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Anders Logg wrote:
On Sun, Sep 07, 2008 at 08:27:41AM +0100, Garth N. Wells wrote:Martin Sandve Alnæs wrote:2008/9/6 Anders Logg <logg@xxxxxxxxx>:On Sat, Sep 06, 2008 at 04:22:09PM +0200, Martin Sandve Alnæs wrote:2008/9/6 Garth N. Wells <gnw20@xxxxxxxxx>:Dag Lindbo wrote:Anders Logg wrote:There seems to be a problem (among many) with the current design of the Function classes (see thread "evaluating higher order mesh function"). In particular, the finite element is missing in DiscreteFunction. My suggestion would be to just add it and let a DiscreteFunction consist of the following four items which are always available: mesh, x, dof_map, finite_element Is this enough, and what other issues to we need to fix?One major issue which I just want to reiterate is ownership of data. As it stands, the DiscreteFunction may or may not be responsible for e.g. the dof vector x, depending on whether local_vector is a NULL pointer or not. Take a look at the thread "Ownership" from Garth on 06/26/2008.Yes, this is a big problem and has caused me a few headaches with bugs. For example, passing a user-defined Function to a function to convert it to a DiscreteFunction via a projection onto a finite element basis causes a problem because the FiniteElement which the projected Function points to goes out of scope once the function is exited.A problem related to this is initialization of the DiscreteFunction. We had a bug previously where the LinearPDE class maintained ownership of the solution vector. The only way to prevent this was to break the encapsulation of DiscreteFunction by making it a friend of LinearPDE (as with XMLFile for the same reasons). Here is some of the code that handles this initializaton today (L101 in LinearPDE.cpp): u.init(mesh, *x, a, 1); DiscreteFunction& uu = dynamic_cast<DiscreteFunction&>(*u.f); uu.local_vector = x; This ain't poetry in my opinion :)Indeed, this isn't nice, and there is something similar in XMLFile.cpp. GarthWe should start to use std::tr1::shared_ptr. There is some support for it with python in swig 1.3.35, which is part of the upcoming Ubuntu IntrepidThe main issue is how we want to initialize Functions, and if one should allow to set members. For simplicity, say that a Function is defined only by a Vector. Then we have a few different situations to consider: 1. Function creates the Vector Function u; Vector& x = u.vector(); 2. Function gets the Vector Vector x; Function u(x); 3. Function gets initialized with a Vector Function u; Vector x; u.init(x); Do we want to support all of 1-3? Things become considerable easier if we can make some simplifying assumptions. How visible would a shared_ptr be in the interface?A shared_ptr must be visible to the user every single place a pointer is passed around, otherwise the reference count won't be correct and we'll just have more problems.So, in pseudo code, would it look something link this? class DiscreteFunction { private: shared_ptr<GenericVector> x; public: DiscreteFunction() : x(new Vector) {} DiscreteFunction(shared_ptr<GenericVector> x) { x(x); } shared_ptr<GenericVector> vec() {return x;} } ? GarthWhat would the user code look like if we use shared_ptr for examples 1-3 above?
I'm experimenting with uBLASVector to get a feel for it. Inevitably, shared_ptr will be visible in the public interface, but I feel only advanced users will see it. Most users will not see it.
What I really like with the shared pointers is getting rid of things like 'bool is_view' and 'GenericMatrix* local_matrix', etc, which can get confusing when they change.
Garth
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