[Numpy-discussion] Recent work for branch cuts / C99 complex maths: problems on mingw

Charles R Harris charlesr.harris@gmail....
Tue Jul 29 09:44:35 CDT 2008

On Tue, Jul 29, 2008 at 8:38 AM, Pauli Virtanen <pav@iki.fi> wrote:

> Tue, 29 Jul 2008 08:13:23 -0600, Charles R Harris wrote:
> [clip]
> > We also need speed. I think we just say behaviour on the branch cuts is
> > undefined, which is numerically true in any case, and try to get the
> > nan's and infs sorted out. But only if the costs are reasonable.
> Well, the branch cut tests have succeeded on all platforms so far, which
> means the behavior is numerically well-defined. I doubt we can lose any
> speed by fixing sqrt in this respect.

Because of the discontinuity, roundoff error makes the behaviour undefined.
It's just a fact of computational life. I suspect we mean slightly different
things by "numerically" ;)

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