Nested align without extra spacing

Question

I am trying to align the + symbols, while also aligning the = symbols, as such

As you can see, I managed to align at the ='s but not the +'s, how can I do that? This is the code I used (using quad to kind of align them):

                x &= a + b (ert)\\
            &\quad\quad + c(ert)\\
            &= abc

When I try something like this:

            x &= a &&+ b (ert)\\
            & &&+ c(ert)\\
            &= abc

I get this:

I also tried alignat, and split inside align, but nothing seems to do the trick.

score 6 · Accepted Answer · answered Jul 29 '22 at 22:28

6

You could use alignat but as you want the wrapped summation to overlap the abc on the last row, a nested aligned is better

\documentclass{article}
\usepackage{amsmath}
\begin{document}
alignat
\begin{alignat}{-1}
    x &= a &&+ b (ert)\
      &    &&+ c(ert)\nonumber\
      &= abc

\end{alignat}
aligned
\begin{align}
    x &=\begin{aligned}[t]
         a &+ b (ert)\
           &+ c(ert)
         \end{aligned}\
      &= abc

\end{align}
\end{document}

answered Jul 29 '22 at 22:28

David Carlisle

757,742

1

-1 alignment points... :-o – Werner Jul 29 '22 at 22:31
@Werner documented feature means "as many as neeeded" actually align is defined to use -1 in that slot rather than have a user argument – David Carlisle Jul 29 '22 at 22:35
Riiight. Found it in the implementation notes (under section 17.4 Simple aligning environments; \start@aligned). – Werner Jul 29 '22 at 23:09
Thanks, that second option worked perfectly, exactly what I was looking for, thank you! Can you tell me, what the [t] option is for? – Tom Jul 30 '22 at 14:23
@Tom t = top, try it without and you will see – David Carlisle Jul 30 '22 at 14:56

Bernard · Answer 2 · 2022-07-30T07:53:36.060

5

It's quite simple with alignat and the \mathrlap command from mathtools:

    \documentclass{article}
    \usepackage{mathtools}
\begin{document}

\begin{alignat*}{2}
 x &amp;= a &amp;&amp;+ b (ert)\\
            &amp; &amp;&amp;+ c(ert)\\
            &amp;=\mathrlap{abc}
\end{alignat*}

\end{document}

edited Jul 30 '22 at 07:53

answered Jul 29 '22 at 22:34

Bernard

271,350

Why a outside the \mathrlap? Just to be complicated? – egreg Jul 30 '22 at 06:50
@egreg: Not quite: I just thought that probably the $a$ s would not be well aligned and I didn't have time to test. This morning, I have more time and I could. You're right: there's no difference, and I'll fix it within seconds. Thank you for your comment! :o) – Bernard Jul 30 '22 at 07:53
What does the \mathrlap do here? In my real code I have a bunch more lines, would I need that for all following lines then? – Tom Jul 30 '22 at 14:24
@Tom; it places in math mode an expression and makes latex believe it has 0 width, so that it adds no horizontal space between the two alignment points. There exists also \mathlap, which is like the basic \llap, but in math mode. To make it fully clear , compare with the spacing you obtain without this command. – Bernard Jul 30 '22 at 15:47

Jasper Habicht · Answer 3 · 2022-07-29T22:23:10.007

Welcome to TeX.SX! You can probably use a \phantom here:

\documentclass{article}
\usepackage{amsmath}
\begin{document}
[
\begin{aligned}
x & = a + b (ert)\
  & \phantom{{} = a} + c (ert)\
  & = abc
\end{aligned}
]
\end{document}

(In case you wonder why the {} are needed: The equals sign is a binary operator which, if it does not have a symbol before and after it, changes its spacing bahavior. See this answer about more on this.)

Nested align without extra spacing

3 Answers3