The Least-Squares Fit function () defines a least-squares fit of a function to the input data, which can be a file, a local table, or a result table. The function can be a general mathematical function with parameterized expressions, such as a+b*cos(x1)+c*sin(x2)+x3+x4^2. The default Function name is lsq1_fun1. The least-squares fit can have multiple function outputs. If a second output is added, it will become lsq1_fun2, a third will become lsq1_fun3, and so on.

Click the Fit Parameters button () to fix the data to the parameters of the function. The computed parameter values from the least-squares fit appear in the Parameters section below. Click the Plot button () to plot the function using the parameters from the least-squares fit. The input data also appears as green squares so that you can see how close those data points are to the fitted function.

Select a Data source — File, Local table, or Result table to define the data source for the least-square fit.

If you select File (the default), enter the complete network path and name of the data file in the Filename field, or click Browse to select a text or data file with data in the Interpolation Data dialog box. You can import data files with comma-separated, semicolon-separated, space-separated, and tab-separated data. You can also click the downward arrow beside the Browse button and choose Browse From () to open the fullscreen Select File window. Click the downward arrow for the Location menu () to choose Show in Auxiliary Data () to move to the row for this file in the Auxiliary Data window, Copy Location (), and (if you have copied a file location) Paste Location (). Also choose a decimal separator from the Decimal separator list: Point (the default) or Comma. Click Import () to import the data into the model; otherwise, COMSOL Multiphysics references the data on your file system. Click Export to save the least-squares data to a file and reference from there instead of including it in the model. Click the Discard button to delete the imported least-squares data from the model. Click the Refresh button ()to ensure that the file is reread when needed.

If you select Local table, enter the function argument values in Column 1 and the corresponding function values in Column 2. Click the Add Argument Column button () below the table to add a column for a new function argument. Click the Add Value Column button () to add a column for a new function value. Use the Delete Column (), Delete Row (), and Clear Table () buttons as desired to edit the table. Use the Load from File () and Save to File () buttons to load or save data to or from the table. You can also click the downward arrow beside the Load from File button and choose Load From () to open the fullscreen Select File window.

If you select Result table, choose the table to use from the Result table list.

When selecting a row in the Settings column, you can edit the name of the function or argument in the Name field underneath and also provide a unit in the Unit field. For the function, also enter the definition of the function in the Expression field, such as a1*x1+a0 for a linear function with two parameters, a0 and a1.

In the table in this section, add the parameters that are used in the function defined under Data Column Settings above and that should be computed using a least-squares fit. Type the name in the Parameter column. The original values in the Value column (default: 0) will be updated when you click the Fit Parameters button, using the values from the least-squares fit. Use the buttons underneath the table to move or delete parameters and to load or save the parameters and their values to or from a file.