As can be seen, the elements are all over the place. What I would like is for all three matrix columns to be the same width, with each column aligned on the right side of the `G`. Is this possible to do without inserting invisible hand-tuned shims everywhere? (In particular, the `a`, `b`, and `\times` subscripts may change in future, and it would be nice to not have to redo all the shims.)
Is it a big and novel enough task that I should ask it as a question on the main site?
Your TeXpertise would again be most appreciated.