Re: Inflection Point Detection

[bpabbott]

On Mar 15, 2011, at 09:50 AM, aegreen <address@hidden> wrote:

bpabbott wrote:
>
> One approach would be to use mkpp, ppder, and ppval. I haven't tested
> this, but ...
>
> pp = mkpp (x, y);
> pp2 = ppder (ppder (pp));
> d2y_by_dx2 = ppval (pp2, x);
> n = find (abs (d2y_by_dx2) == max (abs (d2y_by_dx2)));
> x_inflection = x(n)
>
> Ben
>

I can't seem to get the first step to work. mkpp requires parameters of X, P
or X, P, D. Where P are coefficients? Sorry I am not very familiar with this
at all. I appreciate all the help.

 

My mistake. I should pointed you to spline (still untested by me).

pp = spline (x,y);

pp2 = ppder (ppder (pp)); d2y_by_dx2 = ppval (pp2, x); n = find (abs (d2y_by_dx2) == max (abs (d2y_by_dx2))); x_inflection = x(n)

Ben