The Qwt library has a class QwtSpline which performs a spline interpolation. As far as I understand the user can decide whether a natural or a periodic cubic spline is desired. How the natural spline works is quite clear, but I need the periodic version, and here I have a question:
In order to determine the coefficients of the spline, the function needs to know the length of the period. How do I pass this information? If I have a p-periodic function that I want to interpolate, do I have to pass data points (x[i], y[i]), i = 0, 1, ..., n, with x[n] = x[0] + p and y[n] = y[0]?

Thanks for your help!