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August 28, 2009 1:01pm UTC

Numbering of the boundaries in *.m file

Hello all,

I am working on a parametric geometry model and I want to create my geometry/solution fully in script. I have to say that it is a rather complex geometry and till now I took the short and easy way by first creating my geometry in MatLab script with Comsol functions, exporting it to Comsol, doing the necessary subdomain and boundary settings there, exporting the model back to a "*.m" file (letting Comsol deal with the numbering for me) and proceeding with the solution.

Now, the geometry became more complex and the number of boundaries are not constant anymore and I need to understand how Comsol numbers the boundaries so that I can assign the correct boundary conditions without switching between Comsol and MatLab. When I look at bnd.ind=[] and equ.ind=[] there seems to be a logic behind the numbering but I couldn't be able to find any documentation explaining that systematic.

Thanks in advance,
Onur

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September 4, 2009 8:28am UTC in response to Onur Ilkorur

Re: Numbering of the boundaries in *.m file

Hello,

Comsol increment with a sort of triple loop (for x=1:end; for y=1:end; for z=1:end) to find the boundary number.

I have a matlab code which finds a face (or boundary) number (If you know the boundary position (x,y,z)).
the second matlab code finds vertex number.

I hope codes will help you,

Y.

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November 3, 2009 5:42pm UTC in response to Onur Ilkorur

Re: Numbering of the boundaries in *.m file

Hi,

This is an excellent function! Just should have provided an example of its use.

I would emphasis that the x,y,z co-ordinates are "rubberband" co-ordinates i.e.

face(fem.geom,[3.6e-6 3.8e-6],[4e-6 4.5e-6],[0 40e-6],1e-3,2)

Orginally I entered tol=1 which resulted in all the boundaries in the model being returned, this is because this is the tolerance and 1 = 1m which is larger than my model space.

I am still to work-out what the density is? I have it set to 2 and it is working well!

Good Work!!


Regards,
Tom

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April 13, 2010 3:59am UTC in response to Yannick fargier

Re: Numbering of the boundaries in *.m file

Hi Yannick,

This is amazing, but I cannot seem to get it to work in 2D :( can you advise me on how to get it done into2D? and it will give me the index of boundaries if I'm not wrong.

Thanks!

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November 25, 2010 11:25am UTC in response to MOhmesICx

Re: Numbering of the boundaries in *.m file

Sorry for bringing up this old Thread, but I still find this an important question. Imho the whole usability of the MATLAB LiveLink depends on this feature, e.g. if you have simulations with geometrie-sweeps.

Edit: Just found this Thread: http://www.comsol.de/community/forums/general/thread/8837/ where the problem seems to be discussed in more detail.

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November 26, 2010 2:13pm UTC in response to Ivar Kjelberg

Re: Numbering of the boundaries in *.m file

Hi Ivar,

thanks for your reply! I think that's the point: Why does the user have to care about some numbering methods when using the Matlab LiveLink? Why is there no method to reference e.g. all boundarys that belong to a certain 3D-block by the feature-tag of the block? Every COMSOL 4 example that I could find had a hard-coded list like this:

model.geom('geom1').feature.create('blk1', 'Block'); ...
model.selection('sel1').set([1 2 3 4 7 8]); ...

But what I need is something like this:

model.geom('geom1').feature.create('blk1', 'Block'); ...
model.selection('sel1').set(getAllBoundarysFromFeature('blk1')); ...

I often have to make hundreds of simulations with complex geometry variations via script, and there is no way to know the boundary-numbers in advance and code them hard into the script. For 3.5a it was possible to create a reliable workaround to receive the numbers/ids of faces, subdomains etc. corresponding to a certain geometry. It was very extensive to do this and you had to use some creepy, badly documented functions, but it worked. ;) In COMSOL 4.0a there seems to be no way to do this...

I think I'll wait until I get my hands on the 4.1 Version next week and If I don't get it working in 4.1, I contact the support. I don't understand, why there are so few people with the same problem. Is everyone else using the GUI only? ;-)

kind regards
David

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November 26, 2010 2:33pm UTC in response to David Schäfer

Re: Numbering of the boundaries in *.m file

Hi

I agree with you, and I can only suggest that you ask support too, it might already be on their to do list, but will not be there if nobody asks for it ;)

--
Good luck
Ivar

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