std::inner_product
Defined in header
<numeric>
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template< class InputIt1, class InputIt2, class T >
T inner_product( InputIt1 first1, InputIt1 last1, |
(1) | |
template<class InputIt1, class InputIt2, class T,
class BinaryOperation1, class BinaryOperation2> |
(2) | |
Computes inner product (i.e. sum of products) of the range [first1, last1)
and another range beginning at first2
. The first version uses operator*
to compute product of the element pairs and operator+
to sum up the products, the second version uses op2
and op1
for these tasks respectively.
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(until C++11) |
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(since C++11) |
Contents |
[edit] Parameters
first1, last1 | - | the first range of elements |
first2 | - | the beginning of the second range of elements |
value | - | initial value of the sum of the products |
op1 | - | binary operation function object that will be applied. This "sum" function takes a value returned by op2 and the current value of the accumulator and produces a new value to be stored in the accumulator. The signature of the function should be equivalent to the following: Ret fun(const Type1 &a, const Type2 &b); The signature does not need to have const &. |
op2 | - | binary operation function object that will be applied. This "product" function takes one value from each range and produces a new value. The signature of the function should be equivalent to the following: Ret fun(const Type1 &a, const Type2 &b); The signature does not need to have const &. |
Type requirements | ||
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InputIt1, InputIt2 must meet the requirements of InputIterator .
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T must meet the requirements of CopyAssignable and CopyConstructible .
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[edit] Return value
The inner product of two ranges.
[edit] Possible implementation
First version |
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template<class InputIt1, class InputIt2, class T> T inner_product(InputIt1 first1, InputIt1 last1, InputIt2 first2, T value) { while (first1 != last1) { value = value + *first1 * *first2; ++first1; ++first2; } return value; } |
Second version |
template<class InputIt1, class InputIt2, class T, class BinaryOperation1, class BinaryOperation2> T inner_product(InputIt1 first1, InputIt1 last1, InputIt2 first2, T value, BinaryOperation1 op1 BinaryOperation2 op2) { while (first1 != last1) { value = op1(value, op2(*first1, *first2)); ++first1; ++first2; } return value; } |
[edit] Example
#include <numeric> #include <iostream> #include <vector> #include <functional> int main() { std::vector<int> a{0, 1, 2, 3, 4}; std::vector<int> b{5, 4, 2, 3, 1}; int r1 = std::inner_product(a.begin(), a.end(), b.begin(), 0); std::cout << "Inner product of a and b: " << r1 << '\n'; int r2 = std::inner_product(a.begin(), a.end(), b.begin(), 0, std::plus<int>(), std::equal_to<int>()); std::cout << "Number of pairwise matches between a and b: " << r2 << '\n'; }
Output:
Inner product of a and b: 21 Number of pairwise matches between a and b: 2
[edit] See also
sums up a range of elements (function template) |
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computes the partial sum of a range of elements (function template) |
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(parallelism TS)
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parallelized version of std::inner_product (function template) |