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39 lines
1.2 KiB
Fortran
39 lines
1.2 KiB
Fortran
*DECK ACOSH
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FUNCTION ACOSH (X)
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C***BEGIN PROLOGUE ACOSH
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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 SINGLE 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 ACOSH(X) computes the arc hyperbolic cosine of X.
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C
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C***REFERENCES (NONE)
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C***ROUTINES CALLED R1MACH, XERMSG
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C***REVISION HISTORY (YYMMDD)
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C 770401 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***END PROLOGUE ACOSH
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SAVE ALN2,XMAX
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DATA ALN2 / 0.6931471805 5994530942E0/
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DATA XMAX /0./
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C***FIRST EXECUTABLE STATEMENT ACOSH
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IF (XMAX.EQ.0.) XMAX = 1.0/SQRT(R1MACH(3))
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C
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IF (X .LT. 1.0) CALL XERMSG ('SLATEC', 'ACOSH', 'X LESS THAN 1',
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+ 1, 2)
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C
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IF (X.LT.XMAX) ACOSH = LOG (X + SQRT(X*X-1.0))
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IF (X.GE.XMAX) ACOSH = ALN2 + LOG(X)
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C
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RETURN
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END
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