std:: atan2 (std::valarray)

Computes the inverse tangent of y / x using the signs of arguments to correctly determine quadrant.

The behavior is undefined if x. size ( ) ! = y. size ( ) .

Parameters

Return value

A numeric array containing the results of computation of inverse tangent.

Notes

Unqualified function ( atan2 ) is used to perform the computation. If such function is not available, std:: atan2 is used due to argument-dependent lookup .

The function can be implemented with the return type different from std::valarray . In this case, the replacement type has the following properties:

• All const member functions of std::valarray are provided.
• std::valarray , std::slice_array , std::gslice_array , std::mask_array and std::indirect_array can be constructed from the replacement type.
• For every function taking a const std:: valarray < T > & except begin() and end() (since C++11) , identical functions taking the replacement types shall be added;
• For every function taking two const std:: valarray < T > & arguments, identical functions taking every combination of const std:: valarray < T > & and replacement types shall be added.
• The return type does not add more than two levels of template nesting over the most deeply-nested argument type.

Example

#include <algorithm>
#include <cmath>
#include <iomanip>
#include <iostream>
#include <valarray>
 
void show(char const* title, const std::valarray<double>& va)
{
    std::cout << title << ' ';
    std::for_each(std::begin(va), std::end(va), [](const double x)
    { 
        std::cout << ' ' << std::right << std::setw(4) << x << "°";
    });
    std::cout << '\n';
}
 
const double pi = std::acos(-1.0); // C++20: std::numbers::pi
 
int main()
{
    auto degrees_to_radians = [](double const& x) { return (pi * x / 180); };
    auto radians_to_degrees = [](double const& x) { return (180 * x / pi); };
 
    const std::valarray<double> degrees{-90, -60, -45, -30, 0, 30, 45, 60, 90};
    const std::valarray<double> radians = degrees.apply(degrees_to_radians);
 
    const auto sin = std::sin(radians);
    const auto cos = std::cos(radians);
 
    show("(1)", std::atan2(sin, cos).apply(radians_to_degrees));
    show("(2)", std::atan2(sin/cos, 1.0).apply(radians_to_degrees));
    show("(3)", std::atan2(1.0, cos/sin).apply(radians_to_degrees));
}

(1)   -90°  -60°  -45°  -30°    0°   30°   45°   60°   90°
(2)   -90°  -60°  -45°  -30°    0°   30°   45°   60°   90°
(3)    90°  120°  135°  150°    0°   30°   45°   60°   90°

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

See also