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spparms    See Also

Set parameters for sparse matrix routines

Syntax

Description

spparms('key',value) sets one or more of the tunable parameters used in the sparse linear equation operators, \ and /, and the minimum degree orderings, colmmd and symmmd. In ordinary use, you should never need to deal with this function.

The meanings of the key parameters are

'spumoni'
 Sparse Monitor flag.
0 produces no diagnostic output, the default.
1 produces information about choice of algorithm based on matrix structure, and about storage allocation.
2 also produces very detailed information about the minimum degree algorithms.
'thr_rel',
'thr_abs'
 Minimum degree threshold is thr_rel*mindegree+thr_abs.
'exact_d'
 Nonzero to use exact degrees in minimum degree. Zero to use approximate degrees.
'supernd'
 If positive, minimum degree amalgamates the supernodes every supernd stages.
'rreduce'
 If positive, minimum degree does row reduction every rreduce stages.
'wh_frac'
 Rows with density > wh_frac are ignored in colmmd.
'autommd'
 Nonzero to use minimum degree orderings with \ and /.
'aug_rel',
'aug_abs'
 Residual scaling parameter for augmented equations is 
    aug_rel*max(max(abs(A))) + aug_abs.
For example, aug_rel = 0, aug_abs = 1 puts an unscaled identity matrix in the (1,1) block of the augmented matrix.

spparms, by itself, prints a description of the current settings.

values = spparms returns a vector whose components give the current settings.

[keys,values] = spparms returns that vector, and also returns a character matrix whose rows are the keywords for the parameters.

spparms(values), with no output argument, sets all the parameters to the values specified by the argument vector.

value = spparms('key') returns the current setting of one parameter.

spparms('default') sets all the parameters to their default settings.

spparms('tight') sets the minimum degree ordering parameters to their tight settings, which can lead to orderings with less fill-in, but which make the ordering functions themselves use more execution time.

The key parameters for default and tight settings are


 Keyword
Default
 Tight
values(1)
 'spumoni'
0.0
values(2)
 'thr_rel'
1.1
 1.0
values(3)
 'thr_abs'
1.0
 0.0
values(4)
 'exact_d'
0.0
 1.0
values(5)
 'supernd'
3.0
 1.0
values(6)
'rreduce'
3.0
 1.0
values(7)
'wh_frac'
0.5
 0.5
values(8)
'autommd'
1.0
values(9)
'aug_rel'
0.001
values(10)
'aug_abs'
0.0

See Also

\       Matrix left division (backslash)

colmmd      Sparse column minimum degree permutation

symmmd      Sparse symmetric minimum degree ordering

References

[1] Gilbert, John R., Cleve Moler and Robert Schreiber, "Sparse Matrices in MATLAB: Design and Implementation," SIAM Journal on Matrix Analysis and Applications 13, 1992, pp. 333-356.


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