A cubic spline routine was developed for unequally spaced sequential data points. Cubic spline theory is reviewed. A Visual Basic computer program in Excel was created to fit a spline to input data points. Three testcases are used to validate the routine. Conclusions regarding the cubic spline routine are made.

This project’s documentation is available at cubicspline.pdf.

The Excel code is available at cubicspline.xls.

For a numerical methods mini-project, this document has generated a surprising amount of email. There is apparently a demand for spline interpolation. Please visit my consulting page for support or more information.