Improved Routing and Sorting on Multibutterflies

Abstract. This paper shows that an N -node AKS network (as described by Paterson) can be embedded in a ( 3N / 2 ) -node twinbutterfly network (i.e., a multibutterfly constructed by superimposing two butterfly networks) with load 1, congestion 1, and dilation 2. The result has several implications, including the first deterministic algorithms for sorting and finding the median of n log n items on an n -input multibutterfly in O ( log n ) time, a work-efficient deterministic algorithm for finding the median of n log2 n log log n items on an n -input multibutterfly in O (log n log log n ) time, and a three-dimensional VLSI layout for the n -input AKS network with volume O(n3/2) . While these algorithms are not practical, they provide further evidence of the robustness of multibutterfly networks. We also present a separate, and more practical, deterministic algorithm for routing h -relations on an n -input multibutterfly in O(h + log n) time. Previously, only algorithms for solving h one-to-one routing problems were known. Finally, we show that a twinbutterfly, whose individual splitters do not exhibit expansion, can emulate a bounded-degree multibutterfly with (α,β) -expansion, for any α⋅β < 1/4 .