[klausb]

I need additional, temporary matrices to perform Linear Algebra operations including matrix-matrix multiplications, subtractions and additions. The content of the matrices differs from the coefficient matrix and could be e.g. a subset like the (strictly) lower part. There are multiple matrix classes like lduMatrix or RectangularMatrix.

Which one should be used and how would I construct a new, empty one and e.g. add the lower part or the coefficient matrix?