# [Getdp] Convergence problem with inhomogeneous Helmholtz equation

**Lars Rindorf**
lhr at com.dtu.dk

*Thu Jan 3 18:40:26 CET 2008*

Dear all
I am having some problems with the convergence of the solution of an inhomogeneous Helmholtz equation. The problems occurs for frequencies of the driving term which are about more than five times the fundamental eigenfrequency of the system. For the solver parameters I use the default with the maximum number of iterations increased to 3000. I have tried to change the solver and
the dimension of the Krylov space. Changing the dimension of the Krylov seems to do something, although it does not solve the problem. The driving term of the inhomogeneous equations is applied in a point. I tried a line, and a subdomain and for those the problem was the same.
I've made the model in Comsol, and here there was no problem. I also tried to change my nodal field to a 1P form, but this made no difference.
Can anyone help?
I have attached the files. The model offers two resolutions: 'static' and 'eig'. Choose 'static'. Also choose 'static' for the postoperation.
Kind regards
Lars Rindorf
The Danish Institute of Technology
-------------- next part --------------
A non-text attachment was scrubbed...
Name: square.geo
Type: application/octet-stream
Size: 2633 bytes
Desc: square.geo
URL: <http://www.geuz.org/pipermail/getdp/attachments/20080103/92018349/attachment.geo>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: square.pro
Type: application/octet-stream
Size: 4435 bytes
Desc: square.pro
URL: <http://www.geuz.org/pipermail/getdp/attachments/20080103/92018349/attachment.pro>