[petsc-users] SLEPc EPSGD: too much time in single iteration

[Jose E. Roman]

The value -eps_ncv 5000 is huge.
Better let SLEPc use the default value.

Jose


> El 10 jun 2022, a las 14:24, Jin Runfeng <jsfaraway at gmail.com> escribió:
> 
> Hello!
>  I want to acquire the 3 smallest eigenvalue, and attachment is the log  view output. I can see epssolve really cost the major time. But I can not see why it cost so much time. Can you see something from it?
> 
> Thank you !
> 
> Runfeng Jin
> 
> On 6月 4 2022, at 1:37 凌晨, Jose E. Roman <jroman at dsic.upv.es> wrote:
> Convergence depends on distribution of eigenvalues you want to compute. On the other hand, the cost also depends on the time it takes to build the preconditioner. Use -log_view to see the cost of the different steps of the computation.
> 
> Jose
> 
> 
> > El 3 jun 2022, a las 18:50, jsfaraway <jsfaraway at gmail.com> escribió:
> >
> > hello!
> >
> > I am trying to use epsgd compute matrix's one smallest eigenvalue. And I find a strang thing. There are two matrix A(900000*900000) and B(90000*90000). While solve A use 371 iterations and only 30.83s, solve B use 22 iterations and 38885s! What could be the reason for this? Or what can I do to find the reason?
> >
> > I use" -eps_type gd -eps_ncv 300 -eps_nev 3 -eps_smallest_real ".
> > And there is one difference I can tell is matrix B has many small value, whose absolute value is less than 10-6. Could this be the reason?
> >
> > Thank you!
> >
> > Runfeng Jin
> <log_view.txt>