3.168 FAQ-1177 How to define a constant related to input data in a fitting function?

Last Update: 6/6/2023

If your user-defined fitting function has constant related to input data, you can define it as a parameter and fix it to initial formula.

For example, to define following fitting function

y = y_min + (y_max-y_min)*exp(-k*x)

where k is the parameter to calculate, and y_max and y_min are constants related to input data - y_max is the maximum of Y dataset and y_min is the minimum.

To define constant y_max and y_min in Origin,

  1. In Fitting Function Builder > Variables and Parameters page, define k, y_max, and y_min as Parameters.
    User Define Constant FAQ 1177 1.png
  2. On the Parameter Initialization Code page, specify Initial Formula for y_max and y_min by clicking the triangle button and selecting the desired formula in the fly-out list.
  3. Check Allow Initializing Fixed Parameters to fix y_max and y_min to their initial values.
    User Define Constant FAQ 1177 2.png

Keywords:user defined function, initial value, nonlinear curve fit, constant, metadata