#### 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 circles

This recipe will introduce gnuplot's ability to place objects at locations specified in a datafile or by mathematical functions, and to define their properties dynamically to convey information about the data. The following figure shows how gnuplot plots circles:

We have provided a datafile called `parabolaCircles.text`, which is similar to the `parabola.text` file that we created previously with gnuplot's help, but with a third column that consists of some random numbers. Make sure this file is in your current directory so that gnuplot can find it. Alternatively, use any datafile you like with three columns.

### How to do it…

Enter the following script to make a circle plot:

```set key off
plot "parabolaCircles.text" with circles```

### How it works…

For each point in the datafile, we get a circle with a radius determined by the number in the third column. Here the radii are random, but in practice you can encode some value of interest in the radii, in effect providing a way to plot two values for each point on the x-axis.

For example, the y coordinate can represent a measurement and the radii can indicate the uncertainty in the measurement; or we can get meteorological data and can plot temperature versus time, with the circle radius representing humidity.

The first line in the script turns off the legend that otherwise gnuplot adds by default.