Scotch Brand 5.1.10 - Manual (Page 69)

computed for coarser graphs or meshes. This strategy is not applied to
the coarsest graph or mesh, for which only the low strategy is used.
low=strat
Set the strategy that is used to compute the vertex separator of the
coarsest graph or mesh, at the lowest level of the coarsening process.
rat=rat
Set the threshold maximum coarsening ratio over which graphs or meshes
are no longer coarsened. The ratio of any given coarsening cannot be less
that 0.5 (case of a perfect matching), and cannot be greater than 1.0.
Coarsening stops when either the coarsening ratio is above the maximum
coarsening ratio, or the graph or mesh has fewer node vertices than the
minimum number of vertices allowed.
vert=nbr
Set the threshold minimum size under which graphs or meshes are no
longer coarsened. Coarsening stops when either the coarsening ratio is
above the maximum coarsening ratio, or the graph or mesh has fewer
node vertices than the minimum number of vertices allowed.
t Thinner method. Available only for graph separation strategies. This method
quickly eliminates all useless vertices of the current separator. It searches the
separator for vertices that have no neighbors in one of the two parts, and
moves these vertices to the part they are connected to. This method may
be used to refine separators during the uncoarsening phase of the multi-level
method, and is faster than a vertex Fiduccia-Mattheyses algorithm with {move
=0
}.
v Mesh-to-graph method. Available only for mesh separation strategies. From
the mesh to which this method applies is derived a graph, such that a graph
vertex is associated with every node of the mesh, and a clique is created
between all vertices which represent nodes that belong to the same element.
A graph separation strategy is then applied to the derived graph, and the
separator is projected back to the nodes of the mesh. This method is here
for evaluation purposes only, as mesh separation methods are generally more
efficient than their graph separation counterpart.
strat=strat
Graph separation strategy to apply to the associated graph.
w Graph separator viewer. Available only for graph separation strategies. Ev-
ery call to this method results in the creation, in the current subdirectory,
of partial mapping files called “vgraphseparatevw output nnnnnnnn.map”,
where “nnnnnnnn” are increasing decimal numbers, which contain the cur-
rent state of the two parts and the separator. These mapping files can be
used as input by the gout program to produce displays of the evolving shape
of the current separator and parts. This is mostly a debugging feature, but
it can also have an illustrative interest. While it is only available for graph
separation strategies, mesh separation strategies can indirectly use it through
the mesh-to-graph separation method.
z Zero method. This method moves all of the node vertices to the first part,
resulting in an empty separator. Its main use is to stop the separation process
whenever some condition is true.
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