Reference matrix: 1.50 2.00 0.50 0.00 0.00 2.50 5.00 3.50 0.50 0.00 0.50 4.00 10.00 5.00 0.50 0.00 0.50 5.50 17.00 6.50 0.00 0.00 0.50 7.00 25.50 sprspm matrix (should show only tridiagonals): 1.50 2.00 0.00 0.00 0.00 2.50 5.00 3.50 0.00 0.00 0.00 4.00 10.00 5.00 0.00 0.00 0.00 5.50 17.00 6.50 0.00 0.00 0.00 7.00 25.50