#### 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

## Making an image plot or heat map

The information that is presented in a planar contour plot can also be conveyed by coloring or shading the x-y plane, rather than by drawing contours on it. The resulting graph is called an image plot, or sometimes, a heat map:

Depending on the character of the data to be plotted and the features one wants to call attention to, and to some extent the physical characteristics of the output device, either a contour plot or an image plot might be preferred.

### How to do it…

The previous figure was created using the following script:

```set xrange [-4:4]
set yrange [-4:4]
set iso 100
set samp 100
unset key
unset sur
set view map
set pm3d at b
splot sin(y**2+x**2) - cos(x**2)```

### How it works…

Let's look at the highlighted code line first. This `set pm3d` line, which we used at the beginning of the chapter to plot surfaces, here has the additional clause `at b`, which means at bottom. This says to draw the data color map on the x-y plane rather than on the surface itself. The...