---------- Forwarded message ----------
From: Diego Rojas <dirojasb@gmail.com>
Date: Wed, May 9, 2012 at 3:05 PM
Subject: Re: [R] Finding local maxima on a loess surface
To: David Winsemius <dwinsemius@comcast.net>


Thanks again, would you please try to ilustrate further your point with
this example code. How would you find the coordinates for the maxima on the
surface. Consider that in the surface I'm dealing with there are at least
35 maxima.

require(MASS)
topo.lo <- loess(z ~ x * y, topo, degree = 1, span = 0.25,
                 normalize = FALSE)
topo.mar <- list(x = seq(0, 6.5, 0.1), y = seq(0, 6.5, 0.1))
new.dat <- expand.grid(topo.mar)
topo.pred <- predict(topo.lo, new.dat)
## draw the contour map based on loess predictions

library(rgl)

persp3d(topo.mar$x, topo.mar$y, topo.pred, shade=0.5, col="blue")

Thanks fot your help

On Sat, May 5, 2012 at 9:34 AM, David Winsemius <dwinsemius@comcast.net>wrote:

>
> On May 4, 2012, at 3:00 PM, Diego Rojas wrote:
>
> Thanks, I know about it but i wat to find several local maxima, so in
>> other words I need a way to identify the places in the surface where both
>> slopes are equal to 0 and the second derivative is negative.
>>
>
> There is no way that I know that will produce a mathematical function that
> would support symbolic manipulations of that sort for the results
> obtainable from a loess-object. I was expecting that you would be
> approaching this numerically and doing evaluations on a grid. Testing for
> equality to 0 is not a good practice if following that route. Sign reversal
> would be a more sensible criterion. ( And you _would_ be using
> predict.loess(). )
>
> Still no data example or code offered, so not pursuing further efforts at
> illustration.
>
>
>
>> On Fri, May 4, 2012 at 9:28 AM, David Winsemius <dwinsemius@comcast.net>
>> wrote:
>>
>> On May 3, 2012, at 6:09 PM, Diego Rojas wrote:
>>
>> If a run a LOESS model and then produce a smoothed surface: Is there any
>> way to determine the coordinates of the local maxima on the surface?
>>
>> ?predict    # it has a loess method.
>>
>>       [[alternative HTML version deleted]]
>>
>>
> David Winsemius, MD
> West Hartford, CT
>
>

	[[alternative HTML version deleted]]

