# Aligning sub-equations within align

## Update:

How do I align both the \sum signs and the = signs in the last two equations? I have updated the picture.

## Original Question:

When I use the following code:

$$\begin{split} \label{eq:BILP} \mathpzc{I}^* & = \argmax_{\mathcal{I}} \; \left\{\sum_{i\in \mathcal{V}} \left(\theta_K \cdot \mathbb{I}_{i,j}(1,1) + \theta_K \cdot \mathbb{I}_{i,j}(0,0) \right) + \right.\\ & \qquad \qquad \quad \;\,\;\; \left. \sum_{i\in \mathcal{E}} \theta_{i_0} \cdot \mathbb{I}(x_i=0) + \theta_{i_1} \cdot \mathbb{I}(x_i=1) \right\}\\ & \qquad \qquad \text{s.t.} \; \; \sum_{x_j} \mathbb{I}_{i,j}(1,x_j) = \mathbb{I}(x_i=1) \\ & \qquad \qquad \qquad \sum_{x_i}\mathbb{I}_{i,j}(x_i,1) = \mathbb{I}(x_j=1) \\ & \qquad \qquad \qquad \sum_{x_i,x_j}\mathbb{I}_{i,j}(x_i,x_j) = 1 \\ %& \;\psi_{\mathrm{SAT}}\left(\mathbf{s}, \mathbf{l}\right) = 1 \end{split}$$


I get the following (note the misalignment between the \sum signs, and the = signs highlighted under the red lines):

How can I get them to align? (and avoid using all the artificial \qquad, \, \; spaces)

• Are you maybe missing a pair of parentheses around the argument of the summation on the second line? Just curious.
– Mico
Apr 18, 2012 at 3:17
• You are right @Mico. Thanks for pointing that out! Apr 18, 2012 at 15:28

Use the \bigg variety for bigger delimiters and align the sums. There's a subtlety for the last one, since the long subscript would shift it to the right and \mathclap from mathtools avoids it.

\documentclass{article}

\usepackage{amsmath,amssymb,mathtools}
\DeclareMathOperator*{\argmax}{argmax}
\begin{document}
$$\label{eq:BILP} \begin{split} I^* = \argmax_{\mathcal{I}}\biggl\{ & \sum_{i\in \mathcal{V}} (\theta_K \cdot \mathbb{I}_{i,j}(1,1) + \theta_K \cdot \mathbb{I}_{i,j}(0,0) ) + {}\\ & \sum_{i\in \mathcal{E}} \theta_{i_0} \cdot \mathbb{I}(x_i=0) + \theta_{i_1} \cdot \mathbb{I}(x_i=1) \biggr\}\\ \text{s.t.}\quad & \sum_{x_j} \mathbb{I}_{i,j}(1,x_j) = \mathbb{I}(x_i=1) \\ & \sum_{x_i}\mathbb{I}_{i,j}(x_i,1) = \mathbb{I}(x_j=1) \\ & \sum_{\mathclap{x_i,x_j}}\mathbb{I}_{i,j}(x_i,x_j) = 1 \end{split}$$
\end{document}


• Using the "starred" version of the \DeclareMathoperator macro would under-set rather than side-set the \mathcal{I} element. :-)
– Mico
Apr 18, 2012 at 3:16
• @Mico I didn't notice that; thanks. Apr 18, 2012 at 6:23
• +1 mathtools loads amsmath so there's no need to load both explicitly Apr 18, 2012 at 8:34
• The \mathclap part can also be done via the \smashoperator in mathtools Apr 18, 2012 at 8:57
• Thanks @egreg. I'm wondering if there is a way of getting two things aligned vertically, the \sum signs and the = on the last three equations? Apr 18, 2012 at 15:25