d  <- read.table("inp_iris.txt",skip=1)
x  <-as.matrix(d[,-5])
n<-nrow(x)
m<-ncol(x)
xx  <- x %*% t(x)
ii  <- matrix(1,nrow=n,ncol=n)
dis <- (diag(n)*xx)%*%ii-2*xx+ii%*%(diag(n)*xx) #Distance matrix
mat <- diag(n)-1/n*ii
ary <- -0.5*mat %*% dis %*% mat #Young-Householder's transformation
yy  <- eigen(ary)
emat<- matrix(0,nrow=n,ncol=n)
for(i in 1:n){
    if(0<=yy$values[i])emat[i,i]<-sqrt(yy$values[i])
    if(yy$values[i]<0)emat[i,i]<-0
}
plt <- yy$vectors %*% emat
panel.text<-function(x, y, labels, cex, font, ...){
  usr <- par("usr"); on.exit(par(usr))
  par(usr = c(0,1,0,1) )
  txt <- c("MDS")
  cex<-2
  font<-"Helvetica"
  text(0.5, 0.5, txt, cex = cex)
} 
pairs(
  plt[,1:4],
  diag.panel=NULL,
  text.panel=panel.text,
  pch=21,
  bg=c("red","green","blue")[unclass(d[,5])]
  )
eigen(ary)$values[1:4]