Graphing Two Dimensional Functions

The command used for two-dimensional plots is plot. The simplest use of it is:

plot <function>

For example, to plot x³, type

plot x**3

You should see something like the following pop up in the graphics screen.

For another example, to see what the hyperbolic cosine function looks like, type

plot cosh(x)

This should display

Note that in this picture the scale isn't the best for finding a lot of information about the graph. It tells us that the function gets very large as x gets larger. But if we want to see what the function looks like closer to 0, we need to change the scale. Gnuplot uses an autoscale mechanicism. It sets the scale so that the graph will fit on the screen. To change the scale, use one of the following forms of plot:

plot [x1:x2] [y1:y2] <function>
plot [x1:x2] <function> (To just set the x range)
plot [] [y1:y2] <function> (To just set the y range).

Note, that if you set the range for the x values on one plot, they will stay that way for future plots. To set the default x range back to [-10,10], type the following:

set xrange [-10:10]

Also, if you set the range for the y values, they will stay the same for future plots as well. You can set GnuPlot back to autoscaling the y axis by typing the following:

set autoscale y

For more information on the set xrange and set autoscale commands, use the help command. To see what cosh looks like from x=[-5, 5], type

plot [-5:5] cosh(x)

Or, to see what cosh looks like from y=[0, 10], type

plot [] [0,10] cosh(x)

Table of Contents - Previous - A Simple Example - Next - 3D plots

College of Natural Sciences / University of Northern Iowa / manager@cns.uni.edu