Difference between revisions of "cpp/algorithm/inner product"
m (Text replace - "/sidebar" to "/navbar") |
m (Text replace - "{{eq fun cpp" to "{{eq fun") |
||
| Line 37: | Line 37: | ||
===Possible implementation=== | ===Possible implementation=== | ||
| − | {{eq fun | + | {{eq fun |
| 1= | | 1= | ||
template<class InputIterator1, class InputIterator2, class T> | template<class InputIterator1, class InputIterator2, class T> | ||
Revision as of 04:06, 3 July 2012
Template:ddcl list begin <tr class="t-dsc-header">
<td><numeric>
<td></td> <td></td> </tr> <tr class="t-dcl ">
<td >T inner_product( InputIterator1 first1, InputIterator1 last1,
<td > (1) </td> <td class="t-dcl-nopad"> </td> </tr> <tr class="t-dcl ">
<td > class InputIterator1,
class InputIterator2,
class T,
class BinaryOperation1,
class BinaryOperation2
> T inner_product( InputIterator1 first1, InputIterator1 last1,
InputIterator2 first2, T value,
BinaryOperation1 op1,
<td > (2) </td> <td class="t-dcl-nopad"> </td> </tr> Template:ddcl list end
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.
Contents |
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 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 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 &. |
Return value
The inner product of two ranges.
Possible implementation
| First version |
|---|
template<class InputIterator1, class InputIterator2, class T> T inner_product(InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, T value) { while (first1 != last1) { value = value + *first1 * *first2; ++first1; ++first2; } return value; } |
| Second version |
template<class InputIterator1, class InputIterator2, class T, class BinaryOperation1, class BinaryOperation2> T inner_product(InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, T value, BinaryOperation1 op1 BinaryOperation2 op2) { while (first1 != last1) { value = op1(value, op2(*first1, *first2)); ++first1; ++first2; } return value; } |
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
