4

In many cases I want to write some aligned equation that goes through multiple lines and add a comment for some of the lines (I think if the comments are short enough then it's clearer than explaining everything at the end of the equation). Ideally, all the comments should start on the same vertical line. This is achieved by what's shown in the following example:

\documentclass{article}
\usepackage{amsmath}

\begin{document}
    This is just some text to show where the margin is. Some more and more text yay text is good.
    \begin{align*}
    a + b + c + d + e &= an-expression \\
    &= some-very-longgggggggggg-expression && \text{comment} \\
    &= another-expression && \text{a little longer comment} \\
    &= 0
    \end{align*}
\end{document}

The problem is when some of the equation's lines are too long:

enter image description here

The second comment is inside the right margin, which should not be allowed.

I know it happens because the align environment creates a table and each & sign adds a column, so the second comment cannot be on a different column than the first comment (which is pushed by the equation on its row).

But still, what I would like to happen is that the second comment would end by the right margin. Is there a simple way to achieve that? If possible, I would prefer to not define too complicated commands, even if it means I'll not get exactly what I asked for, but something else that kinda solves the problem.

  • 1
    Welcome to TeX.SX! Could you provide the definition of the macros you are using, or, better, a MWE? – GuM Dec 14 '18 at 20:24
  • where is define \condexp[1]{...}? – Zarko Dec 14 '18 at 20:25
  • @GuM, Zarko, Thanks for the feedback. I edited the question, the example is now fully working. – Ella Shar Dec 14 '18 at 20:36
  • @Zarko I made a different example which is a MWE like GuM suggested. – Ella Shar Dec 14 '18 at 20:59
3

You cannot have all the comments vertically aligned at their left margin, because the wide equation and the wide comment simply don't fit the line.

You can save space by setting the first term on a line by itself and still have the look of a display, avoiding to go to the left margin:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

This is just some text to show where the margin is.
Some more and more text yay text is good.
This is just some text to show where the margin is.
Some more and more text yay text is good.
\begin{align*}
\lefteqn{a + b + c + d + e}\quad \\
&= an-expression \\
&= some-very-longgggggggggg-expression && \text{comment} \\
&= another-expression && \text{a little longer comment} \\
&= 0
\end{align*}

\end{document}

With \lefteqn you hide the width of the term; I added \quad in order not to have the=` signs at the left margin and it turns out that still a tad of space is available.

enter image description here

Another possibility you can explore, but this depends on the actual equations and comments, is breaking the long comment across lines.

\documentclass{article}
\usepackage{amsmath}

\begin{document}

This is just some text to show where the margin is. 
Some more and more text yay text is good.
This is just some text to show where the margin is. 
Some more and more text yay text is good.
\begin{align*}
a + b + c + d + e
&= an-expression \\
&= some-very-longgggggggggg-expression && \text{comment} \\
&= another-expression && \begin{tabular}[t]{@{}l@{}}
                         a little \\
                         longer \\
                         comment
                         \end{tabular} \\
&= 0
\end{align*}

\end{document}

enter image description here

  • Thank you, for my case this is the best solution. Except I've just read about \MoveEqLeft and I think it might be a tiny bit better. What do you think? I posted a separate solution that explains it, hope it's OK. tex.stackexchange.com/a/465987/175237 – Ella Shar Dec 15 '18 at 15:43
1

Well, the following is a very simple trick that “kinda solves the problem”:

% My standard header for TeX.SX answers:
\documentclass[a4paper]{article} % To avoid confusion, let us explicitly 
                                 % declare the paper format.

\usepackage[T1]{fontenc}         % Not always necessary, but recommended.
% End of standard header.  What follows pertains to the problem at hand.

\usepackage{amsmath}



\begin{document}

% \slshape % if uncommented, will the reference to the Magic Theorem be slanted?

Some text before the equation, to show where the right margin lies.  Oh, no, 
that was not enough: \emph{now} it is enough!
\begin{flalign*}
    \textit{formula\_result} &= \textit{short\_term} \\
        &= \textit{muuuuch\_loooonger\_term} + \textit{another\_one}
                && \text{by \ldots} && \\
        &= x-x
                && && \makebox[0pt][r]{by the Magic Theorem} \\
        &= 0
\end{flalign*}
Some text after the equation, to show again the position of the right margin of
the text block.

\end{document}

This is the output I get (on a TeXLive 2016, sorry, but that’s what I’ve got at the moment):

Output of the code

Addition: An even simpler solution using \hidewidth, which, however, does not yield exactly the same printout as the previous one:

% My standard header for TeX.SX answers:
\documentclass[a4paper]{article} % To avoid confusion, let us explicitly 
                                 % declare the paper format.

\usepackage[T1]{fontenc}         % Not always necessary, but recommended.
% End of standard header.  What follows pertains to the problem at hand.

\usepackage{amsmath}



\begin{document}

Some text before the equation, to show where the right margin lies.  Oh, no, 
that was not enough: \emph{now} it is enough!
\begin{flalign*}
    \textit{formula\_result} &= \textit{short\_term} \\
        &= \textit{muuuuch\_loooonger\_term} + \textit{another\_one}
                & \text{by \ldots} & \\
        &= x-x
                & \hidewidth\text{by the Magic Theorem} & \\
        &= 0
\end{flalign*}
Some text after the equation, to show again the position of the right margin of
the text block.

\end{document}

Indeed, IMHO the output is actually better, with both explanations aligned along the right margin:

Output of the second code sample

Second addition: If you object to using plain TeX commands like \hidewidth, you can replace the second example with the following code

% My standard header for TeX.SX answers:
\documentclass[a4paper]{article} % To avoid confusion, let us explicitly 
                                 % declare the paper format.

\usepackage[T1]{fontenc}         % Not always necessary, but recommended.
% End of standard header.  What follows pertains to the problem at hand.

\usepackage{amsmath}



\begin{document}

% \slshape

Some text before the equation, to show where the right margin lies.  Oh, no, 
that was not enough: \emph{now} it is enough!
\begin{flalign*}
    \textit{formula\_result} &= \textit{short\_term} \\
        &= \textit{muuuuch\_loooonger\_term} + \textit{another\_one}
                & \text{by \ldots} & \\
        &= x-x
                & \makebox[0pt][r]{by the Magic Theorem} & \\
        &= 0
\end{flalign*}
Some text after the equation, to show again the position of the right margin of
the text block.

\end{document}

with no change in the output.

  • You can replace \hidewidth{\text{...}} with the simpler \llap{...}. – Bernard Dec 14 '18 at 21:11
  • @Bernard: Yes, but some very influential users, here, object against advertising the use of \llap to newbies… :-) Moreover, perhaps a still better solution could be to move the \hidewidth to the line of the “muuuch loooonger term”: I guess it depends on the context… – GuM Dec 14 '18 at 21:18
  • Of course it has to be used very cautiously. – Bernard Dec 14 '18 at 21:21
  • @Bernard: Well, actually \llap was the first thing I thought of, but I deliberately rejected it. – GuM Dec 14 '18 at 21:24
  • Well, I agree that \llap is not for newbies. But \hidewidth is for wizards. ;-) – egreg Dec 14 '18 at 21:41
1

Googling \lefteqn from egreg's answer I found this answer which is about \MoveEqLeft - a command from mathtools (see 3.4.4 here). So the example becomes:

\documentclass{article}
\usepackage{amsmath}
\usepackage{mathtools}

\begin{document}
    This is just some text to show where the margin is. Some more and more text yay text is good.
    \begin{align*}
    \MoveEqLeft[1] a + b + c + d + e \\
    &= an-expression \\
    &= some-very-longgggggggggg-expression && \text{comment} \\
    &= another-expression && \text{a little longer comment} \\
    &= 0
    \end{align*}
\end{document}

Which yields the following output (same as egreg's):

enter image description here

I think this solution is a bit better than using \lefteqn since \MoveEqLeft was made specifically to solve this problem (according to the documentation).

  • That's essentially equivalent, in my opinion. It allows to not add braces. – egreg Dec 15 '18 at 15:46
  • @egreg And not to add \quad – Ella Shar Dec 15 '18 at 16:17
  • Well, \quad is a space of 1em, so it is exactly what's done by \MoveEqLeft[1]. – egreg Dec 15 '18 at 16:18
0

Here are two possibilities, with the flalign* environment, and \mathrlap from mathtools, or with a simple align* and the fleqn environment from nccmath:

\documentclass{article}
\usepackage{mathtools, nccmath}
\usepackage{showframe}
 \renewcommand{\ShowFrameLinethickness}{0.3pt}

\begin{document}

    This is just some text to show where the margin is. Some more and more text yay text is good.
    \begin{flalign*}
   \mathrlap{ a + b + c + d + e} \\
    &= an-expression \\
    &= some-very-longgggggggggg-expression && \text{comment} \\
    &= another-expression && \text{a little longer comment} \\
    &= 0
    \end{flalign*}
Some other text and another possibility:
\begin{fleqn}
    \begin{align*}
    a + b &+ c + d + e\\
    &= an-expression \\
    &= some-very-longgggggggggg-expression && \text{comment} \\
    &= another-expression && \text{a little longer comment} \\
    &= 0
    \end{align*}
\end{fleqn}

\end{document} 

enter image description here

  • Thanks! Can you make the lines after the first one a little indented? (without adding some \quad on every line) – Ella Shar Dec 14 '18 at 21:33
  • I've adde a second possibility with fleqn. – Bernard Dec 14 '18 at 21:48
  • Thank you! The problem with that second solution is that the first expression (a+b+c+d+e) is actually the output of a command I created (imagine something like \mycommand{a+b+c}{d+e} and it doesn't work to put & in there. Sorry for not including that in the question, I tried to create a good MWE. Should I add the exact command? – Ella Shar Dec 15 '18 at 13:48
  • 1
    In this case, in my 2nd solution, you can replace the first line with something like \makebox[2em][l]{$ a + b + c + d + e $}. – Bernard Dec 15 '18 at 14:15
  • 1
    fleqnmakes the left indent of all equations to 0 (or the value you give as an optional argument). It can be use with align, alignat, gather. It works as a switch (somewhat like the subequations environment). – Bernard Dec 15 '18 at 18:17

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.