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));
