Computing the Inner Product of Two

Computing the Inner Product of Two Sequences
T
inner_product (InputIterator1 beg1, InputIterator1 end1,
InputIterator2 beg2, T initValue)
T
inner_product (InputIterator1 beg1, InputIterator1 end1,
InputIterator2 beg2, T initValue,
BinaryFunc op1, BinaryFunc op2)
• The first form computes and returns the inner product of initValue and all elements in the range
[beg,end) combined with the elements in the range starting with beg2. In particular, it calls the
following for all corresponding elements:
initValue = initValue + elem1 * elem2
• The second form computes and returns the result of calling op for initValue and all elements in
the range [beg,end) combined with the elements in the range starting with beg2. In particular, it
calls the following for all corresponding elements:
initValue = op1(initValue,op2(elem1,elem2))
• Thus, for the values
a1 a2 a3 ...
b1 b2 b3 ...
they compute and return either
initValue + (a1 * b1) + (a2 * b2) + (a3 * b3) + ...
or
initValue op1 (a1 op2 b1) op1 (a2 op2 b2) op1 (a3 op2 b3) op1 ...
respectively.
• If the first range is empty (beg1==end1), both forms return initValue.
• The caller has to ensure that the range starting with beg2 contains enough elements.
• op1 and op2 must not modify their arguments.
• Complexity: linear (numElems calls of operators + and * or numElems calls of op1() and op2(),
respectively).
The following program demonstrates how to use inner_product(). It processes the sum of products
and the product of the sums for two sequences: