Yves, Thank you for your response. The integral in my previous message is correct. But forget it. Let the 1D equation involves term \int(K(x,x')u(x'))dx' where K is known kernel and u is unknown function we are solving for. So to solve it with FEM, one needs to assemble matrix \int\int(K(x,x')\phi_i(x')phi_j(x))dx'dx. Do you mean that I can expand K(x,x') in \sum (a_k b_l \phi_k(x') \phi_l(x)), compute two separable integral and multiply their values?
Another problem is that my kernel has singularity, so it isn't interpolated well by polynomial base functions. The best way I see is to compute the whole matrix not in getFEM but in matlab or mathematica. To do it I need some data from FEM. Exactly, I need base functions and coordinates of area it's defined on. Can getFEM provide this data? Thanks, Ivan 2013/1/18 Yves Renard <[email protected]> > > Dear Ivan, > > Unfortunately, the assembly procedure of Getfem is not designed to compute > such integro-differential term. > May be if you have specific expression for the kernel (if it is simple or > can be expressed on a FEM) it should be possible to adapt something. > > Yves. > > > Le 18/01/2013 12:24, Ivan Melikhov a écrit : > > Hello! > > I need to solve an integro-differential eigenvalue problem and I have > trouble with integral term. Generally, I need to assemble a 4D matrix with > elements > \int\int(\phi_i(r')\phi_j(r')V(r,r')\phi_m(r)\phi_l(r))dr'dr > > I suppose it is > \int\int(\phi_i(r)\phi_j(r')V(r,r')\phi_m(r)\phi_l(r))dr'dr (\phi_i(r) > instead of \phi_i(r')) ? > > > where V(r,r') is known function, \phi_i is the ith base function, dr is > dxdy, dr' is dx'dy'. The question is how can I compute an inner integral > inside comp command in generic_assembly::set? > > Thank you for answers, > Ivan > > > _______________________________________________ > Getfem-users mailing > [email protected]https://mail.gna.org/listinfo/getfem-users > > > > -- > > Yves Renard ([email protected]) tel : (33) 04.72.43.87.08 > Pole de Mathematiques, INSA-Lyon fax : (33) 04.72.43.85.29 > 20, rue Albert Einstein > 69621 Villeurbanne Cedex, FRANCE > http://math.univ-lyon1.fr/~renard > > --------- > >
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