[petsc-dev] [petsc-maint #143637] SNES takes 50 newton iterations

[Hesameddin Ilatikhameneh]

Using -ksp_type preonly -pc_type lu didn't change the number of required newton iterations. 

I don't understand what you mean by "then backoff".

Thanks
Hesam
----- Original Message -----
From: "Matthew Knepley" <petsc-maint at mcs.anl.gov>
To: "petsc-maint" <petsc-maint at mcs.anl.gov>, "Hesameddin Ilatikhameneh" <hilatikh at purdue.edu>
Cc: "For users of the development version of PETSc" <petsc-dev at mcs.anl.gov>
Sent: Tuesday, December 11, 2012 4:09:46 PM
Subject: Re: [petsc-maint #143637] SNES takes 50 newton iterations

On Tue, Dec 11, 2012 at 1:02 PM, Hesameddin Ilatikhameneh
<hilatikh at purdue.edu> wrote:
> Hello,
>
> I want to minimize a simple energy equation (E = E(x0,x1,...,xN)) using nonlinear solver SNES. This way SNES equation F(x) = dE/dxi = 0 and jacobian is J = dF/dx = d2E/dx2. I have attached a report explaining the problem and how I implemented it.
>
> The energy is related to 1D chain of balls connected with springs and the final answer is that all balls spaced equal to ideal distance.
>
> My problem is that SNES takes near 30-50 newton iterations to converge which seems to be too much for such a simple problem.
> I have also attached the code and appreciate your help on this.

Start with -ksp_type preonly -pc_type lu, and then backoff. This gives
you the true Newton
convergence rate.

   Matt

> Thanks
> Hesam
>



--
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which
their experiments lead.
-- Norbert Wiener