Non repeatability issue

Aldo Bonfiglioli aldo.bonfiglioli at
Tue Mar 18 11:52:37 CDT 2008

> 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 
the same testcase produces far more repeatible non-linear convergence 
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).

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.


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

More information about the petsc-users mailing list