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atan
Inverse circular tangent (arctangent).SYNOPSIS:
double x, y, atan();
y = atan(x);
DESCRIPTION:
Returns the radian angle between -pi/2 and +pi/2 whose tangent is x.
Range reduction is from three intervals into the interval from zero to 0.66. The approximant uses a rational function of degree 4/5 of the form x + x**3 P(x)/Q(x).
ACCURACY:
Relative error:
arithmetic domain # trials peak rms
DEC -10, 10 50000 2.4e-17 8.3e-18
IEEE -10, 10 10^6 1.8e-16 5.0e-17