Efficient preconditioners for saddle point systems with trace   constraints coupling 2D and 1D domains
  We study preconditioners for a model problem describing the coupling of two elliptic subproblems posed over domains with different topological dimension by a parameter dependent constraint. A pair of parameter robust and efficient preconditioners is proposed and analyzed. Robustness and efficiency of the preconditioners is demonstrated by numerical experiments. 
Miroslav Kuchta and Magne Nordaas and Joris C. G. Verschaeve and   Mikael Mortensen and Kent-Andre Mardal
math.NA