Procedure

     DACOSH ( Double precision arc hyperbolic cosine )

     DOUBLE PRECISION FUNCTION  DACOSH ( X )

Abstract

     Return the inverse hyperbolic cosine of a double precision
     argument.

Required_Reading

     None.

Keywords

     HYPERBOLIC
     MATH

Declarations

     IMPLICIT NONE

     DOUBLE PRECISION   X

Brief_I/O

     VARIABLE  I/O  DESCRIPTION
     --------  ---  --------------------------------------------------
      X         I   Number whose inverse hyperbolic cosine is desired.

     The function returns the inverse hyperbolic cosine of a double
     precision number.

Detailed_Input

     X        is any double precision number greater than or equal to
              1.

Detailed_Output

     The function returns the inverse hyperbolic cosine of the double
     precision number X.

Parameters

     None.

Exceptions

     1)  If X is less than 1.0D0, the error SPICE(INVALIDARGUMENT) is
         signaled.

Files

     None.

Particulars

     This function simply implements the definition of the inverse
     hyperbolic cosine as follows:

        DACOSH = DLOG (X + DSQRT (X*X-1.D0))

     If the input value is not valid, an error is signaled.

Examples

     The following table gives a few values for X and the resulting
     value of DACOSH.

     X                       DACOSH(X)
     ----------------------------------------------
     1.000000000000000      0.0000000000000000E+00
     10.00000000000000       2.993222846126381
     100.0000000000000       5.298292365610485
     1000.000000000000       7.600902209541989

Restrictions

     1)  The value of the input variable X must be greater than or
         equal to 1.0d0.

Literature_References

     [1]  W.H. Beyer, "CRC Standard Mathematical Tables," CRC Press,
          1987.

Author_and_Institution

     J. Diaz del Rio    (ODC Space)
     H.A. Neilan        (JPL)
     W.M. Owen          (JPL)
     W.L. Taber         (JPL)

Version

    SPICELIB Version 1.2.0, 17-JUN-2021 (JDR)

        Added IMPLICIT NONE statement.

        Edited the header to comply with NAIF standard.

    SPICELIB Version 1.1.0, 17-MAY-1994 (HAN)

        Set the default function value to either 0, 0.0D0, .FALSE.,
        or blank depending on the type of the function.

    SPICELIB Version 1.0.1, 10-MAR-1992 (WLT)

        Comment section for permuted index source lines was added
        following the header.

    SPICELIB Version 1.0.0, 31-JAN-1990 (WMO)