[petsc-users] SLEPc EPS Tolerance

[Jose E. Roman]

What do you mean "the result was still the same"? How do you measure accuracy? Which is the value of the computed residuals? What is the eigenvalue you are computing? Which convergence criterion are you using? 


> El 10 jul 2020, a las 11:56, Eda Oktay <eda.oktay at metu.edu.tr> escribió:
> 
> Hello,
> 
> I am currently using EPS to find 2 smallest eigenvalues and
> corresponding eigenvectors of a matrix in order to be used in spectral
> graph partitioning algorithms. I know that default tolerance is E-8
> and I also tried the solver with tolerances E-2, E-4 and E-6 expecting
> that in every matrix I used, I get the most accurate solution (After
> partitioning the matrix, I look at edge cut for accuracy) when
> tolerance is E-8.
> 
> I even tried E-10 and the result was still the same, sometimes E-4 or
> E-2 gives better results.
> 
> I was wondering if this is normal, if normal then how can we explain
> this? Because in theory, one can expect that if tolerance decreases,
> accuracy increases.
> 
> Thanks!
> 
> Eda