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Simulations with OMEGA BLOCK

From: Lindauer, A <andreas.lindauer2>
Date: Tue, 8 Oct 2013 10:22:08 +0200

Hi NMUSERS,

I have a question regarding the use of OMEGA BLOCK statements in simulations when one (or more) elements of the matrix are 0.

When I use the following lines to describe the OMEGA structure and run the simulation everything works well:

$OMEGA
0 FIX ; IIV_CL2
0.1 ; IIV_V2
0.1 ; IIV_F1
0.01 ; IIV_KA
$OMEGA BLOCK(1) 0.01 ; IOV_KA
$OMEGA BLOCK(1) SAME
$OMEGA BLOCK(1) SAME
$OMEGA BLOCK(1) SAME

However, rewriting the above as a full matrix gives me an error message:

$OMEGA BLOCK(8)
 0 FIX
 0 0.1
 0 0 0.1
 0 0 0 0.01
 0 0 0 0 0.01
 0 0 0 0 0 0.01
 0 0 0 0 0 0 0.01
 0 0 0 0 0 0 0 0.01

NM-TRAN MESSAGES

 AN ERROR WAS FOUND IN THE CONTROL STATEMENTS.

 AN ERROR WAS FOUND ON LINE 75 AT THE APPROXIMATE POSITION NOTED:
  0 0 0 0 0 0 0 0.01

 224 A VARIANCE IS ZERO, BUT THE BLOCK IS NOT FIXED TO ZERO.


I tried numerous different ways of placing the term FIX in the block, or not mentioning it at all - nothing worked, except replacing the 0 diagonal element by a very small number. I know that there are certain constrains of using 0 values in an OMEGA BLOCK (band symmetric form), but I always thought this was only relevant for estimation.
Has anyone come across a similar issue when simulating?

Best regards, Andreas.



Andreas Lindauer, Ph.D.
Associate Principal Scientist, Clinical PKPD
Pharmacokinetics, Pharmacodynamics, and Drug Metabolism
Merck & Co. / MSD


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Received on Tue Oct 08 2013 - 04:22:08 EDT

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