DEREFINE

This routine derefines a mesh by deleting points using the merge routine based on one of the following refine_types. edge will refine if element edge length is less then value. volume will merge if element volume is less than value. The merge routine will first attempt the smallest element edge then the next smallest, etc. aspect will derefine where aspect ratio is less than value. pinchedge will allow merging of adjacent points across a thin layer to eliminate the layer where it is too thin. pinchedge should be used only with pointtype1 and pointtype2 both equal to 2.
Two criteria are currently enabled; minsize and merge. minsize allows merges if the calculation implied by refine_type is less than value. merge will merge the following first_point and second_point. The field option is not enabled and should be left default. The user specifies which merges are acceptable by designating the allowable pointtypes. Nodes with pointtype1 are merged to nodes of pointtype2. If pointtype1 and pointtype2 are both equal to 2, the code only merges if the nodes are both on the same material interface (use pinchedge if deleted nodes should be on different interfaces of the same material). derefine will not merge if an unacceptable element is created. derefine will work on material interfaces if all the children are set with the settets command. Various combinations of derefine may be used to improve the mesh. recon may be used to return to a delaunay mesh after using the derefine command.

FORMAT:

derefine/minsize/field/pointtype1 pointtype2/refine_type/first_point/last_point/stride/value
derefine/merge/first_point/second_point

EXAMPLE:

derefine/minsize//0 0/aspect/ 1 0 0/1.e-3
derefine/minsize//0 2/volume/pset,get,apset/5.
derefine/minsize//10  10/edge/1 0 0/5.
derefine/minsize//2 2/pinchedge/1 0 0/1
derefine/merge/21/22