I have updated the Alglib spline-matrix spreadsheet to use the latest Alglib release, using the Python version, in conjunction with the Excel-Python add-in. To use the spreadsheet requires:
In addition to using the latest Alglib library, the new spreadsheet updates the functions, providing added functionality in applying weights and constraints to fitted functions, and additional examples. The new spreadsheet may be downloaded from xl_Spline-Matrix.zip, including full open-source VBA and Python code linking to the Alglib library. The Alglib code may be downloaded from the link above.
The functions included in the spreadsheet are listed in the screenshot below:
The example below shows a quadratic curve fitted to scattered data with various options and constraints. Results from the Excel LinEst function are also included, which are the same as the Alglib function without weights and constraints.
The xl_LinFit function can be used to fit polynomial curves, as seen above, but this is more conveniently done with the xl_PolyFit function, which also gives much better results for high order polynomials.
Two functions are provided for non-linear fitting. xl_NLFitFunc fits any named Python function to the input data. The function code must be in the file NLFuncs.py.