Synthesis of space-time optimal systolic algorithms for the Choleskyfactorization

Abstract

In this paper we study the synthesis of space-time optimal systolic arrays for the Cholesky Factorization (CF). First, we discuss previous allocation methods and their application to CF. Second, stemming from a new allocation method we derive a space-time optimal array, with nearest neighbor connections, that requires 3N + Θ(1) time steps and N 2/8 + Θ(N) processors, where N is the size of the problem. The number of processors required by this new design improves the best previously known bound, N 2/6 + Θ(N), induced by previous allocation methods. This is the first contribution of the paper. The second contribution stemms from the fact that the paper also introduces a new allocation method that suggests to first perform clever index transformations on the initial dependence graph of a given system of uniform recurrent equations before applying the weakest allocation method, the projection method.