From: "Emily" 
Subject: [NMusers] $COV
Date: Wed, 1 May 2002 12:08:12 +0800


Dear NONMEM users:
I'm working on a nonlear model, and the $COV step can't work.
Here is my control file:
 
$PROB A
$INPUT ID AGE SEX HT WT EVID TIME AMT SS II DV MDV $DATA data
$SUBR ADVAN6 TOL=3 
 
$MODEL COMP=(DEPOT, DEFDOS), COMP=(CENTRAL, DEFOBS)
 
$PK
 TVVM=THETA(1)
 TVKM=THETA(2)
 VM=TVVM*(1+ETA(1))
 KM=TVKM*(1+ETA(2))
 K12=THETA(3)
 V2=THETA(4)
 
$DES
 C2=A(2)/V2
 DADT(1)=-K12*A(1)
 DADT(2)=K12*A(1)-VM*C2/(KM+C2)
 
$ERROR
 Y=F+ERR(1)
 
$THETA
 (0,40);  1 VM
 (0,4);     2 KM
 (0,0.6);   3 K12
 (0,50);  4  V2
 
$OMEGA 0.01, 0.01
 
$SIGMA 40
 
$EST NOABORT PRINT=1
 
$TABLE ID AMT DV
 
$COVARIANCE
 
$SCATTER PRED VS DV UNIT
$SCATTER RES VS WT
 
The $COV step yeild follwing message:
 
R MATRIX ALGORITHMICALLY SINGULAR
COVARIANCE MATRIX UNOBTAINABLE
 
Can anyone give me any suggestion, please?
Thanks a lot !!
 
                                                             Emily