[Tex/LaTex] How to implement an ‘&’ inside a \left( \right) environment

alignequationshorizontal alignmentmath-mode

I've been running into a strange issue. I'm doing some derivations in LaTeX document, and am using the align environment to do so. Some derivations require multi-line brackets, for which I try to use

\left( \right. \\
\left. \right)

However, when I want to align my equations with something inside these brackets, I run into errors. Example:

\begin{align}
blablabla x=y \left(5 + 3 & + \right. \\
& \left. + 1 + 9 + 7 \right)
\end{align}

This runs into trouble, while

\begin{align}
blablabla & \left(5 + 3 + \right. \\
& \left. + 1 + 9 + 7 \right)
\end{align}

works just fine. Hence, I strongly suspect that the problem is caused by the first ampersand being inside the \left( ... \right) environment. Is there any way to get this to work? Any help would be much appreciated.

EDIT: For clarity: I'm looking for a way around the ampersand problem: I would like to have the ampersand inside my \left( ... \right) environment. Is there any way to do this?

Best Answer

A simplified version of your code:

\begin{align}
x = y \left(5 + 3 & + 1\right. 
\end{align}

I strongly suspect that the problem is caused by the ampersand being inside the \left( ... \right. [construct]. ... Is there any way to get this to work?

Your suspicion is correct. A short answer to your question: "No." Medium-length answer: "No way." Long answer: "Hell No."

Why? A \left ... \right pair creates a so-called "math-inner" item. What's inside a math-inner item is, well, not "visible" to the outside world. In particular, the & character cannot be "seen" by the align environment. Since such code cannot be made to work, LaTeX is programmed to throw an error message and stop.

The following code will not throw an error message; however, the sizes of the parentheses may not be what you need:

x = y \left(5 + 3 \right. & \left. + 1\right)

The upshot? Don't overuse left and right! Fortunately, sizing large parentheses manually is not that difficult to accomplish.

Related Solutions

[Tex/LaTex] Aligning inside tabular environment, specific cell

You can use \multicolumn{1}{l}{<content>} for to_the_left to switch the cell alignment just for this cell. If you want to have a vertical line you need to use l| instead, otherwise the line is missing for this cell.

\documentclass{article}
\begin{document}
\begin{tabular}{|r|r|}
   \hline
   111111 & 222222 \\
   \hline
   right & \multicolumn{1}{l|}{left} \\
   \hline
   1 & 2 \\
   \hline
\end{tabular}
\end{document}

Result

[Tex/LaTex] Right align a line in align-environment

The environment you want is multline*, not align*:

\documentclass[11pt]{article}

\usepackage[english]{babel}
\usepackage{amsmath}

\DeclareMathOperator{\HTr}{HTr}

\begin{document}

Here I write a line to be sure of the precise and exact extension of the margin.
\begin{multline*}
\HTr K^\Gamma_{\overline{M}_{-k}}(t) =
  \sum_{\gamma \in H(\Gamma)} \int_X \sum_{[\kappa] \in \Gamma\setminus\Gamma_\gamma}
  \sum_{n=1}^\infty  j(\kappa^{-1}\gamma^n\kappa,z)^k\times{} \\
\times K_{-k,\mathrm{hyp}}(t;\kappa^{-1}\gamma^n\kappa(z),z) \mu_{\mathrm{hyp}}(z)
\end{multline*}
\end{document}

Note the {} after the trailing \times. Also \mathrm{HTr} is wrong and the same is for \text{hyp}; your \backslash should be \setminus.

For splitting lines keeping the alignment at the relation signs, there is multlined (requires mathtools):

\documentclass[11pt]{article}

\usepackage[english]{babel}
\usepackage{mathtools}

\DeclareMathOperator{\HTr}{HTr}

\begin{document}

Here I write a line to be sure of the precise and exact extension of the margin.

\begin{align*}
\HTr K^\Gamma_{\overline{M}_{-k}}(t) 
&= \begin{multlined}[t]
   \sum_{\gamma \in H(\Gamma)} \int_X \sum_{[\kappa] \in \Gamma\setminus\Gamma_\gamma}
     \sum_{n=1}^\infty  j(\kappa^{-1}\gamma^n\kappa,z)^k\times{} \\[2ex]
   \times K_{-k,\text{hyp}}(t;\kappa^{-1}\gamma^n\kappa(z),z) \mu_{\mathrm{hyp}}(z)
   \end{multlined}
\intertext{Now I comment on the next step,}
&= \begin{multlined}[t]
   \sum_{\gamma \in H(\Gamma)} \int_X \sum_{[\kappa] \in \Gamma\setminus\Gamma_\gamma}
     \sum_{n=1}^\infty  j(\kappa^{-1}\gamma^n\kappa,z)^k\times{} \\[2ex]
   \times K_{-k,\mathrm{hyp}}(t;\kappa^{-1}\gamma^n\kappa(z),z) \mu_{\mathrm{hyp}}(z)
   \end{multlined}
\intertext{And finally it simplifies}
&= 0.
\end{align*}
\end{document}

Best Answer

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[Tex/LaTex] Aligning inside tabular environment, specific cell

[Tex/LaTex] Right align a line in align-environment

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