std::pow(std::valarray)(3)

NAME
std::pow(std::valarray) - std::pow(std::valarray)

Synopsis
   Defined in header <valarray>
   template< class T >
   std::valarray<T> pow( const std::valarray<T>& base, const std::valarray<T>& exp (1)
   );
   template< class T >
   std::valarray<T> pow( const std::valarray<T>& base, (2)
                        const typename std::valarray<T>::value_type& vexp );
   template< class T >
   std::valarray<T> pow( const typename std::valarray<T>::value_type& vbase, (3)
                        const std::valarray<T>& exp );
   Raises a value to a power.
   1) Computes the values of each element in the numeric array base raised to the power
   specified by the corresponding element from the numeric array exp.
   The behavior is undefined if base.size() != exp.size().
   2) Computes the values of each element in the numeric array base raised to the power
   vexp.
   3) Computes the values of vbase raised to the power defined by the elements in the
   numeric array exp.

Parameters
   base - numeric array containing the values of the base
   exp - numeric array containing the values of the exponent
   vbase - a value defining the base
   vexp - a value defining the exponent

Return value
   A numeric array containing the results of exponentiation.

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

Example
// Run this code
 #include <cmath>
 #include <cstddef>
 #include <iomanip>
 #include <iostream>
 #include <valarray>
 class show
 {
     friend std::ostream& operator<<(std::ostream& os, show const& r)
     {
         constexpr char const* sup[]
         {
             "\u2070", "\u00B9", "\u00B2", "\u00B3", "\u2074",
             "\u2075", "\u2076", "\u2077", "\u2078", "\u2079"
         };
         for (std::size_t n = 0; n != r.bases.size(); ++n)
         {
             os << std::left << r.bases[n] << std::left;
             if (n < r.exponents.size())
                 os << sup[r.exponents[n] % 10] << ' ';
             else
                 os << " ";
         }
         if (r.results.size() != 0)
         {
             os << '=';
             for (std::size_t n = 0; n != r.results.size(); ++n)
                 os << ' ' << r.results[n];
         }
         return os << '\n';
     }
 public:
     std::valarray<int> bases{}, exponents{}, results{};
 };
 int main()
 {
     constexpr int base{2};
     constexpr int exponent{5};
     const std::valarray<int> bases{1, 2, 3, 4, 5, 6, 7};
     const std::valarray<int> exponents{0, 1, 2, 3, 4, 5, 6};
     const std::valarray<int> powers1 = std::pow(bases, exponents);
     const std::valarray<int> powers2 = std::pow(bases, exponent);
     const std::valarray<int> powers3 = std::pow(base, exponents);
     std::cout
         << "pow(const std::valarray<T>& base, const std::valarray<T>& exp); (1)\n"
         << "base : " << show{bases}
         << "exp : " << show{exponents}
         << "pow : " << show{bases, exponents, powers1}
         << '\n'
         << "pow(const std::valarray<T>& base, const value_type& vexp); (2)\n"
         << "base : " << show{bases}
         << "vexp : " << exponent << '\n'
         << "pow : " << show{bases, std::valarray<int>(exponent, bases.size()), powers2}
         << '\n'
         << "pow(const value_type& vbase, const std::valarray<T>& exp); (3)\n"
         << "vbase: " << base << '\n'
         << "exp : " << show{exponents}
         << "pow : " << show{std::valarray<int>(base, bases.size()), exponents, powers3};
 }

Output:
 pow(const std::valarray<T>& base, const std::valarray<T>& exp); (1)
 base : 1 2 3 4 5 6 7
 exp : 0 1 2 3 4 5 6
 pow : 1⁰ 2¹ 3² 4³ 5⁴ 6⁵ 7⁶ = 1 2 9 64 625 7776 117649
 pow(const std::valarray<T>& base, const value_type& vexp); (2)
 base : 1 2 3 4 5 6 7
 vexp : 5
 pow : 1⁵ 2⁵ 3⁵ 4⁵ 5⁵ 6⁵ 7⁵ = 1 32 243 1024 3125 7776 16807
 pow(const value_type& vbase, const std::valarray<T>& exp); (3)
 vbase: 2
 exp : 0 1 2 3 4 5 6
 pow : 2⁰ 2¹ 2² 2³ 2⁴ 2⁵ 2⁶ = 1 2 4 8 16 32 64
   Defect reports
   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.
      DR Applied to Behavior as published Correct behavior
                       T is deduced from both the scalar and the only deduce T from the
   LWG 3074 C++98 valarray for (2,3), disallowing valarray
                       mixed-type calls

See also
   sqrt(std::valarray) applies the function std::sqrt to each element of valarray
                       (function template)
   pow
   powf raises a number to the given power (\(\small{x^y}\)x^y)
   powl (function)
   (C++11)
   (C++11)
   pow(std::complex) complex power, one or both arguments may be a complex number
                       (function template)

Hidden category:
     * Pages with unreviewed LWG DR marker