NONMEM Users Network Archive

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OMEGA off-diagonal elements parameterized as correlations

From: Paolo Denti <paolo.denti>
Date: Wed, 08 Jul 2009 14:36:37 +0200

Dear all,
I was wondering if it is possible to insert the off-diagonal elements of
OMEGA as correlations rather than covariances, because I find it more

To my greatest happiness, I found the following information in a NONMEM
chm help file:

 | |
 | $OMEGA |

 MEANING: Supplies initial estimates for the NONMEM OMEGA Matrix
 CONTEXT: NM-TRAN Control Record

         [[value1] [value2] [value3] ... [FIXED]] 5
         [[value1] [value2] [value3]] ... L

 $OMEGA BLOCK(3) 6. .005 .3 .0002 .006 .4

Reading on in the file, the [COVARIANCE|CORRELATON] sounded (in spite of
the incorrect spelling) like the panacea I was looking for.
Unfortunately, when I try to compile, I get a message saying that this
option is not available in NONMEM VI. :-(
Is this sadly only a feature planned for future versions of NONMEM?
And if so, does anyone you know of other simple workarounds to use
correlations instead of covariances?

Thank you in advance,

Paolo Denti, Post-Doctoral Fellow
Division of Clinical Pharmacology
Department of Medicine
University of Cape Town

K45 Old Main Building
Groote Schuur Hospital
Observatory, Cape Town
7925 South Africa
phone: +27 21 404 7719
fax: +27 21 448 1989
email: paolo.denti
Received on Wed Jul 08 2009 - 08:36:37 EDT

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