RE: Describing variability
From:Leonid Gibiansky
Subject:RE: [NMusers] Describing variability
Date: Tue, 01 Apr 2003 12:11:44 -0500
Just to make it more specific:
We may need to distinguish the situation when
1. $EST step fails (due to rounding errors) and
2. $EST converges but $COV step fails.
I think (1) is more dangerous and should not be mixed up with (2). We can
skip $COV step for a number of reasons (i.e., long run time), but it would
be best to get $EST convergence, if possible. Still, if we get rounding
errors and cannot get desired precision, we may accept the run if number of
significant digits is 3 (well, may be 2) and the parameter estimates are
independent of the requested precision.
It would be nice to have two NONMEM input parameters to control: precision
of calculations and precision criteria for stop. This would allow to avoid
chasing the process, when the achieved precision is always 0.5 less than
requested one no matter how high (or how low) you fix SIGDIGITS .
Leonid