of large diagonal blocks are likely to be filled at factoring time. However, in
the context of incomplete solving methods such as ILU(k) [29], it can lead
to a significant reduction of the required memory space and time, because it
helps carving large triangular blocks. The parameters of the blocking method
are described below.
cmin=
size
Set the minimum size of the resulting subblocks, in number of columns.
Blocks larger than twice this minimum size are cut into sub-blocks of
equal sizes (within one), having a number of columns comprised between
size
and 2
size
.
The definition of
size
depends on the size of the graph to order. Large
graphs cannot afford very small values, because the number of blocks
becomes much too large and limits the acceleration of BLAS 3 routines,
while large values do not help reducing enough the complexity of ILU(k)
solving.
strat=
strat
Ordering strategy to be performed. After the ordering strategy is applied,
the resulting separators tree is traversed and all of the column blocks
that are larger than 2
size
are split into smaller column blocks, without
changing the ordering that has been computed.
c
Compression method [2]. The parameters of the compression method are
listed below.
rat=
rat
Set the compression ratio over which graphs and meshes will not be
compressed. Useful values range between 0
.
7 and 0
.
8.
cpr=
strat
Ordering strategy to use on the compressed graph or mesh if its size is
below the compression ratio times the size of the original graph or mesh.
unc=
strat
Ordering strategy to use on the original graph or mesh if the size of the
compressed graph or mesh were above the compression ratio times the
size of the original graph or mesh.
d
Block Halo Approximate Minimum Degree method [47]. The parameters of
the Halo Approximate Minimum Degree method are listed below. The Block
Halo Approximate Minimum Fill method, described below, is more efficient
and should be preferred.
cmin=
size
Minimum number of columns per column block. All column blocks of
width smaller than
size
are amalgamated to their parent column block in
the elimination tree, provided that it does not violate the
cmax
constraint.
cmax=
size
Maximum number of column blocks over which some column block will
not amalgamate one of its descendents in the elimination tree. This
parameter is mainly designed to provide an upper bound for block size
in the context of BLAS3 computations ; else, a huge value should be
provided.
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