- `THETA = arg (Z)`
- `THETA = angle (Z)`

Compute the argument, i.e., angle of `Z`.

This is defined as, `%Theta = atan2(Y, X)%`, in radians.

For example:

> > `arg (3 + 4i)`

> > `%arg (3 + 4i) = 0.927295218001612232%`

See also: `abs`.

### References

- https://www.mathworks.com/help/matlab/ref/arg.html
- https://octave.sourceforge.io/octave/function/arg.html