#include <numeric>
  TYPE inner_product( iterator start1, iterator end1, iterator start2, TYPE val );
  TYPE inner_product( iterator start1, iterator end1, iterator start2, TYPE val, BinaryFunction f1, BinaryFunction f2 );

The inner_product() function computes the inner product of [start1,end1) and a range of the same size starting at start2.

inner_product() runs in linear time.