Plotting in MAXIMA

Introduction

A Computer Algebra System like maxima lets you study the properties of functions, but algebraic output does not tell the whole story. Many things are hard to see in formulae and equations, but obvious in a glance at a graph. Even a crude plot is better than none. And crude plots are what maxima has to offer: it can set up and display the simple graphs that gnuplot produces.

Obviously, this requires that you have gnuplot installed in your system. Not so obviously, you'll need to have xmaxima installed as well, because that package contains the glue needed to produce plots in the middle of a maxima session.

Plotting a single-valued function

If you have these pieces installed, you can plot a simple function of one variable. For example, let's plot the function

                   F(x) = (sin (x^2))/x

which we define in maxima by typing

                   F(x):= (sin (x^2))/x;

at the (%i1) prompt.  [ Notice the use of the := operator to define the function. ]

To plot a graph of this function, we can use the command plot2d, which requires that we specify the range of x to be plotted. The range is specified by a 3-item list: the name of the variable on the horizontal axis, followed by the lower and upper limits of its values. These 3 items are separated by commas, and enclosed in square brackets:

                   [x, -5, +5]

We also need to specify the format of the plot, because maxima by itself can't display a plot. If we have xmaxima installed, we can use the option

                   [plot_format, xmaxima]

(again, enclosed in square brackets, and separated from the x-range list by a comma) to produce the plot. So the maxima command line is this:

      plot2d (F(x),  [x, -2, +2], [plot_format, xmaxima])$

The line ends with a dollar sign instead of a semicolon, because we don't need to see the word "done" that is its result.

Plot of the function mentioned above The actual plot appears in a separate window, which is shown at the right. I saved the plot by clicking on the "Save" button seen in its upper margin.

Be careful about the plot window, which is produced by a separate process that remains even if you click on the "Close" button at its upper left corner.

Back to the . . .
MAXIMA Introduction page

or the very basic Maxima page

or the website overview page