I want to be able to draw a smooth curve through my data points. However, I have noticed that XRT/graph does not provide any curve fitting functionality. Is there any way I can do what I want?
XRT/graph is designed to display the data provided to it as best it can. It was never intended to provide data analysis functionality.
However, since XRT/graph will display any data you want in almost any way you want, you can still draw a fitted curve _provided_ that you calculate the data required yourself.
The following example program does just that, using the cubic spline interpolation algorithm.