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