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59 lines
2 KiB
Fortran
59 lines
2 KiB
Fortran
*DECK DXPSI
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DOUBLE PRECISION FUNCTION DXPSI (A, IPSIK, IPSIX)
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C***BEGIN PROLOGUE DXPSI
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C***SUBSIDIARY
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C***PURPOSE To compute values of the Psi function for DXLEGF.
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C***LIBRARY SLATEC
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C***CATEGORY C7C
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C***TYPE DOUBLE PRECISION (XPSI-S, DXPSI-D)
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C***KEYWORDS PSI FUNCTION
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C***AUTHOR Smith, John M., (NBS and George Mason University)
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C***ROUTINES CALLED (NONE)
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C***REVISION HISTORY (YYMMDD)
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C 820728 DATE WRITTEN
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C 890126 Revised to meet SLATEC CML recommendations. (DWL and JMS)
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C 901019 Revisions to prologue. (DWL and WRB)
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C 901106 Changed all specific intrinsics to generic. (WRB)
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C Corrected order of sections in prologue and added TYPE
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C section. (WRB)
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C 920127 Revised PURPOSE section of prologue. (DWL)
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C***END PROLOGUE DXPSI
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DOUBLE PRECISION A,B,C,CNUM,CDENOM
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DIMENSION CNUM(12),CDENOM(12)
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SAVE CNUM, CDENOM
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C
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C CNUM(I) AND CDENOM(I) ARE THE ( REDUCED ) NUMERATOR
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C AND 2*I*DENOMINATOR RESPECTIVELY OF THE 2*I TH BERNOULLI
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C NUMBER.
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C
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DATA CNUM(1),CNUM(2),CNUM(3),CNUM(4),CNUM(5),CNUM(6),CNUM(7),
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1CNUM(8),CNUM(9),CNUM(10),CNUM(11),CNUM(12)
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2 / 1.D0, -1.D0, 1.D0, -1.D0, 1.D0,
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3 -691.D0, 1.D0, -3617.D0, 43867.D0, -174611.D0, 77683.D0,
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4 -236364091.D0/
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DATA CDENOM(1),CDENOM(2),CDENOM(3),CDENOM(4),CDENOM(5),CDENOM(6),
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1 CDENOM(7),CDENOM(8),CDENOM(9),CDENOM(10),CDENOM(11),CDENOM(12)
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2/12.D0,120.D0, 252.D0, 240.D0,132.D0,
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3 32760.D0, 12.D0, 8160.D0, 14364.D0, 6600.D0, 276.D0, 65520.D0/
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C***FIRST EXECUTABLE STATEMENT DXPSI
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N=MAX(0,IPSIX-INT(A))
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B=N+A
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K1=IPSIK-1
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C
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C SERIES EXPANSION FOR A .GT. IPSIX USING IPSIK-1 TERMS.
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C
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C=0.D0
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DO 12 I=1,K1
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K=IPSIK-I
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12 C=(C+CNUM(K)/CDENOM(K))/B**2
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DXPSI=LOG(B)-(C+.5D0/B)
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IF(N.EQ.0) GO TO 20
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B=0.D0
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C
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C RECURRENCE FOR A .LE. IPSIX.
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C
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DO 15 M=1,N
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15 B=B+1.D0/(N-M+A)
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DXPSI=DXPSI-B
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20 RETURN
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END
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