[petsc-users] Krylov-Schur Tolerance

[Christopher Pierce]

It seems to give the same results.  I exported the matrices to Matlab
and checked the estimated condition number of the B matrix which came to
~15 and the 2-norm of the B matrix which was ~10^6.  I'm guessing that
the large matrix norm is the problem.  I glanced over the source for the
RQCG solver and it doesn't seem to use a linear solver which is likely
why it showed better performance.  Do you have any suggestions for
dealing with problems like this?

Chris




On 02/19/17 12:24, Jose E. Roman wrote:
>> El 19 feb 2017, a las 11:00, Christopher Pierce <cmpierce at WPI.EDU> escribió:
>>
>> Thanks,
>>
>> Those changes did improve the tolerances of the solutions.  However, I
>> still have the same problem.  For certain matrices the error is up to
>> 10^4 times as large as the requested tolerances and when using true
>> residual the solver gets stuck on a certain residual norm the solutions
>> and does not converge.  I dumped the settings that I used which I'm
>> attaching here.
>>
>> Chris
> The settings seem correct.
> I would try to solve the problem as a non-symmetric problem: -eps_gen_non_hermitian
> Does it give small residuals? If so, the problem may be that your B-matrix is quite bad (high norm or ill-conditioned).
>
> Jose
>
>