FUNCTION ATANH(X)
C***BEGIN PROLOGUE  ATANH
C***DATE WRITTEN   770401   (YYMMDD)
C***REVISION DATE  820801   (YYMMDD)
C***CATEGORY NO.  C4C
C***KEYWORDS  ARC HYPERBOLIC TANGENT,ATANH,ELEMENTARY FUNCTION
C***AUTHOR  FULLERTON, W., (LANL)
C***PURPOSE  Compute the arc hyperbolic Tangent.
C***DESCRIPTION
C
C ATANH(X) computes the arc hyperbolic tangent of X.
C
C Series for ATNH       on the interval  0.          to  2.50000D-01
C                                        with weighted error   6.70E-18
C                                         log weighted error  17.17
C                               significant figures required  16.01
C                                    decimal places required  17.76
C***REFERENCES  (NONE)
C***ROUTINES CALLED  CSEVL,INITS,R1MACH,XERROR
C***END PROLOGUE  ATANH