Two kinds of Stencil elimination schemes with preserved symmetry are presented.Correlative symmetric positive definite difference equations are obtained.Condition number of coefficient matrix decreases over 7/9 folding ratio than that of five point difference Jacobi's.Their eigenvalues have a good clustered spectrum.Theoretic analysis and numerical experiments show that they are better than un-symmetric ones,and are more useful.

We present a variant restricted Additive Schwarz preconditioner and apply Partial-Newton-Krylov-Schwarz algorithm to solve nonlinear algebraic equations of two-dimensional three-temperature systems. Iteration and CPU time for convergence are decreased. Numerical results show efficiency of the method.