Procedure

     PI ( Value of pi )

     DOUBLE PRECISION FUNCTION PI ( )

Abstract

     Return the value of pi (the ratio of the circumference of
     a circle to its diameter).

Required_Reading

     None.

Keywords

     CONSTANTS

Declarations

    None.

Brief_I/O

     The function returns the value of pi.

Detailed_Input

     None.

Detailed_Output

     The function returns the value of pi (the ratio of a circle's
     circumference to its diameter), determined by the ACOS function.
     That is,

           PI = ACOS ( -1.D0 )

Parameters

     None.

Exceptions

     Error free.

Files

     None.

Particulars

     The first time the function is referenced, the value is computed
     as shown above. The value is saved, and returned directly upon
     subsequent reference.

Examples

     The code fragment below illustrates the use of PI.

        C
        C     Compute the polar radius,
        C
        C                 p
        C          ----------------
        C          1 + e cos(theta)
        C
        C     at evenly spaced values of the polar angle, theta.
        C
              DELTA = PI() / N

              DO I = 0, N
                 R(I) = P / (1.D0 + ECC * COS(I*DELTA))
              END DO

Restrictions

     None.

Literature_References

     None.

Author_and_Institution

     J. Diaz del Rio    (ODC Space)
     W.L. Taber         (JPL)
     I.M. Underwood     (JPL)

Version

    SPICELIB Version 1.0.2, 08-JUL-2020 (JDR)

        Edited the header to comply with NAIF standard.

    SPICELIB Version 1.0.1, 10-MAR-1992 (WLT)

        Comment section for permuted index source lines was added
        following the header.

    SPICELIB Version 1.0.0, 31-JAN-1990 (WLT) (IMU)