Best Practice for Working with Model M-Files

Peter Cendula

Thanks for useful blog! I tried to ‘compact history’ in my rather larger MPH file and I got the error ‘Unknown model parameter’. Is there any way to workaround this?

Thanks
Peter

Lars Gregersen

COMSOL analyzes the structure while performing Compact History, but sometimes has to give up. Please send the MPH-file tosupport@comsol.comso we can have a look.

Mathias Perrin

Thank you for this blog,

I use every day Matlab Livelink with comsol, and I think it is very efficient.

It is a fantastic tool when you combine Matlab advantages (graphics, data posttreatment, highlevel mathematical functions such as FFT, matrix operations) with Comsol advantages (multiphysics approach, numerical computation of complex physical problems).

That’s why I am trying to compile matlab programs using Matlab compiler. The idea is to be able to distribute exécutables that would use a Comsol licence and Matlab runtime libraries.

I am trying to compile a simple script that opens some .mph model, using mphload().

Untill now, I always have some bug at runtime. It is probably a matter of setting correctly the path to the .dll and java files that are needed at runtime.

I discussed with Comsol but they don’t support matlab compiler, and of course matlab do not support compilation of comsol exécutables.

So, if someone ever tried, and has a procedure, or at least some experience, I would be very very glad to know it !

Cheers,

Mathias

Lars Gregersen

Hi

Although not officially supported applications compiled with the Matlab Compiler should work together with Comsol Multiphysics.

When creating your application then include a call to mphstart at the beginning of your application. Make sure to use one of the variants of mphstart that includes a COMSOLPATH. Make sure you use the correct COMSOLPATH at runtime. Comsol has to be installed on the computer in order for the application to run.

If this doesn’t work then please contact support and we’ll see if we can help you. Please include the version of Matlab and your operating system that you are using in the message to us.

Oscar Diaz

Hej Lars,
Nice blog entrances on Matlab livelink. Some of those useful tricks I learned on the way, by creating a model, compacting the history and saving the m-file to check some syntaxis errors and similar.
The program that I did, creates new geometries during the execution process calling different comsol-functions from matlab. Always when the meshing crashed and red text came to the matlab command window, indicating an error and that the execution was cancelled.
Now, after 3h execution, the execution got stocked somewhere, but I cannot find where. While in normal execution, it has been calling the same functions since the early beginning until it just dies…
It might have to do something with memory I guess (not so sure), because the only closing/stopping possible when goes to this problem, is closing the OS command window where the comsol server was started. Then, I go back to Matlab editor, and find out an active breakpoint (green arrow on a code line that stops the execution when the program reaches that code line), even if the comsol server is already closed (not possible to continue in execution). Can it be that the size of the object that is stored in the memory of the Comsol API overflows the memory available (the output files from previous steps is ca. 100MB)
I’ve been stocked here for a long time, do you have any suggestions?

Lars Gregersen

Hi Oscar

Without seeing your script it is hard to guess what goes wrong. It is quite easy to run out of memory when you are creating a large model using a script since you can easily create thousands of geometric objects, physics and settings, which all take up memory, of course.

The most common memory related mistake when creating models and geometries using a script is that when you create a model using
model = ModelUtil.create(‘Model1’)
each subsequent statement you execute will add some information to the model history. This is done such that you later can export an M-file (or VBA- or Java-file) with all you steps. However, exporting such files are rarely useful (since you already have a script that can do what you want) and you can always use “Compact model history” to get what you want.
The solution is to switch history generation off. We always cover this topic at the tutorials we give at the Comsol Conferences. It is also mentioned in the Introduction to LiveLink for Matlab manual where it says you need to write:
model.hist.disable;

If this doesn’t help your case then please send your script/model to Comsol Support where we will have a look at it.

R Karimi

Thanks for your useful blog. I have used COMSOL live link with MATLAB for optimization. My optimization code is written in MATLAB and as the objective function I build a comsol model, run that and use its results. The problem is that when I call the objective function from the optimization code, after 8 to 9 times of calling, the model exits with the error that the solution is not found. However, when I call the objective function separately, with the same inputs from MATLAB, it runs completely. I think the problem is that the previous model is not closed from the last call. How can I close a model in MATLAB Live link?
I would really appreciate if you could help me with it.

Lars Gregersen

Hi Karimi

The most common problem we see when a model doesn’t give a solution when performing optimization is that the parameter values that are determined by your optimization code go outside of the area where the model is well defined. Also you must make sure that the initial values for your model are consistent with your new parameter values.

You can use ModelUtil.remove to remove a model from the Comsol Multiphysics Server, but you should rarely use that.
Simply reload the model using mphload whenever you start a simulation. This way you are certain that your simulation starts with a known state.
If you continue to have problems with your model you can send it to support where we will have a look at it.

Cooper Li

Thanks for the wonderful explanation, is it possible that I could use the COMSOL alone to achieve some MATLAB functions, such as for loop and findpeaks(both of them are MATLAB built-in functions)?

Sincerely,
Li

Chin Neng Leong

Thanks for sharing this.

I’m trying to export deformed geometry using Deformed Configuration. However, I always get the deformed geometry at the last time step. I managed to modify the time in the Deformed Configuration , but I guess I need to update then only can export the interested time point. Does anyone know what’s the Matlab code to update the Deformed Configuration?

Also, I find that .m file only documents the steps until Study. Is there anyway to save all the steps made to the result sections in .m file?

Thanks
Chin Neng