Global Nonlinear Least-Squares Equilibrium Analysis:

Part 5: Parameter Controls Previous: Scan Editing Next: Fitting Information

After selecting a model and running the scan diagnostics, you can initialize the parameters for the model by clicking on the "Initialize Parameters" button, which now is activated. This function will apply a first order fit to the data and using a line search algorithm identify a good starting guess for the molecular weight and the amplitudes. Baselines are set to zero, and association constants are set to a small number. Initial estimates for each parameter for each included scan will be assigned automatically, and the Model Control Window will appear. Each parameter that can be floated will be listed with a "Float" checkbox. If checked, the parameter will be adjusted by the nonlinear least squares fitting routine, otherwise, it will be held constant. By default, none of the floatable parameters are set to be floated, until the "Float Parameters" button is clicked. For constrained fitting, the "Lock" checkbox needs to be checked, and the parameter will only be adjusted within the bounds listed. If the fitting routine attempts to adjust the parameter outside the bounds, the bound LED will flash red, otherwise it will be lit up in green. If constrained fitting is not used, the LED will be turned off. (Note: constrained fitting has not been implemented at this time and is not available yet).

The model control distinguishes between global and local parameters, as well as static scan parameters which were experimentally determined, such as rotor speed, path length, temperature, buffer density, extinction coefficients, reduced molecular weight sigma and the wavelength of the scan.

Before proceeding to the next section, you should now manually review all scans to determine if they are properly included or excluded from the fit. You can control the inclusion of scans in the fit by selecting specific scans with the "Scan Selector:" counter and checking the "Include this Scan in the Fit" checkbox:

If you double-click on scans listed in the scan listbox, you can also toggle if a scan is included or excluded from the global fit. If a scan has been automatically excluded by the "Scan Diagnostics" function, you can override this setting now. Scans overridden in such way will be marked with a red triangle () in the listbox. Check to see if excluded scans suffer from peripheral noise. In such a case you may be able to include the scan after cropping noisy sections from the scan.

IMPORTANT NOTE: For best results, always re-initialize all parameters before proceeding to the fitting session by clicking on the "Initialize Parameters" button when additional scans are excluded or included. The parameters will need to be re-initialized before fitting, or unexpected results can occur. This is not necessary if the default selection of scans is used.

Previous: Scan Editing Parameter Controls Next: Fitting Information

www contact: Borries Demeler

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Last modified on January 12, 2003.