Hi everyone!

I have the following question about setting the boundary conditions for dolfinx:

**Problem ：** For mandatory Dirichlet boundary conditions.

Ax=b for example：`x2`

is known (i.e. Dirichlet boundary condition)

In order to obtain a solution that satisfies the Dirichlet boundary.Often, this equation is treated like this：

So I want to know how dolfinx achieves this?

By `apply_lifting(b,[a],[bcs])`

?

Yes, DOLFINx does this by:

- Supplying bcs to
`assemble_matrix`

, this sets the columns and rows with bcs to the identity row/column - Use apply lifting to get the system above (note still with some rows for the dirichlet bc dofs
- Using set_bc to avoid having to do back substitution after solving the problem

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