std::sqrt(std::valarray) (3) - Linux Manuals

std::sqrt(std::valarray): std::sqrt(std::valarray)

NAME

std::sqrt(std::valarray) - std::sqrt(std::valarray)

Synopsis

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.

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 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> 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.
// Run this code

  #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