Full paper in PDF:
$%J.-L. Lions and E. Zuazúa, The cost of controlling unstable systems: time irreversible systems, Rev. Mat. Univ. Complut. Madrid 10 (1997), no. 2, 481523.%$

The Cost of Controlling Unstable Systems: Time Irreversible Systems
Jacque-Louis LIONS and Enrique ZUAZÚA
Collège de France
3 rue d’Ulm
75231 Paris Cedex 05 -- France
Departamento de Matemática Aplicada
Universidad Complutense
28040 Madrid -- Spain

Received: December 9, 1996
 
Dedicated to Prof. Luiz Adauto Medeiros
in his 70th birthday.
ABSTRACT

We discuss the cost of controlling parabolic equations of the form              h
yt- Dy- k(-D) y =n1w  in a bounded smooth domain _O_  of  n
R  with homogeneous Dirichlet boundary conditions where 0 <h < 1  is fixed. The control n  acts on the system through the open and non-empty subset w  of _O_  . As k -->  oo  the system becomes more and more instable. We analyze the dependence of the control n  on the parameter k  in the context of various different control problems. We show that the norm of the control diverges when the trajectory is driven from an initial state  0    2
y   (- L (_O_)  to the null state at any time T > 0  . However, we prove that the control converges to zero when the null initial state y0 = 0  is driven into a ball of an arbitrary radius e> 0  around a given terminal state y1  (-  L2(_O_)  or when the solution fulfills exactly a finite number of constraints at time T  .

2000 Mathematics Subject Classification: 93B05, 35K05, 35B35.