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

[Barry Smith]

On Dec 11, 2012, at 3:15 PM, Hesameddin Ilatikhameneh <hilatikh at purdue.edu> wrote:

> Using -ksp_type preonly -pc_type lu didn't change the number of required newton iterations. 
   
   http://www.mcs.anl.gov/petsc/documentation/faq.html#newton
> 
> 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
>