Heinz H. Bauschke, J. Y. Bello Cruz, Tran T. A. Nghia, Hung M. Phan, Xianfu Wang. The rate of linear convergence of the Douglas-Rachford algorithm for subspaces is the cosine of the Friedrichs angle. Journal of Approximation Theory, 185:63-79, 2014. [doi]
Abstract is missing.