Re: factorial of negative numbers

On Tue, Jun 16, 2020 at 10:55 AM Bruce Momjian <bruce(at)momjian(dot)us> wrote:

> On Tue, Jun 16, 2020 at 08:31:21AM +0100, Dean Rasheed wrote:
> >
> > Most common implementations do regard factorial as undefined for
> > anything other than positive integers, as well as following the
> > convention that factorial(0) = 1. Some implementations extend the
> > factorial to non-integer inputs, negative inputs, or even complex
> > inputs by defining it in terms of the gamma function. However, even
> > then, it is undefined for negative integer inputs.
>
> Wow, they define it for negative inputs, but not negative integer
> inputs? I am curious what the logic is behind that.
>

It is defined as NaN (or undefined), which is not in the realm of integer
numbers. You might get a clear idea of the logic from [1], where they also
make a case for the error being ERRCODE_DIVISION_BY_ZERO.

[1] http://mathforum.org/library/drmath/view/60851.html

Regards,

Juan José Santamaría Flecha