Thank you. However, everytime, I try to change the finite element method I
get this error
Incompatibility between fem FEM_ARGYRIS and mesh element
GT_LINEAR_PRODUCT(GT_PK(1,1),GT_PK(1,1))
or an error about interpolating on a non lagrangian fem.
also, I forgot to include this part of the code
Fvec = gf_mesh_fem_get(mf,'eval', {f});
F = gf_asm('volumic source', mim, mf, mfd, Fvec);
Dc = zeros(1,dof);
[H, R] = gf_asm('dirichlet', 1, mim, mf, mf, ones(1,dof), Dc);
[Q, Ud] = gf_spmat_get(H, 'dirichlet_nullspace', R);
Oladayo Eluyefa,
Rochester Institute of Technology '15,
B.S., Computational Mathematics,
M.S., Applied and Computational Mathematics.
([email protected], [email protected])
(585)-287-1955
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On Tue, Mar 17, 2015 at 2:18 PM, Yves Renard <[email protected]>
wrote:
> Dear Oladayo Eluyefa,
>
> Your stiffness matrix is ill-conditionned because you use C0 finite
> elements instead of hermite elements. For this problem you do have to use
> hermite element such as argyris one (FEM_ARGYRIS) but for triangles or FVS
> element (FEM_QUADC1_COMPOSITE) on quadrilaterals (but with a specific
> integration method). Additionally, of course, the stiffness matrix will be
> singular unless a Dirichlet condition is prescribed.
>
> Note also that the Kirchhoff-love term is better conditionned that the
> bi-laplacian term and equivalent but with different boundary conditions.
>
> Yves.
>
> ----- Original Message -----
> From: "OLADAYO ELUYEFA (RIT Student)" <[email protected]>
> To: [email protected]
> Sent: Tuesday, March 17, 2015 6:17:22 PM
> Subject: [Getfem-users] Badly Scaled Bilaplacian
>
> I am working on a 4th order 2D Inverse Problem using the matlab OO
> interface in getfem++ . As a result, I calculate the bilaplacian, but I
> keep getting a badly scaled matrix with a close to 0 condition number.
> Below is the code that produces this. Is there a way to correct this.
>
> Thank you
>
> Code:
>
> %% Note equation is -(au'')''=f
> N = 20;
> h = 1/(N+1);
>
>
> m = gf_mesh('cartesian', 0:h:1, 0:h:1);
> mf = gf_mesh_fem(m,1);
> mfd = gf_mesh_fem(m,1);
> [xs, ys] = meshgrid(0:1*h:1, 0:1*h:1);
>
>
> gf_mesh_fem_set(mf, 'fem', gf_fem('FEM_QK(2,4)'));
> gf_mesh_fem_set(mfd, 'fem', gf_fem('FEM_QK(2,4)'));
>
> mim = gf_mesh_im(m, gf_integ('IM_GAUSS_PARALLELEPIPED(2,10)'));
>
> % Boundary conditions:
>
> border = gf_mesh_get(m, 'outer_faces');
> gf_mesh_set(m, 'boundary', 1, border);
>
> % Degrees of freedom
>
> dof = gf_mesh_fem_get(mf, 'nbdof');
> dofa = gf_mesh_fem_get(mfd, 'nbdof');
>
> u = '256.*(x.^2).*(y.^2).*((1-x).^2).*(1-y).^2';
> Us = gf_mesh_fem_get(mfd, 'eval', {u});
>
> a = '1+0.25.*sin(pi.*x).*sin(pi.*y)';
> avec = gf_mesh_fem_get(mfd, 'eval', {a});
> a0 = gf_mesh_fem_get(mfd, 'eval', {1.5})';
>
> K = @(a) gf_asm('bilaplacian', mim, mf, mfd, a);
> K1 = gf_asm('laplacian', mim, mfd, mfd, ones(dofa,1));
>
> L = @(u) gf_asm('volumic',...
> ['u=data(#2);', ...
> 't=comp(Hess(#2).Hess(#2).Base(#1))(:,i,i,:,i,i,:);',...
> 'M(#2,#1)+=t(j,:,:).u(j)'],...
> mim, ...
> mfd, ...
> mf, ...
> u);
>
> M = gf_asm('mass matrix', mim, mf);
> Ma = gf_asm('mass matrix', mim, mfd);
>
>
>
> Oladayo Eluyefa,
>
> Rochester Institute of Technology '15,
> B.S., Computational Mathematics,
> M.S., Applied and Computational Mathematics.
>
> ( [email protected] , [email protected] )
> (585)-287-1955
>
>
>
> CONFIDENTIALITY NOTE : The information transmitted, including attachments,
> is intended only for the person(s) or entity to which it is addressed and
> may contain confidential and/or privileged material. Any review,
> re-transmission, dissemination or other use of, or taking of any action in
> reliance upon this information by persons or entities other than the
> intended recipient is prohibited. If you received this in error, please
> contact the sender and destroy any copies of this information.
>
>
>
>
> Please consider the environment before printing this email.
>
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