Hi everyone ! I used to use the evaluate_basis_all function in dolfin to evaluate basis functions at some points but I can not find it in dolfinx. Can someone tell me where to find it ? Cheers, Fabien

I have written a C++ function for evaluating basis functions at a point in a given cell in my dolfinx add-on dolfinx_mpc.

Ok, it looks like what I want. How do I use it with the python interface ?

The installation instructions are written in the repos readme and is: rm -rf build mkdir -p build cd build cmake -G Ninja -DCMAKE_BUILD_TYPE=Developer ../cpp/ ninja -j3 install cd ../python pip3 install . --upgrade For use-cases of the function, see: https://github.com/jorgensd/dolfinx_mpc/blob/8…

It works fine thanks ! It would be nice to have this functionality directly in doflinx.

You can do all the operations in my function in the dolfinx Python layer, it might just suffer a bit on the performance side.

Yes of course. I am just wondering why there is no function for direct basis functions evaluation in dolfinx, just like the evaluate_basis_all in dolfin. Are there any plans to add this feature in dolfinx ?

Hello dokken, do you have something similar for de derivative of de basis functions?? Or is there any change I can implement to you code to compute the derivatives. I’m not a C++ programmer but I would try.

The DOLFINx way to do this would be to: Figure out which cell the point x is in (using dolfinx.compute_colliding_cells, as done in: Implementation — FEniCSx tutorial ) Pull these coordinates back to the reference element, using mesh.geometry.cmap.pull_back ( dolfinx/fem.cpp at 48ece0087588f5f274a36a…

One more question: is there a transformation needed?? something like: \nabla_x\phi(x)=(\nabla_yT)^{-T}\nabla_y\hat{\phi}(y) with y\in\Omega_{ref}. or is it included in the function??

It is not included in the function, as you only evaluate on the reference element. As it is trivial to compute the Jacobian once you have the point on the reference element (for affine geometries you can compute it at any point of the reference element, but for quadrilaterals/hexahedra, you would n…

Evaluate_basis_all in dolfinx

dolfinx

reckx_sanchez May 3, 2022, 3:10pm 12

thank you very much!!

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Evaluate_basis_all in dolfinx

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