- `Y = sign (X)`

Compute the "signum" function.

This is defined as

> > `%sign (x) = x ./ abs (X)%`

See also: `signbit`.

### References

- https://www.mathworks.com/help/matlab/ref/sign.html
- https://octave.sourceforge.io/octave/function/sign.html
- https://mathworld.wolfram.com/Sign.html
- https://en.wikipedia.org/wiki/Sign_function