[R] Error 'singular gradient' in nonlinear model fitting

[Ravi Varadhan]

Try a different set of starting values for alpha & beta.

Ravi.

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Ravi Varadhan, Ph.D.

Assistant Professor, The Center on Aging and Health

Division of Geriatric Medicine and Gerontology 

Johns Hopkins University

Ph: (410) 502-2619

Fax: (410) 614-9625

Email: rvaradhan at jhmi.edu

Webpage:  http://www.jhsph.edu/agingandhealth/People/Faculty/Varadhan.html

 

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-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On
Behalf Of HongSheng Liao
Sent: Friday, February 15, 2008 12:42 PM
To: r-help at r-project.org
Subject: [R] Error 'singular gradient' in nonlinear model fitting


w.age.female.2004 <- nls(WEIGHT ~ (alpha*TOTAL^beta)/454,
                        start=list(alpha=1, beta=3),
                        data=spottedseatrout2004.female.data)

I am trying to fit above model to length-weight data of a fish species
(spotted seatrout) by year (1999-2006).  The convergence occurred for all
the years except 2002 and 2004.  In these two year, R shows the error
called 'singular gradient' in the model.  Could anyone please help me to
fix the error?  I don't think there are any problems with my data because I
can fit the same model to 2004 data without any problems using SAS.  Thank
you very much in advance.

Hongsheng (Hank) Liao, Ph.D.
Lab Manager
Center for Quantitative Fisheries Ecology
800 West 46th Street
Old Dominion University
Norfolk, Virginia 23508
Phone:757.683.4571
Fax:757.683.5293

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