R help - Sep 2003 - Error from gls call (package nlme)

Hi
I have a huge array with series of data. For each cell in the array I
fit a linear model, either using lm() or gls()

with lm() there is no problem, but with gls() I get an error:

	Error in glsEstimate(glsSt, control = glsEstControl) :
        	computed gls fit is singular, rank 2

as soon as there are data like this:
	> y1 <- c(0,0,0,0)
	> x1 <- c(0,1,1.3,0)
	> gls(y1~x1)
	Error in glsEstimate(glsSt, control = glsEstControl) :
	        computed gls fit is singular, rank 2

of course, this is not a problem for lm()

	> lm(y1~x1)
 
	Call:
	lm(formula = y1 ~ x1)
	 
	Coefficients:
	(Intercept)           x1
	          0            0

I know, that such data does not make "sense" but it is possible, that
something like this occurs in my data-set. Since I call gls() for every
cell of my array in a loop, I don't want such errors to occur, since
this breaks my loop.

what is the problem here? What are potential solutions?

Many thanks

Christoph
-- 
Christoph Lehmann <christoph.lehmann at gmx.ch>

For a quick fix see ?try, in particular the last example there.

Afraid I am no expert in gls (which, you might mention, is in
package nlme) to explain the real cause of the problem.

> -----Original Message-----
> From: Christoph Lehmann [mailto:christoph.lehmann at gmx.ch]
> Sent: 25 September 2003 12:32
> To: r-help at stat.math.ethz.ch
> Subject: [R] Error from gls call (package nlme)
> 
> 
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> 
> Hi
> I have a huge array with series of data. For each cell in the array I
> fit a linear model, either using lm() or gls()
> 
> with lm() there is no problem, but with gls() I get an error:
> 
> 	Error in glsEstimate(glsSt, control = glsEstControl) :
>         	computed gls fit is singular, rank 2
> 
> as soon as there are data like this:
> 	> y1 <- c(0,0,0,0)
> 	> x1 <- c(0,1,1.3,0)
> 	> gls(y1~x1)
> 	Error in glsEstimate(glsSt, control = glsEstControl) :
> 	        computed gls fit is singular, rank 2
> 
> of course, this is not a problem for lm()
> 
> 	> lm(y1~x1)
>  
> 	Call:
> 	lm(formula = y1 ~ x1)
> 	 
> 	Coefficients:
> 	(Intercept)           x1
> 	          0            0
> 
> I know, that such data does not make "sense" but it is possible,
that
> something like this occurs in my data-set. Since I call gls() 
> for every
> cell of my array in a loop, I don't want such errors to occur, since
> this breaks my loop.
> 
> what is the problem here? What are potential solutions?
> 
> Many thanks
> 
> Christoph
> -- 
> Christoph Lehmann <christoph.lehmann at gmx.ch>
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://www.stat.math.ethz.ch/mailman/listinfo/r-help
>
 

Simon Fear
Senior Statistician
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Tel: +44 (0) 1379 644449
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