[petsc-users] a question for iterative solver users

[Umut Tabak]

Dear all,

What could be the benefit of iterative solvers(specifically cg or pcg), 
as a factor, in comparison to direct solvers, on reasonably large sparse 
systems if one has a well conditioned operator matrix.

This question might be a bit abstract(like the one above) though I will 
fire anyway ;) : where does cg or iterative methods really start to beat 
direct solvers, again for a well conditioned operator matrix? I am 
asking this from matrix size point of view.

I could not make, really, use of iterative solvers due to 
ill-conditioned matrices, however at some point of my algorithm, I have 
a matrix which seems to be well conditioned but still MATLAB's backslash 
beats the pcg. This was the reason of the above questions, in a bit 
awkward order.

I would like to hear experiences from the general user community if 
possible.

Best,
Umut