Algebra.Graph.NonEmpty.AdjacencyMap

Alga is a library for algebraic construction and manipulation of graphs in Haskell. See this paper for the motivation behind the library, the underlying theory, and implementation details.

This module defines the data type AdjacencyMap for graphs that are known to be non-empty at compile time. To avoid name clashes with Algebra.Graph.AdjacencyMap, this module can be imported qualified:

import qualified Algebra.Graph.NonEmpty.AdjacencyMap as NonEmpty

The naming convention generally follows that of Data.List.NonEmpty: we use suffix 1 to indicate the functions whose interface must be changed compared to Algebra.Graph.AdjacencyMap, e.g. vertices1.

Data structure

data AdjacencyMap a

The AdjacencyMap data type represents a graph by a map of vertices to their adjacency sets. We define a Num instance as a convenient notation for working with graphs:

0           == vertex 0
1 + 2       == overlay (vertex 1) (vertex 2)
1 * 2       == connect (vertex 1) (vertex 2)
1 + 2 * 3   == overlay (vertex 1) (connect (vertex 2) (vertex 3))
1 * (2 + 3) == connect (vertex 1) (overlay (vertex 2) (vertex 3))

Note: the signum method of the type class Num cannot be implemented and will throw an error. Furthermore, the Num instance does not satisfy several "customary laws" of Num, which dictate that fromInteger 0 and fromInteger 1 should act as additive and multiplicative identities, and negate as additive inverse. Nevertheless, overloading fromInteger, + and * is very convenient when working with algebraic graphs; we hope that in future Haskell's Prelude will provide a more fine-grained class hierarchy for algebraic structures, which we would be able to utilise without violating any laws.

The Show instance is defined using basic graph construction primitives:

show (1         :: AdjacencyMap Int) == "vertex 1"
show (1 + 2     :: AdjacencyMap Int) == "vertices1 [1,2]"
show (1 * 2     :: AdjacencyMap Int) == "edge 1 2"
show (1 * 2 * 3 :: AdjacencyMap Int) == "edges1 [(1,2),(1,3),(2,3)]"
show (1 * 2 + 3 :: AdjacencyMap Int) == "overlay (vertex 3) (edge 1 2)"

The Eq instance satisfies the following laws of algebraic graphs:

• overlay is commutative, associative and idempotent:

        x + y == y + x
  x + (y + z) == (x + y) + z
        x + x == x

• connect is associative:

  x * (y * z) == (x * y) * z

• connect distributes over overlay:

  x * (y + z) == x * y + x * z
  (x + y) * z == x * z + y * z

• connect can be decomposed:

  x * y * z == x * y + x * z + y * z

• connect satisfies absorption and saturation:

  x * y + x + y == x * y
      x * x * x == x * x

When specifying the time and memory complexity of graph algorithms, n and m will denote the number of vertices and edges in the graph, respectively.

The total order on graphs is defined using size-lexicographic comparison:

• Compare the number of vertices. In case of a tie, continue.
• Compare the sets of vertices. In case of a tie, continue.
• Compare the number of edges. In case of a tie, continue.
• Compare the sets of edges.

Here are a few examples:

vertex 1 < vertex 2
vertex 3 < edge 1 2
vertex 1 < edge 1 1
edge 1 1 < edge 1 2
edge 1 2 < edge 1 1 + edge 2 2
edge 1 2 < edge 1 3

Note that the resulting order refines the isSubgraphOf relation and is compatible with overlay and connect operations:

isSubgraphOf x y ==> x <= y

x     <= x + y
x + y <= x * y

Instances

Eq a => Eq (AdjacencyMap a)

Defined in Algebra.Graph.NonEmpty.AdjacencyMap

Methods

(==) :: AdjacencyMap a -> AdjacencyMap a -> Bool

(/=) :: AdjacencyMap a -> AdjacencyMap a -> Bool

(Ord a, Num a) => Num (AdjacencyMap a)

Note: this does not satisfy the usual ring laws; see AdjacencyMap for more details.

Defined in Algebra.Graph.NonEmpty.AdjacencyMap

Methods

(+) :: AdjacencyMap a -> AdjacencyMap a -> AdjacencyMap a

(-) :: AdjacencyMap a -> AdjacencyMap a -> AdjacencyMap a

(*) :: AdjacencyMap a -> AdjacencyMap a -> AdjacencyMap a

negate :: AdjacencyMap a -> AdjacencyMap a

abs :: AdjacencyMap a -> AdjacencyMap a

signum :: AdjacencyMap a -> AdjacencyMap a

fromInteger :: Integer -> AdjacencyMap a

Ord a => Ord (AdjacencyMap a)

Defined in Algebra.Graph.NonEmpty.AdjacencyMap

Methods

compare :: AdjacencyMap a -> AdjacencyMap a -> Ordering

(<) :: AdjacencyMap a -> AdjacencyMap a -> Bool

(<=) :: AdjacencyMap a -> AdjacencyMap a -> Bool

(>) :: AdjacencyMap a -> AdjacencyMap a -> Bool

(>=) :: AdjacencyMap a -> AdjacencyMap a -> Bool

max :: AdjacencyMap a -> AdjacencyMap a -> AdjacencyMap a

min :: AdjacencyMap a -> AdjacencyMap a -> AdjacencyMap a

(Ord a, Show a) => Show (AdjacencyMap a)

Defined in Algebra.Graph.NonEmpty.AdjacencyMap

Methods

showsPrec :: Int -> AdjacencyMap a -> ShowS

show :: AdjacencyMap a -> String

showList :: [AdjacencyMap a] -> ShowS

IsString a => IsString (AdjacencyMap a)

Defined in Algebra.Graph.NonEmpty.AdjacencyMap

Methods

fromString :: String -> AdjacencyMap a

Generic (AdjacencyMap a)

Defined in Algebra.Graph.NonEmpty.AdjacencyMap

Associated Types

type Rep (AdjacencyMap a) :: Type -> Type

Methods

from :: AdjacencyMap a -> Rep (AdjacencyMap a) x

to :: Rep (AdjacencyMap a) x -> AdjacencyMap a

Ord a => Semigroup (AdjacencyMap a)

Defined via overlay.

Defined in Algebra.Graph.NonEmpty.AdjacencyMap

Methods

(<>) :: AdjacencyMap a -> AdjacencyMap a -> AdjacencyMap a

sconcat :: NonEmpty (AdjacencyMap a) -> AdjacencyMap a

stimes :: Integral b => b -> AdjacencyMap a -> AdjacencyMap a

NFData a => NFData (AdjacencyMap a)

Defined in Algebra.Graph.NonEmpty.AdjacencyMap

Methods

rnf :: AdjacencyMap a -> ()

Ord a => ToGraph (AdjacencyMap a)

See Algebra.Graph.NonEmpty.AdjacencyMap.

Defined in Algebra.Graph.ToGraph

Associated Types

type ToVertex (AdjacencyMap a)

Methods

toGraph :: AdjacencyMap a -> Graph (ToVertex (AdjacencyMap a))

foldg :: r -> (ToVertex (AdjacencyMap a) -> r) -> (r -> r -> r) -> (r -> r -> r) -> AdjacencyMap a -> r

isEmpty :: AdjacencyMap a -> Bool

hasVertex :: ToVertex (AdjacencyMap a) -> AdjacencyMap a -> Bool

hasEdge :: ToVertex (AdjacencyMap a) -> ToVertex (AdjacencyMap a) -> AdjacencyMap a -> Bool

vertexCount :: AdjacencyMap a -> Int

edgeCount :: AdjacencyMap a -> Int

vertexList :: AdjacencyMap a -> [ToVertex (AdjacencyMap a)]

edgeList :: AdjacencyMap a -> [(ToVertex (AdjacencyMap a), ToVertex (AdjacencyMap a))]

vertexSet :: AdjacencyMap a -> Set (ToVertex (AdjacencyMap a))

vertexIntSet :: AdjacencyMap a -> IntSet

edgeSet :: AdjacencyMap a -> Set (ToVertex (AdjacencyMap a), ToVertex (AdjacencyMap a))

preSet :: ToVertex (AdjacencyMap a) -> AdjacencyMap a -> Set (ToVertex (AdjacencyMap a))

preIntSet :: Int -> AdjacencyMap a -> IntSet

postSet :: ToVertex (AdjacencyMap a) -> AdjacencyMap a -> Set (ToVertex (AdjacencyMap a))

postIntSet :: Int -> AdjacencyMap a -> IntSet

adjacencyList :: AdjacencyMap a -> [(ToVertex (AdjacencyMap a), [ToVertex (AdjacencyMap a)])]

dfsForest :: AdjacencyMap a -> Forest (ToVertex (AdjacencyMap a))

dfsForestFrom :: [ToVertex (AdjacencyMap a)] -> AdjacencyMap a -> Forest (ToVertex (AdjacencyMap a))

dfs :: [ToVertex (AdjacencyMap a)] -> AdjacencyMap a -> [ToVertex (AdjacencyMap a)]

reachable :: ToVertex (AdjacencyMap a) -> AdjacencyMap a -> [ToVertex (AdjacencyMap a)]

topSort :: AdjacencyMap a -> Either (Cycle (ToVertex (AdjacencyMap a))) [ToVertex (AdjacencyMap a)]

isAcyclic :: AdjacencyMap a -> Bool

toAdjacencyMap :: AdjacencyMap a -> AdjacencyMap0 (ToVertex (AdjacencyMap a))

toAdjacencyMapTranspose :: AdjacencyMap a -> AdjacencyMap0 (ToVertex (AdjacencyMap a))

toAdjacencyIntMap :: AdjacencyMap a -> AdjacencyIntMap

toAdjacencyIntMapTranspose :: AdjacencyMap a -> AdjacencyIntMap

isDfsForestOf :: Forest (ToVertex (AdjacencyMap a)) -> AdjacencyMap a -> Bool

isTopSortOf :: [ToVertex (AdjacencyMap a)] -> AdjacencyMap a -> Bool

type Rep (AdjacencyMap a)

Defined in Algebra.Graph.NonEmpty.AdjacencyMap

type Rep (AdjacencyMap a) = D1 ('MetaData "AdjacencyMap" "Algebra.Graph.NonEmpty.AdjacencyMap" "algebraic-graphs-0.6.1-1GHbchCaOhb8Cb1GtyPsoY" 'True) (C1 ('MetaCons "NAM" 'PrefixI 'True) (S1 ('MetaSel ('Just "am") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 (AdjacencyMap a))))

type ToVertex (AdjacencyMap a)

Defined in Algebra.Graph.ToGraph

type ToVertex (AdjacencyMap a) = a

toNonEmpty :: AdjacencyMap a -> Maybe (AdjacencyMap a)

Convert a possibly empty AdjacencyMap into NonEmpty.AdjacencyMap. Returns Nothing if the argument is empty. Complexity: O(1) time, memory and size.

toNonEmpty empty          == Nothing
toNonEmpty . fromNonEmpty == Just

fromNonEmpty :: AdjacencyMap a -> AdjacencyMap a

Convert a NonEmpty.AdjacencyMap into an AdjacencyMap. The resulting graph is guaranteed to be non-empty. Complexity: O(1) time, memory and size.

isEmpty . fromNonEmpty    == const False
toNonEmpty . fromNonEmpty == Just

Basic graph construction primitives

vertex :: a -> AdjacencyMap a

Construct the graph comprising a single isolated vertex.

hasVertex x (vertex y) == (x == y)
vertexCount (vertex x) == 1
edgeCount   (vertex x) == 0

edge :: Ord a => a -> a -> AdjacencyMap a

Construct the graph comprising a single edge.

edge x y               == connect (vertex x) (vertex y)
hasEdge x y (edge x y) == True
edgeCount   (edge x y) == 1
vertexCount (edge 1 1) == 1
vertexCount (edge 1 2) == 2

overlay :: Ord a => AdjacencyMap a -> AdjacencyMap a -> AdjacencyMap a

Overlay two graphs. This is a commutative, associative and idempotent operation with the identity empty. Complexity: O((n + m) * log(n)) time and O(n + m) memory.

hasVertex z (overlay x y) == hasVertex z x || hasVertex z y
vertexCount (overlay x y) >= vertexCount x
vertexCount (overlay x y) <= vertexCount x + vertexCount y
edgeCount   (overlay x y) >= edgeCount x
edgeCount   (overlay x y) <= edgeCount x   + edgeCount y
vertexCount (overlay 1 2) == 2
edgeCount   (overlay 1 2) == 0

connect :: Ord a => AdjacencyMap a -> AdjacencyMap a -> AdjacencyMap a

Connect two graphs. This is an associative operation with the identity empty, which distributes over overlay and obeys the decomposition axiom. Complexity: O((n + m) * log(n)) time and O(n + m) memory. Note that the number of edges in the resulting graph is quadratic with respect to the number of vertices of the arguments: m = O(m1 + m2 + n1 * n2).

hasVertex z (connect x y) == hasVertex z x || hasVertex z y
vertexCount (connect x y) >= vertexCount x
vertexCount (connect x y) <= vertexCount x + vertexCount y
edgeCount   (connect x y) >= edgeCount x
edgeCount   (connect x y) >= edgeCount y
edgeCount   (connect x y) >= vertexCount x * vertexCount y
edgeCount   (connect x y) <= vertexCount x * vertexCount y + edgeCount x + edgeCount y
vertexCount (connect 1 2) == 2
edgeCount   (connect 1 2) == 1

vertices1 :: Ord a => NonEmpty a -> AdjacencyMap a

Construct the graph comprising a given list of isolated vertices. Complexity: O(L * log(L)) time and O(L) memory, where L is the length of the given list.

vertices1 [x]           == vertex x
hasVertex x . vertices1 == elem x
vertexCount . vertices1 == length . nub
vertexSet   . vertices1 == Set.fromList . toList

edges1 :: Ord a => NonEmpty (a, a) -> AdjacencyMap a

Construct the graph from a list of edges. Complexity: O((n + m) * log(n)) time and O(n + m) memory.

edges1 [(x,y)]     == edge x y
edges1             == overlays1 . fmap (uncurry edge)
edgeCount . edges1 == length . nub

overlays1 :: Ord a => NonEmpty (AdjacencyMap a) -> AdjacencyMap a

Overlay a given list of graphs. Complexity: O((n + m) * log(n)) time and O(n + m) memory.

overlays1 [x]   == x
overlays1 [x,y] == overlay x y

connects1 :: Ord a => NonEmpty (AdjacencyMap a) -> AdjacencyMap a

Connect a given list of graphs. Complexity: O((n + m) * log(n)) time and O(n + m) memory.

connects1 [x]   == x
connects1 [x,y] == connect x y

Relations on graphs

isSubgraphOf :: Ord a => AdjacencyMap a -> AdjacencyMap a -> Bool

The isSubgraphOf function takes two graphs and returns True if the first graph is a subgraph of the second. Complexity: O((n + m) * log(n)) time.

isSubgraphOf x             (overlay x y) ==  True
isSubgraphOf (overlay x y) (connect x y) ==  True
isSubgraphOf (path1 xs)    (circuit1 xs) ==  True
isSubgraphOf x y                         ==> x <= y

Graph properties

hasVertex :: Ord a => a -> AdjacencyMap a -> Bool

Check if a graph contains a given vertex. Complexity: O(log(n)) time.

hasVertex x (vertex y) == (x == y)

hasEdge :: Ord a => a -> a -> AdjacencyMap a -> Bool

Check if a graph contains a given edge. Complexity: O(log(n)) time.

hasEdge x y (vertex z)       == False
hasEdge x y (edge x y)       == True
hasEdge x y . removeEdge x y == const False
hasEdge x y                  == elem (x,y) . edgeList

vertexCount :: AdjacencyMap a -> Int

The number of vertices in a graph. Complexity: O(1) time.

vertexCount (vertex x)        ==  1
vertexCount                   ==  length . vertexList
vertexCount x < vertexCount y ==> x < y

edgeCount :: AdjacencyMap a -> Int

The number of edges in a graph. Complexity: O(n) time.

edgeCount (vertex x) == 0
edgeCount (edge x y) == 1
edgeCount            == length . edgeList

vertexList1 :: AdjacencyMap a -> NonEmpty a

The sorted list of vertices of a given graph. Complexity: O(n) time and memory.

vertexList1 (vertex x)  == [x]
vertexList1 . vertices1 == nub . sort

edgeList :: AdjacencyMap a -> [(a, a)]

The sorted list of edges of a graph. Complexity: O(n + m) time and O(m) memory.

edgeList (vertex x)     == []
edgeList (edge x y)     == [(x,y)]
edgeList (star 2 [3,1]) == [(2,1), (2,3)]
edgeList . edges        == nub . sort
edgeList . transpose    == sort . map swap . edgeList

vertexSet :: AdjacencyMap a -> Set a

The set of vertices of a given graph. Complexity: O(n) time and memory.

vertexSet . vertex    == Set.singleton
vertexSet . vertices1 == Set.fromList . toList
vertexSet . clique1   == Set.fromList . toList

edgeSet :: Ord a => AdjacencyMap a -> Set (a, a)

The set of edges of a given graph. Complexity: O((n + m) * log(m)) time and O(m) memory.

edgeSet (vertex x) == Set.empty
edgeSet (edge x y) == Set.singleton (x,y)
edgeSet . edges    == Set.fromList

preSet :: Ord a => a -> AdjacencyMap a -> Set a

The preset of an element x is the set of its direct predecessors. Complexity: O(n * log(n)) time and O(n) memory.

preSet x (vertex x) == Set.empty
preSet 1 (edge 1 2) == Set.empty
preSet y (edge x y) == Set.fromList [x]

postSet :: Ord a => a -> AdjacencyMap a -> Set a

The postset of a vertex is the set of its direct successors. Complexity: O(log(n)) time and O(1) memory.

postSet x (vertex x) == Set.empty
postSet x (edge x y) == Set.fromList [y]
postSet 2 (edge 1 2) == Set.empty

Standard families of graphs

path1 :: Ord a => NonEmpty a -> AdjacencyMap a

The path on a list of vertices. Complexity: O((n + m) * log(n)) time and O(n + m) memory.

path1 [x]       == vertex x
path1 [x,y]     == edge x y
path1 . reverse == transpose . path1

circuit1 :: Ord a => NonEmpty a -> AdjacencyMap a

The circuit on a list of vertices. Complexity: O((n + m) * log(n)) time and O(n + m) memory.

circuit1 [x]       == edge x x
circuit1 [x,y]     == edges1 [(x,y), (y,x)]
circuit1 . reverse == transpose . circuit1

clique1 :: Ord a => NonEmpty a -> AdjacencyMap a

The clique on a list of vertices. Complexity: O((n + m) * log(n)) time and O(n + m) memory.

clique1 [x]        == vertex x
clique1 [x,y]      == edge x y
clique1 [x,y,z]    == edges1 [(x,y), (x,z), (y,z)]
clique1 (xs <> ys) == connect (clique1 xs) (clique1 ys)
clique1 . reverse  == transpose . clique1

biclique1 :: Ord a => NonEmpty a -> NonEmpty a -> AdjacencyMap a

The biclique on two lists of vertices. Complexity: O(n * log(n) + m) time and O(n + m) memory.

biclique1 [x1,x2] [y1,y2] == edges1 [(x1,y1), (x1,y2), (x2,y1), (x2,y2)]
biclique1 xs      ys      == connect (vertices1 xs) (vertices1 ys)

star :: Ord a => a -> [a] -> AdjacencyMap a

The star formed by a centre vertex connected to a list of leaves. Complexity: O((n + m) * log(n)) time and O(n + m) memory.

star x []    == vertex x
star x [y]   == edge x y
star x [y,z] == edges1 [(x,y), (x,z)]

stars1 :: Ord a => NonEmpty (a, [a]) -> AdjacencyMap a

The stars formed by overlaying a list of stars. An inverse of adjacencyList. Complexity: O(L * log(n)) time, memory and size, where L is the total size of the input.

stars1 [(x, [] )]               == vertex x
stars1 [(x, [y])]               == edge x y
stars1 [(x, ys )]               == star x ys
stars1                          == overlays1 . fmap (uncurry star)
overlay (stars1 xs) (stars1 ys) == stars1 (xs <> ys)

tree :: Ord a => Tree a -> AdjacencyMap a

The tree graph constructed from a given Tree data structure. Complexity: O((n + m) * log(n)) time and O(n + m) memory.

tree (Node x [])                                         == vertex x
tree (Node x [Node y [Node z []]])                       == path1 [x,y,z]
tree (Node x [Node y [], Node z []])                     == star x [y,z]
tree (Node 1 [Node 2 [], Node 3 [Node 4 [], Node 5 []]]) == edges1 [(1,2), (1,3), (3,4), (3,5)]

Graph transformation

removeVertex1 :: Ord a => a -> AdjacencyMap a -> Maybe (AdjacencyMap a)

Remove a vertex from a given graph. Complexity: O(n*log(n)) time.

removeVertex1 x (vertex x)          == Nothing
removeVertex1 1 (vertex 2)          == Just (vertex 2)
removeVertex1 x (edge x x)          == Nothing
removeVertex1 1 (edge 1 2)          == Just (vertex 2)
removeVertex1 x >=> removeVertex1 x == removeVertex1 x

removeEdge :: Ord a => a -> a -> AdjacencyMap a -> AdjacencyMap a

Remove an edge from a given graph. Complexity: O(log(n)) time.

removeEdge x y (edge x y)       == vertices1 [x,y]
removeEdge x y . removeEdge x y == removeEdge x y
removeEdge 1 1 (1 * 1 * 2 * 2)  == 1 * 2 * 2
removeEdge 1 2 (1 * 1 * 2 * 2)  == 1 * 1 + 2 * 2

replaceVertex :: Ord a => a -> a -> AdjacencyMap a -> AdjacencyMap a

The function replaceVertex x y replaces vertex x with vertex y in a given AdjacencyMap. If y already exists, x and y will be merged. Complexity: O((n + m) * log(n)) time.

replaceVertex x x            == id
replaceVertex x y (vertex x) == vertex y
replaceVertex x y            == mergeVertices (== x) y

mergeVertices :: Ord a => (a -> Bool) -> a -> AdjacencyMap a -> AdjacencyMap a

Merge vertices satisfying a given predicate into a given vertex. Complexity: O((n + m) * log(n)) time, assuming that the predicate takes constant time.

mergeVertices (const False) x    == id
mergeVertices (== x) y           == replaceVertex x y
mergeVertices even 1 (0 * 2)     == 1 * 1
mergeVertices odd  1 (3 + 4 * 5) == 4 * 1

transpose :: Ord a => AdjacencyMap a -> AdjacencyMap a

Transpose a given graph. Complexity: O(m * log(n)) time, O(n + m) memory.

transpose (vertex x)  == vertex x
transpose (edge x y)  == edge y x
transpose . transpose == id
edgeList . transpose  == sort . map swap . edgeList

gmap :: (Ord a, Ord b) => (a -> b) -> AdjacencyMap a -> AdjacencyMap b

Transform a graph by applying a function to each of its vertices. This is similar to Functor's fmap but can be used with non-fully-parametric AdjacencyMap. Complexity: O((n + m) * log(n)) time.

gmap f (vertex x) == vertex (f x)
gmap f (edge x y) == edge (f x) (f y)
gmap id           == id
gmap f . gmap g   == gmap (f . g)

induce1 :: (a -> Bool) -> AdjacencyMap a -> Maybe (AdjacencyMap a)

Construct the induced subgraph of a given graph by removing the vertices that do not satisfy a given predicate. Complexity: O(m) time, assuming that the predicate takes constant time.

induce1 (const True ) x == Just x
induce1 (const False) x == Nothing
induce1 (/= x)          == removeVertex1 x
induce1 p >=> induce1 q == induce1 (\x -> p x && q x)

induceJust1 :: Ord a => AdjacencyMap (Maybe a) -> Maybe (AdjacencyMap a)

Construct the induced subgraph of a given graph by removing the vertices that are Nothing. Returns Nothing if the resulting graph is empty. Complexity: O(n + m) time.

induceJust1 (vertex Nothing)                               == Nothing
induceJust1 (edge (Just x) Nothing)                        == Just (vertex x)
induceJust1 . gmap Just                                    == Just
induceJust1 . gmap (\x -> if p x then Just x else Nothing) == induce1 p

Graph closure

closure :: Ord a => AdjacencyMap a -> AdjacencyMap a

Compute the reflexive and transitive closure of a graph. Complexity: O(n * m * log(n)^2) time.

closure (vertex x)       == edge x x
closure (edge x x)       == edge x x
closure (edge x y)       == edges1 [(x,x), (x,y), (y,y)]
closure (path1 $ nub xs) == reflexiveClosure (clique1 $ nub xs)
closure                  == reflexiveClosure . transitiveClosure
closure                  == transitiveClosure . reflexiveClosure
closure . closure        == closure
postSet x (closure y)    == Set.fromList (reachable x y)

reflexiveClosure :: Ord a => AdjacencyMap a -> AdjacencyMap a

Compute the reflexive closure of a graph by adding a self-loop to every vertex. Complexity: O(n * log(n)) time.

reflexiveClosure (vertex x)         == edge x x
reflexiveClosure (edge x x)         == edge x x
reflexiveClosure (edge x y)         == edges1 [(x,x), (x,y), (y,y)]
reflexiveClosure . reflexiveClosure == reflexiveClosure

symmetricClosure :: Ord a => AdjacencyMap a -> AdjacencyMap a

Compute the symmetric closure of a graph by overlaying it with its own transpose. Complexity: O((n + m) * log(n)) time.

symmetricClosure (vertex x)         == vertex x
symmetricClosure (edge x y)         == edges1 [(x,y), (y,x)]
symmetricClosure x                  == overlay x (transpose x)
symmetricClosure . symmetricClosure == symmetricClosure

transitiveClosure :: Ord a => AdjacencyMap a -> AdjacencyMap a

Compute the transitive closure of a graph. Complexity: O(n * m * log(n)^2) time.

transitiveClosure (vertex x)          == vertex x
transitiveClosure (edge x y)          == edge x y
transitiveClosure (path1 $ nub xs)    == clique1 (nub xs)
transitiveClosure . transitiveClosure == transitiveClosure

Miscellaneous

consistent :: Ord a => AdjacencyMap a -> Bool

Check that the internal graph representation is consistent, i.e. that all edges refer to existing vertices, and the graph is non-empty. It should be impossible to create an inconsistent adjacency map, and we use this function in testing.

consistent (vertex x)    == True
consistent (overlay x y) == True
consistent (connect x y) == True
consistent (edge x y)    == True
consistent (edges xs)    == True
consistent (stars xs)    == True