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std::sqrt(std::valarray)

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< cpp‎ | numeric‎ | valarray
Revision as of 10:46, 9 February 2014 by Xan (Talk | contribs)

 
 
 
 
Defined in header <valarray>
template< class T >
valarray<T> sqrt( const valarray<T>& va );

For each element in va computes the square root of the value of the element.

Contents

Parameters

va - value array to apply the operation to

Return value

Value array containing square roots of the values in va.

Notes

Unqualified function (sqrt) is used to perform the computation. If such function is not available, std::sqrt 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 a arguments of type const std::valarray& 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> sqrt(const valarray<T>& va)
{
    valarray<T> other = va;
    for (T &i : other) {
        i = sqrt(i);
    }
    return other;
}

Example

Finds real roots of multiple quadratic equations.

#include <valarray>
#include <iostream>
 
int main()
{
    std::valarray<double> a(1, 8);
    std::valarray<double> b{1, 2, 3, 4, 5, 6, 7, 8};
    std::valarray<double> c = -b;
    // literals must also be of type T (double in this case)
    std::valarray<double> d = std::sqrt((b * b - 4.0 * a * c));
    std::valarray<double> x1 = (-b - d) / (2.0 * a);
    std::valarray<double> x2 = (-b + d) / (2.0 * a);
    std::cout << "quadratic equation    root 1,  root 2" << "\n";
    for (size_t i = 0; i < a.size(); ++i) {
        std::cout << a[i] << "x\u00B2 + " << b[i] << "x + " << c[i] << " = 0   ";
        std::cout << x1[i] << ", " << x2[i] << "\n";
    }
}

Output:

quadratic equation    root 1,  root 2
1x² + 1x + -1 = 0   -1.61803, 0.618034
1x² + 2x + -2 = 0   -2.73205, 0.732051
1x² + 3x + -3 = 0   -3.79129, 0.791288
1x² + 4x + -4 = 0   -4.82843, 0.828427
1x² + 5x + -5 = 0   -5.8541, 0.854102
1x² + 6x + -6 = 0   -6.87298, 0.872983
1x² + 7x + -7 = 0   -7.88748, 0.887482
1x² + 8x + -8 = 0   -8.89898, 0.898979