pcreg<-function(x,y,s=0) {
  x<-as.matrix(x)
  p<-dim(x)[2]
  e<-eigen(t(x)%*%x,symmetric=TRUE)
  beta.ls<-lsfit(x,y,intercept=FALSE)$coef
  B<-diag(c(rep(1,p-s),rep(0,s)))
  beta.pc<-e$vectors%*%B%*%t(e$vectors)%*%as.matrix(beta.ls)
  beta.pc
}