Modeling compartment initial conditinns using ETA()= EPS(1) and CPZERO measure

Dear NM-Users, I need a method to force using EPS(1) intead ETA() for estimating initial steady-state compartment concentration for $DES. Pre-dose TIME for SS-ending is known. I used the following abbreviated codes in ERROR, and NONMEM act well, but predics individual regression stricted to measure CPZERO. sincerely Kazimierz H. Kozlowski $DES DADT(1)=-K*A(1)-K12*A(1)+K21*A(2) DADT(2)=K12*A(1)-K21*A(2) $ERROR COM(1)=ERR(1) ;QUESTION: WHY ERR(1)=0.0 in write-file and in TABLE? WRITE (50,*) COM(1),ERR(1),ICALL,COMACT ; COM(1)=0, ICALL=2 always FZ=THETA(10)*ERR(1)*THETA(10)*ERR(1) ;FZ=ERR**2 FZ1=1.0-FZ*THETA(9)*THETA(9) ;FZ1=1-ERR*2*TH9*2 EXP1=(K-BETA)*EXP(-ALPHA*(IAGE+TIME)) EXP2=(ALPHA-K)*EXP(-BETA*(IAGE+TIME)) EXP3=ALPHA*EXP(-BETA*(IAGE+TIME)) EXP4=BETA*EXP(-ALPHA*(IAGE+TIME)) EN=(C01-(C01*C01-FZ1*(C01*C01-FZ))**0.5)/FZ1;EN=ENDOG. CP(0) CS=EN*(ALPHA-BETA) ;CSS=EN(T=-IAGE) CSS=CS/((K-BETA)*EXP(-ALPHA*IAGE)+(ALPHA-K)*EXP(-BETA*IAGE)) IPR1=F+CSS/(ALPHA-BETA)*(EXP1+EXP2) ;PLASMA CONC. IPR2=A(2)/V1*K21/K12+CSS/(ALPHA-BETA)*(EXP3-EXP4);TISSUE CONC. RZ=CSS/CLE ;ENDOG. RATE IDIF=CP-IPR1 W=(1+IPR1*IPR1*THETA(9)*THETA(9))**0.5 Y=IPR1+W*THETA(10)*ERR(1) $THETA . . . $THETA $SIGMA 1 FIXED ;VARIANCE FOR ERR(1) $EST NOABORT NUMERICAL SLOW METHOD=1 INTERACTION LAPLACIAN POSTHOC SIG=6 MAX=9999 PRINT=1 MSFO=VER1.MSF $COVARIANCE MATRIX=S SLOW COMPRESS PRINT=E $TABLE ID TIME ALPHA CLD CLE BETA V1 RZ NOPRINT FILE=VER1.TAB $TABLE ID TIME C01 ER=COM(1) EN CSS IPR1 IPR2 NOPRINT FILE=VER1.TAB $TABLE ID TIME IAGE K12 K21 K R1 IDIF NOPRINT FILE=VER1.TAB $SCAT CP VS IPR1 UNIT