powerlab=function(p0,palt,new=T,color=1){

nvec=seq(10,1000,10)

power=type2=rep(NA,length(nvec))

for ( i in 1:length(nvec)){

pcrit=p0+1.645*sqrt((p0*(1-p0)/nvec[i]))

z=(pcrit-palt)/sqrt((p0*(1-p0)/nvec[i]))

power[i]=1-pnorm(z)

type2[i]=1-power[i]

if(new) plot(nvec,power,ylim=c(0,1),type="l",col=1)

else lines(nvec,power,ylim=c(0,1),type="l",col=color)

lines(nvec,type2,lty=2,col=color)

lines(nvec,type2,lty=2,col=color)

abline(h=.8,col=color)

n80=nvec[abs(power-.8)==min(abs(power-.8))]

abline(v=n80,col=color)

}

print("this function is written for a greater than test")

n80

}