Integrate-and-fire model with periodic inputs

Introduces a resonance phenomenon from an integrate-and-fire model (IFM) with plural periodic inputs. When two inputs are applied, the IFM usually outputs aperiodic pulse-trains. However when adjusting the parameters of an input, the IFM outputs a periodic pulse-train with a constant pulse interval, while the state is quasi-periodic. This resonance phenomenon was confirmed in the laboratory, and analyzed using the mapping procedure.