NONMEM ODE solver
Dear NMusers,
1. I have some difficulties to find information on the ODE solver
implemented in NONMEM.
Can anyone tell me about the numerical integrator(s) implemented when using
ADVAN6 (recommended for non-stiff) and ADVAN8 (stiff problems)? In
particular, is the integrator able to switch automatically between stiff and
non-stiff resolution techniques?
2. Then, still related to the ODE solver, I was also interested in a message
I¹ve picked up from the archive (from Mark Sale, posted January 2005, see
below), for which I couldn¹t find any answer from the group. Additional
information on these items would be greatly appreciated.
Quoted reply history
_______________________________________________________
From: [EMAIL PROTECTED]
Subject: [NMusers] questions on ODE solver errors
Date: Wed, January 26, 2005 4:40 pm
If the NOABORT option is used for the ODE solvers, and the
ODE solver has "numerical difficulties", giving the message:
NUMERICAL DIFFICULTIES WITH INTEGRATION ROUTINE.
MAXIMUM NO. OF EVALUATIONS OF DIFFERENTIAL EQUATIONS, 100000, EXCEEDED.
0END OF PRED EXIT CODE MESSAGES FROM THE ESTIMATION STEP
But, NONMEM continues to plod along.
Does anyone know what NONMEM does instead? I assume that the OBJ
contribution for that subject cannot be calculated, so, the gradient
for the dimension(s) requiring that OBJ cannot be calculated. Seems
like an error to simply ignore the OBJ contribution from that person
(resulting in a lower OBJ for that function evaluation, and a bad
gradient and Hessian). Is that function evaluation discarded, and
no gradient is generated for that dimension/iteration? But I don't
see a 0 gradient anywhere in the output (I know, in NONMEM V, it
isn't as simple as one function evaluation per dimension (+1))
Thanks
Mark Sale M.D.
Global Director, Research Modeling and Simulation
GlaxoSmithKline
919-483-1808
Mobile
919-522-6668
_______________________________________________________
Thanks for your help in this matter.
Benjamin Ribba
Therapeutic Targeting in Oncology (EA3738)
University Claude Bernard Lyon 1
Faculty of Medicine Lyon-Sud
165, chemin du grand revoyet
69921 Oullins cedex
Tel: +33 4 26 23 59 57 / +33 6 66 06 15 21