NONMEM Users Network Archive

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RE: eigenvalues

From: Matt Hutmacher <matt.hutmacher>
Date: Fri, 6 Nov 2015 15:37:53 -0500

Hello Pavel,

Could you share the COV matrices from Monolix and NONMEM? I have an =
idea of what could be going on, but it would be good to see the matrices =
to check if the hypothesis makes sense.




From: owner-nmusers
On Behalf Of Jeroen Elassaiss-Schaap
Sent: Friday, November 06, 2015 11:34
To: Pavel Belo
Cc: “nmusers
Subject: Re: [NMusers] eigenvalues


Hi Pavel,

For starters, it is simple to calculate using R:
  mymat <- mymat /max(mymat)
 #replace mymat with your nonmem $cov matrix
  eigenval<-eigen(mymat,symm=T)$values # should be similar to nonmem =
  cn1<-max(eigenval)/min(eigenval) # could be compared to the "PK" =
parameters ratio from monolix

Assuming a 25x25 covariance matrix, and theta in 1:10. You will need to =
do some rearrangement of the cells to isolate the off-diagonal elements =
of $OMEGA, but with this approach you can compare apples by apples. =
Until you have done that you will not know whether the platforms provide =
different results or similar wrt the condition number.

The difference in behavior with respect to objective function impact is =
puzzling, assuming you refer to SAEM estimation in Nonmem. My advice =
here would be to focus on (visual) predictive checks, and compare how =
well the two platforms perform on that aspect.

Hope this helps,

+31 6 23118438
-- More value out of your data!

Received on Fri Nov 06 2015 - 15:37:53 EST

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