[petsc-users] SLEPc EPSGD: Can not converge, error estimation floats over 1e-6

[Jose E. Roman]

> El 13 jul 2022, a las 7:59, Runfeng Jin <jsfaraway at gmail.com> escribió:
> 
> Thank you, I will have a try to them.
> 
> I use JD and GD because this matrix is about quantum chemical computing, and it has the property that diagonal elements dominate. This property seems to be suitable for JG and GD. 

This is useful if you want to use a diagonal preconditioner (classical Davidson), but generalized Davidson can take any preconditioner. In PETSc the default preconditioner is not Jacobi but Block Jacobi+ILU.

> 
> > JD and GD are best when you need to compute eigenvalues around a target
> About this, I want to compute only three smallest real eigenvalues, should this be the situation suitable for GD and JD？

No, try Krylov-Schur or LOBPCG.

> 
> Runfeng 
> 
> Jose E. Roman <jroman at dsic.upv.es> 于2022年7月13日周三 12:36写道：
> Does it work with -eps_gd_blocksize 1 ?
> Why do you want to use GD? JD and GD are best when you need to compute eigenvalues around a target. For your case, I would try with the default solver (Krylov-Schur) or with LOBPCG.
> 
> Jose
> 
> 
> > El 13 jul 2022, a las 4:59, Runfeng Jin <jsfaraway at gmail.com> escribió:
> > 
> > Hi!
> > I am trying to find 3 eigenvalues of a matrix 81,160*81,160, and it get 0 eigenvalue after  162320 iterations. I use -eps_monitor and find error estimation floats over 1e-6, I didn't set the tolerance so it should be the default 1e-8. Actually it should achieve 1e-10.
> > 
> > I have tried  JD and GD, both of them can not converge. Does there any ways to help it converge to the 1e-10? 
> > 
> > By the way, I use default Convergence criterion, the output of  -log_view and -eps_monitor  are shown in attachment.
> > Thank you!
> > 
> > Runfeng Jin
> > <eps_monitor-and-log_view.txt>
>