FUNCTION ACOSH(X)
C***BEGIN PROLOGUE  ACOSH
C***DATE WRITTEN   770401   (YYMMDD)
C***REVISION DATE  820801   (YYMMDD)
C***CATEGORY NO.  C4C
C***KEYWORDS  ACOSH,ARC HYPERBOLIC COSINE,ELEMENTARY FUNCTION
C***AUTHOR  FULLERTON, W., (LANL)
C***PURPOSE  Compute the arc hyperbolic Cosine.
C***DESCRIPTION
C
C ACOSH(X) computes the arc hyperbolic cosine of X.
C***REFERENCES  (NONE)
C***ROUTINES CALLED  R1MACH,XERROR
C***END PROLOGUE  ACOSH