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*DECK DGAMR
DOUBLE PRECISION FUNCTION DGAMR (X)
C***BEGIN PROLOGUE DGAMR
C***PURPOSE Compute the reciprocal of the Gamma function.
C***LIBRARY SLATEC (FNLIB)
C***CATEGORY C7A
C***TYPE DOUBLE PRECISION (GAMR-S, DGAMR-D, CGAMR-C)
C***KEYWORDS FNLIB, RECIPROCAL GAMMA FUNCTION, SPECIAL FUNCTIONS
C***AUTHOR Fullerton, W., (LANL)
C***DESCRIPTION
C
C DGAMR(X) calculates the double precision reciprocal of the
C complete Gamma function for double precision argument X.
C
C***REFERENCES (NONE)
C***ROUTINES CALLED DGAMMA, DLGAMS, XERCLR, XGETF, XSETF
C***REVISION HISTORY (YYMMDD)
C 770701 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 900727 Added EXTERNAL statement. (WRB)
C***END PROLOGUE DGAMR
DOUBLE PRECISION X, ALNGX, SGNGX, DGAMMA
EXTERNAL DGAMMA
C***FIRST EXECUTABLE STATEMENT DGAMR
DGAMR = 0.0D0
IF (X.LE.0.0D0 .AND. AINT(X).EQ.X) RETURN
C
CALL XGETF (IROLD)
CALL XSETF (1)
IF (ABS(X).GT.10.0D0) GO TO 10
DGAMR = 1.0D0/DGAMMA(X)
CALL XERCLR
CALL XSETF (IROLD)
RETURN
C
10 CALL DLGAMS (X, ALNGX, SGNGX)
CALL XERCLR
CALL XSETF (IROLD)
DGAMR = SGNGX * EXP(-ALNGX)
RETURN
C
END
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