2.1. FCM We define X = x1,…, xN as the universe of a clustering data set, B = β1,…, βC as the prototypes of C clusters, and U = [uij]N×C as a fuzzy partition matrix, where uij ∈ [0,1] is the membership of xi in a cluster with prototype βj; xi, βj ∈ RP, where P is the data dimensionality, 1 ≤ i ≤ N, and 1 ≤ j ≤ C. The FCM algorithm is derived by minimizing the objective Foretinib molecular weight function [22] JFCMU,B,X=∑j=1C∑i=1Nuijmdij2xi,βj, (1) where m > 1.0 is the weighting exponent

on each fuzzy membership and dij is the Euclidian distance from data vectors xi to cluster center βj. And ∑j=1Cuij=1 ∀i=1,2,…,N,0<∑i=1Nuij

through the problem space by following the current best particles. Each particle keeps track of its coordinates in the problem space which are associated with the best solution that has been achieved so far. The solution is evaluated by the fitness value, which is also stored. This value is called pbest. Another best value that is tracked by the PSO is the best value, obtained so far by any particle in the swarm. The best value is a global best and is called gbest. The search for the better positions follows the rule as Vt+1=wVt+c1r1pbestt−Pt+c2r2gbestt−Pt,Pt+1=Pt+Vt+1, (5) where P and V are position and velocity vector of particle, respectively, w is inertia weight, c1 and c2 are positive constants,

called acceleration coefficients which control the influence of pbest and gbest in search process, and r1 and r2 are random values in the range [0,1]. The fitness value of Anacetrapib each particle’s position is determined by a fitness function, and PSO is usually executed with repeated application of (5) until a specified number of iterations have been exceeded or the velocity updates are close to zero over a number of iterations. 2.3. PSO-Based FCM In this algorithm [26], each particle Partl represents a cluster center vector, which is constructed as Partl=Pl1,…,Plj,…,PlC, (6) where l represents the lth particle, l = 1,2,…L, L is the number of particles, and L < N. Plj is the jth cluster center of particle Partl. Therefore, a swarm represents a number of candidates cluster center for the data vector. Each data vector belongs to a cluster according to its membership function and thus a fuzzy membership is assigned to each data vector.