We analyze approximation and propose a two-level algorithm for finite volume schemes of diffusion equations with structured adaptive mesh refinement. First of all, a typically conservative finite volume scheme was discussed, along with criterion for refining and coarsening interpolation operator. Secondly, non-conforming elements around coarse-fine interface were eliminated by introducing auxiliary triangle elements. A symmetric finite volume element (SFVE) scheme was designed. And further analysis showed the scheme has better approximation. It weakens restrictions. Finally, a two-level algorithm was constructed for SFVE. Theoretical analysis and numerical experiments demonstrate uniform convergence of the algorithm.

Performance of physical-variable based coarsening two-level(PCTL) preconditioner is analyzed for typical linear systems discretizated from two-dimensional(2-D) radiative diffusion equations with photon,electron,ion temperatures(3-T).It reveals that performance of PCTL strongly depends on both coupling of three temperatures and diagonally dominance of three diagonal sub-matrices of coefficient matrix.An adaptive algorithm for sub linear systems in PCTL is proposed.Numerical results show efficiency and robustness of the method.For 37 2-D 3-T linear systems in simulations,PCTL based on the algorithm speeds up 2.5 times compared with classical algebraic multigrid (AMG) preconditioners.

Preconditioners for GMRES method are discussed in solving linear systems discretized from scalar elliptic partial differential equations of second order with jump coeffcient.Based on hierarchical basis,spectral equivalence is established for two kinds of stiffness matrices from quadratic finite element and second order mixed-type finite volume element method,respectively.A preconditioner is proposed by combining equivalence with two-level geometric-algebraic multigrid(GAMG) method which was especially designed for linear systems arising from quadratic finite element discretization.Numerical results confirm correctness of our theoretical analysis.It shows that the preconditioner is quite effcient and robust.