[petsc-users] Jacobian free in SNES

[Konstantinos Kontzialis]

Dear all,

I solve the NS equations with the discontinuous galerkin method. The 
system's residual before going to petsc is the following:

M udot+R(u) = 0                         (1)

R(u) is the part of the residual coming from the spatially discretized 
terms. I need to say that the explicit version of my code runs very well.

But, I want to implement an implicit method for time marching using 
first the backward euler scheme. After linearization I get the following 
form:

M/dt u^{n+1} + dR/du (u^{n+1}-u^{n}) = M/dt u^{n} -R(u^{n})  (2)

How should I define a function seen by SNES for solving the above 
equation in a jacobian free context?


Kostas