Changeset 4666660 in sasview for src/sas/perspectives


Ignore:
Timestamp:
May 17, 2015 5:55:07 PM (10 years ago)
Author:
smk78
Branches:
master, ESS_GUI, ESS_GUI_Docs, ESS_GUI_batch_fitting, ESS_GUI_bumps_abstraction, ESS_GUI_iss1116, ESS_GUI_iss879, ESS_GUI_iss959, ESS_GUI_opencl, ESS_GUI_ordering, ESS_GUI_sync_sascalc, costrafo411, magnetic_scatt, release-4.1.1, release-4.1.2, release-4.2.2, release_4.0.1, ticket-1009, ticket-1094-headless, ticket-1242-2d-resolution, ticket-1243, ticket-1249, ticket885, unittest-saveload
Children:
96423f8
Parents:
1fda506
Message:

Work in progress

Location:
src/sas/perspectives/fitting/media
Files:
2 edited

Legend:

Unmodified
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  • src/sas/perspectives/fitting/media/fitting.rst

    rf256d9b r4666660  
     1.. _Fitting_Documentation: 
     2 
    13Fitting Documentation 
    24===================== 
  • src/sas/perspectives/fitting/media/fitting_help.rst

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    240240 
     241.. _Fitting_Options: 
     242 
    241243Fitting Options 
    242244--------------- 
     
    255257 
    256258These optimisers form the *Bumps* package written by P Kienzle. For more information 
    257 on each optimiser, see the :ref:`Fitting Documentation`. 
     259on each optimiser, see the :ref:`Fitting_Documentation`. 
    258260 
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    292294 
     295.. _Status_bar: 
     296 
    293297Status Bar & Console 
    294298-------------------- 
     
    307311--------------- 
    308312 
    309 One of two fit-engines can be chosen from the Fitting menu bar. The Simple Fit- 
    310 engine uses Scipy's leasqr and the Complex Fit-Engine is a custom optimizer  
    311 that provides a better chance to find the global minimum of the |chi| 2 but that 
    312 requires longer computation time. In order to set a data to a control panel  
    313 (FitPage), see the "DataLoader Help". Once a data set to the FiPage, select a  
    314 model from the combo box. The default parameters of the model will be display.  
    315 Set initial parameters if need. Check and uncheck parameters to fit/fix. Click  
    316 the *'Fit'*  button. When the fitting is finished, the resultant parameter  
    317 values will be displayed with the errors. If a error is missing, it generally  
    318 means that the corresponding parameter is not very depending on the model. The  
    319 chisq/Npt_fit and the plot associated with the fit operation will be also  
    320 updated. 
     313*NB: Before proceeding, ensure that the Single Mode radio button at the bottom of* 
     314*the Data Explorer is checked (see the section* :ref:`Loading_data` *).* 
     315 
     316When data is sent to the fitting perspective it is plotted in a graph window as 
     317markers. 
     318 
     319If a graph does not appear, or a graph window appears but is empty, then the data 
     320has not loaded correctly. Check to see if there is a message in the :ref:`Status_Bar` 
     321or in the *Console* window. 
     322 
     323Assuming the data has loaded correctly, when a model is selected a green model 
     324calculation (or what SasView calls a 'Theory') line will appear in the earlier graph 
     325window, and a second graph window will appear displaying the residuals (the 
     326difference between the experimental data and the theory) at the same X-data values. 
     327 
     328The objective of model-fitting is to find a *physically-plausible* model, and set 
     329of model parameters, that generate a theory that reproduces the experimental data 
     330and gives residual values as close to zero as possible. 
     331 
     332Change the default values of the model parameters by hand until the theory line 
     333starts to represent the experimental data. Then uncheck the tick boxes alongside 
     334all parameters *except* the 'background' and the 'scale'. Click the *Fit* button. 
     335SasView will optimise the values of the 'background' and 'scale' and also display 
     336the corresponding uncertainties on the optimised values. 
     337 
     338*NB: If no uncertainty is shown it generally means that the model is not very* 
     339*dependent on the corresponding parameter (or that one or more parameters are* 
     340*'correlated').* 
     341 
     342In the bottom left corner of the *Fit Page* is a box displaying the normalised value 
     343of the statistical |chi|\  :sup:`2` parameter returned by the optimiser. 
     344 
     345Now check the box for another model parameter and click *Fit* again. Repeat this 
     346process until most or all parameters are checked and have been optimised. As the 
     347fit of the theory to the experimental data improves the value of 'chi2/Npts' will 
     348decrease. A good model fit should easily produce values of 'chi2/Npts' that are 
     349close to zero, and certainly <100. 
     350 
     351SasView has a number of different optimisers (see the section :ref:`Fitting_Options`). 
     352The DREAM optimiser is the most sophisticated, but may not necessarily be the best 
     353option for fitting simple models. If uncertain, try the Levenberg-Marquardt optimiser 
     354initially. 
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