Yes, that sounds like a reasonable change.
On Fri, 10 Apr 2020 at 14:17, jlh <j...@gmx.ch> wrote:
>
> Hello everyone!
>
> I noticed that powers of non-square matrices (with MatPow) do not raise an
> error, e.g. if A = MatrixSymbol('A', 2, 3) then MatPow(A, 10) does not raise.
> I would assume that this is just an oversight, but then I see explicit unit
> tests for MatPow(A, 1), which make me wonder if perhaps there is a reason
> this is supported. However the behavior is not consistent, since A ** 1 does
> raise an error anyway. But then again ZeroMatrix(2, 3) ** 1 does not raise.
>
> As far as I know most textbooks do not define A ** n at all for any value of
> n when A is not square. This might also be of interest:
> https://math.stackexchange.com/questions/101590/what-is-zero-power-of-a-non-square-matrix
>
> So question: Would it be an acceptable breaking change to completely forbid
> powers of non-square matrices, including the barely useful MatPow(A, 0) and
> MatPow(A, 1)? It doesn't seem to break any tests (other than test_matpow.py).
>
> Background: I plan to do some clean-up in the MatPow code to make it follow
> the same convention used in other places, e.g. move the argument validation
> from MatrixExpr.__pow__() to MatPow.__new__() and move some specialized code
> from MatPow.doit() to the _eval_power() methods of respective sub-classes.
>
> Thanks!
>
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