*DECK DGAMRN DOUBLE PRECISION FUNCTION DGAMRN (X) C***BEGIN PROLOGUE DGAMRN C***SUBSIDIARY C***PURPOSE Subsidiary to DBSKIN C***LIBRARY SLATEC C***TYPE DOUBLE PRECISION (GAMRN-S, DGAMRN-D) C***AUTHOR Amos, D. E., (SNLA) C***DESCRIPTION C C Abstract * A Double Precision Routine * C DGAMRN computes the GAMMA function ratio GAMMA(X)/GAMMA(X+0.5) C for real X.gt.0. If X.ge.XMIN, an asymptotic expansion is C evaluated. If X.lt.XMIN, an integer is added to X to form a C new value of X.ge.XMIN and the asymptotic expansion is eval- C uated for this new value of X. Successive application of the C recurrence relation C C W(X)=W(X+1)*(1+0.5/X) C C reduces the argument to its original value. XMIN and comp- C utational tolerances are computed as a function of the number C of digits carried in a word by calls to I1MACH and D1MACH. C However, the computational accuracy is limited to the max- C imum of unit roundoff (=D1MACH(4)) and 1.0D-18 since critical C constants are given to only 18 digits. C C Input X is Double Precision C X - Argument, X.gt.0.0D0 C C Output DGAMRN is DOUBLE PRECISION C DGAMRN - Ratio GAMMA(X)/GAMMA(X+0.5) C C***SEE ALSO DBSKIN C***REFERENCES Y. L. Luke, The Special Functions and Their C Approximations, Vol. 1, Math In Sci. And C Eng. Series 53, Academic Press, New York, 1969, C pp. 34-35. C***ROUTINES CALLED D1MACH, I1MACH C***REVISION HISTORY (YYMMDD) C 820601 DATE WRITTEN C 890531 Changed all specific intrinsics to generic. (WRB) C 890911 Removed unnecessary intrinsics. (WRB) C 891214 Prologue converted to Version 4.0 format. (BAB) C 900328 Added TYPE section. (WRB) C 910722 Updated AUTHOR section. (ALS) C 920520 Added REFERENCES section. (WRB) C***END PROLOGUE DGAMRN