Since it was first published in 2009 my CSpline function has been the most popular download from this site. CSpline (and various associated functions) is used to fit a series of cubic curves through specified points, allowing interpolation along a smooth curve.
The latest version of the spreadsheet is:
The original function is described at Cubic Splines. This was further developed in response to a reader query at Using Cubic Splines in Practice and Cubic Hermitic and Cardinal Splines, and most recently Spline Interpolation Alternatives provided some “on-sheet” methods with similar functionality.
Related spreadsheets were described in Daily Download 13: The ALGLIB maths library and Excel (covering the ALGLIB spline functions) and Daily Download 4: Continuous Beam Analysis (covering the use of cubic splines to model continuous beams, and the SplineBeam function).
The remaining curve generating spreadsheet is:
This includes a function to generate the coordinates of any specified catenary curve, with an option to find the tension force at any point. For more details see A catenary function.