s.  Then the ID of X - or IDX is a column vector of length
 n, where each element is an integer indicating the cluster membership of
 the corresponding element in X.  IDX(i)=c indicates that the ith point in
 X belongs to cluster c. Cluster labels range from 1 to k, and thus
 k=max(IDX) is typically the number of clusters IDX divides X into. The
 cluster label &quot;-1&quot; is reserved for outliers. IDX(i)==-1 indicates that
 the given point does not belong to any of the discovered clusters. Note
 that mat