Hmm, it LOOKS like mvpart may be along the lines of what I want, but is mvpart a nominal classification tree, or can it handle multiple, continuous response variables as well?

--j

Gene Leynes wrote:
This sounds very similar to what I've been working on, but I'm not sure without an example.

My solution has been to use an optimization that normalizes inside the objective function. The betas that are provided by optim are not normalized, however since they were normalized inside the objective function, normalizing them after the fact mirrors the internal workings of the objective function.

see this example:
http://markmail.org/message/ze5237m6gbgvvvyf

Still, after looking at several statistical packages, and considering the thoughtful responses from my post, I think that there must be a better way using existing models, so I've been looking at other packages / models.

On Tue, Apr 7, 2009 at 6:10 PM, Jonathan Greenberg <greenb...@ucdavis.edu <mailto:greenb...@ucdavis.edu>> wrote:

    R'ers:

      I was hoping I could get some direction on this.  I have a
    dataset of the form:

    Y1,Y2,...,YM = f(X1,X2,...,XN), where N is >>> M

    The response data (Y1,Y2,...,YM) is frequency data, such that the
    sum of all Yi = 1.0.  Both Xj and Yi are continuous variables.

    I'm trying to figure out the best approach(es) to solving for the
    model f() -- any ideas?  I could solve each Y one at a time, but
    the lack of constraint worries me, and I'm pretty sure that
    normalizing the data afterwards to sum to 1.0 is not going to work
    out properly.  Thoughts?  I've never worked with multiple response
    statistics before, so I'm mostly trying to get some pointers on
    where to begin investigating...

    --j

--
    Jonathan A. Greenberg, PhD
    Postdoctoral Scholar
    Center for Spatial Technologies and Remote Sensing (CSTARS)
    University of California, Davis
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    Cell: 415-794-5043
    AIM: jgrn307, MSN: jgrn...@hotmail.com
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