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std::pow(std::valarray)

Defined in header <valarray>

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, 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)

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().

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.
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.

Example

#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
LWG 3074	C++98	`T` is deduced from both the scalar and the `valarray` for (2-3), disallowing mixed-type calls	only deduce `T` from the `valarray`