cpp/numeric/math/acos

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

Return value
If no errors occur, the arc cosine of ($arccos(num)$) in the range $[0, &pi;]$, is returned.

If a domain error occurs, an implementation-defined value is returned (NaN where supported).

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.

Domain error occurs if is outside the range.

If the implementation supports IEEE floating-point arithmetic (IEC 60559),
 * If the argument is $+1$, the value is returned.
 * If $|num| > 1$, a domain error occurs and NaN is returned.
 * if the argument is NaN, NaN is returned.