3.26 FAQ-254 How do I fit a single dataset with multiple instances of one function?

Single-Data-Multiple-Fit

Last Update: 2/4/2015

Follow these steps:

1. With a worksheet active, Ctrl + select two or more ranges of data in the same column. With a graph active, use the Regional Data Selector tool, , to select two or more ranges.
2. After your ranges have been set, open the NLFit dialog, by selecting Analysis: Fitting: Nonlinear Curve Fit.
3. Choose a function on the Function Selection under Settings tab.
4. Set the Multi-Data Fit Mode to Global Fit on the Data Selection under Settings tab.
5. On the Parameters tab, you can Share Parameters and on the Constraints under Code tab, you can check the Enable Linear Constraints checkbox and enter constraints as needed. For example, if fitting with Gauss, where each peak has the same width, you would check the Share checkbox for Param w. If fitting with Boltzmann, where basically one Boltzmann is "sitting on top of another", so the top asymptote (A2) of the lower Boltzmann is matched with the lower asymptote (A1) of the upper Boltzmann, you would enter the constraint as A1_2 = A2.

Keywords:replica, peak, repeat