[CIG-CS] Variable viscosity Stokes solver

[Wolfgang Bangerth]

> Now I am a bit confused.  You sent a me a modified version of step-32
> which uses Trilinos explicitly, but the falling block test does not.
> So, are they using the same type of solver?

Almost. step-32 uses Trilinos and AMG as preconditioner for the top left block 
of the Stokes matrix. The modified step-22 we were discussing for the 
variable-viscosity Stokes benchmark uses the same outer solver and the same 
kind of preconditioner but instead of preconditioning the solution of the top 
left block by AMG it just uses UMFPACK. Since it doesn't use AMG, there is no 
need for Trilinos and so I use deal.II's native linear algebra.

That said, the solver and preconditioner is the same, just the implementation 
is different.

Does that make sense?
Best
 W.

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Wolfgang Bangerth                email:            bangerth at math.tamu.edu
                                 www: http://www.math.tamu.edu/~bangerth/