censem=function(y,z,t)
{

#In addition to the observed data y, this program requires censoring times t
# and indicator vector z for the censored data.

	rn=length(y)
	sn <- length(z)
        ybar=mean(y)
        thetam=ybar
	diff <- 1
	iter <- 0

#ehat is the vector of conditional means for the censored data given
#the censoring mechanism. q is the conditional likelihood

exp=exp(-t/thetam)
oexp=exp/(1-exp)
ehat=thetam+t*z-t*(1-z)*oexp
q=-(rn+sn)*log(thetam)-rn*ybar/thetam-sum(ehat)/thetam
	while(abs(diff) > 1e-06 & iter < 1000) {
     thetam=(rn*ybar+sum(ehat))/(rn+sn)
exp=exp(-t/thetam)
oexp=exp/(1-exp)
ehat=thetam+t*z-t*(1-z)*oexp
qnew=-(rn+sn)*log(thetam)-rn*ybar/thetam-sum(ehat)/thetam
		diff <- abs(qnew - q)/max(abs(qnew), 1)
		q=qnew
		iter <- iter + 1
	}
	out <- list(thetam,iter)
        names(out)=c("Theta","No. Iterations")
	out
}