# std::asin(std::valarray)

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< cpp‎ | numeric‎ | valarray

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

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

### Parameters

va | - | value array to apply the operation to

### Return value

Value array containing arc sines of the values in va.

### Notes

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

### Possible implementation

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

        return other; // proxy object may be returned
    }

### Example

Run this code

    #include <cmath>
    #include <iostream>
    #include <numbers>
    #include <valarray>

    int main()
    {
        // take common y-values from unit circle
        const double s22 = std::sqrt(2.0) / 2.0;
        const double s32 = std::sqrt(3.0) / 2.0;
        const std::valarray<double> v1 =
            {-1.0, -s32, -s22, -0.5,  0.0,  0.5, s22,  s32,  1.0};

        // fill with results of radians to degrees conversion
        const std::valarray<double> v2 =
            std::asin(v1) * 180.0 / std::numbers::pi;

        for (std::cout << std::showpos; double n : v2)
            std::cout << n << "° ";
        std::cout << '\n';
    }

Output:

    -90° -60° -45° -30° +0° +30° +45° +60° +90°

### See also

acos(std::valarray) | applies the function std::acos to each element of valarray (function template)
atan(std::valarray) | applies the function std::atan to each element of valarray (function template)
atan2(std::valarray) | applies the function std::atan2 to a valarray and a value (function template)
sin(std::valarray) | applies the function std::sin to each element of valarray (function template)
asinasinfasinl (C++11)(C++11) | computes arc sine (\({\small\arcsin{x}}\)arcsin(x)) (function)
asin(std::complex) (C++11) | computes arc sine of a complex number (\({\small\arcsin{z}}\)arcsin(z)) (function template)

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