The Excel Spline-Matrix spreadsheet has now been updated with several new spline interpolation functions.  See Alglib/Python linear and non-linear fitting functions for links to download and install the necessary Excel-Python and Alglib files.  Also required is Python version 2.7 or 2.6.

The spline functions included in the new version are:

Of which, the new ones are:

xl_PSpline: Parametric spline interpolation

The parametric spline function generates a smooth curve through a series of points, which need not be in order of increasing X.  Output may be specified to be periodic, in which case the curve is extended to the starting point, with slopes adjusted to provide a smooth curve throughout:

xl_Ratinterp provides rational interpolation without poles.  See the Alglib User Guide for background information.

xl_RatInterp output compared with a cubic spline

xl_Spline3D provides 3D Cubic spline interpolation.  The screenshot below shows a very simple example, taken from the Alglib manual.

xl_RBF and xl_RBFGrid provide Radial Basis Function interpolation.  Again see the Alglib User Guide for background information.

In this example the xl_RBF function is used to interpolate concrete shrinkage data, as used in the xl_NonLinFit example:

The xl_RBFGrid function provides the same results, but with more convenient data input, when 2D data is arranged in grid format.