Re: DV Simulation

From:Nick Holford Subject: Re: [NMusers] DV Simulation Date:Fri, 30 May 2003 19:08:04 +1200 Tom, Thanks for the confirmation of more strange quirks of NONMEM. But one of the quirks is actually really useful and I am shocked to see Stuart's assertion that this useful feature is an error that needs to be fixed. > But the error is with the control stream with one $TABLE record. The > table should have only the output from the last subproblem. > So we'll fix this with Ver VI. The current behaviour with one $TABLE FILE and multiple $SIMULATION SUBPROBLEMS works just fine for me because if I ask for 1000 subproblems and also want the $TABLE FILE output then I get output from every SUBPROBLEM by default. But if this "error" is fixed I will only get the $TABLE FILE output from the last subproblem -- throwing away the output from all the previous problems. Why would this be preferable default behaviour? If I really don't want any $TABLE FILE output then I simply dont include $TABLE records. What use would it be to have just the last $TABLE FILE out of 1000 SUBPROBLEMS? The FORWARD option is a horrible solution. As I pointed out earlier this option concatenates output to any existing file even when control streams are executed as separate runs. How often does anyone want to do this? What really needs to be fixed is the utter unreliability of being able to do $SIMULATION and $ESTIMATION in the same problem. If the simulation step generates a strange parameter or DV (as it necessarily will because it can sample anywhere in the distributions) then NONMEM finds it cannot start the $ESTIMATION step for some reason and abandons not only that SUBPROBLEM but all subsequent SUBPROBLEMS! This usually happens around SUBPROBLEM 500 out of 1000 -- hours if not days later. This NONMEM bug is the reason I am forced to use ONLYSIM to create all the simulated data sets I need (1000 or more sometimes) then devise some ad hoc way to work my way through the 1000 simulated data sets one at a time to do the ESTIMATION. Nick -- Nick Holford, Dept Pharmacology & Clinical Pharmacology University of Auckland, 85 Park Rd, Private Bag 92019, Auckland, New Zealand email:n.holford@auckland.ac.nz tel:+64(9)373-7599x86730 fax:373-7556 http://www.health.auckland.ac.nz/pharmacology/staff/nholford/