I. Introduction
Memristors are nanoscale electronic devices which establish a relationship between flux and charge and are considered as the fourth passive circuit element [2]. Since flux is the time integral of voltage and charge is the time integral of current, memristor provides a time integral relationship between voltage and current, like resistors (resistors relation independent from time and rate of change of voltage and current). For these devices, ratio between voltage and current called memristance which is shown with the letter M. Memristance is instantaneous resistance of device which is a function of charge(q). This relation can be expressed as in (1) and (2) [2]: \begin{equation*} V(t)=M\left(q(t)\right)i(t)\tag{1}\end{equation*}