To this purpose, an evolutionary algorithm (EA) called particle swarm optimization (PSO) is used for optimizing the mathematical model shown in Equation 1. The PSO technique is widely used in optimizing different sorts of problems including fine materials, medical science, control theory, energy issues, etc. [33–36]. The important facts that make PSO popular among the researchers are its fastness, avoiding from being trapped in the local optima, and the capability of being employed in any type of optimization problems [37–40]. Methods Particle swarm optimization
overview The PSO is a swarm-based optimization algorithm which is classified as a metaheuristic optimization algorithm. The idea of the PSO rises from the movement of a bird flock which was first introduced learn more by Kennedy and Eberheart [41–45]. The aim of employing PSO algorithm in this study, is to find the best possible values for A, B and C parameters in Equation 2 which leads to have a more accurate DNA sensor model with better I-V characteristic. Each particle at each step is supposed to return a set of three values with respect to A, B and C parameters. Afterwards, these values must be evaluated using a proper fitness function. During the optimization process, the values of A, B and C parameters change, until we can get the best possible solutions. The movement velocity of each
particle is updated regularly, at each step. The location selleck chemicals and velocity of the ith particle at kth step are shown in Equations 4 and 5, respectively. (4)
(5) i = 1, 2, …, nop (number of particles); k = 1, 2, …, k max (maximum Selleckchem TH-302 iteration number) where i is the particle number; k is the iteration number; W refers to the inertia weight coefficient Docetaxel cell line which is decreased continuously from 1.2 to 0.5, r 1 and r 2 are random values between 0 and 1, c 1 and c 2 are acceleration coefficients and set to be equal to 2, denotes the position and is the velocity of particle i at iteration k. There are some social parameters that lead the swarm to the global optimum of the search space which are personal best (Pbest) and global best (Gbest). There is one Pbest for each particle which is the best location experienced by it, while Gbest is the best global optimum point found by the swarm. A simple diagram of the movement of a particle is shown in Figure 2. The number of particles in the swarm is considered as 200 which iterate for 300 runs. Figure 2 PSO algorithm. A simple diagram for movement of a sample particle in PSO. A fitness function must be defined for evaluating the particles at each step. Therefore, there is a fitness value for each particle at each step. In this study, the chosen fitness function is shown in Equation 6 which calculates an error value between the real and modelled data. (6) where I(k) is the experimental waveform of the DNA sensor, represents the value of the modelled waveform for particle i and ψ i is the fitness value for the ith particle.