dolfin team mailing list archive

["Garth N. Wells" <g.n.wells@xxxxxxxxxx>]

Anders Logg wrote:
> Garth, do we really need assembleResidualBC() in FEM?
> 
> I looks to me that
> 
>   assembleResidualBC(A, b, x, ...);
> 
> does the same thing as
> 
>   applyBC(A, b, ...);
>   b -= x;
> 
> ?
>

Not quite. The difference is at nodes where Dirichlet boundary
conditions are applied. In this case, the "residual" is the difference
between the computed solution x (not b) and the boundary condition value
x_bc.

For linear problems it is easy because prior to the solve step b = x =
0.0. The complications arise when using Newton steps or solving
time-dependent problems with non-zero Dirichlet bc's.

Garth


> /Anders
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