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Difference between revisions of "cpp/numeric/valarray/atan2"

From cppreference.com
< cpp‎ | numeric‎ | valarray
m (fmt, {{c}}, headers sorted, "" -> '', v|2-3 -> v|2,3)
m (→‎Example: '°' → "°", i.e. step back from multi-character character constant to string literal, otherwise it does not work.)
 
Line 55: Line 55:
 
     std::for_each(std::begin(va), std::end(va), [](const double x)
 
     std::for_each(std::begin(va), std::end(va), [](const double x)
 
     {  
 
     {  
−
         std::cout << ' ' << std::right << std::setw(4) << x << '°';
+
         std::cout << ' ' << std::right << std::setw(4) << x << "°";
 
     });
 
     });
 
     std::cout << '\n';
 
     std::cout << '\n';

Latest revision as of 13:44, 17 October 2023

 
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std::valarray
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Defined in header <valarray>
template< class T >
std::valarray<T> atan2( const std::valarray<T>& y, const std::valarray<T>& x );
 (1)
template< class T >

std::valarray<T> atan2( const std::valarray<T>& y,

                        const typename std::valarray<T>::value_type& vx );
 (2)
template< class T >

std::valarray<T> atan2( const typename std::valarray<T>::value_type& vy,

                        const std::valarray<T>& x );
 (3)

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

1) Computes the inverse tangent of each pair of corresponding values from y and x.

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

2) Computes the inverse tangent of vx and each value in the numeric array y.
3) Computes the inverse tangent of vy and each value in the numeric array x.

Contents

[edit] Parameters

x, y - numeric arrays to compute inverse tangent of
vy, vx - values to compute inverse tangent of

[edit] Return value

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

[edit] 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:

[edit] Example

Run this code
#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));
}

Output: 

(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°

[edit] Defect reports

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

DR Applied to Behavior as published Correct behavior
LWG 3074 C++98 T is deduced from both the scalar and the valarray for (2,3), disallowing mixed-type calls only deduce T from the valarray

[edit] See also

 applies the function std::asin to each element of valarray
(function template) [edit]
applies the function std::acos to each element of valarray
(function template) [edit]
applies the function std::atan to each element of valarray
(function template) [edit]
(C++11)(C++11)
 arc tangent, using signs to determine quadrants
(function) [edit]
returns the phase angle
(function template) [edit]
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