Finding Paths between Graph Colourings: PSPACE-completeness and Superpolynomial Distances

dc.contributor.authorBonsma, Paul
dc.contributor.authorCereceda, Luis
dc.description.abstractSuppose we are given a graph G together with two proper vertex k-colourings of G, α and β. How easily can we decide whether it is possible to transform α into β by recolouring vertices of G one at a time, making sure we always have a proper k-colouring of G? This decision problem is trivial for k=2, and decidable in polynomial time for k=3. Here we prove it is PSPACE-complete for all k >= 4. In particular, we prove that the problem remains PSPACE-complete for bipartite graphs, as well as for: (i) planar graphs and 4 <= k <= 6, and (ii) bipartite planar graphs and k=4. Moreover, the values of k in (i) and (ii) are tight, in the sense that for larger values of k, it is always possible to recolour α to β. We also exhibit, for every k >= 4, a class of graphs {GN,k:N>0}, together with two k-colourings for each GN,k, such that the minimum number of recolouring steps required to transform the first colouring into the second is superpolynomial in the size of the graph: the minimum number of steps is Ω(2N), whereas the size of GN is O(N2). This is in stark contrast to the k=3 case, where it is known that the minimum number of recolouring steps is at most quadratic in the number of vertices. We also show that a class of bipartite graphs can be constructed with this property, and that: (i) for 4 <= k <= 6 planar graphs and (ii) for k=4 bipartite planar graphs can be constructed with this property. This provides a remarkable correspondence between the tractability of the problem and its underlying structure.en
dc.subject.ddc510 Mathematiken
dc.subject.othervertex recolouringen
dc.subject.othercolour graphen
dc.subject.othersuperpolynomial distanceen
dc.titleFinding Paths between Graph Colourings: PSPACE-completeness and Superpolynomial Distancesen
dc.typeResearch Paperen
tub.affiliationFak. 2 Mathematik und Naturwissenschaften>Inst. Mathematikde
tub.affiliation.facultyFak. 2 Mathematik und Naturwissenschaftende
tub.affiliation.instituteInst. Mathematikde
tub.publisher.universityorinstitutionTechnische Universität Berlinen
tub.series.issuenumber2007, 21en
tub.series.namePreprint-Reihe des Instituts für Mathematik, Technische Universität Berlinen
Original bundle
Now showing 1 - 1 of 1
Thumbnail Image
206.68 KB
Adobe Portable Document Format