*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