mirror of
https://git.planet-casio.com/Lephenixnoir/OpenLibm.git
synced 2025-01-01 06:23:39 +01:00
54 lines
1.6 KiB
Fortran
54 lines
1.6 KiB
Fortran
*DECK D9LGIC
|
|
DOUBLE PRECISION FUNCTION D9LGIC (A, X, ALX)
|
|
C***BEGIN PROLOGUE D9LGIC
|
|
C***SUBSIDIARY
|
|
C***PURPOSE Compute the log complementary incomplete Gamma function
|
|
C for large X and for A .LE. X.
|
|
C***LIBRARY SLATEC (FNLIB)
|
|
C***CATEGORY C7E
|
|
C***TYPE DOUBLE PRECISION (R9LGIC-S, D9LGIC-D)
|
|
C***KEYWORDS COMPLEMENTARY INCOMPLETE GAMMA FUNCTION, FNLIB, LARGE X,
|
|
C LOGARITHM, SPECIAL FUNCTIONS
|
|
C***AUTHOR Fullerton, W., (LANL)
|
|
C***DESCRIPTION
|
|
C
|
|
C Compute the log complementary incomplete gamma function for large X
|
|
C and for A .LE. X.
|
|
C
|
|
C***REFERENCES (NONE)
|
|
C***ROUTINES CALLED D1MACH, XERMSG
|
|
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 900315 CALLs to XERROR changed to CALLs to XERMSG. (THJ)
|
|
C 900720 Routine changed from user-callable to subsidiary. (WRB)
|
|
C***END PROLOGUE D9LGIC
|
|
DOUBLE PRECISION A, X, ALX, EPS, FK, P, R, S, T, XMA, XPA, D1MACH
|
|
SAVE EPS
|
|
DATA EPS / 0.D0 /
|
|
C***FIRST EXECUTABLE STATEMENT D9LGIC
|
|
IF (EPS.EQ.0.D0) EPS = 0.5D0*D1MACH(3)
|
|
C
|
|
XPA = X + 1.0D0 - A
|
|
XMA = X - 1.D0 - A
|
|
C
|
|
R = 0.D0
|
|
P = 1.D0
|
|
S = P
|
|
DO 10 K=1,300
|
|
FK = K
|
|
T = FK*(A-FK)*(1.D0+R)
|
|
R = -T/((XMA+2.D0*FK)*(XPA+2.D0*FK)+T)
|
|
P = R*P
|
|
S = S + P
|
|
IF (ABS(P).LT.EPS*S) GO TO 20
|
|
10 CONTINUE
|
|
CALL XERMSG ('SLATEC', 'D9LGIC',
|
|
+ 'NO CONVERGENCE IN 300 TERMS OF CONTINUED FRACTION', 1, 2)
|
|
C
|
|
20 D9LGIC = A*ALX - X + LOG(S/XPA)
|
|
C
|
|
RETURN
|
|
END
|