I recently stumbled over R, a programming language for data analysis. R is open-source and available on all major platforms (Windows, Linux, Mac).
This post is about how to display (draw) a mathematical function with R.
There’s a very nice and interactive tutorial for R available over at codeschool.com. It’s free and takes about 3 - 4 hours to complete.
To draw a function, use the built-in function curve()
.
Let’s start with something simple:
curve(x^2)
This will plot the function x² and will look like this:
Since we didn’t specify any boundaries for the x and y axes, R used 0..1
for the x axis and chose the y axis to fit.
Of course, we can manually specify the range for the values on the x axis:
curve(x^2, -4, 3)
This will plot x² with -4..3
:
As you can see in this plot, R makes the y axis match the required value range (here: 0..15
).
Sometimes, however, this may not be desired. There are two ways to fix this.
First, you can specify the aspect ratio to be 1 (cause log scales are for quitters). In this case, the x and the y axes will use the same scale:
curve(x^2, -4, 3, asp=1)
will give us:
The other option is to explicitly specify the range for the y axis by using the ylim
parameter:
curve(x^2, -4, 3, ylim=range(c(-1, 4)))
will give us a y axis range of -1..4
:
For more information on curve()
, just type ?curve
in R’s prompt.