Excel - Cardinal spline & Cubic spline & Monotone Cubic Spline UDF
The demo file contains Cardinal Spline & Cubic Spline & Monotone Cubic Spline UDF that create curves that go exactly through all your data points. The advantage of a monotone cubic spline is that it does not 'wobble'. (If you want to interpolate both X and Y values within a 2-dimensional table, then see
Bilinear interpolation and its demo file that also includes spline based interpolation functions.)
Download demo file
(135kB - downloaded 1771 times - Latest version: 2022-01-11, now including both
regular function that returns a single Y value, given X and the datapoints, and
array function that creates a table with X and Y values, given the number of segments to be created between the datapoints provided.)
MS Excel VBA code to be put in a module - array functions
In MS Excel, press Alt+F11 to open the Visual Basic Editor (Windows). Via top menu: Insert → Module. Copy the MS Excel VBA code of the functions into the module.
Generic helper function to read range data into single dimensional array.
Your input data can now be column organized (default table) or row organized (transposed default table).
Cardinal spline
Cubic spline
Monotone cubic spline
Regular function - Single Y value output only, given X value
In MS Excel, press Alt+F11 to open the Visual Basic Editor (Windows). Via top menu: Insert → Module. Copy the MS Excel VBA code of the functions into the module.
Cardinal spline
Cubic spline
Monotone cubic spline