Excellent GUI and command-line curve fitting tool
- John Allspaw in The art of capacity planning

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Fityk [fi:tik] is a program for data processing and nonlinear curve fitting.

Although it is primarily used...

• by scientists who analyse data from powder diffraction, chromatography, photoluminescence and photoelectron spectroscopy, infrared and Raman spectroscopy, and other experimental techniques,

• to fit peaks – bell-shaped functions (Gaussian, Lorentzian, Voigt, Pearson VII, bifurcated Gaussian, EMG, Doniach-Sunjic, etc.),

... the program can be used for any task that requires fitting a curve to 2D (x,y) data.

Features | Download | Documentation | Support

Features

• intuitive graphical interface (and also command line interface),
• support for many data file formats, thanks to the xylib library,
• dozens of built-in functions and support for user-defined functions,
• equality constraints,
• fitting systematic errors of the x coordinate of points (for example instrumental zero error or sample displacement correction in powder diffraction),
• manual, graphical placement of peaks and auto-placement using peak detection algorithm,
• various optimization methods (standard Marquardt least-squares algorithm, Genetic Algorithms, Nelder-Mead simplex),
• handling series of datasets,
• automation with macros (scripts) and embedded Lua for more complex scripting
• the accuracy of nonlinear regression verified with reference datasets from NIST,
• an add-on for powder diffraction data (Pawley refinement)
• modular architecture,
• open source licence (GPL).

Download

In an attempt to make this software self-sustaining and actively developed in the future, new binaries are available to subscribers only:

MS Windows: fityk-1.1.1-setup.exe $

Mac OS X (10.4 or later): fityk-1.1.1-osx.zip $

Linux: deb packages (i386 and x64). Tested only on Ubuntu 10.10. Email me if you need a package for another distro.

Subscribers have access to all versions of the program and to e-mail support. The program can be installed on many computers and can be also used after the end of subscription.

• 1 month subscription: $115 (≈ €90)
• 1 year subscription: $265 (≈ €200)

Students and home users may donate 20% of the normal price to wojdyr@gmail.com using PayPal, MoneyBookers or Flattr.

Versions 0.9.8 and older are free: for Windows and Linux (Ubuntu PPA and RPMs from OBS).

Source code: GitHub

Version 1.1.1 was released on 2011-09-28 (changelog). New version notifications are delivered via email and feeds.

Documentation

• Manual (chapters Introduction, Getting Started, Mini-Language, Data, Models, Curve Fitting, All the Rest) and the same in PDF,
• Fityk Wiki (you are welcome to contribute).

Citing Fityk in academic papers: M. Wojdyr, J. Appl. Cryst. 43, 1126-1128 (2010) [reprint]

Questions?

• Google group fityk-users (you may select “no mail” and use it like forum)
• or wojdyr@gmail.com

Feel free to send questions, comments, requests, bug reports, and success stories. Asking for a new feature usually results in adding the request to the TODO list or, if it already is in the list, in assigning higher priority to it.