# Vertical spacing inside mathtools's multlined

The code

\documentclass{article}
\usepackage{mathtools}
\begin{document}
\begin{align*}
f(1) &= g(1) + g(2) + g(3) \\
f(1) &= g(1) + g(2) + g(3) \\
f(1) &= \!\begin{multlined}[t]g(1) + g(2) + g(3) + g(1) + g(2) + g(3)\\
g(1) + g(2) + g(3) + g(1) + g(2) + g(3)
\end{multlined}
\\
f(1) &= g(1) + g(2) + g(3) \\
f(1) &= g(1) + g(2) + g(3)
\end{align*}
\end{document}


produces

I looked in the mathtools's code and could not see how to set things up so that the vertical spacing between multlined lines is exactly the same as between other amsmath constructs. I know I can say \\[10pt] to adjust one instance, but I'd like to set this up once and for all for all multlineds in the whole document.

Any ideas?

• I don't know either, but I think it is better for an easy understanding of the equations: a multlined environment semantically corresponds to a block that one has to split because there's not enough horizontal space, so the corresponding lines do not have the same status as the other lines, individually. May 11, 2017 at 0:54
• I understand that is the intention, but I find it more distracting than helpful —and the lines look way too cramped, in my opinion. I prefer to have the horizontal spacing as a cue of logical grouping in this situation. May 11, 2017 at 8:41
• In this case, I believe aligned has the usual spacing, and you can align this group by the right side, for instance. May 11, 2017 at 8:45
• That works if the multlined has only two lines, and only then. It usually doesn't. May 11, 2017 at 9:07
• It is known that multlined has certain spacing issues that are not that easy to point point. I hardly ever use any of the multlined stuff and they end up having a very inconsistent look. May 11, 2017 at 11:27

This might help

\usepackage{mathtools}
\MHInternalSyntaxOn
\def\MT_mult_invisible_line: {
\crcr
\global\MH_set_boolean_F:n {mult_firstline}
\hbox to \l_MT_multwidth_dim{}\crcr
\noalign{
\vskip-\baselineskip
%\vskip-\jot
\vskip-\normallineskip
}
}
\MHInternalSyntaxOff


Not quite sure why \jot was added in the first place, probably because of spreadlines.

• Just to nag: Could the \! spacing issue be removed from mathtools, now that amsmath got rid of it? Or has it already happened and I didn't notice it? May 11, 2017 at 11:48
• @campa it is on my top list. But did amsmath actually got rid of it for aligned? I had not noticed May 11, 2017 at 11:57
• Yep, see here. May 11, 2017 at 12:09
• @campa good, though, not sure if the hspace issue in multline is the same. I'll have a look before the next release May 11, 2017 at 12:16
• @campa turns out to be a walk in the park to fix. Until release you can use this (requires etoolbox): \makeatletter \MHInternalSyntaxOn \ifpatchable{\MT_mult_internal:n}{% \MH_if_boolean:nF {outer_mult}{\null\,}% }{ \patchcmd{\MT_mult_internal:n}{% \MH_if_boolean:nF {outer_mult}{\null\,}% }{% \MH_if_boolean:nF {outer_mult}{\alignedspace@left}% }{ \typeout{patched} }{ \typeout{patch failed} } }{\typeout{no, not patchable}} \MHInternalSyntaxOff \makeatother May 22, 2017 at 8:41

Here, I substituted the multilined with a \Longunderstack, where you can set the interline baselineskip explicitly with \setstackgap{L}{...}. I loaded tabstackengine (instead of stackengine), in case you wanted to employ additional tabbing features in your stacks.

\documentclass{article}
\usepackage{mathtools,tabstackengine}
\stackMath
\setstackgap{L}{\baselineskip}
\begin{document}
\begin{align*}
f(1) &= g(1) + g(2) + g(3) \\
f(1) &= g(1) + g(2) + g(3) \\
f(1) &= \Longunderstack[l]{ g(1) + g(2) + g(3) + g(1) + g(2) + g(3)\\
\quad g(1) + g(2) + g(3) + g(1) + g(2) + g(3)
}
\\
f(1) &= g(1) + g(2) + g(3) \\
f(1) &= g(1) + g(2) + g(3)
\end{align*}
\end{document}