objects.get(id=user_id)
user.switch_collection('old-users')
user.save()

Parameters
• collection_name (str) – The database alias to use for saving the document

• keep_created (bool) – keep self._created value after switching collection, else is reset to True

Use switch_db if you need to read from another database

switch_db(db_alias, keep_created=True)

Temporarily switch the database for a document instance.

Only really useful for archiving off data and calling save():

user = User.objects.get(id=user_id)
user.switch_db('archive-db')
user.save()

Parameters
• db_alias (str) – The database alias to use for saving the document

• keep_created (bool) – keep self._created value after switching db, else is reset to True

Use switch_collection if you need to read from another collection

to_dbref()

Returns an instance of DBRef useful in __raw__ queries.

to_dict(extended=False)

Serializes this document to a BSON/JSON dictionary.

Parameters

extended (False) – whether to serialize extended JSON constructs such as ObjectIDs, Binary, etc. into JSON format

Returns

a dict

to_json(pretty_print=False)

Serializes the document to a JSON string.

Parameters

pretty_print (False) – whether to render the JSON in human readable format with newlines and indentations

Returns

a JSON string

to_mongo(*args, **kwargs)

Return as SON data ready for use with MongoDB.

update(**kwargs)

Performs an update on the Document A convenience wrapper to update().

Raises OperationError if called on an object that has not yet been saved.

validate(clean=True)

Ensure that all fields’ values are valid and that required fields are present.

Raises ValidationError if any of the fields’ values are found to be invalid.

class fiftyone.core.odm.sample.NoDatasetSampleDocument(**kwargs)

Backing document for samples that have not been added to a dataset.

Methods:

 clear_field(field_name) Returns a deep copy of the document. fancy_repr([class_name, select_fields, …]) Generates a customizable string representation of the document. from_dict(d[, extended]) Loads the document from a BSON/JSON dictionary. Loads the document from a JSON string. get_field(field_name) has_field(field_name) Returns an iterator over the (name, value) pairs of the public fields of the document. merge(doc[, merge_lists, merge_dicts, overwrite]) Merges the contents of the given document into this document. set_field(field_name, value[, create, …]) to_dict([extended]) to_json([pretty_print]) Serializes the document to a JSON string.

Attributes:

default_fields = {'_media_type': <fiftyone.core.fields.StringField object>, '_rand': <fiftyone.core.fields.FloatField object>, 'filepath': <fiftyone.core.fields.StringField object>, 'id': <fiftyone.core.fields.ObjectIdField object>, 'metadata': <fiftyone.core.fields.EmbeddedDocumentField object>, 'tags': <fiftyone.core.fields.ListField object>}
default_fields_ordered = ('id', 'filepath', 'tags', 'metadata', '_media_type', '_rand')
property media_type
clear_field(field_name)
copy()

Returns a deep copy of the document.

Returns

a SerializableDocument

delete()
fancy_repr(class_name=None, select_fields=None, exclude_fields=None, **kwargs)

Generates a customizable string representation of the document.

Parameters
• class_name (None) – optional class name to use

• select_fields (None) – iterable of field names to restrict to

• exclude_fields (None) – iterable of field names to exclude

• **kwargs – additional key-value pairs to include in the string representation

Returns

a string representation of the document

property field_names
classmethod from_dict(d, extended=False)

Loads the document from a BSON/JSON dictionary.

Parameters
• d – a dictionary

• extended (False) – whether the input dictionary may contain serialized extended JSON constructs

Returns

a SerializableDocument

classmethod from_json(s)

Loads the document from a JSON string.

Returns

a SerializableDocument

get_field(field_name)
has_field(field_name)
property in_db
iter_fields()

Returns an iterator over the (name, value) pairs of the public fields of the document.

Returns

an iterator that emits (name, value) tuples

merge(doc, merge_lists=True, merge_dicts=True, overwrite=True)

Merges the contents of the given document into this document.

Parameters
• doc – a SerializableDocument of same type as this document

• merge_lists (True) – whether to merge the elements of top-level list fields rather than treating the list as a single value

• merge_dicts (True) – whether to recursively merge the contents of top-level dict fields rather than treating the dict as a single value

• overwrite (True) – whether to overwrite (True) or skip (False) existing fields

reload()
save()
set_field(field_name, value, create=True, validate=True, dynamic=False)
to_dict(extended=False)
to_json(pretty_print=False)

Serializes the document to a JSON string.

Parameters

pretty_print (False) – whether to render the JSON in human readable format with newlines and indentations

Returns

a JSON string


text:
• ### Charge-spin correlation in van der Waals antiferromagenet NiPS3(1706.06259)

June 26, 2017 cond-mat.str-el
Strong charge-spin coupling is found in a layered transition-metal trichalcogenide NiPS3, a van derWaals antiferromagnet, from our study of the electronic structure using several experimental and theoretical tools: spectroscopic ellipsometry, x-ray absorption and photoemission spectroscopy, and density-functional calculations. NiPS3 displays an anomalous shift in the optical spectral weight at the magnetic ordering temperature, reflecting a strong coupling between the electronic and magnetic structures. X-ray absorption, photoemission and optical spectra support a self-doped ground state in NiPS3. Our work demonstrates that layered transition-metal trichalcogenide magnets are a useful candidate for the study of correlated-electron physics in two-dimensional magnetic material.
• ### On infrared pseudogap in cuprate and pnictide high-temperature superconductors(1404.7233)

April 29, 2014 cond-mat.supr-con
We investigate infrared manifestations of the pseudogap in the prototypical cuprate and pnictide superconductors: YBa2Cu3Oy and BaFe2As2 (Ba122) systems. We find remarkable similarities between the spectroscopic features attributable to the pseudogap in these two classes of superconductors. The hallmarks of the pseudogap state in both systems include a weak absorption feature at about 500 cm-1 followed by a featureless continuum between 500 and 1500 cm-1 in the conductivity data and a significant suppression in the scattering rate below 700 - 900 cm-1. The latter result allows us to identify the energy scale associated with the pseudogap $\Delta_{PG}$. We find that in the Ba122-based materials the superconductivity-induced changes of the infrared spectra occur in the frequency region below 100 - 200 cm-1, which is much lower than the energy scale of the pseudogap. We performed theoretical analysis of the scattering rate data of the two compounds using the same model which accounts for the effects of the pseudogap and electron-boson coupling. We find that the scattering rate suppression in Ba122-based compounds below $\Delta_{PG}$ is solely due to the pseudogap formation whereas the impact of the electron-boson coupling effects is limited to lower frequencies. The magnetic resonance modes used as inputs in our modeling are found to evolve with the development of the pseudogap, suggesting an intimate correlation between the pseudogap and magnetism.
• ### Phonon-assisted optical excitation in the narrow bandgap Mott insulator Sr3Ir2O7(1401.1325)

Jan. 24, 2014 cond-mat.str-el
We examined the temperature (T) evolution of the optical conductivity spectra of Sr$_3$Ir$_2$O$_7$ over a wide range of 10-400 K. The system was barely insulating, exhibiting a small indirect bandgap of $\sim$0.1 eV. The low-energy features of the optical d-d excitation (${\hbar}{\omega}$ $<$ 0.3 eV) evolved drastically, whereas such evolution was not observed for the O K-edge X-ray absorption spectra. This suggests that the T evolution in optical spectra is not caused by a change in the bare (undressed) electronic structure, but instead, presumably originates from an abundance of phonon-assisted indirect excitations. Our results showed that the low-energy excitations were dominated by phonon-absorption processes which involve, in particular, the optical phonons. This implies that phonon-assisted processes significantly facilitate the charge dynamics in barely insulating Sr$_3$Ir$_2$O$_7$.
• ### Temperature Evolution of Itinerant Ferromagnetism in SrRuO3 Probed by Optical Spectroscopy(1309.0925)

Sept. 4, 2013 cond-mat.str-el
The temperature ($T$) dependence of the optical conductivity spectra $\sigma(\omega)$ of a single crystal SrRuO$_3$ thin film is studied over a $T$ range from 5 to 450 K. We observed significant $T$ dependence of the spectral weights of the charge transfer and interband $d$-$d$ transitions across the ferromagnetic Curie temperature ($T_c$ ~ 150 K). Such $T$ dependence was attributed to the increase in the Ru spin moment, which is consistent with the results of density functional theory calculations. $T$ scans of $\sigma(\Omega, T)$ at fixed frequencies $\Omega$ reveal a clear $T^2$ dependence below $T_c$, demonstrating that the Stoner mechanism is involved in the evolution of the electronic structure. In addition, $\sigma(\Omega, T)$ continues to evolve at temperatures above $T_c$, indicating that the local spin moment persists in the paramagnetic state. This suggests that SrRuO$_3$ is an intriguing oxide system with itinerant ferromagnetism.
• ### Infrared Measurement of the Pseudogap in P-Doped and Co-Doped BaFe2As2 High-Temperature Superconductors(1207.3567)

We report on infrared studies of charge dynamics in a prototypical pnictide system: the BaFe2As2 family. Our experiments have identified hallmarks of the pseudogap state in the BaFe2As2 system that mirror the spectroscopic manifestations of the pseudogap in the cuprates. The magnitude of the infrared pseudogap is in accord with that of the spin-density-wave gap of the parent compound. By monitoring the superconducting gap of both P- and Co-doped compounds, we find that the infrared pseudogap is unrelated to superconductivity. The appearance of the pseudogap is found to correlate with the evolution of the antiferromagnetic fluctuations associated with the spin-density-wave instability. The strong-coupling analysis of infrared data further reveals the interdependence between the magnetism and the pseudogap in the iron pnictides.
• ### Hard x-ray or gamma ray laser by a dense electron beam(1110.5077)

A coherent x-ray or gamma ray can be created from a dense electron beam propagating through an intense laser undulator. It is analyzed by using the Landau damping theory which suits better than the conventional linear analysis for the free electron laser, as the electron beam energy spread is high. The analysis suggests that the currently available physical parameters would enable the generation of the coherent gamma ray of up to 100 keV. The electron quantum diffraction suppresses the FEL action, by which the maximum radiation energy to be generated is limited.
• ### Helical relativistic electron beam and THz radiation(1111.1452)

A THz laser generation utilizing a helical relativistic electron beam propagating through a strong magnetic field is discussed. The initial amplification rate in this scheme is much stronger than that in the conventional free electron laser. A magnetic field of the order of Tesla can yield a radiation in the range of 0.5 to 3 THz, corresponding to the total energy of mJ and the duration of tens of pico-second, or the temporal power of the order of GW.
• ### Overcoming the Child Langmuir law via Pondermotive Potential of the intense lasers(1110.5043)

Oct. 23, 2011 physics.plasm-ph
The maximum current that could be carried in a vacuum tube is given by the so-called Child Langmuir law. A scheme where this limit could be overcome via the pondermotive potential is proposed. The estimation shows that the limit could be overcome by a couple of hundred percents.
• ### Electronic correlations and unconventional spectral weight transfer in BaFe$_{2-x}$Co$_{x}$As$_{2}$(1106.3114)

We report an infrared optical study of the pnictide high-temperature superconductor BaFe$_{1.84}$Co$_{0.16}$As$_{2}$ and its parent compound BaFe$_{2}$As$_{2}$. We demonstrate that electronic correlations are moderately strong and do not change across the spin-density wave transition or with doping. By examining the energy scale and direction of spectral weight transfer, we argue that Hund's coupling \emph{J} is the primary mechanism that gives rise to correlations.
• ### Electronic structure and anomalous band-edge absorption feature in multiferroic MnWO4: An optical spectroscopic study(1004.4254)

April 24, 2010 cond-mat.str-el
We investigated the electronic structure and lattice dynamics of multiferroic MnWO4 by optical spectroscopy. With variation of polarization, temperature, and magnetic field, we obtained optical responses over a wide range of photon energies. The electronic structure of MnWO4 near to the Fermi level was examined, with inter-band transitions identified in optical conductivity spectra above a band-gap of 2.5 eV. As for the lattice dynamics, we identified all the infrared transverse optical phonon modes available according to the group-theory analysis. Although we did not observe much change in global electronic structure across the phase transition temperatures, an optical absorption at around 2.2 eV showed an evident change depending upon the spin configuration and magnetic field. The behavior of this band-edge absorption indicates that spin-orbit coupling plays an important role in multiferroic MnWO4.
• ### Two-Dimensional Confinement of 3d1 Electrons in LaTiO3/LaAlO3 Multilayers(0912.3863)

We report spectroscopic ellipsometry measurements of the anisotropy of the interband transitions parallel and perpendicular to the planes of (LaTiO3)n(LaAlO3)5 multilayers with n = 1-3. These provide direct information about the electronic structure of the two-dimensional (2D) 3d^1 state of the Ti ions. In combination with LDA+U calculations, we suggest that 2D confinement in the TiO2 slabs lifts the degeneracy of the t_{2g} states leaving only the planar d_xy orbitals occupied. We outline that these multilayers can serve as a model system for the study of the t_{2g} 2D Hubbard model.
• ### The electronic structure of epitaxially stabilized 5d perovskite Ca_{1-x}Sr_xIrO_3 (x = 0, 0.5, and 1) thin films: the role of strong spin-orbit coupling(0911.4542)

Nov. 24, 2009 cond-mat.str-el
We have investigated the electronic structure of meta-stable perovskite Ca1-xSrxIrO3 (x = 0, 0.5, and 1) thin films using transport measurements, optical spectroscopy, and first-principles calculations. We artificially fabricated the perovskite phase of Ca1-xSrxIrO3, which has a hexagonal or post perovskite crystal structure in bulk form, by growing epitaxial thin films on perovskite GdScO3 substrates using epi-stabilization technique. The transport properties of the perovskite Ca1-xSrxIrO3 films systematically changed from nearly insulating (or semi-metallic) for x = 0 to bad metallic for x = 1. Due to the extended wavefunctions, 5d electrons are usually delocalized. However, the strong spin-orbit coupling in Ca1-xSrxIrO3 results in the formation of effective total angular momentum Jeff = 1/2 and 3/2 states, which puts Ca1-xSrxIrO3 in the vicinity of a metal-insulator phase boundary. As a result, the electrical properties of the Ca1-xSrxIrO3 films are found to be sensitive to x and strain.
• ### Optical spectroscopic investigation on the temperature-dependent electronic structure evolution of the Jeff,1/2 Mott insulator Sr2IrO4(0910.4377)

Oct. 22, 2009 cond-mat.str-el
We investigated the temperature-dependent evolution of the electronic structure of the Jeff,1/2 Mott insulator Sr2IrO4 using optical spectroscopy. The optical conductivity spectra $\sigma(\omega)$ of this compound has recently been found to exhibit two d-d transitions associated with the transition between the Jeff,1/2 and Jeff,3/2 bands due to the cooperation of the electron correlation and spin-orbit coupling. As the temperature increases, the two peaks show significant changes resulting in a decrease in the Mott gap. The experimental observations are compared with the results of first-principles calculation in consideration of increasing bandwidth. We discuss the effect of the temperature change on the electronic structure of Sr2IrO4 in terms of local lattice distortion, excitonic effect, electron-phonon coupling, and magnetic ordering.
• ### Dual Character of Magnetism in Ferropnictides: Insights from Optical Measurements(0909.3352)

We investigate the electronic structure of EuFe$_{2}$As$_{2}$ using optical spectroscopy and first-principles calculations. At low temperature we observe the evolution of \textit{two} gap-like features, one having a BCS mean-field behavior and another with strongly non-BCS behavior. Using band structure calculations, we identify the former with a spin-Peierls-like partial gap in $d_{yz}$ bands, and the latter with the transition across the large exchange gap in $d_{xz}/d_{xy}$ bands. Our results demonstrate that the antiferromagnetism in the ferropnictides is neither fully local nor fully itinerant, but contains elements of both.
• ### Localized electronic states induced by defects and possible origin of ferroelectricity in strontium titanate thin films(0809.3254)

Sept. 18, 2008 cond-mat.mtrl-sci
Several defect configurations including oxygen vacancies have been investigated as possible origins of the reported room-temperature ferroelectricity of strontium titanate (STO) thin films [Appl. Phys. Letts. 91, 042908 (2007)]. First-principles calculations revealed that the Sr-O-O vacancy complexes create deep localized states in the band gap of SrTiO3 without affecting its insulating property. These results are in agreement with electronic structural changes determined from optical transmission and X-ray absorption measurements. This work opens the way to exploiting oxygen vacancies and their complexes as a source of ferroelectricity in perovskite oxide thin films, including STO.
• ### Bandwidth-Controlled Insulator-Metal Transition and Correlated Metallic State in 5$d$ Transition Metal Oxides Sr$_{n+1}$Ir$_{n}$O$_{3n+1}$ ($n$=1, 2, and $\infty$)(0807.2136)

July 14, 2008 cond-mat.str-el
We investigated the electronic structures of the 5$d$ Ruddlesden-Popper series Sr$_{n+1}$Ir$_{n}$O$_{3n+1}$ ($n$=1, 2, and $\infty$) using optical spectroscopy and first-principles calculations. As 5$d$ orbitals are spatially more extended than 3$d$ or 4$d$ orbitals, it has been widely accepted that correlation effects are minimal in 5$d$ compounds. However, we observed a bandwidth-controlled transition from a Mott insulator to a metal as we increased $n$. In addition, the artificially synthesized perovskite SrIrO$_{3}$ showed a very large mass enhancement of about 6, indicating that it was in a correlated metallic state.
• ### Novel Jeff = 1/2 Mott State Induced by Relativistic Spin-Orbit Coupling in Sr2IrO4(0803.2927)

March 20, 2008 cond-mat.str-el
We investigated electronic structure of 5d transition-metal oxide Sr2IrO4 using angle-resolved photoemission, optical conductivity, and x-ray absorption measurements and first-principles band calculations. The system was found to be well described by novel effective total angular momentum Jeff states, in which relativistic spin-orbit (SO) coupling is fully taken into account under a large crystal field. Despite of delocalized Ir 5d states, the Jeff-states form so narrow bands that even a small correlation energy leads to the Jeff = 1/2 Mott ground state with unique electronic and magnetic behaviors, suggesting a new class of the Jeff quantum spin driven correlated-electron phenomena.
• ### Electronic structures of hexagonal RMnO3 (R = Gd, Tb, Dy, and Ho) thin films(0708.2318)

Aug. 17, 2007 cond-mat.str-el
We investigated the electronic structure of multiferroic hexagonal RMnO3 (R = Gd, Tb, Dy, and Ho) thin films using both optical spectroscopy and first-principles calculations. Using artificially stabilized hexagonal RMnO3, we extended the optical spectroscopic studies on the hexagonal multiferroic manganite system. We observed two optical transitions located near 1.7 eV and 2.3 eV, in addition to the predominant absorption above 5 eV. With the help of first-principles calculations, we attribute the low-lying optical absorption peaks to inter-site transitions from the oxygen states hybridized strongly with different Mn orbital symmetries to the Mn 3d3z2-r2 state. As the ionic radius of the rare earth ion increased, the lowest peak showed a systematic increase in its peak position. We explained this systematic change in terms of a flattening of the MnO5 triangular bipyramid.
• ### Electronic structures of layered perovskite Sr2MO4 (M=Ru, Rh, and Ir)(cond-mat/0607026)

July 4, 2006 cond-mat.str-el
We investigated the electronic structures of the two-dimensional layered perovskite Sr$_{2}$\textit{M}O$_{4}$ (\textit{M}=4\textit{d} Ru, 4\textit{d} Rh, and 5\textit{d} Ir) using optical spectroscopy and polarization-dependent O 1\textit{s} x-ray absorption spectroscopy. While the ground states of the series of compounds are rather different, their optical conductivity spectra $\sigma(\omega)$ exhibit similar interband transitions, indicative of the common electronic structures of the 4\textit{d} and 5\textit{d} layered oxides. The energy splittings between the two $e_{g}$ orbitals, $i.e.$, $d_{3z^{2}-r^{2}}$ and $d_{x^{2}-y^{2}}$, are about 2 eV, which is much larger than those in the pseudocubic and 3\textit{d} layered perovskite oxides. The electronic properties of the Sr$_{2}$\textit{M}O$_{4}$ compounds are discussed in terms of the crystal structure and the extended character of the 4\textit{d} and 5\textit{d} orbitals.
• ### Orbital-selective Mass Enhancements in Multi-band Ca$_{2-x}$Sr$_{x}$RuO$_{4}$ Systems Analyzed by the Extended Drude Model(cond-mat/0504617)

Aug. 9, 2005 cond-mat.str-el
We investigated optical spectra of quasi-two-dimensional multi-band Ca$% _{2-x}$Sr$_{x}$RuO$_{4}$ systems. The extended Drude model analysis on the ab-plane optical conductivity spectra indicates that the effective mass should be enhanced near $x=0.5$. Based on the sum rule argument, we showed that the orbital-selective Mott-gap opening for the $d_{yz/zx}$ bands, the widely investigated picture, could not be the origin of the mass enhancement. We exploited the multi-band effects in the extended Drude model analysis, and demonstrated that the intriguing heavy mass state near $x=0.5$ should come from the renormalization of the $d_{xy}$ band.
• ### The effect of lattice distortion and orbital mixing on the optical and magnetic properties of cubic RMnO$sub 3$ (R = La, Pr, Nd, Gd, Tb)(cond-mat/0504616)

April 25, 2005 cond-mat.str-el
We investigated the $ab$-plane absorption spectra of $R$MnO$%_{3}$ ($R$ = La, Pr, Nd, Gd, and Tb) thin films. As the $R$-ion size decreases, we observed a drastic suppression of the 2 eV peak, \textit{i.e.} the inter-site optical transition between spin- and orbital-aligned states across the Mott gap. We found that both lattice distortion and the corresponding orbital mixing of the ordered orbital state should play an important role in the 2 eV peak suppression. We also found that the 2 eV spectral weight is proportional to the $A$-type antiferromagnetic ordering temperature, which suggests that the magnetic interaction might be sensitively coupled to the orbital mixing.
• ### Optical investigations on $Y_{2-x} Bi_x Ru_2 O_7$: Electronic structure evolutions related to the metal-insulator transition(cond-mat/0504619)

April 25, 2005 cond-mat.str-el
Optical conductivity spectra of cubic pyrochlore $Y_{2-x} Bi_x Ru_2 O_7$ (0.0$\leq${\it x}$\leq$2.0) compounds are investigated. As a metal-insulator transition (MIT) occurs around {\it x}$=$0.8, large spectral changes are observed. With increase of {\it x}, the correlation-induced peak between the lower and the upper Hubbard bands seems to be suppressed, and a strong mid-infrared feature is observed. In addition, the $p-d$ charge transfer peak shifts to the lower energies. The spectral changes cannot be explained by electronic structural evolutions in the simple bandwidth-controlled MIT picture, but are consistent with those in the filling-controlled MIT picture. In addition, they are also similar to the spectral changes of Y$_{2-x}$Ca$_{x}$Ru$_{2}$O$_{7}$ compounds, which is a typical filling-controlled system. This work suggests that, near the MIT, the Ru bands could be doped with the easily polarizable Bi cations.