HaskellForMaths-0.4.8: Combinatorics, group theory, commutative algebra, non-commutative algebra

Math.Combinatorics.Matroid

Description

A module providing functions to construct and investigate (small, finite) matroids.

Synopsis

Documentation

exists :: [a] -> Bool Source

unique :: [t] -> t Source

shortlex :: Ord a => [a] -> [a] -> Ordering Source

isShortlex :: Ord a => [[a]] -> Bool Source

toShortlex :: Ord a => [[a]] -> [[a]] Source

isClutter :: Ord a => [[a]] -> Bool Source

deletions :: [a] -> [[a]] Source

data TrieSet a Source

The data structure that we use to store the bases of the matroid

Constructors

 TS [(a, TrieSet a)]

Instances

 Functor TrieSet Eq a => Eq (TrieSet a) Ord a => Ord (TrieSet a) Show a => Show (TrieSet a)

tsshow :: Show a => TrieSet a -> [Char] Source

tsinsert :: Ord a => [a] -> TrieSet a -> TrieSet a Source

tsmember :: Eq a => [a] -> TrieSet a -> Bool Source

tssubmember :: Ord a => [a] -> TrieSet a -> Bool Source

tstolist :: TrieSet t -> [[t]] Source

tsfromlist :: Ord a => [[a]] -> TrieSet a Source

data Matroid a Source

A datatype to represent a matroid. `M es bs` is the matroid whose elements are `es`, and whose bases are `bs`. The normal form is for the `es` to be in order, for each of the `bs` individually to be in order. (So the TrieSet should have the property that any path from the root to a leaf is strictly increasing).

Constructors

 M [a] (TrieSet a)

Instances

 Functor Matroid Eq a => Eq (Matroid a) Show a => Show (Matroid a)

elements :: Matroid t -> [t] Source

Return the elements over which the matroid is defined.

indeps :: Ord a => Matroid a -> [[a]] Source

Return all the independent sets of a matroid, in shortlex order.

isIndependent :: Ord a => Matroid a -> [a] -> Bool Source

isDependent :: Ord a => Matroid a -> [a] -> Bool Source

isMatroidIndeps :: Ord a => [[a]] -> Bool Source

Are these the independent sets of a matroid? (The sets must individually be ordered.)

fromIndeps :: Ord a => [a] -> [[a]] -> Matroid a Source

Construct a matroid from its elements and its independent sets.

fromIndeps1 :: Ord a => [a] -> [[a]] -> Matroid a Source

vectorMatroid :: (Eq k, Fractional k) => [[k]] -> Matroid Int Source

Given a matrix, represented as a list of rows, number the columns [1..], and construct the matroid whose independent sets correspond to those sets of columns which are linearly independent (or in case there are repetitions, those multisets of columns which are sets, and which are linearly independent).

vectorMatroid' :: (Eq k, Fractional k) => [[k]] -> Matroid Int Source

Given a list of vectors (or rows of a matrix), number the vectors (rows) [1..], and construct the matroid whose independent sets correspond to those sets of vectors (rows) which are linearly independent (or in case there are repetitions, those multisets which are sets, and which are linearly independent).

cycleMatroid :: Ord a => [[a]] -> Matroid Int Source

Given the edges of an undirected graph, number the edges [1..], and construct the matroid whose independent sets correspond to those sets of edges which contain no cycle. The bases therefore correspond to maximal forests within the graph. The edge set is allowed to contain loops or parallel edges.

cycleMatroid' :: Ord a => [[a]] -> Matroid [a] Source

to1n :: Ord a => Matroid a -> Matroid Int Source

Given a matroid over an arbitrary type, relabel to obtain a matroid over the integers.

matroidIsos :: (Ord t3, Ord t2) => Matroid t2 -> Matroid t3 -> [[(t2, t3)]] Source

isMatroidIso :: (Ord a, Ord b) => Matroid a -> Matroid b -> Bool Source

Are the two matroids isomorphic?

matroidAuts :: Ord a => Matroid a -> [Permutation a] Source

Return the automorphisms of the matroid.

isCircuit :: Ord a => Matroid a -> [a] -> Bool Source

A circuit in a matroid is a minimal dependent set.

circuits :: Ord a => Matroid a -> [[a]] Source

Return all circuits for the given matroid, in shortlex order.

isMatroidCircuits :: Ord a => [[a]] -> Bool Source

Are the given sets the circuits of some matroid?

fromCircuits :: Ord a => [a] -> [[a]] -> Matroid a Source

Reconstruct a matroid from its elements and circuits.

isLoop :: Ord a => Matroid a -> a -> Bool Source

An element e in a matroid M is a loop if {e} is a circuit of M.

isParallel :: Ord a => Matroid a -> a -> a -> Bool Source

Elements f and g in a matroid M are parallel if {f,g} is a circuit of M.

isSimple :: Ord a => Matroid a -> Bool Source

A matroid is simple if it has no loops or parallel elements

isBase :: Ord a => Matroid a -> [a] -> Bool Source

A base or basis in a matroid is a maximal independent set.

bases :: Ord a => Matroid a -> [[a]] Source

Return all bases for the given matroid

isMatroidBases :: Ord a => [[a]] -> Bool Source

Are the given sets the bases of some matroid?

fromBases :: Ord a => [a] -> [[a]] -> Matroid a Source

Reconstruct a matroid from its elements and bases.

fundamentalCircuit :: Ord a => Matroid a -> [a] -> a -> [a] Source

Given a matroid m, a basis b, and an element e, `fundamentalCircuit m b e` returns the unique circuit contained in b union {e}, which is called the fundamental circuit of e with respect to b.

u :: Int -> Int -> Matroid Int Source

The uniform matroid U m n is the matroid whose independent sets are all subsets of [1..n] with m or fewer elements.

restriction1 :: Ord a => Matroid a -> [a] -> Matroid a Source

restriction :: Ord a => Matroid a -> [a] -> Matroid a Source

The restriction of a matroid to a subset of its elements

rankfun :: Ord a => Matroid a -> [a] -> Int Source

Given a matroid m, `rankfun m` is the rank function on subsets of its element set

rank :: Ord a => Matroid a -> Int Source

The rank of a matroid is the cardinality of a basis

fromRankfun :: Ord a => [a] -> ([a] -> Int) -> Matroid a Source

Reconstruct a matroid from its elements and rank function

closure :: Ord a => Matroid a -> [a] -> [a] Source

Given a matroid m, `closure m` is the closure operator on subsets of its element set

fromClosure :: Ord a => [a] -> ([a] -> [a]) -> Matroid a Source

Reconstruct a matroid from its elements and closure operator

isFlat :: Ord a => Matroid a -> [a] -> Bool Source

A flat in a matroid is a closed set, that is a set which is equal to its own closure

flats1 :: Ord a => Matroid a -> [[a]] Source

coveringFlats :: Ord t => Matroid t -> [t] -> [[t]] Source

minimalFlat :: Ord a => Matroid a -> [a] Source

flats :: Ord a => Matroid a -> [[a]] Source

The flats of a matroid are its closed sets. They form a lattice under inclusion.

fromFlats :: Ord a => [[a]] -> Matroid a Source

Reconstruct a matroid from its flats. (The flats must be given in shortlex order.)

fromFlats' :: Ord a => [[a]] -> Matroid a Source

isSpanning :: Ord a => Matroid a -> [a] -> Bool Source

A subset of the elements in a matroid is spanning if its closure is all the elements

isHyperplane :: Ord a => Matroid a -> [a] -> Bool Source

A hyperplane is a flat whose rank is one less than that of the matroid

hyperplanes1 :: Ord a => Matroid a -> [[a]] Source

hyperplanes :: Ord a => Matroid a -> [[a]] Source

isMatroidHyperplanes :: Ord a => [a] -> [[a]] -> Bool Source

fromHyperplanes1 :: Ord a => [a] -> [[a]] -> Matroid a Source

fromHyperplanes :: Ord a => [a] -> [[a]] -> Matroid a Source

Reconstruct a matroid from its elements and hyperplanes

affineMatroid :: (Eq k, Fractional k) => [[k]] -> Matroid Int Source

Given a list of points in k^n, number the points [1..], and construct the matroid whose independent sets correspond to those sets of points which are affinely independent.

A multiset of points in k^n is said to be affinely dependent if it contains two identical points, or three collinear points, or four coplanar points, or ... - and affinely independent otherwise.

fromGeoRep :: Ord a => [[a]] -> [[a]] -> [[a]] -> [[a]] -> Matroid a Source

fromGeoRep returns a matroid from a geometric representation consisting of dependent flats of various ranks. Given lists of dependent rank 0 flats (loops), rank 1 flats (points), rank 2 flats (lines) and rank 3 flats (planes), `fromGeoRep loops points lines planes` returns the matroid having these as dependent flats. Note that if all the elements lie in the same plane, then this should still be listed as an argument.

minimal :: Ord a => [[a]] -> [[a]] Source

simpleFromGeoRep :: Ord a => [[a]] -> [[a]] -> Matroid a Source

A simple matroid has no loops or parallel elements, hence its geometric representation has no loops or dependent points. `simpleFromGeoRep lines planes` returns the simple matroid having these dependent flats.

isSimpleGeoRep :: Ord a => [[a]] -> [[a]] -> Bool Source

circuitHyperplanes :: Ord a => Matroid a -> [[a]] Source

List the circuit-hyperplanes of a matroid.

relaxation :: Ord a => Matroid a -> [a] -> Matroid a Source

Given a matroid m, and a set of elements b which is both a circuit and a hyperplane in m, then `relaxation m b` is the matroid which is obtained by adding b as a new basis. This corresponds to removing b from the geometric representation of m.

ex161 :: Num t => [[t]] Source

transversalGraph :: (Num b1, Enum b1) => [[a]] -> [(Either a b, Either a1 b1)] Source

partialMatchings :: Ord a => [(a, a)] -> [[(a, a)]] Source

transversalMatroid :: Ord a => [a] -> [[a]] -> Matroid a Source

Given a set of elements es, and a sequence as = [a1,...,am] of subsets of es, return the matroid whose independent sets are the partial transversals of the as.

dual :: Ord a => Matroid a -> Matroid a Source

The dual matroid

isCoindependent :: Ord a => Matroid a -> [a] -> Bool Source

isCobase :: Ord a => Matroid a -> [a] -> Bool Source

isCocircuit :: Ord a => Matroid a -> [a] -> Bool Source

cocircuits :: Ord a => Matroid a -> [[a]] Source

isColoop :: Ord a => Matroid a -> a -> Bool Source

isCoparallel :: Ord a => Matroid a -> a -> a -> Bool Source

deletion :: Ord a => Matroid a -> [a] -> Matroid a Source

(\\\) :: Ord a => Matroid a -> [a] -> Matroid a Source

contraction :: Ord a => Matroid a -> [a] -> Matroid a Source

(///) :: Ord a => Matroid a -> [a] -> Matroid a Source

isConnected :: Ord a => Matroid a -> Bool Source

A matroid is (2-)connected if, for every pair of distinct elements, there is a circuit containing both

component :: Ord a => Matroid a -> a -> [a] Source

dsum :: (Ord a, Ord b) => Matroid a -> Matroid b -> Matroid (Either a b) Source

The direct sum of two matroids

matroidPG :: (Eq a, Fractional a) => Int -> [a] -> Matroid Int Source

`matroidPG n fq` returns the projective geometry PG(n,Fq), where fq is a list of the elements of Fq

matroidAG :: (Eq a, Fractional a) => Int -> [a] -> Matroid Int Source

`matroidAG n fq` returns the affine geometry AG(n,Fq), where fq is a list of the elements of Fq

fundamentalCircuitIncidenceMatrix :: (Ord a, Num k) => Matroid a -> [a] -> [[k]] Source

Given a matroid m, the fundamental-circuit incidence matrix relative to a base b has rows indexed by the elements of b, and columns indexed by the elements not in b. The bi, ej entry is 1 if bi is in the fundamental circuit of ej relative to b, and 0 otherwise.

fcim :: (Ord a, Num k) => Matroid a -> [a] -> [[k]] Source

fcim' :: (Ord a, Num t) => Matroid a -> [a] -> [[t]] Source

markNonInitialRCs :: (Num a, Eq a) => [[a]] -> [[ZeroOneStar]] Source

substStars :: Num a => [[ZeroOneStar]] -> [a] -> [[[a]]] Source

starSubstitutionsV :: Num a => [a] -> [ZeroOneStar] -> [[a]] Source

representations1 :: (Ord a1, Ord a, Fractional a1) => [a1] -> Matroid a -> [[[a1]]] Source

fcig :: Ord t => Matroid t -> [t] -> [[t]] Source

markedfcim :: Ord a => Matroid a -> [a] -> [[ZeroOneStar]] Source

representations2 :: (Ord a1, Ord a, Fractional a1) => [a1] -> Matroid a -> [[[a1]]] Source

representations :: (Eq fq, Fractional fq, Ord a) => [fq] -> Matroid a -> [[[fq]]] Source

Find representations of the matroid m over fq. Specifically, this function will find one representative of each projective equivalence class of representation.

isRepresentable :: (Eq fq, Fractional fq, Ord a) => [fq] -> Matroid a -> Bool Source

Is the matroid representable over Fq? For example, to find out whether a matroid m is binary, evaluate `isRepresentable f2 m`.

isBinary :: Ord a => Matroid a -> Bool Source

A binary matroid is a matroid which is representable over F2

isTernary :: Ord a => Matroid a -> Bool Source

A ternary matroid is a matroid which is representable over F3

data LMR a b Source

Constructors

 L a Mid R b

Instances

 (Eq a, Eq b) => Eq (LMR a b) (Ord a, Ord b) => Ord (LMR a b) (Show a, Show b) => Show (LMR a b)

seriesConnection :: (Ord a1, Ord a) => (Matroid a, a) -> (Matroid a1, a1) -> Matroid (LMR a a1) Source

parallelConnection :: (Ord a1, Ord a) => (Matroid a, a) -> (Matroid a1, a1) -> Matroid (LMR a a1) Source

twoSum :: (Ord a1, Ord a) => (Matroid a, a) -> (Matroid a1, a1) -> Matroid (LMR a a1) Source

The Fano plane F7 = PG(2,F2)

F7-, the relaxation of the Fano plane by removal of a line

The Pappus configuration from projective geometry

Relaxation of the Pappus configuration by removal of a line

The Desargues configuration

The Vamos matroid V8. It is not representable over any field.

P8 is a minor-minimal matroid that is not representable over F4, F8, F16, ... . It is Fq-representable if and only if q is not a power of 2.

p8' :: (Ord a, Num a) => Matroid a Source

P8- is a relaxation of P8. It is Fq-representable if and only if q >= 4.

P8-- is a relaxation of P8-. It is a minor-minimal matroid that is not representable over F4. It is Fq-representable if and only if q >= 5.

wheelGraph :: (Num a, Enum a) => a -> Graph a Source

w4 :: (Ord a, Num a) => Matroid a Source

Given a matroid m over elements es, the rank polynomial is a polynomial r(x,y), which is essentially a generating function for the subsets of es, enumerated by size and rank. It is efficiently calculated using deletion and contraction.

It has the property that r(0,0) is the number of bases in m, r(1,0) is the number of independent sets, r(0,1) is the number of spanning sets. It can also be used to derive the chromatic polynomial of a graph, the weight enumerator of a linear code, and more.