assemble_system

Question

Hi all,

Can anyone give some information about how the assemble_system works? How the assemble_system generate the stiff matrix and load vector with the given bilinear, linear form and boundary condition? Thanks a lot.

Answer 1

The point is that matrix and vector are assembled together which

• saves resources
• enables application of BC in a symmetric way

For details read dolfin/fem/SystemAssembler.cpp and relevant header files.

Answer 2

For each element assemble_system assembles both
the local matrix A_e and local vector b_e. Then it
enforces the Dirichlet conditions in a symmetric fashion
(i.e. it performs a partial Gaussian elimination to
make the element matrix symmetric). Finally, it assembles
the element matrices and vectors into the global matrix A and
the global vector b.