[petsc-users] Functions for judging the properties of the matrix

[w_ang_temp]

Hello,
    I am sorry that I cannot understand "Make sure to avoid restarts". In the FAQ, it says that using the restarted
GMRES method to get approximations to the condition number. So why saying "avoid restarts" in the next following?
    Besides, there are two questions about GMRES:
    (1) Is the "iterations count" of GMRES with restarted parameters which is outputted by PETSc meaningless?
    (2) Is there only restarted GMRES in PETSc?
    Thanks.
                                                Jim




>>在 2012-08-07 21:59:05，"Matthew Knepley" <knepley at gmail.com> 写道：
>>On Tue, Aug 7, 2012 at 8:56 AM, w_ang_temp <w_ang_temp at 163.com> wrote:


>>Hello, Jed
>>    I am a little puzzled about the "How can I determine the condition number of a matrix?" in the
>>FAQ. The details are as follows:
 
>>    "...For larger matrices, you can run with -pc_type none -ksp_type gmres -ksp_monitor_singular_value
>>-ksp_gmres_restart 1000 to get approximations to the condition number of the operator. This will
>>generally be accurate for the largest singular values, but may overestimate the smallest singular
>>value unless the method has converged. Make sure to avoid restarts...".
   
>>    Since the command "-pc_type none -ksp_type gmres -ksp_monitor_singular_value
>>-ksp_gmres_restart 1000" using restart parameter, so, what does "Make sure to avoid restarts" mean?


>Do not believe the answer after the restart.
 
>>Besides, is the parameter "1000" a reference value which will be changed in specific project in order
>>to be converged? Or must use 1000 to get the condition number?


>The former.


  >  Matt
 
   >> Thanks.
 >>                                                      Jim
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