A = tridiagonal(0, -1, 2, -1); expected = []; unit_test_equals("poisson tridiagonal of size zero is correct", ... expected, ... A); A = tridiagonal(1, -1, 2, -1); expected = [2]; unit_test_equals("poisson tridiagonal of size one is correct", ... expected, ... A); A = tridiagonal(2, -1, 2, -1); expected = [2, -1; ... -1, 2]; unit_test_equals("poisson tridiagonal of size two is correct", ... expected, ... A); A = tridiagonal(3, -1, 2, -1); expected = [2, -1, 0; ... -1, 2, -1; 0, -1, 2]; unit_test_equals("poisson tridiagonal of size three is correct", ... expected, ... A);