[petsc-users] -snes_type test shows differences

[Jed Brown]

On Wed, 10 Feb 2010 15:35:14 -0500, "(Rebecca) Xuefei YUAN" <xy2102 at columbia.edu> wrote:
> Hi,all,
> 
> I was writing analytic Jacobian to my FormJacobian(). However, I found  
> that there are quite big differences between finite difference  
> Jacobian and hand coded Jacobian. To simply the problem, assume that I  
> am solving a very simple equation as the residual function has the  
> form of
> F = fxx*fyy - g.
> Where f is the unknown, g is the given r.h.s.

It looks like you have coded the Picard linearization.  You want the
Newton linearization

  J(f)h = fxx*hyy + hxx*fyy

Jed