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

[w_ang_temp]

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?
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?
    Thanks.
                                                       Jim

 


>>在 2012-07-11 22:19:51，"Jed Brown" <jedbrown at mcs.anl.gov> 写道：

>>On Wed, Jul 11, 2012 at 8:51 AM, w_ang_temp <w_ang_temp at 163.com> wrote:

 
>>Hello,
   
>>    Is there function in PETSc for judging the properties of the matrix A ? Such as positive definitiveness and
 
>>conditional number. I know that there are several functions begin with MatIs+, but it has limited amounts. 


>The Ritz values are estimates of the eigenvalues that you can obtain using KSPSolve() with ->ksp_compute_eigenvalues or -ksp_plot_eigenvalues. Note that these are estimates for the _preconditioned_ >operator, so you should use -pc_type none if you want estimates for the original operator.


>http://www.mcs.anl.gov/petsc/documentation/faq.html#conditionnumber
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