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Multirate Rearrangeable Clos Networks and a Generalized Edge Coloring Problem on Bipartite Graphs
... that the minimum number m(n, r) of middle-state switches for the symmetric 3-stage Clos network C(n, m(n, r), r) to be rearrangeable in the multirate enviroment is at most 2n β 1. This problem is equivalent to a generalized version of the bipartite graph edge coloring problem. The best bounds known so far on the function m(n, r) is 11n/9 β€ m(n, r) β€ 41n/16 + O(1), for n, r β₯ 2, derived by Du-Gao-Hwang-Kim (SIAM J. Comput., 28, 1999). In this paper, we make several contributions. Firstly, we give evidence to show that even a stronger result might hold. In particular, we give a coloring algorithm to show that m(n, r) β€ β(r + 1)n/2β, which implies m(n, 2) β€ β3n/2β- stronger than the conjectured value of 2n β 1. Secondly, we derive that m(2, r) = 3 by an elegant argument. Lastly, we improve both the best upper and lower bounds given above: β5n/4 β β€ m(n, r) β€ 2n β 1 + β(r β 1)/2β, where the upper bound is an improvement over 41n/16 when r is relatively small compared to n. We also conjecture that m(n, r) β€ β2n(1 β 1/2 r)β