On the optimal convergence rate of a Robin-Robin domain decomposition   method
  In this work, we solve a long-standing open problem: Is it true that the convergence rate of the Lions' Robin-Robin nonoverlapping domain decomposition(DD) method can be constant, independent of the mesh size $h$? We closed this twenty-year old problem with a positive answer. Our theory is also verified by numerical tests. 
Wenbin Chen, Xuejun Xu and Shangyou Zhang
math.NA