R help - Mar 2009 - Find inflection points using smooth.spline

Is there any way to identify or infer the inflection points in a smooth
spline object?  I am doing a comparison of various methods of time-series
analysis (polynomial regression, spline smoothing, recursive partitioning)
and I am specifically interested in obtaining the julian dates associated
with the inflection points inferred by the various models.

Tyler

e.g.  http://www.nabble.com/file/p22752459/smooth.spline.pdf
smooth.spline.pdf 
-- 
View this message in context:
http://www.nabble.com/Find-inflection-points-using-smooth.spline-tp22752459p22752459.html
Sent from the R help mailing list archive at Nabble.com.

T.D.Rudolph <prairie.picker <at> gmail.com> writes:
> 
> 
> Is there any way to identify or infer the inflection points in a smooth
> spline object?  I am doing a comparison of various methods of time-series
> analysis (polynomial regression, spline smoothing, recursive partitioning)
> and I am specifically interested in obtaining the julian dates associated
> with the inflection points inferred by the various models.
> 
> Tyler
> 
> e.g.  http://www.nabble.com/file/p22752459/smooth.spline.pdf
> smooth.spline.pdf 

You can get an analog of first and second derivatives via using first and 
second differences:

?diff

If your spline object is spl, try:

diff(diff(spl))

It's possible that you would find lag and rle functions useful as well.

-- 
David Winsemius