Preface

Why gnuplot?

gnuplot is a free, open source plotting program that has been in wide use since 1986. It's used as the graphics backend by many other programs, so plenty of people use gnuplot without knowing it. If you've used Octave, Maxima, statist, gretl, or the Emacs graphing calculator, you've already used gnuplot.

gnuplot was originally designed to visualize scientific data, but its use has expanded to encompass every domain where sophisticated and accurate plotting is required. gnuplot is used in science, engineering, sociology, mapping, business, finance, and computer systems and network monitoring.

gnuplot excels at complex 3D graphing with hidden-line removal and at the rendering of surfaces and contours. It can produce almost any type of graph imaginable (except for pie-charts—but it can be convinced to do this, too, as we'll show later!) for a dizzying array of output devices, and can save plots in almost any type of common file format (and some uncommon ones). It can be installed on any type of computer system you are likely to encounter; there are binaries available for Windows and the sources can be compiled on most reasonably modern machines. I have compiled the latest version (4.4) of gnuplot on both Linux and Macintosh (OS X) computers and verified that all of its advanced features are fully available on both of these architectures. The recipes in this book that illustrate features newly appearing in version 4.4 are marked with [new].

gnuplot can easily be automated. It has its own scripting language and can be controlled from many general-purpose programming languages. gnuplot can also be incorporated into various publishing and document creation workflows to help create professional books, papers, and online documents.

Why this book?

Because of gnuplot's many years of deployment and sophisticated community of expert users, help is usually easy to find in some form. If you are trying to solve a tricky plotting problem, there is a reasonable chance that someone online has either figured it out or is willing to share some ideas about how it might be done.

However, there is little available in the form of a convenient reference with the structure of a cookbook, where you can look for an example of the type of plot you are trying to create and see instantly how it can be done, with a runnable example.

This book is designed to be that combination of reference and tutorial. It goes beyond plotting recipes, however, and will show you how to incorporate your graphs into documents, how to create interactivity, how to program and automate gnuplot, and more. Each example is in the form of a recipe with immediately runnable code in electronic form, and with clear explanations that will show you how to modify the recipe to solve your particular problem. Each recipe is illustrated with the plot created by the procedure, so you can use the book as a visual index that will allow you to quickly find the solution you are looking for.

One of our goals is to show you the major new features in the latest release version of gnuplot, version 4.4.3. Even experienced users of gnuplot are likely to find these sections useful, as we include an illustrative recipe for each new feature; these are specially marked so that features making their first appearance in gnuplot 4.4 can be located quickly. These new features include the use of Unicode characters, transparency, new graph positioning commands, plotting objects, internationalization, circle plots, interactive HTML5 canvas plotting, iteration in scripts, lua/tikz/LaTeX integration, cairo and SVG terminal drivers, and volatile data.

What this book covers

Chapter 1, Plotting Curves, Boxes, Points, and more, covers the basic usage of Gnuplot: how to make all kinds of 2D plots for statistics, modeling, finance, science, and more.

Chapter 2, Annotating with Labels and Legends, explains how to add labels, arrows, and mathematical text to our plots.

Chapter 3, Applying Colors and Styles, covers the basics of colors and styles in gnuplot, plus transparency, and plotting with points and objects.

Chapter 4, Controlling Your Tics, will show you how to get your tic marks and labels just right, along with gnuplot's new internationalization features.

Chapter 5, Combining Multiple Plots, shows how to arrange a set of graphs on the page, and make inset plots.

Chapter 6, Including Plots in Documents, delves into incorporating your plots into technical documents, presentations, and web pages.

Chapter 7, Programming gnuplot and dealing with data, covers how to use gnuplot's built-in programming constructs as well as its ability to be used from any programming language, and how to use the new volatile data features.

Chapter 8, The Third Dimension, shows how to plot surfaces, vectors, heat maps, and lines in a 3D space.

Chapter 9, Using and Making Graphical User Interfaces, introduces several GUIs for gnuplot and includes writing a web application with gnuplot on the backend.

Chapter 10, Surveying Special Topics, covers several special techniques and applications: mapping; labeled contours; colored and broken axes; pictures; and more.

Appendix, Finding help and information, provides a brief list of sources of gnuplot information and education.

What you need for this book

The prerequisites for this book are that you have an installation of gnuplot available for your use and that you are familiar with elementary gnuplot operation (starting gnuplot on the command line and entering a plot command). You should be able to create plots on one of the screen terminals and to save a plot file, as well. Other than that, no specialized knowledge is required to make use of this guide; although we may take examples from various specialized fields, they are incidental to the recipes, which are focused on creating particular types of graphs. The examples of controlling gnuplot from programming languages use simple examples that can be understood even if you don't have experience with the languages used in the recipes.

Who this book is for

Whether you are an old hand at gnuplot or have just started using it, this book is a convenient visual reference that covers the full range of gnuplot's capabilities, including its latest features. This volume is ideal for the gnuplot user who needs complete, runnable scripts to solve specialized graphing problems and clear explanations that will allow him or her to immediately modify them for the tasks at hand.

Conventions

In this book, you will find a number of styles of text that distinguish between different kinds of information. Here are some examples of these styles, and an explanation of their meaning.

Code words in text are shown as follows: "To make a file with data that forms a parabola flipped upside down, tell gnuplot to set table 'parabola.text'"

A block of code is set as follows:

set y2tics -100, 10
set ytics nomirror
plot sin(1/x) axis x1y1,100*cos(x) axis x1y2

When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold:

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

Any command-line input or output is written as follows:

plot 'randomnormal.text' volatile

New terms and important words are shown in bold. Words that you see on the screen, in menus or dialog boxes for example, appear in the text like this: "We clicked on the tab Add plot commands to get the window."

Note

Warnings or important notes appear in a box like this.

Tip

Tips and tricks appear like this.

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