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42 lines
1.3 KiB
Fortran
42 lines
1.3 KiB
Fortran
*DECK C0LGMC
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COMPLEX FUNCTION C0LGMC (Z)
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C***BEGIN PROLOGUE C0LGMC
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C***PURPOSE Evaluate (Z+0.5)*LOG((Z+1.)/Z) - 1.0 with relative
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C accuracy.
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C***LIBRARY SLATEC (FNLIB)
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C***CATEGORY C7A
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C***TYPE COMPLEX (C0LGMC-C)
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C***KEYWORDS FNLIB, GAMMA FUNCTION, 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 Evaluate (Z+0.5)*LOG((Z+1.0)/Z) - 1.0 with relative error accuracy
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C Let Q = 1.0/Z so that
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C (Z+0.5)*LOG(1+1/Z) - 1 = (Z+0.5)*(LOG(1+Q) - Q + Q*Q/2) - Q*Q/4
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C = (Z+0.5)*Q**3*C9LN2R(Q) - Q**2/4,
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C where C9LN2R is (LOG(1+Q) - Q + 0.5*Q**2) / Q**3.
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C
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C***REFERENCES (NONE)
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C***ROUTINES CALLED C9LN2R, R1MACH
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C***REVISION HISTORY (YYMMDD)
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C 780401 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***END PROLOGUE C0LGMC
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COMPLEX Z, Q, C9LN2R
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SAVE RBIG
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DATA RBIG / 0.0 /
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C***FIRST EXECUTABLE STATEMENT C0LGMC
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IF (RBIG.EQ.0.0) RBIG = 1.0/R1MACH(3)
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C
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CABSZ = ABS(Z)
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IF (CABSZ.GT.RBIG) C0LGMC = -(Z+0.5)*LOG(Z) - Z
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IF (CABSZ.GT.RBIG) RETURN
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C
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Q = 1.0/Z
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IF (CABSZ.LE.1.23) C0LGMC = (Z+0.5)*LOG(1.0+Q) - 1.0
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IF (CABSZ.GT.1.23) C0LGMC = ((1.+.5*Q)*C9LN2R(Q) - .25) * Q**2
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C
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RETURN
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END
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