These are settings for the differential equation
solver (DLSODA) that can be accessed via
the R interface. The code listing below is taken directly
from the DLSODA source code.
C----------------------------------------------------------------------- C Optional Inputs. C C The following is a list of the optional inputs provided for in the C call sequence. (See also Part 2.) For each such input variable, C this table lists its name as used in this documentation, its C location in the call sequence, its meaning, and the default value. C The use of any of these inputs requires IOPT = 1, and in that C case all of these inputs are examined. A value of zero for any C of these optional inputs will cause the default value to be used. C Thus to use a subset of the optional inputs, simply preload C locations 5 to 10 in RWORK and IWORK to 0.0 and 0 respectively, and C then set those of interest to nonzero values. C C Name Location Meaning and Default Value C C C HMAX RWORK(6) the maximum absolute step size allowed. C The default value is infinite. C C HMIN RWORK(7) the minimum absolute step size allowed. C The default value is 0. (This lower bound is not C enforced on the final step before reaching TCRIT C when ITASK = 4 or 5.) C C IXPR IWORK(5) flag to generate extra printing at method switches. C IXPR = 0 means no extra printing (the default). C IXPR = 1 means print data on each switch. C T, H, and NST will be printed on the same logical C unit as used for error messages. C C MXSTEP IWORK(6) maximum number of (internally defined) steps C allowed during one call to the solver. C The default value is 500. C C MXHNIL IWORK(7) maximum number of messages printed (per problem) C warning that T + H = T on a step (H = step size). C This must be positive to result in a non-default C value. The default value is 10. C C-----------------------------------------------------------------------
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 reltive 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.