Non repeatability issue

Barry Smith bsmith at
Tue Mar 18 11:59:07 CDT 2008

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 the same time as the -  
>> vecscatter_reproduce? They
>> must be done together.
> No, I tested the two separately. I will do as you suggest.
>> 3) what happens on 1 process? Does it behave exactly the same for  
>> two  identical runs?
> The current testcase is too large to be run on a single processor.
> Tests performed with smaller datasets (both 2 and 3D) have shown  
> that on 1 proc
> subsequent  runs produce identical output.
> It should also be mentioned that, on a different grid (somewhat less  
> stretched)
> the same testcase produces far more repeatible non-linear  
> convergence histories.
> By "far more repeatible" I mean that the output of subsequent runs  
> are NOT
> identical, but the non-linear convergence histories are almost
> superimposed at the "plotting" level, small differences arising only
> when the residuals are close to machine eps.
> On this grid, the linear solver (either BJ+ILU(k) or ASM+ILU(k))
> also behaves far better.
>> 4) there is too much going on here to figure out why you get this   
>> behavior. Can you please
>>  FIX the continuation parameter
> Here I am not sure about the nomenclature: by "continuation  
> parameter" do you
> mean the strategy by which the pseudo-time derivative term is
> progressively reduced so as to revert to a true Newton algorithm?
> My pseudo-time derivative term looks like
> 1/(CFL) * (Volume/dt)
> Volume/dt is locally computed based on an explicit stability
> criterion and CFL is ramped from a starting value (CFL_0, tipically  
> of order 1 or 10)
> using the ratio between the current and initial residuals of one
> of the conservation eqns (mass, tipically).

   Yes, this is what I mean. When you just fix the CFL and run Newton  
runs to completion
is it stable? Then if you ramp up the CFL much more slowly is it  
stable and Newton
convergence much smoother?
> In all previous plots, the fixed point iterations were not shown.
> The fixed point iteration was run only once to generate the
> initial solution used for all Newton runs.

    That's ok; I don't care about that. What I want to see is the CFL  
number plotted with the
Newton residuals.

> Aldo
> -- 
> Dr. Aldo Bonfiglioli
> di Ingegneria e Fisica dell'Ambiente (DIFA)
> Universita' della Basilicata
> V.le dell'Ateneo lucano, 10 85100 Potenza ITALY
> tel:+39.0971.205203 fax:+39.0971.205160

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