an interactive svg interpolation example

This svg example simulates dragging of the four points to be interpolated, using Bezier control points p_0, p_1, p_2, p_3, interpolating f[0],f[1],f[2],f[3]
p_0 = f[0]
p_1 = 1/6 (-5 f[0]+18 f[1]-9 f[2]+2 f[3])
p_2 = 1/6 (2 f[0]-9 f[1]+18 f[2]-5 f[3])
p_3 = f[3]

There exist other interpolations of these points.