Nonlinear Least Squares Curve Fitting
4 Parameter version.
Colby College Chemistry, T. W. Shattuck, 8/28/2015
- For 3-parameter equations use 3-parameter version
The x-y pairs should be input one pair per line with the x value
(the independent variable) first. The x and y values can be separated
by spaces, a tab, or a comma. You can copy and paste from Excel.
Examples of the uses of the fit functions.
You need to input rough guesses for the fit parameters. Sometimes just guessing "1" for
each parameter will work.
For fitting functions with a "c" parameter, you can choose to fix the value.
This option allows you to use "c" as a parameter without varying the value
during least squares adjustment.
If the calculation doesn't converge,
Try using convergence damping.
In cases of slow convergence, enter the results from the previous
non-converged run as guesses for the next run.
Use the "Fit values from initial guesses" output to refine your guesses. In other
words, vary your input guesses to decrease the initial residuals.
Leave the guess for any unused parameter blank.
To print the plot, pull down the File menu and select Page Setup... Set the Print Background Colors and Images checkbox.
For fitting a user input function see John Pezzullo's
Nonlinear Least Squares Curve Fitter.