Question about PK-PD models

I have a question for PK-PD modellers. At present, DOWHIILE may be used in abbreviated code in simulation, initialization-finalization, data average, expectation blocks. These have ICALL\=2 and the eta derivatives are not needed. With nm73, NMTRAN will have a new feature: Use of DOWHILE in data-analytic (ICALL=2) blocks. I have found it helpful for obtaining the eta derivatives to make two restrictions: 639 VARIABLE MODIFIED IN DOWHILE MAY NOT ALREADY BE A RANDOM VARIABLE 640 VARIABLE MODIFIED IN DOWHILE MAY NOT BE MODIFIED MORE THAN ONCE. These restrictions make impossible a loop such as this one: TERM=THETA(1)*EXP(ETA(1)) SUM=0 I=1 DOWHILE (condition) SUM=SUM+TERM TERM=function(TERM) I=I+1 ENDDO You will note that TERM is being modified within DOWHILE, *and* it is random. In every example that I know of, TERM appears linearly, that is, it is multiplied by a non-random variable, and only this multiplier need be changed. My question is: Can anyone think of an example of this sort of loop that might be used in PK/PD modelling, and TERM itself *must* be changed? Possibly a TERM that is a function of two random variables? A few comments: All the elementary functions can be computed with Taylor series, and I think any Taylor series can be computed with DOWHILE with the restrictions. So it needs to be something more complicated. ----------- For example, here are two fragments of code that work correctly. Example 1: EXP function (an exercise using Taylor series) ; Taylor series (actually, Mclaurin series) for exp(F)=SUM of F**I/I! ; FI=F**I ; FACTORIAL=I! FI=1 FACTORIAL=1 TERM=1 SUM=1 I=1 DOWHILE (I<999.and.TERM>.000000000000001) FACTORIAL=FACTORIAL*I FI=FI*F TERM=FI/FACTORIAL SUM=SUM+TERM I=I+1 ENDDO Example 2: Steady state dose into Transit compartment. Past implied doses are summed until their contributions are negligible. DOSE, DOSETIME, IIVAL are set in $PK from AMT, TIME, II on the SS dose record. NN and KTR are set in $PK and are random variables. $DES INPT=0 ABI=1 ; set ABI to satisfy first DOWHILE condition I=1 DOWHILE (I<999 .and. ABI>.000000001) DELTAT=T-dosetime+(I-1)*IIVAL IPT=DOSE*deltat**NN*EXP(-KTR*deltat) INPT=INPT+IPT ABI=ABS(IPT) I=I+1 ENDDO DADT(1)=KINPT*INPT-KTR*A(1) .... -- Alison Boeckmann [email protected]