1.3 Tangent


This Tangent app is for plotting the tangent line along a curve. When using this app, Origin adds a vertical line to the graph, allowing you to move the vertical line to select a point from curve.

A Tangent Preferences dialog is available from the fly out menu. You can save tool settings to a theme file for later use.


Create the Tangent Line

  1. Import Exponential Decay.dat in the <Origin EXE Folder>\Samples\Curve Fitting\ folder. Select Column B, and then select Plot: Basic 2D: Line+Symbol menu to make a Scatter plot.
  2. When the graph is active, click Tangent icon Tangent icon.png from the Apps panel of Origin to open the app's dialog box. When the dialog is open, you can click F1 key open the help file for it.
    Tangent App 01.png
  3. Click OK. You will see that a red vertical line and a blue tangent line are added to the plot. The value of slope is shown at the top. The tangent point is intersected point of the two lines.
    Note: The tangent point will be a data point on the graph.
    Tangent App 02.png
  4. To select the tangent point, drag the red vertical line to select the data point on the curve. As you do this, displayed information regarding the tangent point, is updated.
    Tangent App 04.png

Modify the Smooth method

When the curve is not smooth, the tangent line may not be well-fitted to the curve. In such cases, we can use smoothing to affect the calculated derivatives. This tool supply the Smooth method, On the Derivative tab of the Tangent Preferences dialog box, choose B-Spline or Savitzky-Golay from the Smooth list.

  1. Click the Triangle button.png triangle button at the top right corner of the layer, and select Preferences... from the context menu to reopen Tangent app's settings dialog.
    Tangent App 03.png
  2. Go to the Derivative tab, choose B-Spline as smoothing method
    Tangent App 05.png
    Tangent App 06.png

Output the result

You can update output for the tangent line using the fly-out menu of the app. Also, you can customize the output data and position on the Output tab of Tangent Preferences dialog.

Tangent App 07.png