expected_K = [2, -1, 0, 0, -1;
	      -1, 2, -1, 0, 0;
	      0, -1, 2, -1, 0;
	      0, 0, -1, 2, -1;
	      -1, 0, 0, -1, 2];

actual_K = diffusion_matrix_sparse(5);

unit_test_equals("diffusion_matrix_sparse(5) looks right", ...
		 true, ...
		 isequal(actual_K, expected_K));
