[petsc-users] ill-conditioned problems in PETSc

[w_ang_temp]

Hello,
   
    In fact, I will deal with the large sparse symmetric or unsymmetric (depending on the constitutive
model used for the soil and the formulation of equations) linear system which usually occurs in geotechnical
problems. As you know, In most geotechnical problems, the coefficient matrix can be severely
ill-conditioned, thus calling  for the development of robust and efficient preconditioners and iterative methods.
   
    The iterative method and parallel solver are my choices, actually are required by my professor. As I know,
MUMPS is just an external solver like Matlab. So is it a right way to analyse the preconditioners and iterative
methods provided by PETSc like CG, GMRES, Jacobi, sor, etc. for my work?
   
    Also I do not quite understand the second part of what Barry said ('You will not be able to use the external
solvers with those mode'). So, what does 'those mode' mean. Using quad precision?
   
    Thanks a lot.
                                                        Jim





At 2012-06-28 02:38:25,"Barry Smith" <bsmith at mcs.anl.gov> wrote:
>
>   Also if it the condition number is, say, larger than 10^10 you likely would benefit from using quad precision for the calculations.  http://www.mcs.anl.gov/petsc/documentation/faq.html#precision
>
>   You will not be able to use the external solvers with those mode but since it is 1d likely running sequentially will be fine.
>
>    Barry
>
>
>On Jun 27, 2012, at 9:46 AM, Matthew Knepley wrote:
>
>> On Wed, Jun 27, 2012 at 7:55 AM, w_ang_temp <w_ang_temp at 163.com> wrote:
>> Hello,
>> 
>>     I want to deal with the ill-conditioned problems of Terzaghi's one-dimensional consolidation
>> 
>> finite element equations in geotechnical engineering. So is there special support on ill-conditioned
>> 
>> problems using ksp in PETSc.
>> 
>> 
>> Use a direct solver, like built-in LU,  or in parallel, MUMPS (--download-mumps).
>> 
>>   Matt
>>  
>>     Thanks.
>> 
>>                                                      Jim
>> 
>> 
>> 
>> 
>> 
>> 
>> -- 
>> What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.
>> -- Norbert Wiener
>
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