Re: inexplicit equations in PRED

From: Sam Liao <sliao>
Date: Sat, 26 Sep 2009 23:29:20 -0400

Dear Katya:
It works, thanks for your advice. The reason I need the equilibrium
compartment is to get PRED estimated.

Best regards,
Sam
> 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 - 23:29:20 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.