Hello to everybody, I am working with a problem where I need to directly access the basis functions of a Finite Element. A minimal example would be: >>> from fenics import * >>> mesh = UnitSquareMesh(8,8) >>> V = FunctionSpace(mesh, 'P', 1) >>> V.dim() displays 81. Then I’d like to have a Python …

Is something like the following what you were thinking of? from dolfin import * from numpy import array # Simple mesh/space for testing: mesh = UnitIntervalMesh(3) tree = mesh.bounding_box_tree() V = FunctionSpace(mesh,"CG",1) # Evaluate the i-th basis function at point x: def basis_func(i,x): …

Hello kamensky, it looks great! I tested a little bit and seems to do precisely what I need. May I ask for some further reference, in order to better understand the code and adapt to other similar cases? Thanks a lot

The API for these lower-level manipulations is not as clearly-documented as the main use cases for FEniCS. I mostly found the functions used in the above answer in old forum posts that came up in Google search results. I also stockpile all of the code snippets from my own forum posts in one direct…

Dear Kamensky, thanks for the grep hint, I like it. Coming back to the original problem, there is still something puzzling me. Using precisely your script, where V.dim() is 4, if I evaluate in a for loop like yours: point = array([1 / 3 + 1 / 12]) for i in range(0, V.dim()): \tab print(list_of_…

Interesting! It turns out that I misunderstood what happens with i in the lambda expression. The anonymous function created will take whatever is the value of i in the global scope when it is called, not the one at which it was defined. One trick I found here is to do the following: for i in ran…

Great! Thanks so much: not only it works very well, but I took the opportunity for learning this lambda trick which is definitely good to know. At this point I am wondering if I could go a little bit further: is it maybe possible to obtain a symbolic expression of these functions? Therefore a feat…

Hi, This implementation is very interesting! Do you know if it’s possible to obtain the second derivative of the basis functions over a vector field? Many thanks!

Consider the following in DOLFINx: V = fem.functionspace(msh, ("Lagrange", 1)) basix_element = V.element.basix_element basis_matrix = basix_element.tabulate(0, x_refs)[0, :, :, 0] V.element.basix_element gives you a basix_element class, and then you can use it to evaluate the value of basis funct…

Thank you very much for the answer. In this way, I can access the basis function of the reference triangle (in basix, the element used to create the triangle). How can I access the basis function at any point of a cell (triangle) in any arbitrary geometry? As an example, for x = np.array([[0.0, 0…

Accessing the basis function of a Finite Element

rehm March 19, 2024, 3:53am 9

How can access basis functions, apply this method in new versions of Fenicsx and Dolfinx ?

H(curl) basis function

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Accessing the basis function of a Finite Element

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