The Nonlinear Least Squares Fitter (NLSF)

One of the most powerful and sophisticated components of Origin is its nonlinear least squares fitter, or NLSF. The NLSF allows you to fit a function, or a set of functions, to one or more data sets. Each function, or set of functions, can depend on one or several dependent and/or independent variables and up to 200 parameters and constants. The function can even be represented in terms of the partial derivatives of each parameter! There are nearly 200 built-in functions included with the NLSF. These function are divided into categories of disciplines in science and engineering. An intuitive graphical interface displays the equation, or set of equations, and sample curve for the function selected. Should you be unable to find the function you require among the built-in functions, define a function and Origin will fit it to your data. Once you have your function selected (or created), the NLSF can fit:

•   one dataset to that function with:
  
  
  • weighting
  • multiple peaks (certain peak functions only) and shared peak parameters
  • multiple dependent and/or independent variables
    
    
•   multiple datasets to that function with:
  
  
  • shared parameters between datasets (global curve fitting)
  • weighting for each dataset
  • multiple peaks (certain built-in peak functions only) and shared peak parameters
  • multiple dependent and/or independent variables

While fitting, you also have the option to:

•   Initialize
•   Impose linear constraints
•   Fix up to all but one parameter
•   Plot confidence and prediction bands, as well as a residual curve
•   Adjust the tolerance value which determines when the fit has converged

Click on the image above to learn more about the Nonlinear Curve Fitter by window.
To learn more about nonlinear curve fitting in general, read the "Primer" called "Curve Fitting made easy" that was written by one of our senior developers for the Industrial Physicist web site.