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.

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.),

but it is suitable for fitting any 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 (GPLv2+).

Download

MS Windows: fityk-1.3.1-setup.exe

Mac OS X (10.6 or later): fityk-1.3.1-osx.zip

Linux: binary packages are available in many distros and on Flathub.

Source code: GitHub (releases)

Version 1.3.1 was released on 2016-12-19 (changelog).

Version 1.3.2, with minor changes, was released on 2022-08-06, but binaries haven’t been updated.

Documentation

• Manual (chapters Introduction, Getting Started, Data, Models, Curve Fitting, Scripts, All the Rest).

• PDF, ePUB and older versions of the manual can be downloaded from Read the Docs.

• 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.