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- *DECK DACOSH
- DOUBLE PRECISION FUNCTION DACOSH (X)
- C***BEGIN PROLOGUE DACOSH
- C***PURPOSE Compute the arc hyperbolic cosine.
- C***LIBRARY SLATEC (FNLIB)
- C***CATEGORY C4C
- C***TYPE DOUBLE PRECISION (ACOSH-S, DACOSH-D, CACOSH-C)
- C***KEYWORDS ACOSH, ARC HYPERBOLIC COSINE, ELEMENTARY FUNCTIONS, FNLIB,
- C INVERSE HYPERBOLIC COSINE
- C***AUTHOR Fullerton, W., (LANL)
- C***DESCRIPTION
- C
- C DACOSH(X) calculates the double precision arc hyperbolic cosine for
- C double precision argument X. The result is returned on the
- C positive branch.
- C
- C***REFERENCES (NONE)
- C***ROUTINES CALLED D1MACH, XERMSG
- C***REVISION HISTORY (YYMMDD)
- C 770601 DATE WRITTEN
- C 890531 Changed all specific intrinsics to generic. (WRB)
- C 890531 REVISION DATE from Version 3.2
- C 891214 Prologue converted to Version 4.0 format. (BAB)
- C 900315 CALLs to XERROR changed to CALLs to XERMSG. (THJ)
- C***END PROLOGUE DACOSH
- DOUBLE PRECISION X, DLN2, XMAX, D1MACH
- SAVE DLN2, XMAX
- DATA DLN2 / 0.6931471805 5994530941 7232121458 18 D0 /
- DATA XMAX / 0.D0 /
- C***FIRST EXECUTABLE STATEMENT DACOSH
- IF (XMAX.EQ.0.D0) XMAX = 1.0D0/SQRT(D1MACH(3))
- C
- IF (X .LT. 1.D0) CALL XERMSG ('SLATEC', 'DACOSH',
- + 'X LESS THAN 1', 1, 2)
- C
- IF (X.LT.XMAX) DACOSH = LOG (X+SQRT(X*X-1.0D0))
- IF (X.GE.XMAX) DACOSH = DLN2 + LOG(X)
- C
- RETURN
- END
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