code: public Matrix mtimes(Matrix m2) {
  		if (m2 instanceof DenseDoubleMatrix2D) {
  			final DenseDoubleMatrix2D result = new BlockDenseDoubleMatrix2D((int) getRowCount(),
  					(int) m2.getColumnCount(), layout.blockStripe, BlockOrder.ROWMAJOR);
  			Mtimes.DENSEDOUBLEMATRIX2D.calc(this, (DenseDoubleMatrix2D) m2, result);
  			return result;
  		} else {
  			return super.mtimes(m2);
  		}
  	}
docs: Shortcut to create a BlockMatrix for target