# Bordermatrix from LaTeX

How would I create an output similar to the result produced by this LaTeX code:

M = \bordermatrix{~ & x & y \cr
A & 1 & 0 \cr
B & 0 & 1 \cr}


which when compiled, looks like

-

This seems to work, at least for your example:

TraditionalForm @ Grid[{{Null, Grid[{{x, y}}]}, {TableForm@{{A}, {B}},
MatrixForm[IdentityMatrix[2]]}}]


You can make a little function that generalises it:

makeBordermatrix[mat_?MatrixQ, top_?VectorQ, side_?VectorQ] :=
Grid[{{Null, Grid[{top}]}, {TableForm[Transpose@{side}],
MatrixForm[mat]}}]


So we have:

makeBordermatrix[IdentityMatrix[3], {x, y, z}, {A, B, C}]


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By the way, welcolme to Mathematica.SE James! –  Verbeia Apr 26 '12 at 5:08
Ah nice, I didn't quite manage to get TraditionalForm to give it this way –  The Toad Apr 26 '12 at 5:12
This isn't very robust, though: try makeBordermatrix[IdentityMatrix[3] {aaaaaaaaaa, 0, 0}, {x, y, z}, {A, B, C}] and the columns get misaligned. To fix this, you could make each element of the top row have an Overlay in which all matrix entries below it are stacked on top of each other with Opacity[0], to force the top row to accomodate the maximum width of the row. –  Jens Apr 26 '12 at 6:53
@Jens I know, I didn't enforce matching dimensions or lengths of objects (limited lunch break time), but it would be straightforward to do. –  Verbeia Apr 26 '12 at 6:58