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40 lines
1.4 KiB
Fortran
40 lines
1.4 KiB
Fortran
*DECK DACOSH
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DOUBLE PRECISION FUNCTION DACOSH (X)
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C***BEGIN PROLOGUE DACOSH
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C***PURPOSE Compute the arc hyperbolic cosine.
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C***LIBRARY SLATEC (FNLIB)
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C***CATEGORY C4C
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C***TYPE DOUBLE PRECISION (ACOSH-S, DACOSH-D, CACOSH-C)
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C***KEYWORDS ACOSH, ARC HYPERBOLIC COSINE, ELEMENTARY FUNCTIONS, FNLIB,
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C INVERSE HYPERBOLIC COSINE
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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 DACOSH(X) calculates the double precision arc hyperbolic cosine for
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C double precision argument X. The result is returned on the
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C positive branch.
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C
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C***REFERENCES (NONE)
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C***ROUTINES CALLED D1MACH, 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***END PROLOGUE DACOSH
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DOUBLE PRECISION X, DLN2, XMAX, D1MACH
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SAVE DLN2, XMAX
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DATA DLN2 / 0.6931471805 5994530941 7232121458 18 D0 /
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DATA XMAX / 0.D0 /
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C***FIRST EXECUTABLE STATEMENT DACOSH
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IF (XMAX.EQ.0.D0) XMAX = 1.0D0/SQRT(D1MACH(3))
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C
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IF (X .LT. 1.D0) CALL XERMSG ('SLATEC', 'DACOSH',
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+ 'X LESS THAN 1', 1, 2)
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C
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IF (X.LT.XMAX) DACOSH = LOG (X+SQRT(X*X-1.0D0))
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IF (X.GE.XMAX) DACOSH = DLN2 + LOG(X)
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C
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RETURN
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END
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