[Getfem-users] Sign of model_pb - residual in Classical_Newton

[Konstantinos Poulios]

I have found some difficulties in nonlinear solutions in combination
with the new brick system. For a very simple nonlinear model that I
have converted from the old brick system, the classical_Newton
subroutine diverges. Trying to trace down the problem I realized that
in the first iteration step the residual of the model_pb object used
in the classical_Newton subroutine, has a different sign as the
corresponding one in the old brick system. I my test case the residual
I have checked was exclusively due to a source_term. Perhaps the
following two screenshots could be helpful to understand:

http://files.ubuntu-gr.org/forum/logari81/getfem/getfem_old_brick_system.png
http://files.ubuntu-gr.org/forum/logari81/getfem/getfem_new_brick_system.png

Was this sign difference to expect? Should this sign difference be
taken into consideration when migrating bricks from the old system to
the new one? Could it be a bug? My question affects version 4.0.0.

Kostas