Rajesh,
 
To change the margins, use par(mar)::
 
  M <- matrix(nrow=4,ncol=4,data=0)
  M[2,1]<-1  ;M[4,2]<-2;M[3,4]<-3;M[1,3]<-4

 par (mar=c(0,0,0,0))
   pp<-plotmat(M,pos=c(1,2,1),curve=0.)
 
Karline

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