std::acos(std::valarray)

For each element in va computes arc cosine of the value of the element.

[edit] Parameters

[edit] Return value

Value array containing arc cosines of the values in va.

[edit] Notes

Unqualified function (acos) is used to perform the computation. If such function is not available, std::acos 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.

[edit] Possible implementation

template<class T>
valarray<T> acos(const valarray<T>& va)
{
    valarray<T> other = va;
    for (T& i : other)
        i = acos(i);
 
    return other; // proxy object may be returned
}

[edit] Example

#include <cmath>
#include <iostream>
#include <numbers>
#include <valarray>
 
int main()
{
    // take common x-values from unit circle
    const double s32 = std::sqrt(3.0) / 2.0;
    const double s22 = std::sqrt(2.0) / 2.0;
    std::valarray<double> v1 = {-1.0, -s32, -s22, -0.5, 0.0, 0.5, s22, s32, 1.0};
    std::valarray<double> v2 = std::acos(v1) * 180.0 / std::numbers::pi;
 
    for (double n : v2)
        std::cout << n << "° ";
    std::cout << '\n';
}

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[edit] See also