# std::pow(std::valarray)

< cpp‎ | numeric‎ | valarray
 Defined in header  template< class T > std::valarray pow( const std::valarray& base, const std::valarray& exp ); (1) template< class T > std::valarray pow( const std::valarray& base,                       const typename std::valarray::value_type& vexp ); (2) template< class T > std::valarray pow( const typename std::valarray::value_type& vbase,                       const std::valarray& 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.

## Contents

### 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:

### 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