cpp/numeric/math/atan

@1-3@ Computes the principal value of the arc tangent of.

Return value
If no errors occur, the arc tangent of ($arctan(num)$) in the range $[-, +]$ radians, is returned.

If a range error occurs due to underflow, the correct result (after rounding) is returned.

Error handling
Errors are reported as specified in math_errhandling.

If the implementation supports IEEE floating-point arithmetic (IEC 60559),
 * If the argument is ±0, it is returned unmodified
 * If the argument is +∞, +&pi;/2 is returned
 * If the argument is -∞, -&pi;/2 is returned
 * if the argument is NaN, NaN is returned