Set OP=MOD (default) to modify the frequency and intensity of adaptive
meshing for an existing adaptive mesh domain (with the same element set name)
or to define a new adaptive mesh domain.
Set OP=NEW if all adaptive mesh domains that are currently in effect
should be removed. To remove only selected adaptive mesh domains, use OP=NEW and respecify all adaptive mesh domains that are to be
retained.
The OP parameter must be the same for all uses of the
ADAPTIVE MESH option within a single step.