CLHS: Constant Variable PI

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Constant Variable PI

Value:

an implementation-dependent long float.

Description:

The best long float approximation to the mathematical constant <PI>.

Examples:

     ;; In each of the following computations, the precision depends
     ;; on the implementation.  Also, if `long float' is treated by
     ;; the implementation as equivalent to some other float format
     ;; (e.g., `double float') the exponent marker might be the marker
     ;; for that equivalent (e.g., `D' instead of `L').
     pi =>  3.141592653589793L0
     (cos pi) =>  -1.0L0

     (defun sin-of-degrees (degrees)
       (let ((x (if (floatp degrees) degrees (float degrees pi))))
         (sin (* x (/ (float pi x) 180)))))

See Also: None.

Notes:

An approximation to <PI> in some other precision can be obtained by writing `(float pi x)`, where `x` is a float of the desired precision, or by writing `(coerce pi` type`)`, where type is the desired type, such as short-float.

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