Re: [Numpy-discussion] Should numpy.sqrt(-1) return 1j rather than?nan?

[Stefan v. d. W. <st...@su...>]

On Thu, Oct 12, 2006 at 10:53:12AM -0400, Alan G Isaac wrote:
> On Thu, 12 Oct 2006, Stefan van der Walt apparently wrote:=20
> > I tried to explain the argument at=20
> > http://www.scipy.org/NegativeSquareRoot=20
>=20
> Helpful.  But you start off by saying:
>         In mathematics, the above assumption is true -- that=20
>         the square root of -1 is 1j.
>=20
> Since square root is (here) a function, and part of the=20
> function definition is the domain and codomain, this=20
> statement is not correct.  If the codomain is real numbers,=20
> the domain must correspondingly be (a subset of) the=20
> nonnegative reals.  The nan output is the result of an=20
> **invalid** input.
>=20
> So the question is really: "Why is a negative real number an=20
> invalid input in this implementation", or "Why in this=20
> implementation is the type of the output restricted by the=20
> type of the input?" You get a good start on answering that.

You are more than welcome to change the wiki if you can think of a
simpler way to explain the problem... In fact, I would encourage that
-- I just put it there as a starting point.

Cheers
St=E9fan