c/numeric/math/atan

@1-6@ Computes the principal value of the arc tangent of. @7@ Type-generic macro: If the argument has type,  is called. Otherwise, if the argument has integer type or the type,  is called. Otherwise,  is called. If the argument is complex, then the macro invokes the corresponding complex function (catanf, catan, catanl).

Return value
If no errors occur, the arc tangent of ($arctan(arg)$) 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.

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.