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I'd like to align multiple equations below each other such that the central operator is always centered, but have a column for commenting on the right and a column for \iff-arrows and \Rightarrow-arrows on the left. This is as far as I got:

\begin{align*} && A &\aprecdot \mathfrak{G}^{\signminus 1}_1(\mathfrak{G}(C)) && \text{by \eqref{eq:C}} \\ \iff && \mathfrak{G}(A) &\cprecdot \mathfrak{G}(\mathfrak{G}^{\signminus 1}_1(\mathfrak{G}(C))) && \text{by \eqref{eq:D}} \\ \iff && \mathfrak{G}(A) &\cprecdot \mathfrak{G}(C) && \text {by axiom 1.} \\ \iff && \mathfrak{G}^{\signminus 1}_1(\mathfrak{G}(A)) &\aprecdot \mathfrak{G}^{\signminus 1}_1(\mathfrak{G}(C)) \\ \iff && A &\aprecdot B \end{align*}

It works quite well, but the problem is that if I have several of these below each other, separated by text, this looks ugly because the column widths are quite different. Therefore I want to put the \iff-arrows to the left border and the comments, while left-aligned, at a fixed distance from the right border. How can I do this?

Thanks in advance.

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    Welcome to TeX.SX! Please complete the code to a compilable example. In particular the commands \aprecdot, \cprecdot and \signminus should be defined. Commented Oct 29, 2014 at 18:03
  • depending on how long (how many lines) your "list" becomes, you might consider using \intertext or \shortintertext (requires mathtools) within a single align* structure. Commented Oct 29, 2014 at 18:37
  • The flalign environment might be what you need. Commented Oct 29, 2014 at 20:10
  • @egreg Sorry, should have removed these. Anyway, here are the definitions: \newcommand{\cprecdot}{\mathbin{\prec\!\!\! \cdot}}, \newcommand{\aprecdot}{\mathbin{\dot{\ast}}} and \newcommand{\signminus}{\scalebox{0.5}[1.0]{$-$}}. That shouldn't matter though Commented Oct 30, 2014 at 10:50

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I agree with A. Ellet. flalign is probably the best option if you are trying to have any kind of commentary. Here is a more basic example which just solves for a specific variable:

\documentclass{article} \usepackage{amsmath} \usepackage{amssymb} \begin{document} \begin{flalign*} && d &= v_{o}t + \frac{1}{2}at^{2} && \text{A kinematic equation} \\ \Rightarrow && d - v_{o}t &= \frac{1}{2}at^{2} && \text{Another comment} \\ \Rightarrow && \frac{2(d - v_{o}t)}{a} &= t^{2} && \text{One here too} \\ \Rightarrow && \sqrt{\frac{2(d - v_{o}t)}{a}} &= t && \text{Solved for $t$} \end{flalign*} \end{document}

This produces Screenshot Of Output

I'm not really sure how to get the comments and arrows closer to the overall equation though.

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  • Thanks! This is exactly what I was looking for, I didn't want the comments any nearer anyway. Works perfectly! Commented Oct 30, 2014 at 11:15
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You can center the entries in a column of an amsmath alignment with a trick involving the internals of amsmath. The alignment is first scanned to get the column widths, which are stored in \maxcolumn@width under the format

\or<widht1>\or<width2>\or...

so we can exploit this by defining a macro \Cen that just passes its second argument when the measuring is made and then uses the computed column width to center its argument. The macro has two arguments: the first is the column number, the second is the material.

I have also changed the definition of \cprecdot to be a relation symbol rather than a binary operation. I also introduced a shorthand for \mathfrak{G} and removed \signminus which just gives a very bad result (but the document is yours, so do as you prefer).

\documentclass{article} \usepackage{amsmath,amssymb,graphicx} \newcommand{\cprecdot}{\prec\joinrel\mathrel{\cdot}} \newcommand{\aprecdot}{\mathbin{\dot{\ast}}} \newcommand{\fG}{\mathfrak{G}} \makeatletter \newcommand{\Cen}[2]{% \ifmeasuring@ #2% \else \makebox[\ifcase\expandafter #1\maxcolumn@widths\fi]{$\displaystyle#2$}% \fi } \makeatother \begin{document} \begin{align*} && \Cen{3}{A \aprecdot \fG^{-1}_1(\fG(C))} && \text{by \eqref{eq:C}} \\ &\iff & \Cen{3}{\fG(A) \cprecdot \fG(\fG^{-1}_1(\fG(C)))} && \text{by \eqref{eq:D}} \\ &\iff & \Cen{3}{\fG(A) \cprecdot \fG(C)} && \text {by axiom 1.} \\ &\iff & \Cen{3}{\fG^{-1}_1(\fG(A)) \aprecdot \fG^{-1}_1(\fG(C))} \\ &\iff & \Cen{3}{A \aprecdot B} \end{align*} \end{document}

enter image description here

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I'm not entirely clear on what effect you want, but here's an example of using the flalign environment.

% arara: pdflatex % arara: pdflatex % arara: open \documentclass{article} \usepackage{amsmath,amssymb} \let\aprecdot\cdot \let\signminus\pm \let\cprecdot\cdot \pagestyle{empty} \usepackage{lipsum} \begin{document} \lipsum[1] \begin{flalign*} & & & A & \aprecdot \mathfrak{G}^{\signminus 1}_1(\mathfrak{G}(C)) & & & & \text{by \eqref{eq:C}} \\ & \iff & & \mathfrak{G}(A) & \cprecdot \mathfrak{G}(\mathfrak{G}^{\signminus 1}_1(\mathfrak{G}(C))) & & & & \text{by \eqref{eq:D}} \intertext{Here's something in the middle of the text} & \iff & & \mathfrak{G}(A) & \cprecdot \mathfrak{G}(C) & & & & \text {by axiom 1.} \\ & \iff & & \mathfrak{G}^{\signminus 1}_1(\mathfrak{G}(A)) & \aprecdot \mathfrak{G}^{\signminus 1}_1(\mathfrak{G}(C)) \\ & \iff & & A & \aprecdot B \end{flalign*} \lipsum[2] \end{document}

Also, since you only provided a partial example, I wasn't sure where \aprecdot,\signimuns, or \cprecdot were defined....

enter image description here

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