Element weighting

Hello everyone!

I'm working on a hyper-reduction method where each element in the mesh has a unique weight.

The weights must be applied to the local element stiffness matrices during the assembly to the bilinear form.
Is there a way of doing that given a vector of element weights?

Or else is there a way to get single element stiffness matrices in global coordinates?

Thank you
Nils

You can do this quite easily with a c++ extension. Basically you need to follow the first two steps of the c++ tutorial here: ngsolve.org/docu/latest/mylittlengs/1_Basic/README.html

You can for example parse the elementwise coefficients as a list or a numpy array and store them in a c++ array. Then in the evaluate function of your coefficient you query the element number by Then return the corresponding value from the array.

You can then use this CoefficientFunction in your stiffness bilinearform.

I hope this helps, if you run into problems write again. This part of the documentation is not often used yet.

Best
Christopher

Hello Christopher,

thank you for the help.
I got as far as making a CoefficientFunction that gives the element number.

But I need the CoefficientFunction to know the element weights. You said to store the weights in an array. At what point can I do that?

I tried to initialize with the array.
The idea was to initialize my custom CoefficientFunction like this: But that didn't work: It seems like the issue is to initialize the ngsolve CoefficientFunction with to many arguments.
You can find my .hpp file in the attachments.

How can I fix that issue or is there a better way of passing the element weights to my c++ CoefficientFunction?

Thanks in advance
Nils

Hi Nils,
the code in your hpp seems ok, I expect the problem is in the binding code. Can you send the cpp file as well?
Best

You can find the remaining code in the attachments.

The export of the constructor is wrong, the template arguments for the py::init must be the arguments for the constructor: best