I am looking for math software that will fit a set of points with a cubic spline (or other technique)....then allow the user to change the shape of the curve by dragging it...and continuously fit the curve as the dragging is occurring (or fit the curve after the dragging has stopped). The point on the curve that is being dragged must not deform it enough such that the curve becomes discontinuous. Does such software exist? I have been working on generating a set of curves that will help solve an engineering problem I am working on...but each time I apply a new curve, I am finding I must readjust it. Finding a new set of curves takes a couple of hours....considering this is an iterative process...I may be working on this problem forever. Any suggestions would be great.