Fityk is A Multi-platform Open-source Data-analysis Package for Scientists

Fityk is A Multi-platform Open-source Data-analysis Package for Scientists

Fityk [fi:tik] is an open-source program for data processing and nonlinear curve fitting, that works for Windows, Linux and macOS.


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.),

but it is suitable for fitting any curve to 2D (x,y) data.


  • 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 license (GPLv2+).


  • Windows: Windows 7, 8.1, and 10
  • macOS: 10.6+
  • Linux: Debian, Linux Mint, MX Linux, Arch Linux, Ubuntu, Fedora, and openSUSE.
  • Linux Flatpak package


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