Dolfinx uses lifting. This means that in the matrix every row and colum with a bc dof is set to the identity row, and then the corresponding Ag is subtracted from the RHs. See Why the coupling blocks in the stiffness matrix are zero? - #4 by dokken
How to set BCs for PETSc Matrices and PETSc Vectors in dolfinx - #2 by dokken
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dolfinx.fem — DOLFINx 0.6.0 documentation
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