[Numpy-discussion] matrix multiply
Anne Archibald
peridot.faceted@gmail....
Sun Apr 6 12:49:49 CDT 2008
On 06/04/2008, Alan G Isaac <aisaac@american.edu> wrote:
> Just checking:
> it's important to me that this won't change
> the behavior of boolean matrices, but I don't
> see a test for this. E.g., ::
>
> >>> import numpy as N
> >>> A = N.mat('1 0;1 1',dtype='bool')
> >>> A**2
> matrix([[ True, False],
> [ True, True]], dtype=bool)
I have no desire to change the behaviour of boolean matrices, and I'll
write a test, but what is it supposed to do with them? Just produce
reduce(dot,[A]*n)? For zero it will give the identity, and for
negative powers some sort of floating-point inverse. Currently for
positive powers it should produce the right answer provided
multiplication is associative (which I think it is).
The inverse actually poses a problem: should it return (A**(-1))**n or
(A**n)**(-1)? (No, they're not the same for boolean matrices.)
Anne
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