A super-efficient way to compute the sum of A[i] * B[i

Hi Folks,

I need a super-efficient way to compute the sum of A[i] * B[i] for i=1 to n.

For example, suppose A is this:

<row>
    <col>0.9</col>
    <col>0.3</col>
</row>

and B is this:

<row>
    <col>0.2</col>
    <col>0.8</col>
</row>

I want to compute:

(0.9 * 0.2) + (0.3 * 0.8)

Here's one way to do it:

sum(for $i in 1 to count($A/col) return number($A/col[$i]) *
number($B/col[$i]))

I suspect that is not the most efficient approach.

What is the most efficient approach? I will be doing hundreds of thousands of
these computations, so I want to use the most efficient approach.

/Roger