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Anomalies in conductance and localization length of disordered ladders

We discuss the conditions under which an anomaly occurs in conductance and localization length of Anderson model on a lattice. Using the ladder hamiltonian and analytical calculation of average conductance we find the set of resonance conditions which complements the $π$-coupling rule for anomalies. We identify those anomalies that might vanish due to the symmetry of the lattice or the distribution of the disorder. In terms of the dispersion relation it is known from strictly one-dimensional model that the lowest order (i.e., the most strong) anomalies satisfy the equation $E(k)=E(3k)$. We show that the anomalies of the generalized model studied here are also the solutions of the same equation with modified dispersion relation.