FUNCTION PSI(X)
C***BEGIN PROLOGUE  PSI
C***DATE WRITTEN   770401   (YYMMDD)
C***REVISION DATE  820801   (YYMMDD)
C***CATEGORY NO.  C7C
C***KEYWORDS  DIGAMMA FUNCTION,PSI FUNCTION,SPECIAL FUNCTION
C***AUTHOR  FULLERTON, W., (LANL)
C***PURPOSE  Computes the Psi (or Digamma) function.
C***DESCRIPTION
C
C PSI(X) calculates the psi (or digamma) function for real argument X.
C PSI(X) is the logarithmic derivative of the gamma function of X.
C
C Series for PSI        on the interval  0.          to  1.00000D+00
C                                        with weighted error   2.03E-17
C                                         log weighted error  16.69
C                               significant figures required  16.39
C                                    decimal places required  17.37
C
C Series for APSI       on the interval  0.          to  2.50000D-01
C                                        with weighted error   5.54E-17
C                                         log weighted error  16.26
C                               significant figures required  14.42
C                                    decimal places required  16.86
C***REFERENCES  (NONE)
C***ROUTINES CALLED  CSEVL,INITS,R1MACH,XERROR
C***END PROLOGUE  PSI