fix typo in tutorial 502 and content error

The sum of those two matrices would be L + A, however, we want Q = L - 2A , or the negative of that if we want positive-definite.

Former-commit-id: 503b43d07f07e56082198e60950b9cb22f0be42f

tutorial/tutorial.md.REMOVED.git-id

@@ -1 +1 @@
-81c8a0d29caab90b96cb6372b610a0ea4c48cb11
+24049c9ad2cc3eff90b021f5f1d017c8c042e6da