dgamln.f
DOUBLE PRECISION FUNCTION DGAMLN (Z, IERR)
C***BEGIN PROLOGUE DGAMLN
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Warning: this routine is not intended to be user-callable.
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C***SUBSIDIARY
C***PURPOSE Compute the logarithm of the Gamma function
C***LIBRARY SLATEC
C***CATEGORY C7A
C***TYPE DOUBLE PRECISION (GAMLN-S, DGAMLN-D)
C***KEYWORDS LOGARITHM OF GAMMA FUNCTION
C***AUTHOR Amos, D. E., (SNL)
C***DESCRIPTION
C
C **** A DOUBLE PRECISION ROUTINE ****
C DGAMLN 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 Z IS D0UBLE PRECISION
C Z - ARGUMENT, Z.GT.0.0D0
C
C OUTPUT DGAMLN IS DOUBLE PRECISION
C DGAMLN - NATURAL LOG OF THE GAMMA FUNCTION AT Z.NE.0.0D0
C IERR - ERROR FLAG
C IERR=0, NORMAL RETURN, COMPUTATION COMPLETED
C IERR=1, Z.LE.0.0D0, NO COMPUTATION
C
C
C***REFERENCES COMPUTATION OF BESSEL FUNCTIONS OF COMPLEX ARGUMENT
C BY D. E. AMOS, SAND83-0083, MAY, 1983.
C***ROUTINES CALLED D1MACH, I1MACH
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 DGAMLN defined for Z negative. (WRB)
C***END PROLOGUE DGAMLN