SLATEC Routines --- GAMLN ---

*DECK GAMLN
      REAL FUNCTION GAMLN (Z, IERR)
C***BEGIN PROLOGUE  GAMLN
C***SUBSIDIARY
C***PURPOSE  Compute the logarithm of the Gamma function
C***LIBRARY   SLATEC
C***CATEGORY  C7A
C***TYPE      SINGLE PRECISION (GAMLN-S, DGAMLN-D)
C***KEYWORDS  LOGARITHM OF GAMMA FUNCTION
C***AUTHOR  Amos, D. E., (SNL)
C***DESCRIPTION
C
C         GAMLN COMPUTES THE NATURAL LOG OF THE GAMMA FUNCTION FOR
C         Z.GT.0.  THE ASYMPTOTIC EXPANSION IS USED TO GENERATE VALUES
C         GREATER THAN ZMIN WHICH ARE ADJUSTED BY THE RECURSION
C         G(Z+1)=Z*G(Z) FOR Z.LE.ZMIN.  THE FUNCTION WAS MADE AS
C         PORTABLE AS POSSIBLE BY COMPUTING ZMIN FROM THE NUMBER OF BASE
C         10 DIGITS IN A WORD, RLN=MAX(-ALOG10(R1MACH(4)),0.5E-18)
C         LIMITED TO 18 DIGITS OF (RELATIVE) ACCURACY.
C
C         SINCE INTEGER ARGUMENTS ARE COMMON, A TABLE LOOK UP ON 100
C         VALUES IS USED FOR SPEED OF EXECUTION.
C
C     DESCRIPTION OF ARGUMENTS
C
C         INPUT
C           Z      - REAL ARGUMENT, Z.GT.0.0E0
C
C         OUTPUT
C           GAMLN  - NATURAL LOG OF THE GAMMA FUNCTION AT Z
C           IERR   - ERROR FLAG
C                    IERR=0, NORMAL RETURN, COMPUTATION COMPLETED
C                    IERR=1, Z.LE.0.0E0,    NO COMPUTATION
C
C***REFERENCES  COMPUTATION OF BESSEL FUNCTIONS OF COMPLEX ARGUMENT
C                 BY D. E. AMOS, SAND83-0083, MAY, 1983.
C***ROUTINES CALLED  I1MACH, R1MACH
C***REVISION HISTORY  (YYMMDD)
C   830501  DATE WRITTEN
C   830501  REVISION DATE from Version 3.2
C   910415  Prologue converted to Version 4.0 format.  (BAB)
C   920128  Category corrected.  (WRB)
C   921215  GAMLN defined for Z negative.  (WRB)
C***END PROLOGUE  GAMLN