Simple plotting

Two simple scripts for creating plots from the command line: one for plotting functions and the other for plotting points. The scripts require the NumPy and matplotlib modules.

The graphs produced aren't intended to be of publication quality. The goal is to make readable graphs very quickly.

Functions

For these, everything is given on the command line.

plot 'function(s)' minx maxx [miny maxy]

Three arguments are required: the function itself, which would normally be enclosed in quotes to avoid problems with shell interpretation; the minimum x value; and the maximum x value. The last two arguments, the minimum and maximum y values are optional—if they aren't given, the script will figure them out. A common reason to specify the y limits is if the function "blows up" between the x limits and the extreme y values make the rest of the graph look flat.

The function can include any Python expression or function, including those in the NumPy library. There's no need to use a numpy prefix.

More than one function can be specified; separate them with a semicolon. Thus, something like

plot 'tan(x); x' pi 3*pi/2-.01 0 5

can be used to find the intersection of the two given functions. This example also shows that you can use expressions in the limits.

The result of plot is an 800×600 PNG image that's sent to standard output. Normally, this would be redirected to a file,

plot 'tan(x); x' pi 3*pi/2-.01 0 5 > plot.png

and viewed in whatever graphics program the user prefers. No controls for tick marks or grid spacing are provided—this is quick and dirty plotting.

A PDF can be produced by using the -p or --pdf switch:

plot -p 'tan(x); x' pi 3*pi/2-.01 0 5 > plot.png

Given that both PNG and PDF start with "p," the -p switch is poorly named, but I couldn't think of a better one.

Points

The script that plots lists of points, pplot, gets its data from standard input. On the Mac, it would be common to pass data in from the clipboard this way:

pbpaste | pplot

As with plot, pplot produces an 800×600 PNG image that's sent to standard output, so one would normally redirect this to a file:

pbpaste | pplot > plot.png

Each line of the input data represents one (x, y) point. The x and y values can be separated by tabs, spaces, or commas.

Normally, pplot plots the points only. If you want to connect the points with a line, use the -l option:

pbpaste | pplot -l > plot.png