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

[Kirk, Benjamin (JSC-EG311)]

Have you tried devel mode? It uses compiler flags similar to optimized mode but leaves asserts on too. 

Otherwise, I agree with Cody that there may be an uninitialized value that is silently being set to 0 in debug mode but contains garbage in optimized mode. 

-Ben


On Jul 14, 2013, at 7:26 AM, "Cody Permann" <codypermann at gmail.com> wrote:

> 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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