psi.f
FUNCTION PSI (X)
C***BEGIN PROLOGUE PSI
C***PURPOSE Compute the Psi (or Digamma) function.
C***LIBRARY SLATEC (FNLIB)
C***CATEGORY C7C
C***TYPE SINGLE PRECISION (PSI-S, DPSI-D, CPSI-C)
C***KEYWORDS DIGAMMA FUNCTION, FNLIB, PSI FUNCTION, SPECIAL FUNCTIONS
C***AUTHOR Fullerton, W., (LANL)
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
C***REFERENCES (NONE)
C***ROUTINES CALLED COT, CSEVL, INITS, R1MACH, XERMSG
C***REVISION HISTORY (YYMMDD)
C 770401 DATE WRITTEN
C 890531 Changed all specific intrinsics to generic. (WRB)
C 890531 REVISION DATE from Version 3.2
C 891214 Prologue converted to Version 4.0 format. (BAB)
C 900315 CALLs to XERROR changed to CALLs to XERMSG. (THJ)
C 900727 Added EXTERNAL statement. (WRB)
C 920618 Removed space from variable names. (RWC, WRB)
C***END PROLOGUE PSI