std::pow(std::valarray) - cppreference.com (original) (raw)

| Defined in header | | | | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | --- | | | 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, const typename std::valarray<T>::value_type& vexp ); | (2) | | | template< class T > std::valarray<T> pow( const typename std::valarray<T>::value_type& vbase, const std::valarray<T>& exp ); | (3) | |

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().

1. Computes the values of each element in the numeric array base raised to the power vexp.

2. Computes the values of vbase raised to the power defined by the elements in the numeric array exp.

[edit] Parameters

[edit] Return value

A numeric array containing the results of exponentiation.

[edit] 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.

[edit] Example

#include #include #include #include #include   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 bases{}, exponents{}, results{}; };   int main() { constexpr int base{2}; constexpr int exponent{5}; const std::valarray bases{1, 2, 3, 4, 5, 6, 7}; const std::valarray exponents{0, 1, 2, 3, 4, 5, 6}; const std::valarray powers1 = std::pow(bases, exponents); const std::valarray powers2 = std::pow(bases, exponent); const std::valarray powers3 = std::pow(base, exponents);   std::cout << "pow(const std::valarray& base, const std::valarray& exp); (1)\n" << "base : " << show{bases} << "exp  : " << show{exponents} << "pow  : " << show{bases, exponents, powers1} << '\n' << "pow(const std::valarray& base, const value_type& vexp); (2)\n" << "base : " << show{bases} << "vexp : " << exponent << '\n' << "pow  : " << show{bases, std::valarray(exponent, bases.size()), powers2} << '\n' << "pow(const value_type& vbase, const std::valarray& exp); (3)\n" << "vbase: " << base << '\n' << "exp  : " << show{exponents} << "pow  : " << show{std::valarray(base, bases.size()), exponents, powers3}; }

Output:

pow(const std::valarray& base, const std::valarray& 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& 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& 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

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[edit] See also