# 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 1327 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**