On Mon, 9 Jun 2008, Ayman Oweida wrote:
After many months, I am now banging my head against the wall because I can't find a
solution to this seemingly trivial problem. Any help would be appreciated:
I am trying to apply a nonlinear fitting routine to a 3D MR image on a voxel-by-voxel basis. I've
tested the routine using simulated data and things went well. As for the real data, the fitting
routine works variably. By variably, I mean the following: with a specific set of
starting parameters the routine would work for the first 10 voxels, for another set of starting values the
routine would work for the first 1000 voxels and so on. NEVER was I able to get starting values
that would allow the routine to run entirely! The error I would get after fitting the limited
number of voxels is:
"Error in approx(x, fx, n = 2 * n.pts + 1) :
need at least two non-NA values to
interpolate"
I think the error is from the library Bolstad since I'm using the
sintegral function as part of the fitting equation. I've tried
numerous nonlinear functions including: nlm, optim and nlminb, but all
stop after performing the fit on a limited number of voxels. I
took the values for which the fitting routine stops and I applied
different starting values to them and it works! I'm still using
the same voxel/parameter values and I am sure they are not NA values as
per the error!
Reread the error message. It does NOT say that there are NA values. It
only says that you 'need at least two non-NA values'.
Ok, I think the problem is clear. any solutions?
The problem is not clear.
Here is some advice:
PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html and provide commented,
minimal, self-contained, reproducible code.
Often, developing the 'minimal' example helps you to perceive the
underlying difficulty. Without it, you will only get very general advice
and off-hand guesses about where your problem lies, which may not move you
closer to a solution.
---
So here is some of that general advice: find out why approx() sends you
that error message.
One way to do this is to set
options(error=recover)
before running your function. And then inspect objects in the frame in
which the error occurred and in the frames leading up to the one in which
the error was triggered. See
?recover
HTH,
Chuck
I am new to this complex world of statistical analysis.
Your help is very very much appreciated.
Thanks,
Ayman
Montreal Neurological Institute
Montreal, Canada
[[alternative HTML version deleted]]
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
Charles C. Berry (858) 534-2098
Dept of Family/Preventive Medicine
E mailto:[EMAIL PROTECTED] UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/ La Jolla, San Diego 92093-0901
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
