A = [2, 1, 1, 0; ... 1, 2, 0, 1; ... 1, 0, 2, 0; ... 0, 1, 0, 1]; expected = { [1,2], [1,3], [2,3], [2,4], [3,4] }; actual = envelope(A); unit_test_equals("envelope works on an example", ... true, ... isequal(actual, expected));