Use a pair of iterators i and j to traverse the two sequences [ first1...last1 ) and [ first2...first2

( last1 - first1 )). Apply the formula init = init op1 ( * i op2 * j ) and return the final value of init . Note that init is not automatically initialized to zero prior to this operation. The first version automatically sets op1 to operator+ and op2 to operator* .

Declaration


  
#include <numeric>

template< class InputIterator1, class InputIterator2, class T >
T inner_product
  (
  InputIterator1 first1,
  InputIterator1 last1,
  InputIterator2 first2,
  T init
  );

template
  <
  class InputIterator1,
  class InputIterator2,
  class T,
  class BinaryOperation1,
  class BinaryOperation2
  >
T inner_product
  (
  InputIterator1 first1,
  InputIterator1 last1,
  InputIterator2 first2,
  T init,
  BinaryOperation1 op1,
  BinaryOperation2 op2
  );

Complexity

Time complexity is linear. Space complexity is constant.

Example <ospace/osstd/examples/inrprod0.cpp>


    #include <iostream>
#include <numeric>

int numbers1[ 5 ] = { 1, 2, 3, 4, 5 };
int numbers2[ 5 ] = { 1, 2, 3, 4, 5 };

void
main()
  {
  int result;

  result = inner_product( numbers1, numbers1 + 5, numbers2, 0 );

  cout << "Inner product = " << result << "\n";
  }

Inner product = 55

Example <ospace/osstd/examples/inrprod1.cpp>


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

void
main()
  {
  vector< int > v1( 3 );
  vector< int > v2( v1.size() );
  for ( size_t i = 0; i < v1.size(); ++i )
    {
    v1[ i ] = i + 1;
    v2[ i ] = v1.size() - i;
    }
  ostream_iterator< int > iter( cout, " " );
  cout << "Inner product sum of products ) of:\n\t";
  copy( v1.begin(), v1.end(), iter );
  cout << "\n\t";
  copy( v2.begin(), v2.end(), iter );

  int result = inner_product( v1.begin(), v1.end(), v2.begin(), 0 );

  cout << "\nis: " << result << "\n";
  }

Inner product (sum of products) of:
        1 2 3
        3 2 1
is: 10

Example <ospace/osstd/examples/inrprod2.cpp>


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

int
add( int a_, int b_ )
  {
  return a_ + b_;
  }

int
mult( int a_, int b_ )
  {
  return a_ * b_;
  }

void
main()
  {
  vector< int > v1( 3 );
  vector< int > v2( v1.size() );
  for ( size_t i = 0; i < v1.size(); ++i )
    {
    v1[ i ] = i + 1;
    v2[ i ] = v1.size() - i;
    }
  ostream_iterator< int > iter( cout, " " );
  cout << "Inner product( product of sums ):\n\t";
  copy( v1.begin(), v1.end(), iter );
  cout << "\n\t";
  copy( v2.begin(), v2.end(), iter );

  int result = inner_product
    (
    v1.begin(),
    v1.end(),
    v2.begin(),
    1,
    mult,
    add
    );

  cout << "\nis: " << result << "\n";
  }

Inner product (product of sums) of:
        1 2 3
        3 2 1
is: 64

inner_product

Library

Declaration

Complexity

Example <ospace/osstd/examples/inrprod0.cpp>

Example <ospace/osstd/examples/inrprod1.cpp>

Example <ospace/osstd/examples/inrprod2.cpp>