Fitting Tab

The Fitting tab provides a centralized view and control over all parameters that enter the R-matrix fit. It allows setting initial values, parameter limits, and nuisance parameter flags.

Parameter Tables

Parameters are organized into three sub-tabs:

Level Parameters

Displays one row for each level-channel combination with the following columns:

Column	Description
Name	Identifier for the parameter (level energy or channel width).
Value	Current parameter value (editable).
Lower Limit	Lower bound for the parameter during fitting (leave empty for no bound).
Upper Limit	Upper bound for the parameter during fitting (leave empty for no bound).
Error	Prior uncertainty for use as a nuisance parameter.
Fit Error	Uncertainty from the fit result (read-only, populated after fitting).
Use as Nuisance	Check to treat this parameter as a nuisance parameter with a Gaussian prior in the chi-squared calculation.

Normalization Parameters

Lists the normalization factors for each data segment that has Vary Norm? enabled. These parameters scale the data yield during fitting.

Energy Shift Parameters

Lists the energy shift parameters for each data segment that has Vary Energy Shift? enabled.

Controls

Refresh from Current

Rebuild the parameter table from the current GUI state (particle pairs, levels, segments).

Load from .sav File

Import parameters from a param.sav file generated by a previous fit. The normalization file (normalizations.out) from the same directory is loaded automatically.

Populate Wigner Limits

Automatically set upper and lower limits based on the Wigner limit (single-particle limit) for reduced width amplitudes. This provides physically motivated bounds for the fit.

Clear Limits

Remove all upper and lower limit constraints from all parameters.

Tip

Using the Populate Wigner Limits feature is a good starting point for constraining fits, especially for initial explorations of parameter space. Limits can then be adjusted manually as needed.