On the finitary content of Dykstra's cyclic projections algorithm

Abstract: We study the asymptotic behaviour of the well-known Dykstra's algorithm through the lens of proof-theoretical techniques. We provide an elementary proof for the convergence of Dykstra's algorithm in which the standard argument is stripped to its central features and where the original compactness principles are circumvented, additionally providing highly uniform primitive recursive rates of metastability in a full general setting. Moreover, under an additional assumption, we are even able to obtain effective general rates of convergence. We argue that such additional condition is actually necessary for the existence of general uniform rates of convergence.