Alignment within align portion of subequations

I am trying to align equations within an align environment. Below is a MWE

\documentclass{report}
\usepackage{amsmath}

\begin{document}

\begin{subequations}
\begin{align}
3 & : & A = X \\
2 & : & A = Y \\
2 & : & A = XY
\end{align}
\end{subequations}

\end{document}


In this example, the 'A's are out of alignment because (I assume) the columns are right justified. I'd really like to use aligned commands, something along the lines of

\documentclass{report}
\usepackage{amsmath}

\begin{document}

\begin{subequations}
\begin{align}{rcl}
3 & : & A = X \\
2 & : & A = Y \\
1 & : & A = XY
\end{align}
\end{subequations}

\end{document}


Sorry for my simple example, tried to make MWE as small as possible.

• Use alignat ? – Henri Menke Nov 7 '19 at 20:44

What you obtain is normal: when you have several alignment points, all alignment columns, but the first, have to be introduced by an ampersand, and inside this column, the alignment point is specified by a second ampersand, so that two alignment points require 3 ampersands. If the last one is missing, it is implicitly added at the end of each row, so that the second column is right aligned.

The correct code is this:

      \begin{align}
3 & : & &A = X \\
2 & : & &A = Y \\
2 & : & &A = XY
\end{align}


or maybe, if you want to ensure the = are aligned, use 3 & : & A & = X, &c.

• That solved the problem perfectly. Thank you for the fast response! – llopes Nov 7 '19 at 21:02