Memristor nonlinear model

We are all familiar with the classic, passive circuit components resistor, capacitor, and inductor. In a 1971 paper, however, Leon Chua argued that there was room for a fourth basic component, which he called memristor, short for memory resistor (Chua, 1971). The memristor is a special kind of resistor in which the resistance is dependent on the net amount of charge having passed through it. Hence, sending a current in one direction 

the memristor can be treated as a nonlinear resistor. The nonlinearity lies in the fact that the memristance is a function both of time and an internal state variable x, that is M(x,t). This state variable is often (but not always) proportional to the electric charge Q. 

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