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| ANSI Common Lisp 12 Numbers 12.2 Dictionary of Numbers
12.2.49 phase | Function
  Syntax: phase number phase Arguments and Values: number - a number. phase - a number. Description: phase 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 real number is zero; that of a negative real 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))` Examples:
       (phase 1)  0.0s0
       (phase 0)  0.0s0
       (phase (cis 30))  -1.4159266
       (phase #c(0 1))  1.5707964
Exceptional Situations: Should signal type-error if its argument is not a number. Might signal arithmetic-error. See Also: Section 12.1.3.3 Rule of Float Substitutability Allegro CL Implementation Details: None.

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