Customers has the requirement to fit a 3D scattered plot with a nonlinear curve and draw the fitted curve on top of the scattered plot. This can be achieved by creating user’s own multivariate fitting functions y=f(x) and z=g(x). In this example, assume user has the dataset plotted as 3D points in the following graph and wants to fit the points with two functions: y = a + b*x and z = c0 + c1*x + c2*x^2 + c3*x^3, we will show how to perform the fitting and make the fitted curve plot. Please download the attached zip file and open the opj in Origin to follow the steps below.

1. Select menu **Tools:Fitting Function Organizer…** to open the dialog. In the left select the User Defined folder. Click New Function button on the right to start define a new fitting function. In **Function Name** text window, enter a name **LinePoly3**. Set **Independent Variables** as **x**, **Dependent Variables** as **y, z**，**Parameter Names** as **a,b,c0,c1,c2,c3**. In the Function edit box, enter:

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y = a*x + b; z = c0 + c1*x + c2*x^2 +c3*x^3; |

2. Scroll down to **Parameter Settings** section, click on the button besides the editing box to open up the **Parameter Settings** dialog. Set all the initial values to 1. Click** OK** to close the dialog, then click **Save** to save the function.

3. Open the opj file Highlight the entire worksheet, select from menu **Analysis: Fitting: Nonlinear Curve Fit…** to open the dialog. With **Settings** tab activated, select **Function Selection** in the left panel. In the **Category** dropdown list, select** User Defined**. In **Function** dropdown list, select function **LinePoly3** just created. The fitted curves with initially-guessed parameters are also displayed in the bottom panel. Click **Fit** to perform the fitting.

4. Go to the result sheet **FitNLCurve1**, Highlight column C, right click and select from context menu **Set as: Z**. Move the mouse to the left/right edge of the highlighted column until the cursor changes to graph shape, press down mouse and drag to the original 3D plot.

5. The fitted curve is now addedto the graph. Double click the new plot to enter the plot details dialog, make the following customization to obtain the final graph.

## 2 Responses

## Tien

can you help me smooth 3-D surface plotting from data sheet. Thank you so much.

My email tien.ntan@gmail.com

Thank you so much.

## snow

Please email tech@originlab.com with your product Serial Number for technical support.

Thanks, Snow