std::inner_product

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C++
 
算法库
功能
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Functions
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修改序列操作
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Non-modifying sequence operations
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all_of
any_of
none_of		（C++11）
（C++11）
（C++11）
for_each
count
count_if
mismatch
equal
修改序列操作
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Modifying sequence operations
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分区操作
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Partitioning operations
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is_partitioned（C++11）
partition
partition_copy（C++11）
排序操作（排序的区间）
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Sorting operations (on sorted ranges)
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is_sorted（C++11）
is_sorted_until（C++11）
sort
二进制搜索操作（排序的区间）
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Binary search operations (on sorted ranges)
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设置操作（排序的区间）
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Set operations (on sorted ranges)
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堆的操作
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Heap operations
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最小/最大操作
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Minimum/maximum operations
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数字操作
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Numeric operations
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iota（C++11）
accumulate
inner_product
C库
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C library
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Defined in header <numeric>
template< class InputIt1, class InputIt2, class T >

T inner_product( InputIt1 first1, InputIt1 last1,

                 InputIt2 first2, T value );
 (1)
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 );
 (2)
计算内积（即产品的总和）的范围[first1, last1)和其他范围内开始在first2。第一个版本使用operator*计算元素对产品和operator+总结的产品，第二个版本使用op2和op1这些任务.
Original:
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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目录

[编辑] 参数

first1, last1 -
第一范围内的元素
Original:
the first range of elements
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first2 -
的第二范围内的元素的开头
Original:
the beginning of the second range of elements
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value -
初始值的乘积的总和
Original:
initial value of the sum of the products
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op1 - binary operation function object that will be applied.
此函数需要一个返回值op2的累加器的当前值，并产生一个新的值被存储在累加器中.
Original:
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.
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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 &.
The types  Type1 and  Type2 must be such that objects of types T and Type3 can be implicitly converted to  Type1 and  Type2 respectively. The type  Ret must be such that an object of type T can be assigned a value of type  Ret. ​

op2 - binary operation function object that will be applied.
这个函数接受一个值从每个范围，并产生一个新的价值.
Original:
This function takes one value from each range and produces a new value.
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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 &.
The types  Type1 and  Type2 must be such that objects of types InputIt1 and InputIt2 can be dereferenced and then implicitly converted to  Type1 and  Type2 respectively. The type  Ret must be such that an object of type Type3 can be assigned a value of type  Ret. ​

Type requirements
-
InputIt1, InputIt2 must meet the requirements of InputIterator.
-
T must meet the requirements of CopyAssignable and CopyConstructible.

[编辑] 返回值

两个范围的内积.
Original:
The inner product of two ranges.
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[编辑] 可能的实现

First version 
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;
}

[编辑] 为例

#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

[编辑] 另请参阅
总结了一系列的元素
Original:
sums up a range of elements
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（函数模板） [edit]
计算的部分和一定范围的元素
Original:
computes the partial sum of a range of elements
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（函数模板） [edit]
来自“http://zh.cppreference.com/mwiki/index.php?title=cpp/algorithm/inner_product&oldid=28078”