Combinatorial Search for Strong Shift Equivalence

Abstract: The most important open problem of symbolic dynamics consists in finding a procedure to decide whether two subshifts of finite type are conjugate or, equivalently, whether two nonnegative integer matrices are strong shift equivalent. While the problem remains hard in general, the literature also contains specific examples of matrices that are not known to be strong shift equivalent: the Baker matrices, and Ashley's eight-by-eight. These specific examples have been open for 30 years. Using computer experiments, we show that the Baker matrices are indeed strong shift equivalent for small values of k, and that Ashley's eight-by-eight matrix is indeed strong shift equivalent to the one-by-one matrix 2