===affil2:
MPI Magdeburg, Research Group Computational Methods in Systems and Control Theory, Magdeburg, Germany
===firstname:
Heiko K.
===firstname4:
Martin
===firstname3:
Jens
===lastname2:
Benner
===lastname:
Weichelt
===firstname5:

===affil6:

===lastname3:
Saak
===email:
heiko.weichelt@mathematik.tu-chemnitz.de
===lastname6:

===affil5:

===otherauths:

===lastname4:
Stoll
===affil4:
MPI Magdeburg, Research Group Computational Methods in Systems and Control Theory, Magdeburg, Germany
===lastname7:

===affil7:

===firstname7:

===postal:
Research group Mathematics in Industry and Technology
Chemnitz University of Technology
Department of Mathematics
Reichenhainer Str. 41
D-09126 Chemnitz 
Germany  
===firstname6:

===ABSTRACT:
To explore feedback control of flow problems we consider the Stokes equations that describe instationary, incompressible flows for low Reynolds numbers. After a standard finite element discretization we get a differential-algebraic system of
differential index two. We show how to reduce this index with a
projection method to get a generalized state space system, where a
linear quadratic control approach can be applied. This leads to large-scale saddle point systems which have to be solved. For obtaining a fast iterative solution of those systems we derive efficient preconditioners based on the approaches due to Wathen et al. [\textsc{Elman/Silvester/Wathen 2005, Stoll/Wathen 2011}]. The main results can be extended to non-symmetric Navier-Stokes equations.

(Student Paper)
===affil3:
MPI Magdeburg, Research Group Computational Methods in Systems and Control Theory, Magdeburg, Germany
===lastname5:

===affilother:

===title:
Efficient Solution of Large-Scale Saddle Point Systems Arising in Feedback Control of the Stokes Equations
(Student Paper)
===firstname2:
Peter