4.2.2.31 Modifying Derived Parameters in Build-in Functions

Summary

Derived parameters are additional parameters computed using the fitted parameter values. You can define your own derived parameters for any built-in or user-defined fitting functions.
They are not involved in the fitting process and are computed only at the end of the fitting session.


What you will learn

  • How to add derived parameters in a built-in fitting function by Fitting Function Organizer.
  • How to remove derived parameters in a built-in fitting function by Fitting Function Organizer.

Adding Derived Parameters

    The built-in Gauss function fits the peak area with the following equation: y=y_0+\frac A{w\sqrt{\pi/2}}e^{-2\frac{(x-x_c)^2}{w^2}}
    Suppose that you also want to know the peak height, which can be computed as follows: h=\frac A{w\sqrt{\pi/2}}

  1. Select Tool: Fitting Function Organizer in the menu. In the left panel of the dialog, select Origin Basic Funcions: Gauss.
  2. Go to Derived Parameters section and input the h=A/(w*sqrt(PI/2))

    Add Derived Para 01a.png

    Note:
    • Each derived parameter should be specified in a separate row.
    • Derived parameters cannot be computed from other derived parameters.
  3. Click on Save and the OK button.
  4. Create a new workbook and import the data file \samples\curve fitting\Gaussian.dat, using Data: Import from File: Single ASCII.
  5. Highlight column A and B, then select Analysis: Fitting: Nonlinear Curve Fit to open the Nonlinear Curve Fitting dialog, and select Gauss from the Function drop-down list.

    Add Derived Para 04a.png
  6. Go to Code tab and click Derived parameters on the left panel. You can see the Derived Parameters listed on the right panel.

    Add Derived Para 02a.png
  7. Click Fit button to generate report sheets. After fitting, Origin will compute the height and include the result in the Parameters table on the fitting results worksheet.

    Add Derived Para 03a.png
  8. If you want to obtain the confidence interval for derived parameters, you can click on the green lock and select Change Parameters to go back to the NLFit dialog. Click Advanced option under Settings tab, expand Quantities node on the right panel and check the LCL and UCL checkboxes under Fit Parameters branch. Click Fit button to recalculate.

    Derive LCL.png
  9. Then confidence interval 95% LCL and 95% UCL are calculated for both parameters and derived parameters as below:

    Derive LCL1.png

Removing Derived Parameters

You can also remove derived parameters from result sheet. Continue with the tutorial above, follow the steps below:

  1. Select Tool: Fitting Function Organizer in the menu to open the dialog again. In the left panel of the dialog, select Origin Basic Functions: Gauss.
  2. Go to Derived Parameters section and remove expression h=A/(w*sqrt(PI/2)) from that panel.

    Add Derived Para 05a.png
  3. You may need to wait one or two seconds before the Save button is enabled. Click Save button and then OK button to close dialog.
  4. Click on the green lock on the top left corner in result sheet FitNL1 to change parameters and click Fit button again in the appeared NLFit (Gauss) dialog. We will see the derived parameter h has been removed from result table.

    Add Derived Para 06a.png