12.1 Introduction to Plotting

To make the plots, Maxima can use an external plotting package or its own graphical interface Xmaxima (see the section on Plotting Formats). The plotting functions calculate a set of points and pass them to the plotting package together with a set of commands specific to that graphic program. In some cases those commands and data are saved in a file and the graphic program is executed giving it the name of that file to be parsed.

When a file is created, it will begiven the name maxout_xxx.format, where xxx is a number that is unique to every concurrently-running instance of Maxima and format is the name of the plotting format being used (gnuplot, xmaxima, mgnuplot or geomview).

There are commands to save the plot in a graphic format file, rather than showing it in the screen. The default name for that graphic file is maxplot.extension, where extension is the extension normally used for the kind of graphic file selected, but that name can also be specified by the user.

The maxout_xxx.format and maxplot.extension files are created in the directory specified by the system variable maxima_tempdir. That location can be changed by assigning to that variable (or to the environment variable MAXIMA_TEMPDIR) a string that represents a valid directory where Maxima can create new files. The output of the Maxima plotting command will be a list with the names of the file(s) created, including their complete path, or empty if no files are created. Those files should be deleted after the maxima session ends.

If the format used is either gnuplot or xmaxima, and the maxout_xxx.gnuplot or maxout_xxx.xmaxima was saved, gnuplot or xmaxima can be run, giving it the name of that file as argument, in order to view again a plot previously created in Maxima. Thus, when a Maxima plotting command fails, the format can be set to gnuplot or xmaxima and the plain-text file maxout_xxx.gnuplot (or maxout_xxx.xmaxima) can be inspected to look for the source of the problem.

The additional package draw provides functions similar to the ones described in this section with some extra features, but it only works with gnuplot. Note that some plotting options have the same name in both plotting packages, but their syntax and behavior is different. To view the documentation for a graphic option opt, type ?? opt in order to choose the information for either of those two packages.