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In [[graph theory]], the '''graph bandwidth problem''' is to label the ''n'' vertices ''v<sub>i</sub>'' of a graph ''G'' with distinct integers ''f''(''v<sub>i</sub>'') so that the quantity <math>\max\{\,| f(v_i) - f(v_j)| : v_iv_j \in E \,\}</math> is minimized (''E'' is the edge set of ''G'').<ref>{{harv|Chinn|Chvátalová|Dewdney|Gibbs|1982}}</ref> | |||
The problem may be visualized as placing the vertices of a graph at distinct integer points along the ''x''-axis so that the length of the longest edge is minimized. Such placement is called '''linear graph arrangement''', '''linear graph layout''' or '''linear graph placement'''.<ref name=feige/> | |||
The '''weighted graph bandwidth problem''' is a generalization wherein the edges are assigned weights ''w<sub>ij</sub>'' and the [[Loss function|cost function]] to be minimized is <math>\max\{\, w_{ij} |f(v_i) - f(v_j)| : v_iv_j \in E \,\}</math>. | |||
In terms of matrices, the (unweighted) graph bandwidth is the [[bandwidth (matrix theory)|bandwidth]] of the [[symmetric matrix]] which is the [[adjacency matrix]] of the graph. | |||
==Bandwidth formulas for some graphs== | |||
For several families of graphs, the bandwidth <math>\varphi(G)</math> is given by an explicit formula. | |||
The bandwidth of a [[path graph]] <math>P_n</math> on n vertices is <math>1</math>, and for a complete graph <math>K_m</math> we have <math>\varphi(K_n)=n-1</math>. For the [[complete bipartite graph]] <math>K_{m,n},</math> | |||
:<math>\varphi(K_{m,n}) = \lfloor (m-1)/2\rfloor+n</math>, assuming <math>m \ge n\ge 1</math>, | |||
which was proved by Chvátal.<ref>A remark on a problem of Harary. V. Chvátal, ''Czechoslovak Mathematical Journal'' '''20'''(1):109–111, 1970. [http://dml.cz/dmlcz/100949 http://dml.cz/dmlcz/100949]</ref> As a special case of this formula, the [[star graph]] <math>S_k = K_{k,1}</math> on ''k''+1 vertices has bandwidth <math>\varphi(S_{k}) = \lfloor (k-1)/2\rfloor+1</math>. | |||
For the [[hypercube graph]] <math>Q_n</math> on <math>2^n</math> vertices the bandwidth was determined by {{harvtxt|Harper|1966}} to be | |||
:<math>\varphi(Q_n)=\sum_{m=0}^{n-1} \binom{m}{\lfloor m/2\rfloor}.</math> | |||
Chvatálová showed<ref>Optimal Labelling of a product of two paths. J. Chvatálová, ''Discrete Mathematics'' '''11''', 249–253, 1975.</ref> that the bandwidth of the <math>(m \times n)</math> [[lattice graph|square grid graph]] <math>P_m \times P_n</math>, that is, the [[Cartesian product of graphs|Cartesian product]] of two path graphs on <math>m</math> and <math>n</math> vertices, is equal to <math>\min\{m,n\}</math>. | |||
==Bounds== | |||
The bandwidth of a graph can be bounded in terms of various other graph parameters. For instance, letting χ(''G'') denote the [[chromatic number]] of ''G'', | |||
:φ(''G'') ≥ χ(''G'')-1; | |||
letting diam(''G'') denote the [[diameter (graph theory)|diameter]] of ''G'', the following inequalities hold:<ref>{{harvnb|Chinn|Chvátalová|Dewdney|Gibbs|1982}}</ref> | |||
:<math>\lceil (n-1)/\mathrm{diam}(G) \rceil \le \varphi(G) \le n - \mathrm{diam}(G)</math>, | |||
where <math>n</math> is the number of vertices in <math>G</math>. | |||
If a graph <math>G</math> has bandwidth <math>k</math>, then its [[pathwidth]] is at most <math>k</math> {{harv|Kaplan|Shamir|1996}}, and its [[tree-depth]] is at most <math>k\log(n/k)</math> {{harv|Gruber|2012}}. In contrast, as noted in the previous section, the star graph <math>S_k</math>, a structurally | |||
very simple example of a [[tree (graph theory)|tree]], has comparatively large bandwidth. Observe that the [[pathwidth]] of <math>S_k</math> is 1, and its tree-depth is 2. | |||
Some graph families of bounded degree have sublinear bandwidth: {{harvtxt|Chung|1988}} proved that if ''T'' is a tree of maximum degree at most ''∆'', then | |||
:<math>\varphi(T) \le 5n / \log_\Delta n</math>. | |||
More generally, for [[planar graph]]s of bounded maximum degree at most ''∆'', a similar bound holds (cf. {{harvnb|Böttcher|Pruessmann|Taraz|Würfl|2010}}): | |||
:<math>\varphi(G) \le 20n / \log_\Delta n </math>. | |||
==Computing the bandwidth== | |||
Both the unweighted and weighted versions are special cases of the [[quadratic bottleneck assignment problem]]. | |||
The bandwidth problem is [[NP-hard]], even for some special cases.<ref>Garey–Johnson: GT40</ref> Regarding the existence of efficient | |||
[[approximation algorithm]]s, it is known that the bandwidth is [[hardness of approximation|NP-hard to approximate]] within any constant, and this even holds when the input graphs are restricted to [[caterpillar tree]]s {{harv|Dubey|Feige|Unger|2010}}. On the other hand, a number of polynomially-solvable special cases are known.<ref name=feige>"Coping with the NP-Hardness of the Graph Bandwidth Problem", Uriel Feige, ''[[Lecture Notes in Computer Science]]'', Volume 1851, 2000, pp. 129-145, {{doi|10.1007/3-540-44985-X_2}}</ref> A [[heuristic]] algorithm for obtaining linear graph layouts of low bandwidth is the [[Cuthill–McKee algorithm]]. | |||
==Applications== | |||
The interest in this problem comes from some application areas. | |||
One area is [[sparse matrix]]/[[band matrix]] handling, and general algorithms from this area, such as [[Cuthill–McKee algorithm]], may be applied to find approximate solutions for the graph bandwidth problem. | |||
Another application domain is in [[electronic design automation]]. In [[standard cell]] design methodology, typically standard cells have the same height, and their [[placement (EDA)|placement]] is arranged in a number of rows. In this context, graph bandwidth problem models the problem of placement of a set of standard cells in a singe row with the goal of minimizing the maximal [[propagation delay]] (which is assumed to be proportional to wire length). | |||
==See also== | |||
*[[Pathwidth]], a different NP-complete optimization problem involving linear layouts of graphs. | |||
==References== | |||
{{reflist}} | |||
*{{cite doi|10.1016/j.ejc.2009.10.010}} | |||
*{{cite doi|10.1002/jgt.3190060302}} | |||
*{{cite | |||
| last = Chung | |||
| first = Fan R. K. | |||
| author-link = | |||
| last2 = | |||
| first2 = | |||
| author2-link = | |||
| year = 1988 | |||
| date = | |||
| publication-date = | |||
| contribution = Labelings of Graphs | |||
| contribution-url = | |||
| editor-last = | |||
| editor-first = | |||
| editor-link = | |||
| editor2-last = Beineke | |||
| editor2-first = Lowell W. | |||
| editor2-link = | |||
| title = Selected Topics in Graph Theory | |||
| edition = | |||
| series = | |||
| place = | |||
| publication-place = | |||
| publisher = Academic Press | |||
| volume = | |||
| pages = 151–168 | |||
| id = | |||
| isbn = 978-0-12-086203-0 | |||
| doi = | |||
| oclc = | |||
| url = http://www.math.ucsd.edu/~fan/mypaps/fanpap/86log.PDF | |||
}} | |||
*{{cite doi|10.1016/j.jcss.2010.06.006}} | |||
* {{cite book | |||
| last = Garey | |||
| first = M.R. | |||
| authorlink = Michael Garey | |||
| coauthors = [[David S. Johnson|Johnson, D.S.]] | |||
| title = [[Computers and Intractability: A Guide to the Theory of NP-Completeness]] | |||
| year = 1979 | |||
| publisher = W.H. Freeman | |||
| location = New York | |||
| isbn = 0-7167-1045-5 | |||
}} | |||
*{{Citation | |||
| title = On Balanced Separators, Treewidth, and Cycle Rank | |||
| year = 2012 | |||
| author = Gruber, Hermann | |||
| journal = Journal of Combinatorics | |||
| pages = 669–682 | |||
| volume = 3 | |||
| issue = 4 | |||
}} | |||
*{{cite doi|10.1016/S0021-9800(66)80059-5}} | |||
*{{Citation | |||
| title = Pathwidth, bandwidth, and completion problems to proper interval graphs with small cliques | |||
| year = 1996 | |||
| journal = SIAM Journal on Computing | |||
| pages = 540–561 | |||
| volume = 25 | |||
| last1 = Kaplan | first1 = Haim | |||
| last2 = Shamir | first2 = Ron }} | |||
* | |||
==External links== | |||
*[http://www.csc.kth.se/~viggo/wwwcompendium/node53.html Minimum bandwidth problem], in: Pierluigi Crescenzi and Viggo Kann (eds.), ''A compendium of NP optimization problems.'' Accessed May 26, 2010. | |||
[[Category:Graph algorithms]] | |||
[[Category:Combinatorial optimization]] | |||
[[Category:NP-hard problems]] | |||
[[Category:Graph invariants]] |
Revision as of 20:02, 20 March 2013
In graph theory, the graph bandwidth problem is to label the n vertices vi of a graph G with distinct integers f(vi) so that the quantity is minimized (E is the edge set of G).[1] The problem may be visualized as placing the vertices of a graph at distinct integer points along the x-axis so that the length of the longest edge is minimized. Such placement is called linear graph arrangement, linear graph layout or linear graph placement.[2]
The weighted graph bandwidth problem is a generalization wherein the edges are assigned weights wij and the cost function to be minimized is .
In terms of matrices, the (unweighted) graph bandwidth is the bandwidth of the symmetric matrix which is the adjacency matrix of the graph.
Bandwidth formulas for some graphs
For several families of graphs, the bandwidth is given by an explicit formula.
The bandwidth of a path graph on n vertices is , and for a complete graph we have . For the complete bipartite graph
which was proved by Chvátal.[3] As a special case of this formula, the star graph on k+1 vertices has bandwidth .
For the hypercube graph on vertices the bandwidth was determined by Template:Harvtxt to be
Chvatálová showed[4] that the bandwidth of the square grid graph , that is, the Cartesian product of two path graphs on and vertices, is equal to .
Bounds
The bandwidth of a graph can be bounded in terms of various other graph parameters. For instance, letting χ(G) denote the chromatic number of G,
- φ(G) ≥ χ(G)-1;
letting diam(G) denote the diameter of G, the following inequalities hold:[5]
where is the number of vertices in .
If a graph has bandwidth , then its pathwidth is at most Template:Harv, and its tree-depth is at most Template:Harv. In contrast, as noted in the previous section, the star graph , a structurally very simple example of a tree, has comparatively large bandwidth. Observe that the pathwidth of is 1, and its tree-depth is 2.
Some graph families of bounded degree have sublinear bandwidth: Template:Harvtxt proved that if T is a tree of maximum degree at most ∆, then
More generally, for planar graphs of bounded maximum degree at most ∆, a similar bound holds (cf. Template:Harvnb):
Computing the bandwidth
Both the unweighted and weighted versions are special cases of the quadratic bottleneck assignment problem. The bandwidth problem is NP-hard, even for some special cases.[6] Regarding the existence of efficient approximation algorithms, it is known that the bandwidth is NP-hard to approximate within any constant, and this even holds when the input graphs are restricted to caterpillar trees Template:Harv. On the other hand, a number of polynomially-solvable special cases are known.[2] A heuristic algorithm for obtaining linear graph layouts of low bandwidth is the Cuthill–McKee algorithm.
Applications
The interest in this problem comes from some application areas.
One area is sparse matrix/band matrix handling, and general algorithms from this area, such as Cuthill–McKee algorithm, may be applied to find approximate solutions for the graph bandwidth problem.
Another application domain is in electronic design automation. In standard cell design methodology, typically standard cells have the same height, and their placement is arranged in a number of rows. In this context, graph bandwidth problem models the problem of placement of a set of standard cells in a singe row with the goal of minimizing the maximal propagation delay (which is assumed to be proportional to wire length).
See also
- Pathwidth, a different NP-complete optimization problem involving linear layouts of graphs.
References
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External links
- Minimum bandwidth problem, in: Pierluigi Crescenzi and Viggo Kann (eds.), A compendium of NP optimization problems. Accessed May 26, 2010.
- ↑ Template:Harv
- ↑ 2.0 2.1 "Coping with the NP-Hardness of the Graph Bandwidth Problem", Uriel Feige, Lecture Notes in Computer Science, Volume 1851, 2000, pp. 129-145, 21 year-old Glazier James Grippo from Edam, enjoys hang gliding, industrial property developers in singapore developers in singapore and camping. Finds the entire world an motivating place we have spent 4 months at Alejandro de Humboldt National Park.
- ↑ A remark on a problem of Harary. V. Chvátal, Czechoslovak Mathematical Journal 20(1):109–111, 1970. http://dml.cz/dmlcz/100949
- ↑ Optimal Labelling of a product of two paths. J. Chvatálová, Discrete Mathematics 11, 249–253, 1975.
- ↑ Template:Harvnb
- ↑ Garey–Johnson: GT40