I want to define the trial and test functions for a mixed problem: Blockquote from ufl import TrialFunction, TestFunction, dot, div, inner ,dx from dolfinx import mesh, fem from mpi4py import MPI import numpy as np from ufl import (VectorElement, FiniteElement, MixedElement ) Lx,Ly = 1,1.1 …

[image] Lio97: sigma, u = TrialFunction(MixedSpace) tau, v = TestFunction(MixedSpace) use TrialFunctions and TestFunctions

One more question please: How can I turn PETScMatrix to a numpy array?

I used the mentioned code and I get : ‘petsc4py.PETSc.Mat’ object has no attribute ‘shape’. Did you mean: ‘scale’?

I have found the solution. For others to benafit (With fenicsx, I don’t know if it works with fenics) if you have a petsc matrix B and you want to convert it to numpy, just use convertToDense(B))

Note that this only works for small problems, see Conversion from array to PETSc and from PETSc to array - #4 by dokken

Thank you. But I encountered now a new problem: when I change the domain to quads I get the following: Error: raise self._exception_type(self._format_raw(*message)) ufl.log.UFLException: Cellname “quadrilateral” invalid for “Raviart-Thomas” finite element. This is the code: Blockquote from …

RT is not defined on quadrilaterals DefElement: Raviart–Thomas You Need to use RTCF DefElement: Q H(div)

There is something that I don’t get or I’m missing. I have previously defined it on a different problem with traig/quads elements and I get the correct results: The code runs for both domains: Blockquote from dolfinx.mesh import create_unit_square, create_box, CellType from dolfinx import mesh…

How to define trial and test functions for mixed problems

General

violetus July 8, 2023, 12:40am 5

Please consider reading @dokken solution on this post Conversion from array to PETSc and from PETSc to array.

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How to define trial and test functions for mixed problems

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