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[Andre Massing <question114825@xxxxxxxxxxxxxxxxxxxxx>]

Question #114825 on DOLFIN changed:
https://answers.launchpad.net/dolfin/+question/114825

    Status: Open => Answered

Andre Massing proposed the following answer:
Onsdag 16. juni 2010 17.55.35 skrev Phil Marinier :
> New question #114825 on DOLFIN:
> https://answers.launchpad.net/dolfin/+question/114825
> 
> I need to make many instances of DirichletBC, but I exactly how many is a
> user function. As such, I am using a loop to create my bcs.
> 
> 
> 	for(int j = 0; j < numberCathodes; j++){
> 
> 		cathode = &cathodes[j];
> 
> 		//assemble
> 		CathodeBC(iInit, cathode, phiCBC0);
> 
> 		// create anodic and cathodic boundary condition Functions from BCs
> 		numRows = PhiCBC0.vector().size();
> 		rows = new dolfin::uint[numRows];
> 		for(dolfin::uint j = 0; j < numRows; j ++)
> 			rows[j] = j;
> 		PhiCBC0.vector().set(phiCBC0, numRows, rows);
> 		delete [] rows;
> 
> 		//Define boundary condition
> 		DirichletBC cbc0(V, PhiCBC0, *cathode);
> 		bcsTEMP.push_back(cbc0);
> 	}
> 
> where bcsTEMP is a std::vector<dolfin::DirichletBC>
> 
> This does not work, since DirichletBC is abstract and so I can't make it a
> type for a vector.

As far as I can see is DirichletBC is not abstract. Did you mean the 
BoundaryCondition class? 

> Trying to use pointers will obviously not work, since
> once the object goes out of scope, it is cleaned up, and I end up
> following a dangling pointer to nowhere.

Hmm, maybe I miss a point here, but why does it not work for pointers? 
If you add your boundary conditions by 
 
 std::vector<const BoundaryCondition*> bcs;
  bcs.push_back( new YourFancyBoundaryConditionClass(.....) );
 
you can just go through the vector bcs and delete your objects before bcs is 
going out of scope.

> 
> I am going to make my own class called dirichletBC, the only difference
> being that I over load the apply() method, since it is the one that is
> virtual. My question is which apply() should I use?
> 
> Since my VariationalProblem is Laplaces equation with a single bilinear
> form and a single linear form ( a(V, V) and L(V) ), I assume that I need
> to apply the boundary condition to a matrix and a vector, hence using:
> 
> 00171 void DirichletBC::apply(GenericMatrix& A, GenericVector& b) const
> 00172 {
> 00173   apply(&A, &b, 0);
> 00174 }
> 
> Is that right? Is there something else I need to do to make this work? is
> there an easier way to make this work? Do you need more information about
> my problem?
> 
> Thank you for your help.

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