dolfin team mailing list archive

["Johan Hoffman" <jhoffman@xxxxxxxxxx>]

Looks great! This opens up for moving the initial conditions to the
main-file, where I think they belong.

/Johan


> Hi everyone!
>
> As you may have noticed, I've been working on some new demos in
> src/demo/pde. As a consequence, I have fixed a couple of issues with
> the Function class that we've had previously. In particular, you no
> longer have to initalize a Vector for a Function used as initial value
> in time-steppig.
>
> Here's an illustration from the new convection-diffusion demo:
>
> // Linear system and solver
> Matrix A;
> Vector x, b;
> GMRES solver;
>
> // Create functions
> ConvectionDiffusion::BilinearForm::TrialElement element;
> Function u0 = 0.0;
> Function u1(x, mesh, element);
>
> // Create forms
> ConvectionDiffusion::BilinearForm a(velocity, delta);
> ConvectionDiffusion::LinearForm L(u0, velocity, f, delta);
>
> // Assemble left-hand side
> FEM::assemble(a, A, mesh);
>
> // Parameters for time-stepping
> real T = 0.3;
> real k = 0.01;
> real t = k;
>
> // Output file
> File file("temperature.pvd");
>
> // Start time-stepping
> Progress p("Time-stepping");
> while ( t < T )
> {
>   // Assemble load vector and set boundary conditions
>   FEM::assemble(L, b, mesh);
>   FEM::applyBC(A, b, mesh, element, bc);
>
>   // Solve the linear system
>   solver.solve(A, x, b);
>
>   // Save the solution to file
>   file << u1;
>
>   // Update progress
>   p = t / T;
>
>   // Move to next interval
>   t += k;
>   u0 = u1;
> }
>
> Note in particular the following things that you couldn't do before:
>
> 1. Function u0 = 0.0;
>
> This initializes a Function that is constant equal to zero.
>
> 2. u0 = u1;
>
> This updates the values of u0 to those of u1. u0 will change from
> being a constant Function to a discrete Function and automatically
> create a new Vector (previously x0) and copy the values from x1.
> The next time, it will keep the previously created Vector and just
> copy the values.
>
> I haven't actually checked the solution so I'll just keep my fingers
> crossed I didn't break anything... :-)
>
> /Anders
>
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