[18862] in s-news-athena
Re: [S] nls() fails in a loop
daemon@ATHENA.MIT.EDU (Henrik Aalborg-Nielsen)
Thu Aug 5 04:05:54 1999
Date: Thu, 5 Aug 1999 08:50:48 +0200 (METDST)
From: Henrik Aalborg-Nielsen <immhan@student.dtu.dk>
To: ROS Mathieu <mim78@cict.fr>
Cc: s-news@wubios.wustl.edu
In-Reply-To: <Pine.SGI.3.95.990804090248.12601A-100000@ondine.cict.fr>
Message-Id: <Pine.HPP.3.95.990805083901.20118A-100000@srv4.gbar.dtu.dk>
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Instead of restart(), which has been suggested by other readers of this
list, I would suggest a small modification of nls(). The idea is to
replace 'stop' in
if(z$control[5])
stop(switch(as.integer(z$control[5]),
"step factor reduced below minimum",
"maximum number of iterations exceeded",
"singular gradient matrix",
"singular design matrix",
"singular gradient matrix"))
with 'return'. In the function calling the modified nls() a test like
if(is.null(class(nls.output))) {
<things to do in case of non-convergence>
}
else {
<normal operation>
}
will then be appropriate.
On Wed, 4 Aug 1999, ROS Mathieu wrote:
> hello Splus users,
> I'm using nls() in a cross-validation loop (no way to avoid it now...)
> with 180 iterations but with my initial values
> (start(a=-50,b=10,c=-0,009)) it stops after some iterations
> with a 'step factor reduced below minimum' error.
> How can I handle this problem without entering new starting points at each
> step ?
> any help will be appreciated
>
> Mathieu
Regards,
Henrik
--------------------------------------------------------------------------
Henrik Aalborg Nielsen
Department of Mathematical Modelling
Section for Statistics Fax: +45 4588 1397
Time Series Group Phone: +45 4525 3418
Technical University of Denmark E-mail: han@imm.dtu.dk
Building 321, 2800 Lyngby, Denmark URL: http://www.imm.dtu.dk/~han
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