Plot Lognormal Probability Density in R

Question

I am trying to generate a plot for Lognormal Probability Density in R, with 3 different means log and standards deviation log. I have tried the following, but my graph is so ugly and does not look good at all.

 x<- seq(0,10,length = 100)
 a <- dlnorm(x, meanlog = 0, sdlog = 1, log = FALSE)
 b <- dlnorm(x, meanlog = 0, sdlog = 1.5, log = FALSE)
 g <- dlnorm(x, meanlog = 1.5, sdlog = 0.2, log = FALSE)
 plot(x,a, lty=5, col="blue", lwd=3)
 lines(x,b, lty=2, col = "red")
 lines(x,g, lty=4, col = "green")

I even was trying to add legend on the right top for each mean log and standard deviation log, but it would not work with me. I was wondering if someone could guide me out with that.

Right top of the graph

Answer 1

There is really nothing wrong in your code. You just forgot to:

• use type = "l" in plot;
• set a good ylim to hold all lines.

Here is a simple solution with matplot:

matplot(x, cbind(a,b,g), type = "l", ylab = "density", main = "log-normal",
        col = 1:3, lty = 1:3)

To add legend, use

legend("topright",
       legend = c("mu = 0, sd = 1", "mu = 0, sd = 1.5", "mu = 1.5, sd = 0.2"),
       col = 1:3,
       lty = 1:3)

You can also read ?plotmath for adding expressions. Try changing the legend argument above to:

legend = c(expression(ln(y) %~% N(0,1)),
           expression(ln(y) %~% N(0,1.5)),
           expression(ln(y) %~% N(1.5,0.2)))