< cpp‎ | numeric‎ | valarray
Defined in header <valarray>
template< class T >
valarray<T> acos( const valarray<T>& va );

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


va - value array to apply the operation to

Return value

Value array containing arc cosines of the values in va.


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:

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;


#include <cmath>
#include <iostream>
#include <valarray>
const double pi = 4.0 * atan(1.0);
int main()
    // take common x-values from unit circle
    std::valarray<double> v1 = {-1.0, -sqrt(3.0)/2.0, -sqrt(2.0)/2.0, -0.5, 0.0, 0.5, sqrt(2.0)/2.0, sqrt(3.0)/2.0, 1.0};
    std::valarray<double> v2 = std::acos(v1) * 180.0 / pi;;
    for(double n : v2)
        std::cout << std::fixed << n << ' ';
    std::cout << '\n';


180.000000 150.000000 135.000000 120.000000 90.000000 60.000000 45.000000 30.000000 0.000000

See also

applies the function std::asin to each element of valarray
(function template)
applies the function std::atan to each element of valarray
(function template)
applies the function std::atan2 to a valarray and a value
(function template)
applies the function std::cos to each element of valarray
(function template)
computes arc cosine (arccos(x))
computes arc cosine of a complex number (arccos(z))
(function template)