1. Analysis of QENS data at ILL
SINE 2020 – WP 10
Analysis of QENS data at ILL

2. Situation at ILL
No unique or generally accepted software for QENS analysis
Agathe (M. Bée, 90’s, ILL96BE11T): Only Unix (Linux?)
IDA (J. Wuttke)
FITMO4 (A. Desmedt, HMI)
QENS_Fit (S. Rols, NIST, IDL, included in Lamp)
PAN and RAINS (in DAVE)
mQfit (N. Martinez, Python, 2015)
Str_Fit (D. Richard, ILL, IDL, in Lamp)
Other user programs (e.g. using Minuit, Igor, Octave, etc.) …
Going Mantid for data reduction
Interested in fitting tools in Mantid

3. Str_Fit Started as a simple tool to fit simple peaks in Salsa
Extended to a more general and flexible fitting tool
Specific QENS models added only recently

4. Str_Fit 1D and 2D fits Tied and common (2D) parameters
Two fitting motors (but both Levenberg-Marquardt)
Small library of standard QENS models: delta, Lorentzian, Brownian and Jump Diffusion, Rotational diffusion, jumps between equivalent sites, localized translation, …
User-defined formula

5. Wish list for a QENS fitting soft
Extensive documentation, including examples and tutorials
Intuitive GUI, but possibility to fit from command line
Able to fit in background using multiple cores or cluster
Able to save and load complete session
Accept input from multiple instruments or formats
Publication quality plots
Simultaneous fitting of Q-dependent spectra and multiple data sets
Possibility to choose between different fitting methods (LM, MC, Bayes, GA …)
Provide methods to estimate fit reliability
Simple, but complete methods to apply constraints on fit parameters
Extensive library of models and possibility to add easily new models
More: Fourier Transform of input data (fitting in  and in time), handle multiple scattering, possibility of reducing the weight of the elastic peak in the fit, fit both QENS and fixed window scan data, …