Thanks, Uwe. Actually, I didn't mean to make this complicated--simple vector x and values at x in a vector y. Just wanted to determine the local minima and maxima of y[x], but y is not continuous (but is a "smooth" function of x). I will probably use hist or density to do it and then look at these curves or cuts.
Sean On Jun 15, 2005, at 8:16 AM, Uwe Ligges wrote: > Sean Davis wrote: > >> I have data in the form of (x,y) pairs and would like to find local >> minima and maxima (typically the zeros of the 2nd derivative) of the >> y values. I looked at numericDeriv, but I don't have an "expression" >> per se. I looked at optim, also, but it looks like it will find only >> one "global" max or min. I can code up my own piecewise derivatives, >> but wondered if there is an existing function to do this. > > If you don't have derivatives, and you don't have an expression, and > you don't have a criteria how to minimize, please tell me of any known > method that can handle your problem well enough. > > You could look whether y[i-1] <y[i] and y[i+1]<y[i] if y is ordered > according to x, if this most trivial and very non-robust method fits > to your definition... > > Uwe Ligges > > >> Thanks, >> Sean >> ______________________________________________ >> [email protected] mailing list >> https://stat.ethz.ch/mailman/listinfo/r-help >> PLEASE do read the posting guide! >> http://www.R-project.org/posting-guide.html ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
