# R/MSEcom.R In COR: The COR for Optimal Subset Selection in Distributed Estimation

#### Documented in MSEcom

```#' Caculate the MSE values of the COR criterion in simulation
#'
#' @param K is the number of subsets
#' @param nk is the length of subsets
#' @param alpha is the significance level
#' @param X is the observation matrix
#' @param y is the response vector
#'
#' @return MSEx,MSEA,MSEc,MSEm,MSEa
#' @export

#' @examples
#'  p=6;n=1000;K=2;nk=500;alpha=0.05;sigma=1
#'  e=rnorm(n,0,sigma); beta=c(sort(c(runif(p,0,1))));
#'  data=c(rnorm(n*p,5,10));X=matrix(data, ncol=p);
#'  y=X%*%beta+e;
#'  MSEcom(K=K,nk=nk,alpha=alpha,X=X,y=y)

MSEcom=function(K=K,nk=nk,alpha=alpha,X=X,y=y){
n=nrow(X);p=ncol(X)
beta=solve(t(X)%*%X)%*%t(X)%*%y;
L=M=N=E=W=c(rep(1,K));I=diag(rep(1,nk));betam=matrix(rep(0,p*K), ncol=K)
R=matrix(rep(0,n*nk), ncol=n); Io=matrix(rep(0,nk*K), ncol=nk);
mr=matrix(rep(0,K*nk),ncol=nk)
for (i in 1:K){
mr[i,]=sample(1:n,nk,replace=T);
r=matrix(c(1:nk,mr[i,]),ncol=nk,byrow=T);
R[t(r)]=1
Io[i,]=r[2,]
X1=R%*%X;y1=R%*%y;
ux=solve(crossprod(X1))
sy=sqrt((t(y1)%*%(I-X1%*%solve(crossprod(X1))%*%t(X1))%*%y1)/(length(y1)-p))
L[i]= sy*sum(sqrt(diag(ux)))*(qt(1-alpha/2, length(y1)-p)-qt(alpha/2, length(y1)-p))
W[i]= sum(diag(t(ux)%*% ux))
M[i]=  det(X1%*%t(X1))
N[i]=t(y1)%*% y1
E[i]=t(y1)%*%(I-X1%*%solve(crossprod(X1)) %*%t(X1))%*% y1/(length(y1)-p)
betam[,i]=solve(t(X1)%*%X1)%*%t(X1)%*%y1
}
int=intersect(intersect(Io[which.min(W),],Io[which.min(M),]),Io[which.min(N),])
Xc=X[int,];yc= y[int]; I=diag(rep(1,length(int)))
#t(yc)%*%(I-Xc%*%solve(crossprod(Xc))%*%t(Xc))%*% yc/(n-p)
minL=L[which.min(L)]
minM=M[which.min(M)]
minN=N[which.min(N)]
minE=E[which.min(E)]
lW=length(Io[which.min(W),])
lWM=length(intersect(Io[which.min(W),],Io[which.max(M),]))
lWMN=length(intersect(intersect(Io[which.min(W),],Io[which.max(M),]),Io[which.min(N),]))
betac=solve(t(Xc)%*%Xc)%*%t(Xc)%*%yc;
Xx= X[Io[which.max(M),],];yx= y[Io[which.max(M),]]
betax=solve(t(Xx)%*%Xx)%*%t(Xx)%*%yx;
XA= X[Io[which.min(W),],];yA= y[Io[which.min(W),]]
betaA=solve(t(XA)%*%XA)%*%t(XA)%*%yA;
betamm=apply(betam,1, median);betaa=apply(betam,1, mean);
MSEx=sum(beta-betax)^2; MSEA=sum(beta-betaA)^2;
MSEc=sum(beta-betac)^2;MSEm=sum(beta-betamm)^2;
MSEa=sum(beta-betaa)^2;
return(list(MSEx=MSEx,MSEA=MSEA,MSEc=MSEc,MSEm=MSEm,MSEa=MSEa))
}
```

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COR documentation built on Dec. 7, 2021, 1:08 a.m.