r9atn1.f
FUNCTION R9ATN1 (X)
C***BEGIN PROLOGUE R9ATN1
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Warning: this routine is not intended to be user-callable.
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C***SUBSIDIARY
C***PURPOSE Evaluate ATAN(X) from first order relative accuracy so that
C ATAN(X) = X + X**3*R9ATN1(X).
C***LIBRARY SLATEC (FNLIB)
C***CATEGORY C4A
C***TYPE SINGLE 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 ATAN(X) from first order, that is, evaluate
C (ATAN(X)-X)/X**3 with relative error accuracy so that
C ATAN(X) = X + X**3*R9ATN1(X).
C
C Series for ATN1 on the interval 0. to 1.00000D+00
C with weighted error 2.21E-17
C log weighted error 16.66
C significant figures required 15.44
C decimal places required 17.32
C
C***REFERENCES (NONE)
C***ROUTINES CALLED CSEVL, INITS, R1MACH, XERMSG
C***REVISION HISTORY (YYMMDD)
C 780401 DATE WRITTEN
C 890206 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 R9ATN1