SLATEC Routines --- D9ATN1 ---

*DECK D9ATN1
      DOUBLE PRECISION FUNCTION D9ATN1 (X)
C***BEGIN PROLOGUE  D9ATN1
C***SUBSIDIARY
C***PURPOSE  Evaluate DATAN(X) from first order relative accuracy so
C            that DATAN(X) = X + X**3*D9ATN1(X).
C***LIBRARY   SLATEC (FNLIB)
C***CATEGORY  C4A
C***TYPE      DOUBLE PRECISION (R9ATN1-S, D9ATN1-D)
C***KEYWORDS  ARC TANGENT, ELEMENTARY FUNCTIONS, FIRST ORDER, FNLIB,
C             TRIGONOMETRIC
C***AUTHOR  Fullerton, W., (LANL)
C***DESCRIPTION
C
C Evaluate  DATAN(X)  from first order, that is, evaluate
C (DATAN(X)-X)/X**3  with relative error accuracy so that
C        DATAN(X) = X + X**3*D9ATN1(X).
C
C Series for ATN1       on the interval  0.          to  1.00000E+00
C                                        with weighted error   3.39E-32
C                                         log weighted error  31.47
C                               significant figures required  30.26
C                                    decimal places required  32.27
C
C***REFERENCES  (NONE)
C***ROUTINES CALLED  D1MACH, DCSEVL, INITDS, XERMSG
C***REVISION HISTORY  (YYMMDD)
C   780401  DATE WRITTEN
C   890531  Changed all specific intrinsics to generic.  (WRB)
C   891115  Corrected third argument in reference to INITDS.  (WRB)
C   891115  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   900720  Routine changed from user-callable to subsidiary.  (WRB)
C***END PROLOGUE  D9ATN1