#### Overview of this book

gnuplot is the world's finest technical plotting software, used by scientists, engineers, and others for many years. It is in constant development and runs on practically every operating system, and can produce output in almost any format. The quality of its 3d plots is unmatched and its ability to be incorporated into computer programs and document preparation systems is excellent. gnuplot Cookbook ñ it will help you master gnuplot. Start using gnuplot immediately to solve your problems in data analysis and presentation. Quickly find a visual example of the graph you want to make and see a complete, working script for producing it. Learn how to use the new features in gnuplot 4.4. Find clearly explained, working examples of using gnuplot with LaTeX and with your own computer programming language. You will master all the ins and outs of gnuplot through gnuplot Cookbook. You will learn to plot basic 2d to complex 3d plots, annotate from simple labels to equations, integrate from simple scripts to full documents and computer progams. You will be taught to annotate graphs with equations and symbols that match the style of the rest of your text, thus creating a seamless, professional document. You will be guided to create a web page with an interactive graph, and add graphical output to your simulation or numerical analysis program. Start using all of gnuplot's simple to complex features to suit your needs, without studying its 200 page manual through this Cookbook.
gnuplot Cookbook
Credits
www.PacktPub.com
Preface
Free Chapter
Plotting Curves, Boxes, Points, and more
Annotating with Labels and Legends
Applying Colors and Styles
Combining Multiple Plots
Programming gnuplot and Dealing with Data
The Third Dimension
Using and Making Graphical User Interfaces
Surveying Special Topics
Finding Help and Information
Index

## Plotting multiple curves

You will often want to plot more than one curve on a single graph, all sharing the same axes. This is simple in gnuplot: just separate the functions or datafiles by commas, and gnuplot will plot them in a sequence of colors or curve styles, with a legend so you can identify them. The following figure shows the plotting of multiple curves:

It will be useful to have some datafiles on your disk for use with some of the plotting recipes. You could make them by hand with a text editor or write a program in your favorite language to generate them, but gnuplot can do this itself. To make a file with data that forms a parabola flipped upside down, tell gnuplot to `set table 'parabola.text'`. Make sure to include the quotes around the filename. Then say `plot -x**2`. This writes a table out to the file `parabola.text` rather than making a picture. Now, say `unset table`. You should have a file called `parabola.text` in the directory in which you started gnuplot. Keep it around so we can use it later.

### How to do it…

After setting your terminal back to the graphics device you want to use at the gnuplot console, type the following command:

`plot [-1:1] 'parabola.text', -x, -x**3`

### How it works…

Gnuplot plots the curves using three different colors, dash styles, or line thicknesses, depending on the terminal in use, with a legend so you can tell them apart. The functions are plotted as smooth curves, as we did earlier, and the data from the file is plotted as a series of points, by default; one for each point in the range. This can all be adjusted, as we shall see in Chapter 3, Applying Colors and Styles.

Take a look at the datafile that gnuplot created to see the format it understands. After several comment lines beginning with the "#" character, we find a series of x coordinates and y values. The last character on each of these lines is a letter: "i" if the point is in the active range, "o" if it is out of range, or "u" if it is undefined.