Thanks for the informative answer, I moved over the DiffSystem and I
think I worked out some incorrect math, but now I am back to square one
with the initial condition of the transient problem. I added this line
to the end of my Nem2DSystem:init_data () call (Nem2DSystem is the name
of my class that inherits FEMSystem ):
this->project_solution(initial_value,
NULL,(this->get_equation_systems()).parameters);
where the initial value function is defined similar to the
non-DiffSystem example with an initial condition:
Number Nem2DSystem::initial_value (const Point& p,
const Parameters& parameters,
const std::string& sysname,
const std::string& unkname)
and I get a compile error that I cannot figure out:
nem2dsystem.C: In member function \u2018virtual void
Nem2DSystem::init_data():
nem2dsystem.C:149: error: no matching function for call to
\u2018Nem2DSystem::project_solution(<unresolved overloaded function
type>, NULL, Parameters&)
/home/grad/nasser/nemfem/libmesh-0.6.2/include/solvers/system.h:165:
note: candidates are: void System::project_solution(Number (*)(const
Point&, const Parameters&, const std::string&, const std::string&),
Gradient (*)(const Point&, const Parameters&, const std::string&, const
std::string&), Parameters&) const
I guess I have to study C++ templates a little more, but any ideas?
Nasser Mohieddin Abukhdeir
Graduate Student (A.D. Rey Research Group)
McGill University - Department of Chemical Engineering
http://webpages.mcgill.ca/students/nabukh/web/
http://people.mcgill.ca/alejandro.rey/
Roy Stogner wrote:
>
> On Wed, 23 Apr 2008, Nasser Mohieddin Abukhdeir wrote:
>
>> *** Solving time step 0, time = 1e-07 ***
>> ERROR: LASPACK Error:
>> in ILUFactor for Mat:
>> Factorization produces zero pivot elements.
>> [0] src/numerics/laspack_linear_solver.C, line 276, compiled Apr 21 2008
>> at 14:01:19
>> Aborted
>>
>> Basically I added my expressions for the residual and Jacobian and
>> removed all of the boundary condition code because I need to impose
>> Neuman BCs (which from what I understand is implicitely taken care of by
>> the FEM algorithm).
>
> Homogeneous natural BCs are implicitly taken care of by the FEM
> formulation, but just what the "natural boundary condition" is depends
> on your precise formulation; if you've got something complicated, take
> a look at what boundary integrals pop out of your integration by parts
> to double-check that what you're setting to zero is what you want to
> be setting to zero.
>
>> I initialized t=0 with an acceptable solution to the equations, so I
>> just expected some smooth sailing...
>
> You're solving a transient problem, then? In an all-Neumann problem
> with no reaction terms you can often get a singular matrix doing a
> steady solve (since the problem itself isn't uniquely defined); but
> for a transient problem, the mass matrix coming from the time
> integration should prevent anything like that from happening.
>
>> I am also wondering about DiffSystem, should I just scrap my work with
>> ex13 and start with DiffSystem?
>
> There are tradeoffs. DiffSystem makes it easier to add some new
> features (e.g. adaptive time stepping, more complex nonlinear
> equations) to your code, but it also means you'll have to make
> more changes to your code to keep up with the library.
>
> When you construct a DiffSystem subclass, you read:
> "Warning, This code is untested, experimental, or likely to see future
> API changes"
>
> The "untested" and "experimental" adjectives no longer apply, but
> "future API changes" certainly does. I'm probably going to alter even
> the most basic class methods to make it work better multithreaded.
> The changes should be straightforward (methods will take reference
> parameter(s) instead of using certain member variables), but it's
> never fun when your code suddenly requires repair because a new
> library version made backwards incompatible API changes.
> ---
> Roy
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