Dear All,
May I seek your suggestion on a simple issue. I want to draw vertical lines
at some positions in the following R plot. To be more specific, I wish to
draw vertical lines at d=c(5.0,5.5,6) and they should go till
p=c(0.12,0.60,0.20) .  I haven't  found any way out, though made several
attempts. Please run the following commands first if you are interested in!

#######################################################

psi1<-function(alpha1,beta1,alpha2,beta2,d){
exp(alpha1+beta1*d)/((1+exp(alpha1+beta1*d))*(1+exp(alpha2+beta2*d)))
                                           }
alpha1<--3.5
beta1<-1
alpha2<--6
beta2<-0.72

d<-seq(0.5,10,0.01)
plot(d,psi1(alpha1,beta1,alpha2,beta2,d),type="l",pch=18, ylim=c(0,1),
xlab="Dose", ylab="Probabilitty")

##########################################################


Many thanks for the help!

Regards,
Jamil.

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