- `V = gamma (Z)`

Compute the Gamma function.

The Gamma function is defined as

`%gamma (z) = integral (t^(z-1) * exp (-t), t, 0, Inf)%`

Programming Note: The `gamma` function can grow quite large even for small
input values. In many cases it may be preferable to use the natural logarithm
of the gamma function (`gammaln`) in calculations to minimize loss of
precision. The final result is then `exp (RESULT_USING_GAMMALN)`.

See also: `gammainc`, `gammaln`, `factorial`.

### References

- https://www.mathworks.com/help/matlab/ref/gamma.html
- https://octave.sourceforge.io/octave/function/gamma.html
- https://mathworld.wolfram.com/GammaFunction.html
- https://en.wikipedia.org/wiki/Gamma_function