How to make concentric circles in the plot of r

Use the command draw.circle of package plotrix :

x <- seq(-3, 3, by=0.01)
y <- x^2
plot(y ~ x, asp=1, type="l")

library(plotrix)
draw.circle(1, 1, 1, border="red")
draw.circle(1, 1, 2, border="green")
draw.circle(1, 1, 3, border="blue")

The syntax of the draw.circle command is very simple:

• The first argument is the coordinate of the center of the circle on the x-axis

• The second argument is the center coordinate of the circle on the y-axis

• The third argument is the radius value of the circle

I changed their border with the border argument just to emphasize the difference between drawn circles. By default, their border is black.

Building on Marcus Nunes' excellent response, you could also use the symbols() function of the graphics package.

Just remember to use add=TRUE (for it to add the circle to a preexisting plot) and inches = FALSE , so that the natural circle radius scale, reported as circles , is that of the x axis %.

x <- seq(-3, 3, by=0.01)
y <- x^2
plot(y ~ x, asp=1, type="l")

symbols(1, 1, circles=1, inches=FALSE, fg="red", add=TRUE)
symbols(1, 1, 2, inches=FALSE, fg="green", add=TRUE)  # circles é o 3º arg
symbols(1, 1, 3, inches=FALSE, fg="blue", add=TRUE)

Abs!