COMPLEX FUNCTION CATAN(Z)
C***BEGIN PROLOGUE  CATAN
C***DATE WRITTEN   770801   (YYMMDD)
C***REVISION DATE  820801   (YYMMDD)
C***CATEGORY NO.  C4A
C***KEYWORDS  ARC TANGENT,COMPLEX,ELEMENTARY FUNCTION
C***AUTHOR  FULLERTON, W., (LANL)
C***PURPOSE  Computes the complex arc Tangent.
C***DESCRIPTION
C
C CATAN(Z) calculates the complex trigonometric arc tangent of Z.
C The result is in units of radians, and the real part is in the first
C or fourth quadrant.
C***REFERENCES  (NONE)
C***ROUTINES CALLED  R1MACH,XERROR
C***END PROLOGUE  CATAN