Changes in src/sas/sasgui/perspectives/fitting/media/fitting_help.rst [47ace50:8b89396] in sasview

File:

• src/sas/sasgui/perspectives/fitting/media/fitting_help.rst (modified) (7 diffs)

src/sas/sasgui/perspectives/fitting/media/fitting_help.rst

@@ -180 +180 @@
 *checked*\ .
 
-Also note that the 'Fit Parameters' have been split into two sections: those
-which can be polydisperse (shape and orientation parameters) and those which are
-not (eg, scattering length densities).
-
 A model file generated by this option can be viewed and further modified using
 the :ref:`Advanced_Plugin_Editor` .
 
-**SasView version 4.2** made it possible to specify whether a plugin created with
-the *New Plugin Model* dialog is actually a form factor P(Q) or a structure factor
-S(Q). To do this, simply add one or other of the following lines under the *import*
-statements.
+Note that the New Plugin Model Feature currently does not allow for parameters
+to be polydisperse.  However they can be edited in the Advanced Editor.
+
+
+**SasView version 4.2** made it possible to specify whether a plugin created
+with the *New Plugin Model* dialog is actually a form factor P(Q) or a structure
+factor S(Q). To do this, simply add one or other of the following lines under
+the *import* statements.
 
 For a form factor::
@@ -200 +200 @@
      structure_factor = True
 
-If the plugin is a structure factor it is *also* necessary to add two variables to
-the parameter list::
+If the plugin is a structure factor it is *also* necessary to add two variables
+to the parameter list::
 
      parameters = [
@@ -426 +426 @@
 See :ref:`Assessing_Fit_Quality`.
 
-The objective of model-fitting is to find a *physically-plausible* model, and
-set of model parameters, that generate a theory that reproduces the experimental
-data and minimizes the values of the residuals.
+The objective of model-fitting is to find a *physically-plausible* model, and set
+of model parameters, that generate a theory that reproduces the experimental data
+and gives residual values as close to zero as possible.
 
 Change the default values of the model parameters by hand until the theory line
-starts to represent the experimental data. Then check the tick boxes alongside
-the 'background' and 'scale' parameters. Click the *Fit* button. SasView
-will optimise the values of the 'background' and 'scale' and also display the
-corresponding uncertainties on the optimised values.
-
-.. note::
-   If the uncertainty on a fitted parameter is unrealistically large, or if it
-   displays as NaN, the model is most likely a poor representation of the data,
-   the parameter in question is highly correlated with one or more of the other
-   fitted parameters, or the model is relatively insensitive to the value of
-   that particular parameter.
-
-In the bottom left corner of the *Fit Page* is a box displaying a normalised
-value of the statistical $\chi^2$ parameter (the reduced $\chi^2$,
-See :ref:`Assessing_Fit_Quality`) returned by the optimiser.
+starts to represent the experimental data. Then uncheck the tick boxes alongside
+all parameters *except* the 'background' and the 'scale'. Click the *Fit* button.
+SasView will optimise the values of the 'background' and 'scale' and also display
+the corresponding uncertainties on the optimised values.
+
+*NB: If no uncertainty is shown it generally means that the model is not very*
+*dependent on the corresponding parameter (or that one or more parameters are*
+*'correlated').*
+
+In the bottom left corner of the *Fit Page* is a box displaying the normalised value
+of the statistical $\chi^2$ parameter returned by the optimiser.
 
 Now check the box for another model parameter and click *Fit* again. Repeat this
-process until all relevant parameters are checked and have been optimised. As
-the fit of the theory to the experimental data improves, the value of 'Reduced
-Chi2' will decrease. A good model fit should produce values of Reduced Chi2
-close to one, and certainly << 100. See :ref:`Assessing_Fit_Quality`.
+process until most or all parameters are checked and have been optimised. As the
+fit of the theory to the experimental data improves the value of 'chi2/Npts' will
+decrease. A good model fit should easily produce values of 'chi2/Npts' that are
+close to one, and certainly <100. See :ref:`Assessing_Fit_Quality`.
 
 SasView has a number of different optimisers (see the section :ref:`Fitting_Options`).
@@ -466 +462 @@
 *the Data Explorer is checked (see the section* :ref:`Loading_data` *).*
 
-This mode is an extension of the :ref:`Single_Fit_Mode` that allows for some
-relatively extensive constraints between fitted parameters in a single *FitPage*
-or between several *FitPage*'s (eg, to constrain all fitted parameters to be the
-same in a contrast series of *FitPages* except for the solvent sld parameter,
-constrain the length to be twice that of the radius in a single *FitPage*,
-fix the radius of the sphere in one *FitPage* to be the same as the radius of
-the cylinder in a second *FitPage*, etc).
+This mode is an extension of the :ref:`Single_Fit_Mode` that fits two or more data
+sets *to the same model* simultaneously. If necessary it is possible to constrain
+fit parameters between data sets (eg, to fix a background level, or radius, etc).
 
 If the data to be fit are in multiple files, load each file, then select each file
@@ -509 +501 @@
 next to *Add Constraint?* in the *Fit Constraints* box.
 
-To constrain all identically named parameters to fit *simultaneously* to the
-same value across all the *Fitpages* use the *Easy Setup* drop-down buttons in
-the *Const & Simul Fit* page.
-
 *NB: You can only constrain parameters that are set to refine.*
+
+When ready, click the *Fit* button on the *Const & Simul Fit* page, NOT the *Fit*
+button on the individual *FitPage*'s.
+
+Simultaneous Fits without Constraints
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The results of the model-fitting will be returned to each of the individual
+*FitPage*'s.
+
+Note that the chi2/Npts value returned is the SUM of the chi2/Npts of each fit. To
+see the chi2/Npts value for a specific *FitPage*, click the *Compute* button at the
+bottom of that *FitPage* to recalculate. Also see :ref:`Assessing_Fit_Quality`.
+
+Simultaneous Fits with Constraints
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Use the *Easy Setup* drop-down buttons in the *Const & Simul Fit* page to set
+up constraints between *FitPage*'s.
 
 Constraints will generally be of the form
@@ -528 +535 @@
 Many constraints can be entered for a single fit.
 
-When ready, click the *Fit* button on the *Const & Simul Fit* page, NOT the *Fit*
-button on the individual *FitPage*'s.
-
 The results of the model-fitting will be returned to each of the individual
 *FitPage*'s.
 
-Note that the Reduced Chi2 value returned is the SUM of the Reduced Chi2 of
-each fit. To see the Reduced Chi2 value for a specific *FitPage*, click the 
-*Compute* button at the bottom of that *FitPage* to recalculate. Note that in
-doing so the degrees of freedom will be set to Npts.
-See :ref:`Assessing_Fit_Quality`.  Moreover in the case of constraints the
-degrees of freedom are less than one might think due to those constraints.
+Note that the chi2/Npts value returned is the SUM of the chi2/Npts of each fit. To
+see the chi2/Npts value for a specific *FitPage*, click the *Compute* button at the
+bottom of that *FitPage* to recalculate. Also see :ref:`Assessing_Fit_Quality`.
 
 .. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ
@@ -765 +766 @@
 .. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ
 
-.*Document History*
-
-| 2017-09-10 Paul Butler
-| 2017-09-15 Steve King
-| 2018-03-05 Paul Butler
+.. note::  This help document was last changed by Paul Butler, 10 September
+   2017