Re: factorial of negative numbers

On Tue, 16 Jun 2020 at 06:00, Ashutosh Bapat
<ashutosh.bapat@2ndquadrant.com> wrote:
>
> Divison by zero is really undefined, 12345678 * 12345678 (just some numbers) is out of range of say int4, but factorial of a negative number has some meaning and is defined but PostgreSQL does not support it.
>

Actually, I think undefined/out-of-range is the right error to throw here.

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.

Regards,
Dean

[1] https://en.wikipedia.org/wiki/Factorial
[2] https://en.wikipedia.org/wiki/Gamma_function