It turns out to a be a bug in my FormFunctionLocal(DMDALocalInfo *info,PetscScalar **x,PetscScalar **f,AppCtx *user). I forgot to initialize the array f. Zero the array f solved the problem and gave consistent result.
Just curious, why does not petsc initialize the array f to zero by default inside petsc when passing the f array to FormFunctionLocal? I have another quick question about the array x passed to FormFunctionLocal. If I want to know the which x is evaluated, how can I output x in a vector format? Currently, I created a global vector vecx and a local vector vecx_local, get the array of vecx_local_array, copy the x to vecx_local_array, scatter to global vecx and output vecx. Is there a quick way to restore the array x to a vector and output? Thank you. Best, Xiangdong On Mon, Apr 28, 2014 at 10:28 PM, Barry Smith <bsm...@mcs.anl.gov> wrote: > > On Apr 28, 2014, at 3:23 PM, Xiangdong <epsco...@gmail.com> wrote: > > > Hello everyone, > > > > When I run snes program, > > ^^^^ what SNES program”? > > > it outputs "SNES Function norm 1.23456789e+10". It seems that this norm > is different from residue norm (even if solving F(x)=0) > > Please send the full output where you see this. > > > and also differ from norm of the Jacobian. What is the definition of > this "SNES Function Norm”? > > The SNES Function Norm as printed by PETSc is suppose to the 2-norm of > F(x) - b (where b is usually zero) and this is also the same thing as the > “residue norm” > > Barry > > > > > Thank you. > > > > Best, > > Xiangdong > >
