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specifies the which
approach is used to estimate the local truncation error and which
norm is used. The available methods are dd/pointwise
(divided differences for LTE estimate with a pointwise norm to
measure the error), dd/global (divided differences for the
LTE estimate with a global norm to measure the error), and
milne, which uses a Milne's device to estimate the LTE and a
pointwise norm to measure the error. The Milne approach uses a
second TR step over the second half of the interval (and, hence an
expensive third nonlinear solve). Although that approach has had a
good deal of success with quasi-equilibrium diffusion models, it
seem to be prone to oscillations from the lack of A-stability in the
TR-TR step when used with fully kinetic models.
The default is dd/pointwise.
Dan Yergeau
Wed Jun 18 19:17:04 PDT 1997