New Post: Can this be done faster?

The majority of my computation time is spent on this:

            DeltaEncoder.Clear()
            For col = 0 To NumberOfObs - 1
                DeltaEncoder += NeuronError.Column(col).OuterProduct(InputWithBias.Column(col))
            Next col
            DeltaEncoder /= NumberOfObs

The NumberOfObs is 2000.
NeuronError is a 100x2000 densematrix.
InputWithBias is a 101x2000 densematrix.

I basically need to find the sum(or average) of all the observation vectors in NeuronError outer-multiplied with their corresponding observation vector in InputWithBias.

This is part of a backpropogation algorithm.

Perhaps it would be faster to first transpose each matrix and then do rowvector outerproducts?

It seems like this operation would have been named/optimized since it is involved in backprop.
Any suggestions?