inner_product inner_product Category: algorithms Component type: function Prototype Inner_product is an overloaded name; there are actually two inner_product functions. 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 BinaryFunction1, class BinaryFunction2> T inner_product(InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, T init, BinaryFunction1 binary_op1, BinaryFunction2 binary_op2); Description Inner_product calculates a generalized inner product of the ranges [first1, last1) and [first2, last2). The first version of inner_product returns init plus the inner product of the two ranges [1]. That is, it first initializes the result to init and then, for each iterator i in [first1, last1), in order from the beginning to the end of the range, updates the result by result = result + (*i) * *(first2 + (i - first1)). The second version of inner_product is identical to the first, except that it uses two user-supplied function objects instead of operator+ and operator*. That is, it first initializes the result to init and then, for each iterator i in [first1, last1), in order from the beginning to the end of the range, updates the result by result = binary_op1(result, binary_op2(*i, *(first2 + (i - first1))). [2] Definition Defined in the standard header numeric, and in the nonstandard backward-compatibility header algo.h. Requirements on types For the first version: InputIterator1 is a model of Input Iterator. InputIterator2 is a model of Input Iterator. T is a model of Assignable. If x is an object of type T, y is an object of InputIterator1's value type, and z is an object of InputIterator2's value type, then x + y * z is defined. The type of x + y * z is convertible to T. For the second version: InputIterator1 is a model of Input Iterator. InputIterator2 is a model of Input Iterator. T is a model of Assignable. BinaryFunction1 is a model of Binary Function. BinaryFunction2 is a model of Binary Function. InputIterator1's value type is convertible to BinaryFunction2's first argument type. InputIterator2's value type is convertible to BinaryFunction2's second argument type. T is convertible to BinaryFunction1's first argument type. BinaryFunction2's return type is convertible to BinaryFunction1's second argument type. BinaryFunction1's return type is convertible to T. Preconditions [first1, last1) is a valid range. [first2, first2 + (last1 - first1)) is a valid range. Complexity Linear. Exactly last1 - first1 applications of each binary operation. Example int main() { int A1[] = {1, 2, 3}; int A2[] = {4, 1, -2}; const int N1 = sizeof(A1) / sizeof(int); cout << "The inner product of A1 and A2 is " << inner_product(A1, A1 + N1, A2, 0) << endl; } Notes [1] There are several reasons why it is important that inner_product starts with the value init. One of the most basic is that this allows inner_product to have a well-defined result even if [first1, last1) is an empty range: if it is empty, the return value is init. The ordinary inner product corresponds to setting init to 0. [2] Neither binary operation is required to be either associative or commutative: the order of all operations is specified. See also accumulate, partial_sum, adjacent_difference, count Copyright © 1999 Silicon Graphics, Inc. All Rights Reserved. TrademarkInformation