“…For this purpose, the following lemmas need to be introduced.Lemma (). On the matrices A and B, we have the following results (a) The eigenvalues of the matrices A and B are (b) A and B have the same eigenvectors, that is (c) There are real symmetric positive define matrices R and S such that R 2 = H, S 2 = M . Lemma (). For any grid functions u ∈ X h , we have …”