specification of corAR1()

Sorry to bother the list, I figured out where the problem is, I should specify the argument name "form=" in the corAR1():

lme(score~Machine,data=Machines2,random=list(Worker=pdSymm(~0+Machine)),correlation=corAR1(form=~time|Worker/Machine))

----- Original Message -----
From: array chip <arrayprofile at yahoo.com>
To: "r-sig-mixed-models at r-project.org" <r-sig-mixed-models at r-project.org>
Cc: 
Sent: Wednesday, August 10, 2011 10:07 AM
Subject: [R-sig-ME] specification of corAR1()

Hi all, I am struggling to learn to use corAR1() correlation structure. Let me use the Machines data set from nlme package as an example:

I added a time variable to create a new dataset:

Machines2<-cbind(Machines, time=c(1,2,3))

This one runs without any problem:

lme(score~Machine,data=Machines2,random=list(Worker=pdSymm(~0+Machine)),correlation=corAR1())

But all of the following generated the same error message:

lme(score~Machine,data=Machines2,random=list(Worker=pdSymm(~0+Machine)),correlation=corAR1(~time))
lme(score~Machine,data=Machines2,random=list(Worker=pdSymm(~0+Machine)),correlation=corAR1(~time|Worker))
lme(score~Machine,data=Machines2,random=list(Worker=pdSymm(~0+Machine)),correlation=corAR1(~time|Worker/Machine))

"Error in abs(value) : Non-numeric argument to mathematical function"

Did I misunderstand something here?

Thanks very much!

John

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