Re: factorial of negative numbers

On Thu, Jun 18, 2020 at 1:57 PM Peter Eisentraut <
peter(dot)eisentraut(at)2ndquadrant(dot)com> wrote:

> On 2020-06-18 09:43, Juan José Santamaría Flecha wrote:
> > The gamma function from math.h returns a NaN for negative integer
> > values, the postgres factorial function returns a numeric, which allows
> > NaN. Raising an out-of-range error seems only reasonable for an integer
> > output.
>
> But this is not the gamma function. The gamma function is undefined at
> zero, but factorial(0) returns 1. So this is similar but not the same.
>

factorial(n) = gamma(n + 1)

> Moreover, functions such as log() also error out on unsupportable input
> values, so it's consistent with the spec.
>

If factorial() ever gets extended to other input types it might get
inconsistent, should !(-1.0) also raise an error?

Logarithm is just different case:

https://en.wikipedia.org/wiki/Logarithm#/media/File:Log4.svg

Regards,

Juan José Santamaría Flecha