2009/6/23 Emmanuel Thomé <emmanuel.th...@gmail.com>:
>
>
> I wonder what happens here:
>
> tiramisu ~ $ sage
> ----------------------------------------------------------------------
> | Sage Version 4.0, Release Date: 2009-05-29 |
> | Type notebook() for the GUI, and license() for information. |
> ----------------------------------------------------------------------
> sage: p=3
> sage: n=1000
> sage: K=GF(p)
> sage: KP.<x>=PolynomialRing(K)
> sage: MS=MatrixSpace(K,n,n);
> sage: A=MS.random_element()
> sage: MSP=MatrixSpace(KP,n,n);
> sage: time xI=x*MSP.identity_matrix()
> CPU times: user 17.37 s, sys: 0.15 s, total: 17.52 s
> Wall time: 17.54 s
> sage: time xI=diagonal_matrix([x for i in range(n)])
> CPU times: user 32.18 s, sys: 0.14 s, total: 32.33 s
> Wall time: 32.34 s
> sage: time xI.determinant()
> <got fed up before it finishes...>
>
Type xl.determinant?? to see:
..
# fall back to very very stupid algorithm -- expansion by minors.
# TODO: surely there is something much better, even in total
generality...
# this is ridiculous.
d = self._det_by_minors(self._ncols)
self.cache('det', d)
return d
William
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