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advan8 vs. advan13

From: nonmem
Date: Sun, 01 Nov 2009 14:58:55 +0000 (GMT)

Hello Nonmem Users,
When I tried simple simulations and changed advan13 to advan8, some concentrations changed. Equations were stiff. Then I added TRANS1 to the $SUBROUTINE statements. ADVAN13 output did not change. ADVAN8 output changed and looked exactly like ADVAN13 output. Do you know what happened?
(Another thing I noted is that when IMP is used, the lower boundary for bioavailability cannot be 0.)

----- Original Message -----
From: nonmem
Date: Sunday, November 1, 2009 8:34 am
Subject: Re: [NMusers] advan8 vs. advan13
To: nmusers

> It seems like advan8 has integration difficulties when both LAG
> time and variability in Ka are implemented. Method=IMP has
> dificulties when advan8 has integration difficulties. Instead
> if reporting issues, it keeps running. The objective function
> is very low even when bioavailability is almost zero. Removing
> LAG and eta of Ka may fix it.
> ----- Original Message -----
> From: nonmem
> Date: Sunday, November 1, 2009 12:04 am
> Subject: [NMusers] advan8 vs. advan13
> To: nmusers
> > Hello NONMEM users,
> >
> > Because advan13 was recomended for both stiff and nonstiff
> > differential equations, I used it for stiff differential
> > equations. It appeared that some results looked too sensitive
> > to a parameters representing a "slow" processes. I did not
> > observe it with nonmem6. When I used advan8, the objective
> > function changed from 10228.853 (the final value; diagnostic
> > plots looked good) to 5512.594 (the first value; I im still
> > waiting for the final value of the objective function).
> >
> > Does it mean that advan13 should be used with caution when the
> > equations are stiff or advan13 cannot replace advan8?
> >
> > Thanks,
> > Pavel
> >

Received on Sun Nov 01 2009 - 09:58:55 EST

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