Re: [Numpy-discussion] =?iso-8859-1?q?Should_numpy=2Esqrt=28-1=29_ret?= =?iso-8859-1?q?urn_1j_rather_than=09nan=3F?=

[Alan G I. <ai...@am...>]

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

Helpful.  But you start off by saying:
        In mathematics, the above assumption is true -- that=20
        the square root of -1 is 1j.

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.

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.

Cheers,
Alan Isaac