Writing down an equation involving some xymatrices in xy-pic

Question

I'm trying to do something that TikZ is probably more than capable of doing, but I am lazy so I'm trying to do it in xy-pic instead. What I am trying to do is write down an equation involving xymatrices, e.g. [thing1] = [thing2] + [thing3] where all three [thing]s are xymatrices. The problem when I naively try to do this is that the equal signs are aligning with the first row of the xymatrices, and I would really like them to be centered instead, in between the first and second rows. (Or, you know, wherever the center of the rows happens to be.)

What's an easy way to do this?

Answer 1

\[
  \vcenter{\xymatrix{A\\B}} = \vcenter{\xymatrix{a\\b}}
\]