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51 lines
1.6 KiB
Fortran
51 lines
1.6 KiB
Fortran
*DECK BETA
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FUNCTION BETA (A, B)
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C***BEGIN PROLOGUE BETA
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C***PURPOSE Compute the complete Beta function.
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C***LIBRARY SLATEC (FNLIB)
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C***CATEGORY C7B
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C***TYPE SINGLE PRECISION (BETA-S, DBETA-D, CBETA-C)
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C***KEYWORDS COMPLETE BETA FUNCTION, FNLIB, SPECIAL FUNCTIONS
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C***AUTHOR Fullerton, W., (LANL)
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C***DESCRIPTION
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C
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C BETA computes the complete beta function.
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C
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C Input Parameters:
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C A real and positive
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C B real and positive
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C
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C***REFERENCES (NONE)
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C***ROUTINES CALLED ALBETA, GAMLIM, GAMMA, R1MACH, XERMSG
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C***REVISION HISTORY (YYMMDD)
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C 770601 DATE WRITTEN
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C 890531 Changed all specific intrinsics to generic. (WRB)
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C 890531 REVISION DATE from Version 3.2
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C 891214 Prologue converted to Version 4.0 format. (BAB)
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C 900315 CALLs to XERROR changed to CALLs to XERMSG. (THJ)
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C 900326 Removed duplicate information from DESCRIPTION section.
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C (WRB)
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C 900727 Added EXTERNAL statement. (WRB)
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C***END PROLOGUE BETA
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EXTERNAL GAMMA
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SAVE XMAX, ALNSML
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DATA XMAX, ALNSML /0., 0./
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C***FIRST EXECUTABLE STATEMENT BETA
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IF (ALNSML.NE.0.0) GO TO 10
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CALL GAMLIM (XMIN, XMAX)
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ALNSML = LOG(R1MACH(1))
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C
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10 IF (A .LE. 0. .OR. B .LE. 0.) CALL XERMSG ('SLATEC', 'BETA',
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+ 'BOTH ARGUMENTS MUST BE GT 0', 2, 2)
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C
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IF (A+B.LT.XMAX) BETA = GAMMA(A) * GAMMA(B) / GAMMA(A+B)
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IF (A+B.LT.XMAX) RETURN
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C
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BETA = ALBETA (A, B)
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IF (BETA .LT. ALNSML) CALL XERMSG ('SLATEC', 'BETA',
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+ 'A AND/OR B SO BIG BETA UNDERFLOWS', 1, 2)
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C
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BETA = EXP (BETA)
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C
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RETURN
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END
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