#### 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

## Graphing parametric curves

Gnuplot can graph functions whose x and y values depend on a third variable, called a parameter. In this way, more complicated curves can be drawn. The following plot resembles a lissajous figure, which can be seen on an oscilloscope when sine waves of different frequencies are controlling the x and y axes:

### How to do it…

The following script creates the previous figure:

```set samples 1000
set parametric
plot sin(7*t), cos(11*t) notitle```

### How it works…

We want more samples than the default 100 for a smoother plot, hence the first line. The second line (highlighted) changes the way gnuplot interprets plot commands; now the two functions (in the third line) are understood to provide x and y coordinates in the plane as the parameter `t` is varied. Once we say `set parametric`, then we can say `plot x(t), y(t)`, and the plot will trace out a curve given by `x` and `y` as `t` is varied between the limits given in trange.

### There's more…

The range of values that `t` varies through to draw the plot defaults to `[-5:5]`. Try out different ranges to see what happens by setting the `trange`. For example, you can say `set trange [0:2]` and then `replot` to see the effect.