These are settings for the differential equation
solver (lsoda) that can be accessed via
the R interface. The code listing below is taken directly
from the lsoda source code.
The following items can be set
hmax (HMAX below); decrease hmax when
you want to limit how big of a step the solver can take when
integrating from one time to the next time. However be aware
that smaller hmax will result in longer run times.
hmin (HMIN below); don't fiddle with this
unless you know what you're doing.
ixpr (IXPR below)
maxsteps (MXSTEP below); increase this
number when the solver has a long interval between
two integration times (e.g. when observation records are
far apart).
mxhnil (MXHNIL below); don't usually
modify this one
atol - the absolute solver tolerance; decrease
this number (e.g. to 1E-10 or 1E-20 or 1E-50) when the
value in a compartment can get extremely small; without this
extra (lower) tolerance, the value can get so low that the number
can randomly become negative. However be aware that more precision
here will result in longer run times.
rtol - the relative solver tolerances; decrease this
number when you want a more precise solution. However be aware
that more precision here will result in longer run times.