[petsc-users] Question on PCSHELL with TS

[Praveen C]

Dear all

I am trying to solve a steady state problem using TSPSEUDO and am unclear about the preconditioner. The PDE is 3-d compressible Euler/NS equations solved with FV on unstructured grids.

I am using matrix-free approach (-snes_mf_operator) and want to provide my own matrix-free preconditioner using PCSHELL.

For the problem

du/dt = R(u)

the update would be 

[I - dt*J(u)]*du = dt*R(u),   J(u) = R’(u)

u = u + du

Does my PCSHELL have to provide a preconditioner for J or for I - dt*J ?

Thanks
praveen