[wenc]

> Imagine a polynomial (in the smooth space). You can capture a particular set of points that uniquely determines the polynomial. In some circumstances you can use these samples to reconstruct the original polynomial by interpolating between any of the two points.

This is not duality though and you do lose information.

For instance let’s say one has a cubic polynomial and one samples 5 points from it and stores those points. If one didn’t know the original order was cubic, and if one tried to interpolate over the 5 points to fit a quintic, that would be an incorrect reconstruction.

[adamnemecek]

You don't lose information if you pick your points correctly (you store only the extrema). In the cubic case, you need the two extrema (one minimum and one maximum and you need to know whether each extremum is a min or max) and then interpolate between them.

[wenc]

Unfortunately this is incorrect. Extrema do not always exist (consider y=x^3) and they do not uniquely define a polynomial (y=x^2 and y=x^4 both have minima at x=0).

[adamnemecek]

Unfortunately this is incorrect. Those minima are not the same. Remember that dual points have a real part and a dual part that indicates the rate of change at that point. The real part is the same but the dual is different.

[wenc]

My point is it’s not possible to uniquely reconstruct an arbitrary polynomial by just knowing the extrema because there may be information loss in the general case. I will stop here.

[adamnemecek]

It is possible if you know the rate of change which you do with dual points. Like you don’t interpolate just position but also the dual parts I.e. rate of change.