# gamln.f

          REAL FUNCTION GAMLN (Z, IERR)
    C***BEGIN PROLOGUE  GAMLN
    ....
    ....
    Warning:   this routine is not intended to be user-callable.
    ....
    ....
    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