# Aligned multiline equations

I'm using an align environment in a long derivation. Each equality is aligned at the equal sign. Individual lines are too long to fit the page, so I need wrap them. However, I don't just want them to continue in the next line as I usually do and maybe indent them with a \quad, I want them to align with the opening bracket which contains all the terms. I've been looking into the aligned environment which sort of does what I want, but now the aligned lines are vertically centered with the beginning of the equality:

\begin{align*}
Z &= Tr_\text{el, ph}\bigl[\exp(-\beta H)\bigr]\\
&= \int\mathcal{D}q Tr_\text{el}\biggl[T_\tau\exp\biggl(-\int_0^\beta d\tau\sum_j\Bigl[
\begin{aligned}
&-t\sum_\sigma\bigl(c_{j\sigma}^\dag(\tau)c_{j+1,\sigma}(\tau)+\text{h.c.}\bigr)\\
&+\tfrac{M}{2}\bigl(\dot q_j(\tau)^2+\omega_0^2q_j(\tau)^2\bigr)\\
&-g\sqrt{2M\omega_0}\sum_\sigma n_{j\sigma}(\tau)q_j(\tau)\Bigr]\biggr)\biggr]
\end{aligned}\\
&= ...
\end{align*}

This is what I would like it to look (photoshopped):

I imagine, I'm not the first one to have this problem. I did a thorough search before posting this question, so before you mark this as a duplicate, please consider carefully if the alleged duplicate really addresses my issue.

• You are missing the [t] option for aligned. You might also want to add a \! before \begin{aligned} – daleif Jul 24 '15 at 13:49
• Very nice, I missed that indeed. Is there maybe a way to center the equation number vertically? It was, before I added [t] but now it is on the same height has the equal sign. Maybe that's more reasonable anyway... – Jonas Jul 24 '15 at 13:54
• No (AFAIK), the [t] changes the baseline, thus I only add it to constructions that are not individually numbered. Yuo could add a single equation number to the entire calculation instead. – daleif Jul 24 '15 at 13:56
• I'll write something a little longer, there are stuff here you should never do. – daleif Jul 24 '15 at 13:57

To get aligned to line up with the first line remember the [t] option.

Don't use \text for anything but textual comments in display math. This _\text{el} is not a textual comment. Better to use another construction.

\documentclass[a4paper]{memoir}
\usepackage{mathtools}
\DeclareMathOperator\Tr{Tr}
% for text only subscripts
\newcommand\tsub[1]{_\textup{#1}}% or \textnormal
% never use \text for anything but textual comments
\begin{document}
\begin{align*}
Z &= \Tr\tsub{el,ph}\bigl[\exp(-\beta H)\bigr]\\
&= \int\mathcal{D}q
\Tr\tsub{el}\biggl[T_\tau\exp\biggl(-\int_0^\beta d\tau\sum_j\Bigl[
\!
\begin{aligned}[t]
&-t\sum_\sigma\bigl(c_{j\sigma}^\dag(\tau)c_{j+1,\sigma}(\tau)+\text{h.c.}\bigr)\\
&+\tfrac{M}{2}\bigl(\dot q_j(\tau)^2+\omega_0^2q_j(\tau)^2\bigr)\\
&-g\sqrt{2M\omega_0}\sum_\sigma n_{j\sigma}(\tau)q_j(\tau)\Bigr]\biggr)\biggr]
\end{aligned}\\
&= ...
\end{align*}

The above waste a bit too much space IMO. Here is another

\begin{align*}
Z &= \Tr\tsub{el,ph}\bigl[\exp(-\beta H)\bigr]\\
&= \int\mathcal{D}q
\Tr\tsub{el}
\begin{aligned}[t]
\biggl[&T_\tau\exp\biggl(-\int_0^\beta d\tau\sum_j
\Bigl[
-t\sum_\sigma\bigl(c_{j\sigma}^\dag(\tau)c_{j+1,\sigma}(\tau)+\text{h.c.}\bigr)
\\
&+\tfrac{M}{2}\bigl(\dot q_j(\tau)^2+\omega_0^2q_j(\tau)^2\bigr)
\sqrt{2M\omega_0}\sum_\sigma
n_{j\sigma}(\tau)q_j(\tau)\Bigr]\biggr)\biggr]
\end{aligned}
\\
&= ...
\end{align*}
\end{document}

• Thanks for the additional comments. el and ph are short for "electronic" and "phononic", so I would in fact consider them textual comments. Placing the three additive terms in separate lines make referring to them in the surrounding text easier. – Jonas Jul 24 '15 at 14:21
• A different question, but I can't help to notice: you used \DecaleMathOperator to define the trace, I usually use \operatorname. Is there a reason why one is preferable? – Jonas Jul 24 '15 at 14:24
• Less typing. Also \DeclareMathOperator* easily makes a \lim like operator (where linits go above and below in displayed math) – daleif Jul 24 '15 at 14:26
• As for your comments to el and ph those are not textual comments, they are textual indices. Big difference. Textual indices should always be upright (just as operator names), but \text is italic then the surrounding text is italic! – daleif Jul 24 '15 at 14:28
• Great, the \lim-like behavior is actually what I want! – Jonas Jul 24 '15 at 14:31