You can download a spreadsheet from here:
http://newtonexcelbach.wordpress.com/20 ... functions/which has four spline interpolation functions:
CSplineInt1D =CSplineInt1D(X Coords, Y Coords, UBX, End Type 1, End 1, End Type 2, End 2)
AkimSplineInt1D =AkimSplineInt1D(X Coords, Y Coords, UBX)
HSplineInt1D =HSplineInt1D(X Coords, Y Coords, Derivatives, UBX)
CRSplineInt1D =CRSplineInt1D(X Coords, Y Coords, UBX, End Type, Tension)
For these you need to evaluate the function as a number of points, and the functions will fit a spline to those points and return the integral.
You might also like to have a look at:
http://newtonexcelbach.wordpress.com/20 ... uadrature/which has routines that will evaluate the integral of a function entered as text, using the Tanh-Sinh method.