Non linear curve fit
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## Non linear curve fit

This dialog is activated by selecting the command Non Linear Curve Fit... from the Analysis Menu. This command is active if a plot is active and is not active is a table is selected.

This dialog is used to fit discrete data points with a mathematical function. The fitting is done by minimizing the least square difference between the data points and the Y values of the function.

The top of the dialog box is used to choose a function among the one which are already define. Four types of functions are availables: the user defined functions which have been save, the classical functions proposed by QtiPlot in the analysis menu, the simple elementary built-in functions, and external functions via pluggins.

To choose one of these functions, you just have to select it and to click on the checkbox under the selector.

If you want to define your own function, you can use the bottom half of the dialog box. You can write you own mathematical expression or add expressions obtained with the function selector. Then you need to define the parameters which have to be fitted in a comma separated list.

Figure 5.32. The first step of the Non Linear Curve Fit... dialog box.

This first step is used to define the function which will be used for the fitting

The second step is to define the parameters for the fit. Your have to give initial guess for the fitting parameters.

Figure 5.33. The second step of the Non Linear Curve Fit... dialog box.

This second step is used to define the parameters of the fitting

After the fit, the log window is opened to show the results of the fitting process.

A new table is created for each fit, it include all the X and Y values used to compute and to plot the fitted function. This table is hidden by default, but it can be found and viewed with the project explorer.

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