parabolasingle = function(r,k,noise,n0,nostep,maxr) {
# plots a state space rendering of the May's equation

#r - intrinsic growth rate
#k - carrying capacity
#n0 - initial population size
#nostep - number of steps for simulation

#maxr is used to plot everything in the same scale if called several times

   if (maxr < r)
      maxr=r;
   x=seq(0,100,by=k/100)
   titl = paste("R value:",r)
   matplot(x,cbind(x,r*x*(k-x)/k),type="l",lty=1,lwd=2,col=c("green","blue"),
           xlim = c(0,k), ylim=c(0,maxr*k/2),main=titl,
           xlab="Population size at the step t", ylab = "Population size at the step t+1")
   n=maysingle(r,k,noise,n0,nostep);
   for (t in 1:(nostep-1)) {
      lines(c(n[t], n[t]),c(n[t],n[t+1]),col="red")
      lines(c(n[t], n[t+1]),c(n[t+1],n[t+1]),col="red")
   }
}