[petsc-users] [Libmesh-users] Really Really Really Weird SNES behaviour

[Cody Permann]

Sounds like a memory corruption problem. I know several users that are
experts at writing code like that.

Unfortunately, it can be difficult to track down on OS X due to a lack
of working memory analysis tools.
1. Since this problem popped up after you changed your initial
condition, you may just want to start by carefully looking at your
code and thinking about cases where your variables might not be
initialized, or where calculations could potentially produce underflow
or overflow conditions.
2. If you have access to a Linux box, then you will have bounds
checked STL containers at your disposal in debug mode.  You'll also be
able to run your code through valgrind.  Both of those operations are
relatively easy to perform.  Let us know if you have any questions.

Cody

Sent from my iPhone

On Jul 13, 2013, at 11:17 PM, subramanya sadasiva <potaman at outlook.com> wrote:

> Hi, I am observing some really really really weird SNES behavior in my SNESVI code called through Libmesh. This behaviour appeared after I changed some initial conditions and only happens in an optimized build. I am running this code on a Macbook pro running os x 10.8..
> When the debug code is run, the residuals computed for the initial conditions provided give norms which are of the expected magnitude.. so the SNES_Monitor output is,
> solving the cahn hilliard time step  0 SNES Function norm 8.223262421671e-01  1 SNES Function norm 3.793806858333e-03Nonlinear solve did not converge due to DIVERGED_MAX_IT iterations 1
> The output from SNES_Monitor with the optimized code on the other hand is,
> solving the cahn hilliard time step  0 SNES Function norm 5.153882032022e+19  1 SNES Function norm 1.446612980133e+19Nonlinear solve did not converge due to DIVERGED_MAX_IT iterations 1
>
> Absolutely nothing else has changed in the code except that one code is built with a debugging and one with an optimized version of the code.
> Any ideas?Subramanya
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