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

[Jose E. Roman]

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