# Online change-point detection by the stopping rule. Function to determine whether a process with continually arrving data should be terminated, based on the proposed stopping rule. ```r stopping.rule(ARL, H, mu, M, cor, old.data, new.data) ``` ## Arguments - `ARL`: The expected value of the stopping time when there is no change, eg. ARL = 5000. - `H`: The window size so that the stopping rule only considers H observations from the current time, eg. H=100. - `mu`: The mean vector of the observation with dimension 1 by p, can be estimated from a training sample through the function "nuisance.est". - `M`: M dependence, can be estimated from a training sample through the function "nuisance.est", eg. M=0 means data are temporally independent. - `cor`: A value used to obtain the standard deviation of the test statistic in the stopping rule, can be estimated from a training sample through the function "nuisance.est". - `old.data`: The observed sequence of data. The dataset has dimension H by p, where H is the window size, or the number of observed data (row), and p is the number of components (column). - `new.data`: A newly arrived observation with dimension 1 by p. ## Returns Returns a list with items "decision" and "old.updated". See below for more detail. - **decision**: returns 1 if the stopping rule detects a change point, and returns 0 otherwise. - **old.updated**: The updated observed dataset in this step, with dimension H by p. The Hth observation is the newly arrived observation, and the rest H-1 observations come from the previous dataset. ## References Li, L. and Li, J. (2020) "Online Change-Point Detection in High-Dimensional Covariance Structure with Application to Dynamic Networks." arXiv:1911.07762. ## Examples ```r # The following is an example to detect covariance structure change # in a real-time manner, in the sense that we pretend that # the observations in the dataset continually arrive in time. # At each time, we determine whether the process should be # terminated through the proposed stopping rule. # there is an immediate change point at n0=200 p<-200;n<-10000;n0<-200 #n0 is traing sample size rho<-0.6;M<-2 H<-100;ARL<-5000 Gam1<-diag(1,p,p) times<-1:p d<-abs(outer(times, times, "-")) sigma<-rho^d Gam2<-eigen(sigma,symmetric=TRUE)$vectors%*%diag(sqrt(eigen(sigma,symmetric=TRUE)$values),p) Gam<-cbind(Gam1,Gam2) data_Mat<-matrix(0,n0,p) L<-M+1 Z<-matrix(rnorm(p*(n+L-1)),p*(n+L-1),1) vec.coef<-1/rep(c(L:1),each=p) for(j in 1:n0){ Gam.m<-Gam[,1:p] Gam.mat<-t(apply(Gam.m,1,rep,L))*matrix(vec.coef,ncol=L*p,nrow=p,byrow=TRUE) data_Mat[j,]<-matrix((Gam.mat%*%Z[((j-1)*p+1):((j+L-1)*p),]),1,p,byrow=FALSE) } old.data<-data_Mat nuisance.results<-nuisance.est(old.data) mu<-nuisance.results$mu.hat M<-nuisance.results$M.hat cor<-nuisance.results$cor.hat j<-n0+1;decision = 0 while(decision==0){ Gam.m<-Gam[,(p+1):(2*p)] Gam.mat<-t(apply(Gam.m,1,rep,L))*matrix(vec.coef,ncol=L*p,nrow=p,byrow=TRUE) new.data<-matrix((Gam.mat%*%Z[((j-1)*p+1):((j+L-1)*p),]),1,p,byrow=FALSE) result<-stopping.rule(ARL,H,mu,M,cor,old.data,new.data) decision<-result$decision old.data<-result$old.updated cpt.est<-j-n0 j<-j+1 } print(cpt.est) #The point where the detection procedure terminates. ```

stopping.rule function