Show equation number only once in align environment

Question

I want the equation number to be shown only at the last line, or better, somewhere in the middle of all. So instead of (1), (2), ... only (1). I use \begin{align} ... \end{align}

possible duplicate of How to get only one vertically centered equation number in align environment with two equations — Jukka Suomela, May 06 '11 at 13:00

score 272 · Answer 1 · edited Oct 20 '23 at 01:24

272

Use \nonumber to do so:

\begin{align}
  a & b \nonumber \\ % no number is shown
  c & d \\ % there is a number
  e & f \nonumber % no number
\end{align}

$align output demonstrating use of \nonumber to avoid two of three lines getting numbered$

edited Oct 20 '23 at 01:24

cfr

198,882

answered May 06 '11 at 16:00

Yotam

7,109

31

What if I only have two lines?.. – Cm7F7Bb Jan 18 '18 at 10:36
2

@Cm7F7Bb not sure if this is what you mean, but you can use \nonumber in an align environment with only two lines. Only the line without \nonumber ending it will have number in the output – Skeleton Bow Aug 18 '20 at 19:47
6

@SkeletonBow - They presumably mean "how can I get the equation number vertically centered if there are only two lines (or any even number of lines)?". The split environment does this (but doesn't work with multiple alignment columns), but \nonumber does not. – Nathaniel Johnston Jul 06 '21 at 13:58
It looks like \nonumber doesn't work within the \added{} command from the changes package. – Paul Wintz Oct 11 '21 at 02:06

score 262 · Accepted Answer · edited Oct 20 '23 at 01:38

262

You can use the split environment from the amsmath package:

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{align}
\begin{split}
  a &= b \
  &=c \
  &=d \
  &=e
\end{split}
\end{align}
\end{document}

edited Oct 20 '23 at 01:38

cfr

198,882

answered May 06 '11 at 01:25

Gonzalo Medina

505,128

137

you could also simply put \nonumber at the end of each equation line for which you don't want an equation no. – prettygully May 06 '11 at 01:44
4

You could also see this question: http://tex.stackexchange.com/questions/13396/how-to-get-only-one-vertically-centered-equation-number-in-align-environment-with/17483#17483 – Ryan Reich May 06 '11 at 02:04
32

@prettygully: if the number of lines is even, then \notag (or \nonumber) won't vertically center the tag. – Gonzalo Medina May 06 '11 at 02:06
2

@prettygully: I think you should also write your comment as an answer. @Gonzalo Medina: sometimes you want the number at the end, rather than centered; I often do so. (While the OP prefers centered, not everyone will.) – Niel de Beaudrap May 06 '11 at 12:17
8

is there a simple way to adapt this solution for multiple alignment columns? It looks like \begin{align*}\begin{split} A &= B & C&= D \\ A &= B & C&= D \end{split}\end{align*} doesn't work. – phfaist Aug 14 '20 at 14:24

score 31 · Answer 3 · edited Oct 20 '23 at 01:36

31

You can use the aligned environment from the amsmath package:

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{gather}
\begin{split}
  m &=n \
    &=o \
    &=p \
    &=q
\end{split}\
\begin{aligned}
  a &=b + 1 \
  c &=d \
  e &=f \
  g &=h
\end{aligned}
\end{gather}
\end{document}

This is generally recommended for straightforward expressions rather than embedding a sub-structure within align. See the user's manual for amsmath (amsldoc.pdf on ctan or type texdoc amsmath if you have a tex live installation).

Edit: changed equation environment to gather to allow multiple sub-structures, and added an example of split as requested. Since single letters on either side of the equals sign will give the illusion that everything is aligned, I lengthened one line to show that the alignments of the two sub-structures are really offset from one another.

This result will get two equation numbers; either may be removed by use of \notag, but the positioning will not be optimal. Sadly, I don't have a solution for that.

edited Oct 20 '23 at 01:36

cfr

198,882

answered May 06 '11 at 12:45

barbara beeton

88,848

4

Mildly ironic that in an answer to a question on alignment, you had an error in your code alignment! A case of misalliance (in tribute to Britain's answer to Tom Lehrer). – Andrew Stacey May 06 '11 at 12:48
I think this is the right answer, but with the wrong example. To typeset a multi-line equation such as a = b = c = d = e, you should not use anything from the align family, but something like split. Could you perhaps change the example so that it is something like "a = b, c = d, e = f, g = h", so that it is clearly multiple equations that you want to align. This is not just semantics; there might be a difference in the vertical spacing, and you should use the right command for the right purpose. – Jukka Suomela May 06 '11 at 12:59
This is exactly what I was looking for, something that has the nice symmetric labelling of split but also supports multiple columns like align. – Aditya Sriram Jun 27 '19 at 18:18

score 16 · Answer 4 · answered Apr 24 '17 at 04:42

I realize this question is now quite old, but I've found wrapping the nested equation/aligned in an environment handy since I want single numbers for multi-line equations quite a bit. One hitch is that LaTeX will add a space to the next line unless you do something about it. Here's an nalign environment that is like align but with one (centered) equation number for all the lines.

\newenvironment{nalign}{
    \begin{equation}
    \begin{aligned}
}{
    \end{aligned}
    \end{equation}
    \ignorespacesafterend
}

Show equation number only once in align environment

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