Hi,

 

I just wonder if R is still used for PK analysis. However, I have to use R
for some purposes anyways. Here is a really strange problem I am running
into and I hope to get some assistance from the group. The following code
works fine in S-Plus (Population estimates and MAP estimates look reasonable
).

 

cs.fit<-nlme  (  CONC~phenoModel(CID,TIME, DOSE, lCl, lV),

fixed = lCl+lV ~1, random = pdDiag(lCl+lV ~1),

data = cs1grp, start = c(-5, 0), na.action=na.include, naPattern = ~
!is.na(CONC)

                     )

 

But if I run the same problem in R, I get the following error: "Error in
chol((value + t(value))/2) : the leading minor of order 1 is not positive
definite"

 

These are simulated data with a total of 100 subjects studied at one dose
level and rich sampling scheme. (I can send the dataset, if required. I had
some unsuccessful attempts to send by default). If it was a problem with
parameterization of the model , I don't understand how come sparse sampling
in generic "Phenobarb" data does not have a problem in R or S. BTW, the
exact same code for "Phenobarb" runs in R and S-Plus w/o any modification
needed.

 

Thank you in anticipation.

 

Pravin

 

Pravin Jadhav

 


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