Jérôme Monnot, Université Paris-Dauphine, LAMSADE, France … · 2017-09-12 · 1 - Bazgan et...
Transcript of Jérôme Monnot, Université Paris-Dauphine, LAMSADE, France … · 2017-09-12 · 1 - Bazgan et...
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Weighted Upper Domination
Arman Boyacı, Bogazici University, TurkeyJérôme Monnot, Université Paris-Dauphine, LAMSADE, France
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Abstract
- Upper Domination Number: the cardinality of maximum minimal dominating set
- NP-complete even in planar and co-bipartite graphs.- Polynomial-time solvable in strongly perfect graphs (bipartite, split).- We show that the weighted version is NP-complete even in very
restricted cases of bipartite and split graphs.
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Domination+Private Neighbor (possibly itself)
D D’
A vertex set D is dominating if all vertices outside of D have a neighbour in D.
D is minimal dominating set if D is dominating and minimal for inclusion.
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(G) = 2 Γ(G) = 3
Minimum Domination Upper Domination
A graph may have dominating sets of different cardinalities.
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Maximum Minimal Dominating Set (a.k.a. Upper Domination)
Some Other MaxMin / MinMax Problems Considered in the Literature:
- Minimum Maximal Matching
- Minimum Maximal Independent Set
- Maximum Minimal Vertex Cover
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1 - Bazgan et al., The Many Facets of Upper Domination, Theoretical Computer Science, 2017 (accepted)2 - Aboueisha et al., Upper Domination: towards a dichotomy through boundary properties, Algorithmica, 2017 (accepted)3 - Hare et al., Linear-time computability of combinatorial problem generalized-series-parallel graphs, Discrete Algorithms, 19874 - Cheston et al, Classes of graphs for which upper fractional domination equals independence, upper domination, and upper irredundance, Discrete Applied Mathematics, 1994
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A verset set I is independent if none of the vertices in I is adjacent to none of the vertices of I.
A vertex set S is irredundant if every element of S has a private neighbor.
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Maximal Irredundant Sets
Minimal Dominating Sets
Every maximal independent set is a minimal dominating set.
Every minimal dominating set is a maximal irredundant set.
Maximal Independent
Sets
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Maximal Irredundant Sets
Minimal Dominating Sets
Maximal Independent
Sets
ir(G) IR(G)
(G) Γ(G)i(G) (G)
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Well-known domination chain
ir(G) ≤ (G) ≤ i(G) ≤ (G) ≤ Γ(G) ≤ IR(G)Maximal Irredundant Sets
Minimal Dominating Sets
Maximal Independent
Sets
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A graph where (G) = Γ(G) = IR(G)
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When (G) = Γ(G) = IR(G) ?
Most general answer is: If G is a strongly perfect graph*.
And fortunately, maximum independent set in strongly perfect graphs is solvable in polynomial-time.
*Every induced subgraph H has an independent vertex set meeting all maximal cliques of H.
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Weighted Upper Domination Set(WUDS)
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We may have w(G) < Γw(G) even for a simple path graph
1 2 2 1
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Main results
Theorem: Computing WUDS is strongly NP-hard for 3-subregular split graphs, even for bi-valued weights.
Theorem: Computing WUDS is strongly NP-hard for planar bipartite graphs of maximum degree 4, even for tri-valued weights.
Corollary: For any >0, WUDS is not O(n1-
)-approximable in split graphs on n vertices, even for bi-valued weights, unless NP ≠ ZPP
Corollary: WUDS is APX-complete in bipartite graphs.
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Remark 1
Theorem. Computing WUDS is strongly NP-hard for 3-subregular split graphs, even for bi-valued weights.
The strongest hardness result that we can produce.
A 2-subregular split graph.
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Remark 2
WUDS with performance ratio O(n) is always
possible.
By taking any maximal independent set containing
a vertex of maximum weight wmax
.
By Corollary: For any >0, WUDS is not O(n1-
)-approximable in split graphs on n vertices, even for bi-valued weights, unless NP ≠ ZPP.
This is the best we can have for split graphs.
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Theorem. Computing WUDS is strongly NP-hard for 3-subregular split graphs, even for bi-valued weights.
Reduction is done from THE MAXIMUM INDUCED MATCHING PROBLEM.
✔❌
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L R
Bipartite Planar Subcubic
L
w(v) = n
Split 3-subregular
R
w(v) = 1
Construction
d(v)=2 d(v)=3
G G’
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Claim
MIM of G of size at least k ≥ 1 ⇔ UDS of G’ of weight at least nk ≥ n
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MIM of G of size at least k ≥ 1 ⇒ UDS of G’ of weight at least nk ≥ n
G
{k1 - D dominates G’.2 - D is minimal.3 - w(D) ≥ nk.
L R
G’
n
n
nnn
1
1
11111
L’ R’
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UDS of G’ of weight at least nk ≥ n ⇒ MIM of G of size at least k ≥ 1
G’
n
n
nnn
1
1
11111
1 - |L’∩D| is at least k.2 - M is an induced matching.
G
L RL’ R’
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- Complexity of UDS in special graph classes- Unweighted: line graphs, d-regular graphs for d>4,- Weighted: series-parallel, permutation, interval and many more.
- Equivalent problems:- Min Max Matching ~ Min Edge Dominating Set- Min Max Independent Set ~ Min Independent Dominating Set
- Recognition of well-dominated graphs
- For every graph G in series - parallel graphs, do we have (G) = Γ(G)?
Open Problems
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1 - Bazgan et al., The Many Facets of Upper Domination, Theoretical Computer Science, 2017 (accepted)2 - Aboueisha et al., Upper Domination: towards a dichotomy through boundary properties, Algorithmica, 2017 (accepted)3 - Hare et al., Linear-time computability of combinatorial problem generalized-series-parallel graphs, Discrete Algorithms, 19874 - Cheston et al, Classes of graphs for which upper fractional domination equals independence, upper domination, and upper irredundance, Discrete Applied Mathematics, 1994
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Thank you.
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Dynamic Programming for WUDS in trees
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Theorem: UDS is not O(n1 - ϵ)-approximable even in co-bipartite graphs.
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A split graph is called a p-subregular if for l ∈ L, dG
(l) - |L| + 1 ≤ p and for r ∈ R, dG
(r) ≤ p.
A 2-subregular split graph.
L R