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Simple Fit.opx
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A simplified tool to perform curve fitting.

Screen Shot and Video:

This tool provides a convenient way to perform curve fitting. With the data plotted, simply open the tool, type the desired equation, specify initial parameters and generate your report. You do not need to even save or create a fitting function.

The tool only supports one independent variable (x) and one dependent variable (y).

Download the file Simple Fit.opx, and then drag-and-drop onto the Origin workspace. An icon will appear in the Apps Gallery window.


  1. Create a graph of the XY data with optional error bars, and click the Simple Fit app icon.
  2. Choose one of the fitting types: linear, polynomial, or nonlinear.
  3. If error bar is present in the graph, you can optionally perform a weighted fitting (weighting method: instrumental) by checking the Weighted Fit check box.
  4. If there are multiple plots in the graph, you can optionally fit all plots (individually) by checking the Fit All Curves in the Graph check box.
  5. To display the 95% confidence/prediction band, check the corresponding check box.
  6. When performing nonlinear fitting:
    1. Define the fitting function:
      • To use an existing function, check the Use Existing Function check box and select desired function.
      • To use a new function, uncheck the Use Existing Function, enter the function definition into the "y(x)" edit box, using "x" as independent variable.
    2. Specify or change desired initial parameter values.
    3. Click the 1 Iter. button to perform one iteration at a time, or the Fit button to perform iterations until the tolerance is reached or the maximum number of iterations (400) has reached. Before each operation, you can change or fix parameter values.
      The last column about statistics can be changed to show one of Residual Sum of Squares, Reduced Chi-Sqr, R-Square and Adj. R-Square by context menu.
    4. To save the fitting function, click the Save as... button. The fitting function will be saved in User Defined category.
      If you do not save the function, it will not be available for selection next time the tool used.


  • when performing linear regression, the last column about statistics can be change to show one of Residual Sum of Squares, Pearson's r, R-Square and Adj. R-Square by context menu.
  • When performing weighted fitting, the error values reported on the fit parameters are NOT scaled by the sqrt(reduced chi-square) value.


v4.2 Bug fix.
v3.1 Span to full axis range.
v3 Bug fix.
v2.6 Report more details about linear regression.
v2.5 Localization.
v2.3 Bug fix.
v2.2 Bug fix.
v2.1 More data points in fitted curve.
v2 Support multiple datasets in nonlinear fitting as well as linear fitting and polynomial fitting.

Reviews and Comments:




07/06/2022OriginLabHi Chitra,

"NANUM and masked weights are excluded". It means if your y error includes missing values, points with missing values as y error will be excluded in the analysis.

In Linear tab, it uses line function. In Nonlinear tab, the equation is the one you typed in the dialog's edit box.

This app is just a simple form of Origin's built-in fit tools. You can see the detailed interpretation in Origin's document.

07/06/2022Chitra Shuklahw I have performed linear regression and fixed the errors with intercept. this automatically enhances our Rsquare value. Simple fit report shows WEithed Fit: Enabled (NANUM amd masked weights are excluded).
What does really mean?
How can we access which equation this app is using?
Jow can we interpret these results in our researc manuscript if details are not available?




05/25/2022 u-n