# Introduction

## What’s This Program for?

Fityk is a program for nonlinear fitting of analytical functions (especially peak-shaped) to data (usually experimental data). The most concise description: peak fitting software. There are also people using it to remove the baseline from data, or to display data only.

It is reportedly used in crystallography, chromatography, photoluminescence and photoelectron spectroscopy, infrared and Raman spectroscopy, to name but a few. Although the author has a general understanding only of experimental methods other than powder diffraction, he would like to make it useful to as many people as possible.

Fityk offers various nonlinear fitting methods, simple background subtraction and other manipulations to the dataset, easy placement of peaks and changing of peak parameters, support for analysis of series of datasets, automation of common tasks with scripts, and much more. The main advantage of the program is flexibility - parameters of peaks can be arbitrarily bound to each other, e.g. the width of a peak can be an independent variable, the same as the width of another peak, or can be given by complex (and general for all peaks) formula.

## GUI vs CLI

The program comes in two versions: the GUI (Graphical User Interface) version - more comfortable for most users, and the CLI (Command Line Interface) version (named cfityk to differentiate).

technical note

The GUI version is written using the wxWidgets library. It runs on Unix species with GTK+, on MS Windows and (with some problems) on MacOS X.

If the CLI version was compiled with the GNU Readline Library, command line editing, `TAB`-expanding and command history will be available. On Unix, the gnuplot program can be used for data visualization.

## About...

Fityk is free software; you can redistribute and modify it under the terms of the GPL, version 2 or (at your option) any later version.

To download the latest version of the program or to contact the author visit http://fityk.nieto.pl/.

This manual is written using ReStructuredText. All corrections and improvements are welcome. Use the `Show Source` link to get the source of the page, edit it and send me either the modified version or a patch.

The following people have contributed to this manual (in chronological order): Marcin Wojdyr (maintainer), Stan Gierlotka, Jaap Folmer, Michael Richardson.

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