[petsc-dev] Matrix Free Conjugate Gradient

[Hesameddin Ilatikhameneh]

Hello, 

We have a very large system (100M variables) which we want to minimize its energy. We are using Petsc extensively for matrix operations.
I know that it is theoretically possible to use conjugate gradient method without storing Jacobian matrix (which is very huge in this case) since the conjugate gradient needs Jacobian times a vector not Jacobian itself.

I read your manual about matrix free methods but I couldn't find where I can determine that function to Jacobian times a vector.

I appreciate your help.

Thanks
Hesam