# Re: inexplicit equations in PRED

From: Ekaterina Gibiansky <EGibiansky>
Date: Sat, 26 Sep 2009 21:59:16 -0400

Sam,
You do not need an equilibrium compartment, you can solve the equation explicitly:

\$DES
K1 = A(1)/V1-A(2)-KD
C = 0.5*(K1+ SQRT(K1*K1+4*KD*A(1)/V1))
DADT(2)= KSYN - KDEG*A(2) -(KINT - KDEG)*C*A(2)/(KD+C)

If you would like to use the equilibrium compartment just for the sake of test,
E(3) should denote the equation that needs to be solved as E(3)=0. Thus,
something like this:

\$AESINITIAL
INIT=1
A(3)=0.001
\$AES
K1 = A(1)/V1-A(2)-KD
E(3) = A(3)-0.5*(K1+ SQRT(K1*K1+4*KD*A(1)/V1))
\$DES
DADT(2)= KSYN - KDEG*A(2) -(KINT - KDEG)*A(3)*A(2)/(KD+A(3))

Regards,
Katya

-------------------------
Ekaterina Gibiansky, Ph.D.
CEO&CSO, QuantPharm LLC
Web: www.quantpharm.com
Email: EGibiansky at quantpharm.com
Tel: (301)-717-7032

Sam wrote:
> Dear nmusers:
> I would like to continued this thread started by Robert. I tried the
> \$AES method suggested by Katya in my PK model where the first two
> compartments are defined in \$DES while the third compartment is defined
> as an equilibrium algebraic equation in \$AES. I got error msg shown
> below. Could anyone tell what is missing in my code?
>
> "LUDATN IS UNABLE TO INVERT JACOBIAN (DA) FOR AES
> VARIABLES
>
> ERROR OCURRED WHILE ATTEMPTING TO OBTAIN INITIAL VALUES FOR DY/DT"
>
> Sam Liao
> ===== sim02.lst =====================================================
> \$PROB A TMDD MODEL
> \$INPUT C ID TIME DV AMT RATE DOSE EVID CMT SS
> \$DATA sim01.csv IGNORE=C
> \$MODEL
> COMP=(CENTRAL)
> COMP=(RTOT)
> COMP=(A3 EQUILIBRIUM)
> \$PK
> CL = THETA(1)* EXP(ETA(1))
> V1 = THETA(2)* EXP(ETA(2))
>
> K10= CL/V1
>
> KSYN= THETA(3)* EXP(ETA(3))
> KDEG= THETA(4)* EXP(ETA(4))
> KINT= THETA(5)* EXP(ETA(5))
> KD = THETA(6)* EXP(ETA(6))
>
> BL= KSYN/KDEG
> A_0(2)=BL ;BOUNDARY CONDITION FOR EQUATION 3
> \$AESINITIAL
> INIT=1
> A(3)=0.001
> \$AES
> K1 = A(1)/V1-A(2)-KD
> E(3) = 0.5*(K1+ SQRT(K1*K1+4*KD*A(1)/V1))
> \$DES
> DADT(2)= KSYN - KDEG*A(2) -(KINT - KDEG)*A(3)*A(2)/(KD+A(3))
>
> .............
>> Robert,
>>
>> You can do it using ADVAN9 with NEQUILIBRIUM option in \$MODEL, and
>> \$AESINITIAL and \$AES blocks. E.g. (where A(13) is what is F in your
>> example) :
>>
>> \$MODEL NEQUILIBRIUM=1
>> COMP(COMP1)
>> ....
>> COMP(COMP13)
>>
>> \$PK
>> ...
>>
>> \$AESINITIAL
>> INIT = 0; 0=APPROXIMATE, 1=EXACT
>> A(13)=0.001
>> \$AES
>> E(13)=A(9)-A(13)-A(13)*A(10)/(KSS+A(13))-A(13)*A(12)/(KSS2+A(13))
>>
>> \$DES
>> ...
>>
>> \$ERROR
>> Y = A(13)+EPS(1)
>>
>> Regards,
>> Katya
>>
>> --------------------------
>> Ekaterina Gibiansky, Ph.D.
>> CEO&CSO, QuantPharm LLC
>> Web: www.quantpharm.com
>> Email: EGibiansky
>> Tel: (301)-717-7032
>>
>>
>> Robert Kalicki wrote:
>>> Dear NMusers,
>>>
>>> Most of the models are pre-defined (ADVANx), expressed as a system of
>>> differential equations or provided in the form of an explicit
>>> mathematical equation (PRED).
>>>
>>> Is it possible to deal with nonlinear inexplicit equations like y =
>>> f(x,y) where both differential equations and explicit solution
>>> equation are not known or not obvious.
>>>
>>>
>>>
>>> Concretely, using PRED, one would find F on the both sides:
>>>
>>> F = f(X) + g(F)
>>>
>>> Y = F+EPS(1)
>>>
>>>
>>>
>>>
>>>
>>>
>>> Best regards,
>>>
>>> Robert
>>>
>>>
>>>
>>>
>>>
>>> ___________________________________________
>>> Robert M. Kalicki, MD
>>>
>>> Postdoctoral Fellow
>>>
>>> Department of Nephrology and Hypertension
>>>
>>> Inselspital
>>>
>>> University of Bern
>>>
>>> Switzerland
>>>
>>>
>>>
Received on Sat Sep 26 2009 - 21:59:16 EDT

The NONMEM Users Network is maintained by ICON plc. Requests to subscribe to the network should be sent to: nmusers-request@iconplc.com.

Once subscribed, you may contribute to the discussion by emailing: nmusers@globomaxnm.com.