Sum of products of two arrays (dotproduct)

Question

First off, I know my title can be formulated better, but my math classes are so far gone I can\'t remember the correct words anymore..

I need to do something like this (

Answer 1

Solutions with LINQ

int[] digits1 = new int[10]{0,1,2,3,4,5,6,7,8,9};
int[] digits2 = new int[10]{0,1,2,3,4,5,6,7,8,9};

int result1 = digits1.Zip(digits2, (x, y) => x * y).Sum();

int result2 = digits1.Select((x, y) => x * digits2.ElementAt(y)).Sum();

int result3 = digits1.Select((n, i) => n * digits2[i]).Sum();

// Ani answer
int result4 = Enumerable.Range(0, digits1.Length)
    .Sum(i => digits1[i] * digits2[i]);

Performance test 100000 iterations:

Queries
Fn: Result 1       Ticks 135306
Fn: Result 2       Ticks 2470614
Fn: Result 3       Ticks 130034
Fn: Result 4       Ticks 123374

-------------

Fastest
Fn: Result 4       Ticks 123374
Fn: Result 3       Ticks 130034
Fn: Result 1       Ticks 135306
Fn: Result 2       Ticks 2470614