Abstract
Abstract. We generalize the construction of Gabber and Galil to essentially every unimodular matrix in SL 2 (Z). It is shown that every parabolic or hyperbolic fractional linear transformation explicitly defines an expander of bounded degree and constant expansion. Thus all but a vanishingly small fraction of unimodular matrices define expanders.
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Cai, JY. Essentially Every Unimodular Matrix Defines an Expander . Theory Comput. Systems 36, 105–135 (2003). https://doi.org/10.1007/s00224-002-1017-y
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DOI: https://doi.org/10.1007/s00224-002-1017-y