7
\begin{equation}
    \begin{aligned}
        [c\mathbf{v}+c'\mathbf{v}',\mathbf{w}]=&c[\mathbf{v},\mathbf{w}]+c'[\mathbf{v}',\mathbf{w}],\\
        [\mathbf{v},c\mathbf{w}+c'\mathbf{w}']=&c[\mathbf{v},\mathbf{w}]+c'[\mathbf{v},\mathbf{w}'],
    \end{aligned}
\end{equation}

In this code, [c\mathbf{v}+c'\mathbf{v}',\mathbf{w}] is not shown in the equation. Is it because of the aligned environment? How to fix it?

yo'
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eccstartup
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1 Answers1

13

Update Jan. 2021. The current version of the amsmath package, 2020/09/23 v2.17i, no longer generates the problem described in the OP's query. Hence, taking "precautions" such as inserting a \relax or {} element before a [ element at the start of a line is no longer necessary.

What you're experiencing is the fact that the aligned environment -- as set up by the amsmath package -- is set to scan ahead for a positioning argument such as [t] or [b]. Material that's found in square brackets but which doesn't meet this format is simply discarded.

I can think of two solutions:

  • Insert \relax before the left square bracket (it will stop the bracket from being interpreted as an argument);

  • Insert {} (an empty math atom) before the left square bracket;

  • Load the mathtools package instead of the amsmath package, as the former takes care to disable this generally-unexpected-and-unwelcome setting.

A separate matter: To get the correct (and symmetric) amount of spacing around the = symbols, you should write &= rather than =&.

Mico
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