I don't seem to see the attachment... But I have to ask:
If the assembly function was taken from example 3 (2 does no assembly(?)),
are you constraining the hanging degrees of freedom? That is, is there a
line like
// We have now built the element matrix and RHS vector in terms
// of the element degrees of freedom. However, it is possible
// that some of the element DOFs are constrained to enforce
// solution continuity, i.e. they are not really "free". We need
// to constrain those DOFs in terms of non-constrained DOFs to
// ensure a continuous solution. The
// \p DofMap::constrain_element_matrix_and_vector() method does
// just that.
dof_map.constrain_element_matrix_and_vector (Ke, Fe, dof_indices);
(c.f. example 10)
-Ben
On 11/28/08 1:32 PM, "jurak" <[EMAIL PROTECTED]> wrote:
> Dear all,
>
> I was testing ExactSolution class by a simple program that solves
> Poisson equation
> on a unite rectangle, using P1 elements on triangles, and calculates
> convergence
> rate of the method by using uniform refinement of the initial mesh.
>
> To my surprise I obtained the following errors and rates:
>
> E R R O R C
> O N V E R G E N C E R A T E
> H1 L2 Linf
> H1 L2 Linf
> ===== ===== ======= ===== ===== ======
> 3.469577e-01 1.363935e-02 3.209919e-02
> 1.744062e-01 4.888679e-03 1.110995e-02 0.992308 1.480259 1.530684
> 8.753062e-02 2.352227e-03 5.084924e-03 0.994592 1.055418 1.127554
> 4.406352e-02 1.495102e-03 3.113305e-03 0.990203 0.653783 0.707779
>
> The convergence in L2 norm is too slow (should be of second order).
>
> My guess is that I am missing here something fairly obvious, but I can't
> find what.
> The assembly function is taken from example 2, and the refining loop is
> given here:
>
> for(int refinement=0; refinement < max_refinement; ++ refinement)
> {
>
> system.solve();
>
> ex_sol.compute_error("Poisson","p");
>
> l2_error = ex_sol.l2_error("Poisson","p");
> h1_error = ex_sol.h1_error("Poisson","p");
> linf_error = ex_sol.l_inf_error("Poisson","p");
>
> out_file << std::scientific
> << h1_error << " " << l2_error << " "<< linf_error<< " ";
> if(refinement >0)
> out_file << std::fixed
> << std::log2(h1_error_old/h1_error)<< " "
> << std::log2(l2_error_old/l2_error) << " "
> << std::log2(linf_error_old/linf_error);
> out_file <<std::endl;
>
> h1_error_old = h1_error;
> l2_error_old = l2_error;
> linf_error_old = linf_error;
>
> mesh_refinement.uniformly_refine();
> es.reinit();
> }
>
> I give the whole program in the attachment. Thanks for your help.
>
> Mladen Jurak
>
>
>
> <http://web.math.hr/%7Ejurak>
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