matroid-getters {zonohedra}

matroid get functions

Description

get some important members of a matrix

Usage

## S3 method for class 'matroid'
getground( x )

## S3 method for class 'matroid'
gethyperplane( x )

## S3 method for class 'matroid'
getmatrix( x )

## S3 method for class 'matroid'
getloop( x )

## S3 method for class 'matroid'
getmultiple( x )

Arguments

x

a matroid object, as returned from the constructor matroid()

Value

getground() returns an vector of positive integers in strictly increasing order = the ground set of the matroid x.

gethyperplane() returns a list of vectors of positive integers = the hyperplanes of the matroid.
If x is the simplification of an "original matroid", the "lmdata" attribute of the returned list is set to the loop and multiple group data of the "original hyperplanes". These hyperplanes can be recovered using unsimplify().
If x was constructed from a matrix, these hyperplanes are sorted in decreasing order by length. The non-trivial hyperplanes come first, followed by the trivial hyperplanes. A hyperplane is trivial iff it is independent in the matroid. For a matroid of rank 3, a hyperplane is trivial iff it has 2 points.

getmatrix() returns the matrix passed to the matroid.matrix() constructor, or NULL if the list constructor was used. The column names are labeled with the ground set.

getloop() returns an integer vector with the loops of x. If x is simple, it is the empty vector.

getmultiple() returns a list of integer vectors - the multiple groups of x. If x is simple, it is the empty list.

References

Matroid - Wikipedia. https://en.wikipedia.org/w/index.php?title=Matroid&oldid=1086234057

See Also

rank(), simplify(), unsimplify(), getsimplified(),

Examples

# construct a classic matroid with 7 points, but assign an unusual ground set
mat = matroid( classics.genlist[['TRD']], ground=11:17 )

getmatrix( mat )

##       11 12 13 14       15       16       17
##  [1,]  1  1  1  1 1.732051 0.000000 0.000000
##  [2,]  1  1 -1 -1 0.000000 1.732051 0.000000
##  [3,]  1 -1  1 -1 0.000000 0.000000 1.732051