Separate long math text under sum symbol into different lines?

Question

I have the following equation, where there is a lot of stuff under the sum symbol:

\begin{equation}
d(\vec{x},\vec{y})=
  \sum_{Z_{xy}\in\vec{Z}_{xy},\forall x\in\vec{x},\forall y\in\vec{y}} 
    f(Z_{xy})
\end{equation}

In the resulting document, I find it kind of hard to read. Is there a way to write the equation to make the result more readable, e.g. putting the stuff under the sum symbol on different lines?

Why write under Sum, when mathematical correct is write to right. \begin{equation} d(\vec{x},\vec{y})= \sum_{Z_{xy}\in\vec{Z}_{xy}} f(Z_{xy}),\forall x\in\vec{x},\forall y\in\vec{y} \end{equation} — MiMo, Jun 10 '12 at 10:34
I agree with you but without the correct spacing, it is as bad as OP's. To be super-picky about it, forall is not the same as over all. With forall the author is relying on the reader's understanding for bad notation. — percusse, Jun 10 '12 at 13:18
This is mathematically incorrect (if the notation has not introduced formally). But the \forall is definitely misused. — egreg, Jun 10 '12 at 13:33
If you want to write a fraction instead, refer to amsmath - In math mode, how do I make the fraction bar "invisible"? - TeX - LaTeX Stack Exchange. — user202729, Dec 13 '22 at 06:45

score 195 · Accepted Answer · edited Nov 22 '17 at 14:41

195

You can use the \substack command from the amsmath package, like this:

\begin{equation}
  d(\vec{x},\vec{y}) =
  \sum_{\substack{Z_{xy}\in\vec{Z}_{xy}\\
                  \forall x\in\vec{x}\\
                  \forall y\in\vec{y}}}
        f(Z_{xy}) 
\end{equation}

However, the result still doesn’t look good, because of the extra spacing around the sum symbol:

$Image showing the result of the ‘\substack’ command$

To fix this, you can use the \mathclap command from the mathtools package, like this:

\begin{equation}
 d(\vec{x},\vec{y}) =
    \sum_{\mathclap{\substack{Z_{xy}\in\vec{Z}_{xy}\\
                              \forall x\in\vec{x}\\
                               \forall y\in\vec{y}}}}
          f(Z_{xy}) 
\end{equation}

$Image showing the result of the ‘\mathclap’ and ‘\substack’ commands$

But perhaps you might be happy using only \mathclap, and not \substack. The result looks good as long as the subscript is not too wide.

\begin{equation}
  d(\vec{x},\vec{y}) =
    \sum_{\mathclap{{Z_{xy}\in\vec{Z}_{xy},
          \forall x\in\vec{x},
          \forall y\in\vec{y}}}} f(Z_{xy})
\end{equation}

$Image showing the result of the ‘\mathclap’ command$

The mathtools package also have several other useful commands for typesetting mathematics, including more commands for improving the display of subscripts and superscripts. I very much recommend taking a look at its documentation.

edited Nov 22 '17 at 14:41

Malcolm

405

answered Nov 01 '11 at 19:52

Karl Ove Hufthammer

4,929

25

The \forall symbols should be omitted. – egreg Jun 10 '12 at 13:34
4

@egreg: Maybe one should just write three sums in total, the first two over x\in\vec{x} and y\in\vec{y}? – Hendrik Vogt Jun 10 '12 at 13:51
2

@HendrikVogt I'd use a two line \substack: \sum_{\substack{Z_{xy}\in\vec{Z}_{xy}\\x\in\vec{x},y\in\vec{y}}} – egreg Jun 10 '12 at 13:56
@KarlOveHufthammer You forgot \\. – Karlo Mar 22 '17 at 14:13
Looks good, but seems not to work in rmarkdown's beamer_presentations. Can that be confirmed? – jay.sf Oct 29 '17 at 15:26

Ian Thompson · Answer 2 · 2023-01-27T13:08:41.560

23

Try the \substack command from the amsmath package, details of which are found here

edited Jan 27 '23 at 13:08

answered Feb 28 '11 at 23:43

Ian Thompson

43,767

In case anyone else needs that old link: https://ctan.org/pkg/amsmath – psitae Jan 25 '23 at 20:53
1

@psitae --- An ftp link! I've been here a long time. I've updated the link in the answer. – Ian Thompson Jan 27 '23 at 13:09

VIVID · Answer 3 · 2023-01-22T17:45:33.690

4

[For those who are looking for MathJax way] it can be done without \substack as

\sum_{a=b \\ b=c \\ c=a}

wich results in

edited Jan 22 '23 at 17:45

answered Dec 21 '20 at 11:20

VIVID

195

3

doesn't seem to work for me. I am in the 'align' environment. – Danyal Mar 16 '21 at 05:22
Doesn't work for me, either. – relatively Jan 20 '23 at 14:15
3

This definitely doesn’t work in LaTeX. Unfortunately, it does in MathJax, which is not a reason for advertising it here. – egreg Jan 22 '23 at 21:57

score 1 · Answer 4 · answered Mar 02 '23 at 11:45

1

Using A \atop B. E.g:

\sum_{{n\in \mathbb{N}}\atop{n= even}}^{100} a_n

answered Mar 02 '23 at 11:45

C.F.G

552

Separate long math text under sum symbol into different lines?

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