Try a ksp_tol of 1.e-14 instead of 1.e-12?
Barry
On Mar 31, 2008, at 8:11 AM, Aldo Bonfiglioli wrote:
> Barry, Matt
> I am back on the Non repeatability issue with answers
> to your questions.
>
>> 2) did you do the -ksp_rtol 1.e-12 at the same time as the -
>&
Barry, Matt
I am back on the Non repeatability issue with answers
to your questions.
> 2) did you do the -ksp_rtol 1.e-12 at the same time as the -
> vecscatter_reproduce? They
> must be done together.
The enclosed plot (res_vs_step) shows the mass residual
history versus the Ne
> 1) Are you sure the -vecscatter_reproduce is working, run with -
> options_left and see if
> says the option was not used.
I have harwired it into the 2.3.3-p8, following your suggestion.
> 2) did you do the -ksp_rtol 1.e-12 at the same time as the -
> vecscatter_reproduce? They
> must be do
>
>
> 1) You have way too many Newton steps. Newton is quadratically
>convergent, so if
> you have 100+ steps, it means you are very very far from the
>solution when you
> begin. In this region, Newton is a really bad algorithm and can
>be very very
> sensitive to perturbations. I wo
On Mar 18, 2008, at 11:52 AM, Aldo Bonfiglioli wrote:
>> 1) Are you sure the -vecscatter_reproduce is working, run with -
>> options_left and see if
>> says the option was not used.
>
>
> I have harwired it into the 2.3.3-p8, following your suggestion.
>
>> 2) did you do the -ksp_rtol 1.e-12 at
>
> 1)Have you made runs where you require, say -ksp_rtol 1.e-12 to
> eliminate the effects of
> not solving the linear systems accurately?
I have performed two runs with ksp_rtol = 1.e-12. The relevant plots are
enclosed
where comparisons are made with PETSc's default for ksp_rtol.
In one
1) Are you sure the -vecscatter_reproduce is working, run with -
options_left and see if
says the option was not used.
2) did you do the -ksp_rtol 1.e-12 at the same time as the -
vecscatter_reproduce? They
must be done together.
3) what happens on 1 process? Does it behave exactly the same fo
To me this looks like
1) You have way too many Newton steps. Newton is quadratically
convergent, so if
you have 100+ steps, it means you are very very far from the
solution when you
begin. In this region, Newton is a really bad algorithm and can
be very very
sensitive to pertur
Barry,
thanks for your prompt reply.
> 1)Have you made runs where you require, say -ksp_rtol 1.e-12 to
> eliminate the effects of
> not solving the linear systems accurately?
I am trying this right now, although it may require very many linear
iterations, particularly in the last Newton ste
Aldo,
Actually it is far easier than I thought. I have added the
argument -vecscatter_reproduce
that will cause the receives to always be processed in the same order
(though order or
operations in the MPI reductions may still result in slightly
different convergence histories.)
to
Aldo,
I would scale the turbulence equation to match the scaling of the
rest of the equations.
I suspect you are ramping up the CFL number too quickly. For a
"continuation" type
Newton method to work well (in my mindset anyways), you need to have
the solution
well converged b
Aldo,
1)Have you made runs where you require, say -ksp_rtol 1.e-12 to
eliminate the effects of
not solving the linear systems accurately?
2) Have you run the exact example that you ran with geometric
decomposition also with
the parmetis decomposition? Is that what you sent? (This is t
Dear all,
this is a follow-up to an old mail concerning non-repeatibility
issues in a parallel environment.
We are solving the steady 3D RANS eqns using
Newtons's algorithm. All equations (turbulence included)
are fully coupled.
Our non-linear convergence history shows remarkable
non-repeatibilit
The 2d results, as noted, are reasonable and expected behavior.
The 3d results are not acceptable, when sometimes it converges
and sometimes it does not. I would use a 1e-12 KSP rtol and a similar
1e-12 SNES rtol; does it now always converge? If not then I suspect there
may be some error in t
Dear users,
in the notes attached here we address an issue concerning
nonrepeatability.
We know this is a known issue in parallel floating point programs,
but we would like to be sure we are interpreting
things correctly a not mis-using PETSc.
Comments are welcome.
Regards,
Aldo
--
Dr. Aldo Bon
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