Dear Tom,

Here is an example of data, python script generated from mantid fitting (sent as txt as our mailing system does not like sending .py file) and a plot that shows how bad the fit is, although mantid believe this is a perfectly acceptable fit.
If you get the starting parameters near spot on, it will eventually refine.
This is trying to fit a back to back expo, typical of time of flight data on a diffractometer (but I have seen similar things with simple gaussian!) 
Other programs (also using LM methods) do a good job. in particular, the python fitting routines seem to do the job. 

Hope this helps,

P

Dr Pascal Manuel
ISIS Pulsed Neutron and Muon Facility
STFC Rutherford Appleton Laboratory
Chilton
Oxfordshire OX11 0QX
United Kingdom
Office: + 44 (0)1235 446290
Beamline : +44 (0)1235 567080
Mobile: +44(0) 7833 965011 (also for WhatsApp)
ZoomID : https://ukri.zoom.us/j/5735149151
Skype : pascal.manuel73

From: Hampson, Thomas (STFC,RAL,ISIS) <thomas.hampson@stfc.ac.uk>
Sent: Wednesday, November 22, 2023 5:32 PM
To: ISIS Instrument Scientist <ISISInstsci@stfc.ac.uk>
Cc: Foxley, Sarah (STFC,RAL,ISIS) <sarah.foxley@stfc.ac.uk>; Farooq, Rabiya (STFC,RAL,ISIS) <Rabiya.Farooq@stfc.ac.uk>; Haigh, Jonathan (STFC,RAL,ISIS) <Jonathan.Haigh@stfc.ac.uk>
Subject: RE: Mantid fitting engine replacement
 

Hi All,

 

Many thanks to those of you who have replied so far with examples that demonstrate the limitations of our current fitting framework. I will respond to you individually shortly to make sure I have enough information to add them to the fitbenchmarking dataset.

 

If anyone else has any examples of problems they’ve had with fitting in Mantid then I would be grateful for your response. More data will help us make a better informed decision about the potential replacement of the fitting engine.

 

Regards,

Tom Hampson

 

 

From: Hampson, Thomas (STFC,RAL,ISIS)
Sent: 08 November 2023 12:38
To: ISIS Instrument Scientist <ISISInstsci@stfc.ac.uk>
Cc: Foxley, Sarah (STFC,RAL,ISIS) <sarah.foxley@stfc.ac.uk>; Farooq, Rabiya (STFC,RAL,ISIS) <Rabiya.Farooq@stfc.ac.uk>; Haigh, Jonathan (STFC,RAL,ISIS) <jonathan.haigh@stfc.ac.uk>
Subject: Mantid fitting engine replacement

 

Dear ISIS Instrument Scientists,

 

We are in the process of evaluating potential replacements for the Mantid fitting engine and need your input. We are seeking real examples that will help us quantify the limitations of the current engine.

 

Specifically, we would appreciate your feedback on any issues you've encountered with the Mantid fitting engine, such as:

 

- Sensitivity to initial parameter values

- Slow performance

- Getting stuck in local minima

 

To assist us in this evaluation, please provide examples with the following information:

 

- Fit function used

- Data used in the fit

- Fit range

- Initial parameter values

- Any additional information you believe is relevant

 

The data you provide will be used with the FitBenchmarking tool, maintained by RSE in ISIS. This will help us determine whether there is a more suitable replacement.

 

We also welcome any general feedback on the fitting in Mantid and the fitting interface.

 

The deadline for your input is the end of November.

 

Your contributions will greatly assist us in making informed decisions about the future of the Mantid fitting engine.

 

Thank you for your assistance.

 

Sincerely,

Tom Hampson (on behalf of the Mantid team)