"sim.thresh" <-
function(sim,assoc=NULL)
  {
    if(!(is.matrix.csr(sim) || is.matrix(sim)) || (nrow(sim) != ncol(sim)) || (nrow(sim)==0))
      stop("Invalid sim matrix")
    return(as(as(nrow(sim),"matrix.diag.csr"),"matrix.csr"))
  }