! REV PROCESSED 213 LINES OF CODE. PROGRAM DONE. REAL FUNCTION GAMMA1(X) use da_control, only : pi !D DOUBLE PRECISION FUNCTION DGAMMA(X) !---------------------------------------------------------------------- ! ! THIS ROUTINE CALCULATES THE GAMMA FUNCTION FOR A REAL ARGUMENT X. ! COMPUTATION IS BASED ON AN ALGORITHM OUTLINED IN REFERENCE 1. ! THE PROGRAM USES RATIONAL FUNCTIONS THAT APPROXIMATE THE GAMMA ! FUNCTION TO AT LEAST 20 SIGNIFICANT DECIMAL DIGITS. COEFFICIENTS ! FOR THE APPROXIMATION OVER THE INTERVAL (1,2) ARE UNPUBLISHED. ! THOSE FOR THE APPROXIMATION FOR X .GE. 12 ARE FROM REFERENCE 2. ! THE ACCURACY ACHIEVED DEPENDS ON THE ARITHMETIC SYSTEM, THE ! COMPILER, THE INTRINSIC FUNCTIONS, AND PROPER SELECTION OF THE ! MACHINE-DEPENDENT CONSTANTS. ! ! !******************************************************************* !******************************************************************* ! ! EXPLANATION OF MACHINE-DEPENDENT CONSTANTS ! ! BETA - RADIX FOR THE FLOATING-POINT REPRESENTATION ! MAXEXP - THE SMALLEST POSITIVE POWER OF BETA THAT OVERFLOWS ! XBIG - THE LARGEST ARGUMENT FOR WHICH GAMMA(X) IS REPRESENTABLE ! IN THE MACHINE, I.E., THE SOLUTION TO THE EQUATION ! GAMMA(XBIG) = BETA**MAXEXP ! XINF - THE LARGEST MACHINE REPRESENTABLE FLOATING-POINT NUMBER; ! APPROXIMATELY BETA**MAXEXP ! EPS - THE SMALLEST POSITIVE FLOATING-POINT NUMBER SUCH THAT ! 1.0+EPS .GT. 1.0 ! XMININ - THE SMALLEST POSITIVE FLOATING-POINT NUMBER SUCH THAT ! 1/XMININ IS MACHINE REPRESENTABLE ! ! APPROXIMATE VALUES FOR SOME IMPORTANT MACHINES ARE: ! ! BETA MAXEXP XBIG ! ! CRAY-1 (S.P.) 2 8191 966.961 ! CYBER 180/855 ! UNDER NOS (S.P.) 2 1070 177.803 ! IEEE (IBM/XT, ! SUN, ETC.) (S.P.) 2 128 35.040 ! IEEE (IBM/XT, ! SUN, ETC.) (D.P.) 2 1024 171.624 ! IBM 3033 (D.P.) 16 63 57.574 ! VAX D-FORMAT (D.P.) 2 127 34.844 ! VAX G-FORMAT (D.P.) 2 1023 171.489 ! ! XINF EPS XMININ ! ! CRAY-1 (S.P.) 5.45E+2465 7.11E-15 1.84E-2466 ! CYBER 180/855 ! UNDER NOS (S.P.) 1.26E+322 3.55E-15 3.14E-294 ! IEEE (IBM/XT, ! SUN, ETC.) (S.P.) 3.40E+38 1.19E-7 1.18E-38 ! IEEE (IBM/XT, ! SUN, ETC.) (D.P.) 1.79D+308 2.22D-16 2.23D-308 ! IBM 3033 (D.P.) 7.23D+75 2.22D-16 1.39D-76 ! VAX D-FORMAT (D.P.) 1.70D+38 1.39D-17 5.88D-39 ! VAX G-FORMAT (D.P.) 8.98D+307 1.11D-16 1.12D-308 ! !******************************************************************* !******************************************************************* ! ! ERROR RETURNS ! ! THE PROGRAM RETURNS THE VALUE XINF FOR SINGULARITIES OR ! WHEN OVERFLOW WOULD OCCUR. THE COMPUTATION IS BELIEVED ! TO BE FREE OF UNDERFLOW AND OVERFLOW. ! ! ! INTRINSIC FUNCTIONS REQUIRED ARE: ! ! INT, DBLE, EXP, LOG, REAL, SIN ! ! ! REFERENCES: AN OVERVIEW OF SOFTWARE DEVELOPMENT FOR SPECIAL ! FUNCTIONS W. J. CODY, LECTURE NOTES IN MATHEMATICS, ! 506, NUMERICAL ANALYSIS DUNDEE, 1975, G. A. WATSON ! (ED.), SPRINGER VERLAG, BERLIN, 1976. ! ! COMPUTER APPROXIMATIONS, HART, ET. AL., WILEY AND ! SONS, NEW YORK, 1968. ! ! LATEST MODIFICATION: OCTOBER 12, 1989 ! ! AUTHORS: W. J. CODY AND L. STOLTZ ! APPLIED MATHEMATICS DIVISION ! ARGONNE NATIONAL LABORATORY ! ARGONNE, IL 60439 ! !---------------------------------------------------------------------- INTEGER I,N LOGICAL PARITY !D DOUBLE PRECISION REAL :: & C,CONV,EPS,FACT,HALF,ONE,P,Q,RES,SQRTPI,SUM,TWELVE, & TWO,X,XBIG,XDEN,XINF,XMININ,XNUM,Y,Y1,YSQ,Z,ZERO DIMENSION C(7),P(8),Q(8) !---------------------------------------------------------------------- ! MATHEMATICAL CONSTANTS !---------------------------------------------------------------------- DATA ONE,HALF,TWELVE,TWO,ZERO/1.0E0,0.5E0,12.0E0,2.0E0,0.0E0/, & SQRTPI/0.9189385332046727417803297E0/ !D DATA ONE,HALF,TWELVE,TWO,ZERO/1.0D0,0.5D0,12.0D0,2.0D0,0.0D0/, !D 1 SQRTPI/0.9189385332046727417803297D0/, !---------------------------------------------------------------------- ! MACHINE DEPENDENT PARAMETERS !---------------------------------------------------------------------- DATA XBIG,XMININ,EPS/35.040E0,1.18E-38,1.19E-7/, & XINF/3.4E38/ !D DATA XBIG,XMININ,EPS/171.624D0,2.23D-308,2.22D-16/, !D 1 XINF/1.79D308/ !---------------------------------------------------------------------- ! NUMERATOR AND DENOMINATOR COEFFICIENTS FOR RATIONAL MINIMAX ! APPROXIMATION OVER (1,2). !---------------------------------------------------------------------- DATA P/-1.71618513886549492533811E+0,2.47656508055759199108314E+1, & -3.79804256470945635097577E+2,6.29331155312818442661052E+2, & 8.66966202790413211295064E+2,-3.14512729688483675254357E+4, & -3.61444134186911729807069E+4,6.64561438202405440627855E+4/ DATA Q/-3.08402300119738975254353E+1,3.15350626979604161529144E+2, & -1.01515636749021914166146E+3,-3.10777167157231109440444E+3, & 2.25381184209801510330112E+4,4.75584627752788110767815E+3, & -1.34659959864969306392456E+5,-1.15132259675553483497211E+5/ !D DATA P/-1.71618513886549492533811D+0,2.47656508055759199108314D+1, !D 1 -3.79804256470945635097577D+2,6.29331155312818442661052D+2, !D 2 8.66966202790413211295064D+2,-3.14512729688483675254357D+4, !D 3 -3.61444134186911729807069D+4,6.64561438202405440627855D+4/ !D DATA Q/-3.08402300119738975254353D+1,3.15350626979604161529144D+2, !D 1 -1.01515636749021914166146D+3,-3.10777167157231109440444D+3, !D 2 2.25381184209801510330112D+4,4.75584627752788110767815D+3, !D 3 -1.34659959864969306392456D+5,-1.15132259675553483497211D+5/ !---------------------------------------------------------------------- ! COEFFICIENTS FOR MINIMAX APPROXIMATION OVER (12, INF). !---------------------------------------------------------------------- DATA C/-1.910444077728E-03,8.4171387781295E-04, & -5.952379913043012E-04,7.93650793500350248E-04, & -2.777777777777681622553E-03,8.333333333333333331554247E-02, & 5.7083835261E-03/ !D DATA C/-1.910444077728D-03,8.4171387781295D-04, !D 1 -5.952379913043012D-04,7.93650793500350248D-04, !D 2 -2.777777777777681622553D-03,8.333333333333333331554247D-02, !D 3 5.7083835261D-03/ !---------------------------------------------------------------------- ! STATEMENT FUNCTIONS FOR CONVERSION BETWEEN INTEGER AND FLOAT !---------------------------------------------------------------------- CONV(I) = REAL(I) !D CONV(I) = DBLE(I) PARITY=.FALSE. FACT=ONE N=0 Y=X IF(Y.LE.ZERO)THEN !---------------------------------------------------------------------- ! ARGUMENT IS NEGATIVE !---------------------------------------------------------------------- Y=-X Y1=AINT(Y) RES=Y-Y1 IF(RES.NE.ZERO)THEN IF(Y1.NE.AINT(Y1*HALF)*TWO)PARITY=.TRUE. FACT=-PI/SIN(PI*RES) Y=Y+ONE ELSE RES=XINF GOTO 900 ENDIF ENDIF !---------------------------------------------------------------------- ! ARGUMENT IS POSITIVE !---------------------------------------------------------------------- IF(Y.LT.EPS)THEN !---------------------------------------------------------------------- ! ARGUMENT .LT. EPS !---------------------------------------------------------------------- IF(Y.GE.XMININ)THEN RES=ONE/Y ELSE RES=XINF GOTO 900 ENDIF ELSEIF(Y.LT.TWELVE)THEN Y1=Y IF(Y.LT.ONE)THEN !---------------------------------------------------------------------- ! 0.0 .LT. ARGUMENT .LT. 1.0 !---------------------------------------------------------------------- Z=Y Y=Y+ONE ELSE !---------------------------------------------------------------------- ! 1.0 .LT. ARGUMENT .LT. 12.0, REDUCE ARGUMENT IF NECESSARY !---------------------------------------------------------------------- N=INT(Y)-1 Y=Y-CONV(N) Z=Y-ONE ENDIF !---------------------------------------------------------------------- ! EVALUATE APPROXIMATION FOR 1.0 .LT. ARGUMENT .LT. 2.0 !---------------------------------------------------------------------- XNUM=ZERO XDEN=ONE DO 260 I=1,8 XNUM=(XNUM+P(I))*Z XDEN=XDEN*Z+Q(I) 260 CONTINUE RES=XNUM/XDEN+ONE IF(Y1.LT.Y)THEN !---------------------------------------------------------------------- ! ADJUST RESULT FOR CASE 0.0 .LT. ARGUMENT .LT. 1.0 !---------------------------------------------------------------------- RES=RES/Y1 ELSEIF(Y1.GT.Y)THEN !---------------------------------------------------------------------- ! ADJUST RESULT FOR CASE 2.0 .LT. ARGUMENT .LT. 12.0 !---------------------------------------------------------------------- DO 290 I=1,N RES=RES*Y Y=Y+ONE 290 CONTINUE ENDIF ELSE !---------------------------------------------------------------------- ! EVALUATE FOR ARGUMENT .GE. 12.0, !---------------------------------------------------------------------- IF(Y.LE.XBIG)THEN YSQ=Y*Y SUM=C(7) DO 350 I=1,6 SUM=SUM/YSQ+C(I) 350 CONTINUE SUM=SUM/Y-Y+SQRTPI SUM=SUM+(Y-HALF)*LOG(Y) RES=EXP(SUM) ELSE RES=XINF GOTO 900 ENDIF ENDIF !---------------------------------------------------------------------- ! FINAL ADJUSTMENTS AND RETURN !---------------------------------------------------------------------- IF(PARITY)RES=-RES IF(FACT.NE.ONE)RES=FACT/RES 900 GAMMA1=RES !D900 DGAMMA = RES ! ---------- LAST LINE OF GAMMA ---------- END FUNCTION GAMMA1