Inefficient MatrixVectorMult_DDRM.innerProduct

[audetto]

I have noticed that innerProduct

ejml/main/ejml-ddense/src/org/ejml/dense/row/mult/MatrixVectorMult_DDRM.java

Lines 338 to 344 in 2c9d1dc

	for (int k = 0; k < B.numCols; k++) {
	double sum = 0;
	for (int i = 0; i < B.numRows; i++) {
	sum += a[offsetA + i]*B.data[k + i*cols];
	}
	output += sum*c[offsetC + k];
	}

performs a lot worse (2x minimum, but varies with size, 1000s) than my original naive implementation.

I think I figured out the reason.

The access of the matrix data likely trashes the CPU cache, because it keeps jumping column: B.data[k + i*cols], where i is incremented in the inner loop.

If I swap the loops, I get a back the lost speed.

Before I provide a PR, is there any reason this is does this way?