# std::cos(std::valarray)

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< cpp‎ | numeric‎ | valarray

Defined in header `<valarray>` |  |
template< class T > valarray<T> cos( const valarray<T>& va ); |  |

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

### Parameters

va | - | value array to apply the operation to

### Return value

Value array containing cosines of the values in `va`.

### Notes

Unqualified function (cos) is used to perform the computation. If such function is not available, std::cos 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.
  - All functions accepting an argument of type const std::valarray& except `begin()` and `end()` (since C++11) should also accept the replacement type.
  - All functions accepting two arguments of type const std::valarray& should accept every combination of const std::valarray& and the replacement type.
  - The return type does not add more than two levels of template nesting over the most deeply-nested argument type.

### Possible implementation

    template< class T >
    valarray<T> cos( const valarray<T>& va )
    {
        valarray<T> other = va;
        for (T &i : other)
            i = cos(i);

        return other; // proxy object may be returned
    }

### Example

Run this code

    #include <cmath>
    #include <iomanip>
    #include <iostream>
    #include <valarray>

    void show(const char* title, const std::valarray<float>& data)
    {
        const int w { 9 };
        std::cout << std::setw(w) << title << " | ";
        for (float x : data)
            std::cout << std::setw(w) << x << " | ";
        std::cout << '\n';
    }

    int main()
    {
        const std::valarray<float> x { .1, .2, .3, .4 };
        const auto sin = std::sin(x);
        const auto cos = std::cos(x);
        const auto z = (sin * sin) + (cos * cos);

        show("x"     , x  );
        show("sin(x)", sin);
        show("cos(x)", cos);
        show("z"     , z  );
    }

Output:

            x |       0.1 |       0.2 |       0.3 |       0.4 |
       sin(x) | 0.0998334 |  0.198669 |   0.29552 |  0.389418 |
       cos(x) |  0.995004 |  0.980067 |  0.955337 |  0.921061 |
            z |         1 |         1 |         1 |         1 |

### See also

sin(std::valarray) | applies the function std::sin to each element of valarray (function template)
tan(std::valarray) | applies the function std::tan to each element of valarray (function template)
acos(std::valarray) | applies the function std::acos to each element of valarray (function template)
cos cosf cosl (C++11)(C++11) | computes cosine (\({\small\cos{x} }\)cos(x)) (function)
cos(std::complex) | computes cosine of a complex number (\({\small\cos{z} }\)cos(z)) (function template)

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