[petsc-users] How to use multigrid?

[w_ang_temp]

>At 2012-11-04 21:52:23,"Mark F. Adams" <mark.adams at columbia.edu> wrote:
>Just to add to Jed and Matt's comments:


>1) What are your equations (I really don't care what physics you are modeling, its the equations that we see).  Is is a scalar div (alpha(x) grad ) u?
 
The linear system Ax=b is resulted from the finite element discretization. It is a algebraic equation, based from a elliptic equation, my opinion.

 
>2) Try using hyper (-pc_type hyper -pc_hypre_type boomeramg).  Look at "PCApply              448", this should be like 10-20.  Configure your systems with -->download-hyper=1 if you do not have it.


>3) Why do you say it is ill conditioned?  Stretched grids? large jumps in material coefficients?  Why do you think it is illoconditioned?
 
Pragmatic geotechnical problems often involve materials with  highly varied material zones, such as in soil-structure interaction problems or soil-water
coupled problems.([1]summary;[2-4])
Reference:
[1]Krishna Bahadur Chaudhary. Preconditioners for soil-structure interaction problems with significant material stiffness contrast[D].
[2]S.H.Chan. A modified Jacobi preconditioner for solving ill-conditioned Biot's consolidation equations using symmetric quasi-minimal residual
method.International journal for numerical and analytical methods in geomechanics[J].
[3]Kok-Kwang Phoon. Iterative solution of large-scale consolidation and constraint finite element equations for 3D problems.International e-Conference on
Modern Trends in Foundation Engineering[J].
[4]Massimiliano, etc. Ill-conditioning of finite element poroelasticity equations. International Journal of Solids and Structures[J].
 
Thanks.
 
                                                                                                       Jim


 
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