On May 19, 2011, at 1:43 AM, Tian(ICT) wrote:
> I encountered a strange problem.
> I am using VC2008. When I debuged the code line by line using the VC, the
> user FormJacobian was never called, instead, the SNES seems use matrix free
> Jacobian. But if I run the code in command line (no debugger attached), the
> log file showed that the user FormJacobian was called. What is the reason for
> this?
There is not logical explanation for this. Running in the debugger should
not trigger a different code path then not in the debugger. Also SNES will
never use matrix-free unless you specifically ask for it.
What can happen is that SNES may decide (for some reason) that the initial
residual norm is small enough and hence never try a Newton step. If there are
some uninitialized variables or other problems in the code the run in and out
of the debugger could be different hence different "function values". Run with
-snes_monitor -ksp_monitor_true_residual -snes_view -snes_converged_reason
-ksp_converged_reason.
Ideally in this situation you would run with valgrind
http://www.mcs.anl.gov/petsc/petsc-as/documentation/faq.html#valgrind or a
similar tool to check that the code is memory corruption free.
Barry
>
> -Rong
