inner_product

Header

template<class InputIterator1, class InputIterator2, class T>
inline T inner_product(InputIterator first, InputIterator last, InputIterator first2, T init)

template<class InputIterator1, class InputIterator2, class T, class BinOp1, class BinOp2> inline 
T inner_product(InputIterator1 first, InputIterator1 last, InputIterator2 first2, T init, BinOp1 binary_op1, BinOp2 binary_op2)

inner_product adds the product of the input sequences to a total.

inner_product computes its result by initializing the accumulator acc with init and then modifying it with: acc = acc + (*i1) * (*i2) - or - acc = binary_op1(acc, binary_op2(*i1, *i2)) for every iterator i1 in the range [first, last) and iterator i2 in the range [first2, first2 + (last - first)) in order.

Sample

#include <iostream>
#include <numeric>
#include <functional>
#include <vector>
#include <iterator>

using namespace std;


typedef vector < float > FloatArray;
typedef ostream_iterator < float, char, char_traits<char> >
FloatOstreamIt;

void main ()
{
    FloatOstreamIt itOstream(cout," ");

    // Initialize the arrays
    FloatArray rgF1, rgF2;
    for (int i=1; i<=5; i++) {
        rgF1.push_back(i);
        rgF2.push_back(i*i);
    };

    // Print the arrays
    cout << "Array 1: ";
    copy(rgF1.begin(),rgF1.end(),itOstream);
    cout << endl;
    cout << "Array 2: ";
    copy(rgF2.begin(),rgF2.end(),itOstream);
    cout << endl;

    // Compute the inner_product of the arrays.  This is the
    // sum of the products (S.O.P) of the corresponding elements
    float ip1 = inner_product(rgF1.begin(),rgF1.end(),rgF2.begin(),0);
    cout << "The inner product (S.O.P) of Array1 and Array2 is "
       << ip1
       << endl;

    // Compute the inner_product of the arrays.  This is the
    // product of the sums (P.O.S.) of the corresponding elements
    float ip2 = inner_product(rgF1.begin(),rgF1.end(),rgF2.begin(),1,
                            multiplies<float>(),plus<float>());
    cout << "The inner product (P.O.S.) of Array1 and Array2 is "
       << ip2
       << endl;
}

Program Output

Array 1: 1 2 3 4 5
Array 2: 1 4 9 16 25
The inner product (S.O.P) of Array1 and Array2 is 225
The inner product (P.O.S.) of Array1 and Array2 is 86400