[petsc-users] looking for examples on solving linear systems of matrix-free matrices

[jinshan wu]

Hi all, I am new to this list. But it seems to have a lot of resources and 
friendly people here.

I need to solve a huge linear system. In order to save some memory, I am 
thinking to store the matrices in its own data structure other than in real 
matrices. I understand that petsc can do that via GMRES (and others) 
without accessing matrix elements . So my question is where can we find some 
example? I am perfectly fine with supplying the matrix-vector product part by my 
own. I need more infor on how to connect it to the solver in petsc. 

Also another technical question: do we have to perform the preconditioner? 

thanks,
Jinshan