*DECK DGAMLM SUBROUTINE DGAMLM (XMIN, XMAX) C***BEGIN PROLOGUE DGAMLM C***PURPOSE Compute the minimum and maximum bounds for the argument in C the Gamma function. C***LIBRARY SLATEC (FNLIB) C***CATEGORY C7A, R2 C***TYPE DOUBLE PRECISION (GAMLIM-S, DGAMLM-D) C***KEYWORDS COMPLETE GAMMA FUNCTION, FNLIB, LIMITS, SPECIAL FUNCTIONS C***AUTHOR Fullerton, W., (LANL) C***DESCRIPTION C C Calculate the minimum and maximum legal bounds for X in gamma(X). C XMIN and XMAX are not the only bounds, but they are the only non- C trivial ones to calculate. C C Output Arguments -- C XMIN double precision minimum legal value of X in gamma(X). Any C smaller value of X might result in underflow. C XMAX double precision maximum legal value of X in gamma(X). Any C larger value of X might cause overflow. C C***REFERENCES (NONE) C***ROUTINES CALLED D1MACH, XERMSG C***REVISION HISTORY (YYMMDD) C 770601 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 900315 CALLs to XERROR changed to CALLs to XERMSG. (THJ) C***END PROLOGUE DGAMLM DOUBLE PRECISION XMIN, XMAX, ALNBIG, ALNSML, XLN, XOLD, D1MACH C***FIRST EXECUTABLE STATEMENT DGAMLM ALNSML = LOG(D1MACH(1)) XMIN = -ALNSML DO 10 I=1,10 XOLD = XMIN XLN = LOG(XMIN) XMIN = XMIN - XMIN*((XMIN+0.5D0)*XLN - XMIN - 0.2258D0 + ALNSML) 1 / (XMIN*XLN+0.5D0) IF (ABS(XMIN-XOLD).LT.0.005D0) GO TO 20 10 CONTINUE CALL XERMSG ('SLATEC', 'DGAMLM', 'UNABLE TO FIND XMIN', 1, 2) C 20 XMIN = -XMIN + 0.01D0 C ALNBIG = LOG (D1MACH(2)) XMAX = ALNBIG DO 30 I=1,10 XOLD = XMAX XLN = LOG(XMAX) XMAX = XMAX - XMAX*((XMAX-0.5D0)*XLN - XMAX + 0.9189D0 - ALNBIG) 1 / (XMAX*XLN-0.5D0) IF (ABS(XMAX-XOLD).LT.0.005D0) GO TO 40 30 CONTINUE CALL XERMSG ('SLATEC', 'DGAMLM', 'UNABLE TO FIND XMAX', 2, 2) C 40 XMAX = XMAX - 0.01D0 XMIN = MAX (XMIN, -XMAX+1.D0) C RETURN END