setdiffMatrix shortens Matrix2Curt by those rows that are in both matrices.
matrix, which will be shortened by x rows
matrix whose rows will be compared to those of Matrix2Curt x rows in Matrix2compare equal rows of Matrix2Curt (order of rows is irrelevant). Has the same number of columns as Matrix2Curt.
V$CurtedMatrix[n-x,k] Shortened Matrix2Curt