In this post, we continue learning about the R programming interface. Making simple X-Y plots using a mathematical expression of the type

y = f(x)

is a nice way to learn how functions behave and for finding out the roots of polynomial functions. In R, the **curve** command can handle almost anything you wish to plot and analyze. Let’s assume that you have a function of the form:

y = (x – 1)(x – 2)(x – 3)

In this case, we already know that the roots of this function [x values where y = f(x) = 0] are x = 1, x = 2 and x = 3. Thus, picking a range of x-values over which this function shows some interesting behavior is easy. Let’s pick the range from x = 0.75 to x = 3.25.

This is how you would plot this function in the X-Y plane using R:

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curve((x-1)*(x-2)*(x-3),from=0.75,to=3.25) |

To overlay another plot on the same window, use “add = TRUE” as an additional parameter to the curve command. For example, to insert a blue-colored horizontal line (y = 0) in the above plot, use:

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> curve(0*x,from=0.75,to=3.25,col='blue',add=TRUE) |

You can control the number of points “n” used to draw the curve (default n = 101), add custom labels for the axes and draw logarithmic plots. Consult this link for additional details about all the parameters we can use for the curve command.