returns the phase
of number (the angle part of its polar representation)
in radians, in the range
- pi (exclusive) if minus zero is not supported, or
- pi (inclusive) if minus zero is supported,
to pi (inclusive). The phase of a positive
is zero; that of a negative
number is pi .
The phase of zero is defined to be zero.
If number is a complex float,
the result is a float of the same type
as the components of number.
If number is a float, the result is a
float of the same type.
If number is a rational or a complex rational,
the result is a single float.
The branch cut for phase lies along the negative real
axis, continuous with quadrant II. The range consists of that portion of
the real axis between - pi (exclusive) and pi (inclusive).
The mathematical definition of phase is as follows:
(phase x) = (atan (imagpart x) (realpart x))