26579916
A Monge Property for the D-dimensional Transportation Problem
Abstract In 1963, Hoffman gave necessary and sufficient conditions under which a family of O( mn )-time greedy algorithms solves the classical two-dimensional transportation problem with m sources and n sinks. One member of this family, an algorithm based on the “northwest corner rule”, is of particular interest, as its running time is easily reduced to O(m + n). When restricted to this algorithm, Hoffman's result can be expressed as follows: the northwest-corner-rule greedy algorithm solves the two-dimensional transportation problem for all source and supply vectors if and only if the problem's cost array C = { c [ i , j ]} possesses what is known as the (two-dimensional) Monge property, which requires c [ i 1 , j 1 ] + c [ i 2 , j 2 ] ⩽ c [ i 1 , j 2 ] + c [ i 2 , j 1 ] for i 1 i 2 and j 1 j 2 . This paper generalizes this last result to a higher dimensional variant of the transportation problem. We show that the natural extension of the northwest-corner-rule greedy algorithm solves an instance of the d -dimensional transportation problem if and only if the problem's cost array possesses a d -dimensional Monge property recently proposed by Aggarwal and Park in the context of their study of monotone arrays. We also give several new examples of cost arrays with this d -dimensional Monge property.
5711141
Selection and sorting in totally monotone arrays
A two-dimensional arrayA={a[i, j]} is calledtotally monotone if, for alli1<i2 andj1<j2,a[i1,j1]<a[i1,j2] impliesa[i2,j1]<a[i2,j2]. Totally monotone arrays were introduced in 1987 by Aggarwal, Klawe, Moran, Shor, and Wilber, who showed that several problems in computational geometry and VLSI river routing could be reduced to the problem of finding a maximum entry in each row of a totally monotone array. In this paper we consider several selection and sorting problems involving totally monotone arrays and give a number of applications of solutions for these problems. In particular, we obtain the following results for anm × n totally monotone arrayA:1.Thek largest (ork smallest) entries in each row ofA can be computed inO(k(m + n)) time. This result allows us to determine thek farthest (ork nearest) neighbors of each vertex of a convexn-gon inO(kn) time.2.Provided the transpose ofA is also totally monotone, thek largest (ork smallest) entries overall inA can be computed inO(m + n + k lg(mn/k)) time. This result allows us to find thek farthest (ork nearest) pairs of vertices from a convexn-gon inO(n + k lg(n2/k)) time.3.The rows ofA can be sorted inO(mn) time whenm ≥n and inO(mn(1 + lg(n/m))) time whenm < n. This result allows us to solve the of Ω(S) on the number of combinations of row permutations possible for a totally monotone array would imply an Ω(lgS) lower bound on the time necessary to sort the array's rows in a linear decision tree model.)4.In Subsection 4.2 we applied our algorithm for sorting the rows of a totally monotone array to the neighbor-ranking problem for the vertices of a convex polygonP. We then extended this technique to arbitrary point sets. It remains open whether our two selection algorithms for totally monotone arrays, which we also applied to the vertices of a convex polygon, can likewise be applied to arbitrary point sets.
9022148
Parallel Searching in Generalized Monge Arrays
Abstract. This paper investigates the parallel time and processor complexities of several searching problems involving Monge, staircase-Monge, and Monge-composite arrays. We present array-searching algorithms for concurrent-read-exclusive-write (CREW) PRAMs, hypercubes, and several hypercubic networks. All these algorithms run in near-optimal time, and their processor-time products are all within an 
 $O (\lg n)$ factor of the worst-case sequential bounds. Several applications of these algorithms are also given. Two applications improve previous results substantially, and the others provide novel parallel algorithms for problems not previously considered.
9979797
A truncated least squares approach to the detection of specular highlights in color images
One of the most difficult aspects of dealing with illumination effects in computer vision is accounting for specularity in the images of real objects. The specular regions in an image are often saturated - which creates problem for all image processing algorithms that use decision thresholds. Such algorithms include those for edge detection, region segmentation, etc. Detecting specularity and whenever possible compensating for it are obviously advantageous. Along these lines, this paper represents a new specularity detection and compensation method which is based on the notion of truncated least-squares approximation to the function that maps the color distribution between two images of an object under different illumination conditions. We also present a protocol for the evaluation of the current method for specularity detection. Our protocol as currently formulated uses human subjects to grade the specularity detection method.
13229931
A Haptic Teleoperation Approach Based on Contact Force Control
This paper presents a new teleoperation approach using a virtual spring, and local contact force control on the slave robot. The operational space framework provides the control structure needed to achieve decoupled task dynamics. A virtual spring connects the master and slave systems and a closed-loop force controller compensates for the dynamics of the slave system, rendering transparent the effector of the slave robotic system. The active force control approach allows the desired motion and contact forces to be combined in a single force command. The required performance and robustness of force control are achieved by a full state reconstruction using a modified Kalman estimator, which addresses disturbances and modeling uncertainties. The performance of both telepresence and force control are further improved by on-line stiffness estimation of the object in contact with the effector. The redundancy of the mobile manipulation system is addressed through a decoupled decomposition of task and posture dynamics.
17114395
Efficient multicast stream authentication using erasure codes
We describe a novel method for authenticating multicast packets that is robust against packet loss. Our focus is to minimize the size of the communication overhead required to authenticate the packets. Our approach is to encode the hash values and the signatures with Rabin's Information Dispersal Algorithm (IDA) to construct an authentication scheme that amortizes a single signature operation over multiple packets. This strategy is especially efficient in terms of space overhead, because just the essential elements needed for authentication (i.e., one hash per packet and one signature per group of packets) are used in conjunction with an erasure code that is space optimal. Using asymptotic techniques, we derive the authentication probability of our scheme using two different bursty loss models. A lower bound of the authentication probability is also derived for one of the loss models. To evaluate the performance of our scheme, we compare our technique with four other previously proposed schemes using empirical results.
12592675
A New Approach for Active Stereo Camera Calibration
By active stereo we mean a stereo vision system that allows for independent panning and tilting for each of the two cameras. One advantage of active stereo in relation to regular stereo is the former's wider effective field of view; if an object is too close to the camera baseline, the depth to the object can still be estimated accurately by panning the cameras appropriately. Another advantage of active stereo is that it can yield a larger number of depth measurements simultaneously for each position of the platform on which the camera system is mounted. Panning and tilting over a large angular range, while being the main reason for the advantages of active stereo, also make it more challenging to calibrate such systems. For a calibration procedure to be effective for active stereo, the estimated parameters must be valid over the entire range of the pan and tilt angles. This paper presents a new approach to the calibration of such vision systems. Our method is based on the rationale that an active stereo calibration procedure must explicitly estimate the locations and the orientations of the pan and tilt rotating axes for the cameras through a closed-form solution. When these estimates for the axes are combined with the homogeneous transform relationships that link the various coordinate frames, we end with a calibration that is valid over a large variation in the pan and tilt angles.
404376
Power-aware deterministic block allocation for low-power way-selective cache structure
This paper proposes a power-aware cache block allocation algorithm for the way-selective set-associative cache on embedded systems to reduce energy consumption without additional delay or performance degradation. For this goal, way selection logic and specialized replacement policy are designed to enable only one way of set-associative cache as in the direct-mapped cache. Overall cache access time becomes almost the same as that of a conventional set associative cache with accessing additional way selection logic. Because data array can be accessed without waiting for tag comparison, multiplexer delay can be removed totally. The simulation result shows that the proposed architecture can reduce a per access power consumption by 59% over conventional set-associative caches with average 0.06% of negligible performance loss.