Directed Low Diameter Decomposition for Structured Digraphs
Pith reviewed 2026-07-01 03:06 UTC · model grok-4.3
The pith
Directed graphs with pathwidth pw admit low-diameter decompositions with diameter linear in pw.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
Any directed graph with pathwidth pw admits an (O(pw), Δ)-LDD. The integrality gap of the Directed Non-Bipartite Sparsest-Cut LP relaxation on an n-vertex graph with treewidth tw is O(tw log n). Both statements follow from a refined analysis of the quasipartition construction that works on bounded-treewidth and bounded-pathwidth digraphs.
What carries the argument
The refined quasipartition construction that produces both the linear-in-pw LDD and the O(tw log n) integrality gap.
If this is right
- Every directed graph of pathwidth pw has an (O(pw), Δ)-LDD.
- The directed non-bipartite sparsest-cut LP has integrality gap O(tw log n) on all treewidth-tw graphs.
- The previous exponential dependence on pw for LDDs is replaced by linear dependence.
- The previous O(tw log² n) integrality-gap bound is tightened by one logarithmic factor.
Where Pith is reading between the lines
- The same refinement technique may produce improved LDDs or cut approximations for other width measures such as branchwidth.
- Faster approximation algorithms for directed cut and clustering problems become possible on the subclass of low-pathwidth or low-treewidth digraphs.
- The linear LDD bound may combine with dynamic-programming methods that already run in 2^O(pw) n time to give end-to-end polynomial dependence on pw for some problems.
Load-bearing premise
The existing quasipartition construction admits a tighter analysis that removes the extra logarithmic factor from the gap and yields linear dependence on pathwidth.
What would settle it
An explicit directed graph of pathwidth pw on which every LDD requires diameter ω(pw), or an n-vertex treewidth-tw digraph whose directed non-bipartite sparsest-cut LP gap is ω(tw log n).
Figures
read the original abstract
Low diameter decompositions, or LDDs for short, are a fundamental primitive in the design of efficient graph algorithms. Roughly speaking, an LDD is a distribution over partitions of the vertices into bounded-diameter clusters such that nearby vertices are likely to be clustered together. Recently, there has been growing interest in lifting the notion of LDDs into \emph{directed graphs}. In particular, there are two natural directed analogues. The first is a directed LDD, where after removing a random subset of edges, every strongly connected component has a small diameter. The second is a quasipartition, which imposes the stronger requirement that whenever one vertex can still reach another after the edge removal, the two vertices must be close in the original directed metric. Every quasipartition yields an LDD, but the converse does not necessarily hold. In this work, we initiate the systematic study of LDDs in structured directed graphs. As our first main result, we show that any directed graph with pathwidth $\mathsf{pw}$ admits an $(O(\mathsf{pw}), \Delta)$-LDD. This improves upon the previous best-known $(2^{O(\mathsf{pw}^2)}, \Delta)$-LDD construction, which was implicitly derived from the quasipartition result of Salmasi, Sidiropoulos, and Sridhar [SODA'19]. As our second result, we show that the integrality gap of the Directed Non-Bipartite Sparsest-Cut LP relaxation on an $n$-vertex graph with treewidth $\mathsf{tw}$ is $O(\mathsf{tw} \log n)$. This improves upon the $O(\mathsf{tw}\log^2 n)$ bound of M\'emoli, Sidiropoulos, and Sridhar [ICALP'16, Algorithmica'18]. We obtain this result through the refined analysis of the quasipartition construction of M\'emoli et al. for bounded treewidth graphs.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper claims two main results on directed low-diameter decompositions (LDDs) and related quasipartitions in structured digraphs. For any directed graph with pathwidth pw it constructs an (O(pw), Δ)-LDD, improving the prior (2^{O(pw²)}, Δ) bound implicitly obtained from Salmasi et al. (SODA'19). For the Directed Non-Bipartite Sparsest-Cut LP on n-vertex graphs of treewidth tw it proves an integrality gap of O(tw log n), improving the O(tw log² n) bound of Mémoli et al. (ICALP'16, Algorithmica'18). Both improvements are obtained by a refined analysis of the existing quasipartition construction of Mémoli, Sidiropoulos and Sridhar rather than a new construction.
Significance. If the refined analysis is correct, the results tighten the dependence on pathwidth and treewidth for two fundamental primitives, removing an exponential factor in the LDD bound and a logarithmic factor in the integrality gap. Such improvements are useful for approximation algorithms and exact algorithms on low-treewidth/pathwidth digraphs. The paper explicitly builds on and credits the prior quasipartition construction, which is a positive feature when the improvement arises from careful re-analysis.
minor comments (2)
- [Abstract] The abstract and introduction should explicitly state whether the O(pw) LDD bound is with respect to the directed metric or the underlying undirected metric, and whether Δ is the maximum out-degree or total degree; this notation is used without definition in the provided abstract.
- [Introduction / Technical sections] The claim that the new integrality gap follows from 'refined analysis' of the Mémoli et al. quasipartition should be accompanied, in §3 or the relevant technical section, by a short comparison table or paragraph highlighting exactly which step in the original analysis is tightened and by how much.
Simulated Author's Rebuttal
We thank the referee for their positive summary, recognition of the significance of the improvements, and recommendation for minor revision. We appreciate the note that the work builds on and credits the prior quasipartition construction.
Circularity Check
No significant circularity identified
full rationale
The paper's central results—an (O(pw), Δ)-LDD for pathwidth-pw digraphs and an O(tw log n) integrality gap for the directed sparsest-cut LP on treewidth-tw graphs—are obtained by refining the analysis of an existing quasipartition construction due to Mémoli, Sidiropoulos, and Sridhar (ICALP'16/Algorithmica'18). This prior construction is external to the present authors and is not derived from or fitted to the target bounds; the improvement consists of a tighter analysis that removes a log factor. No self-definitional steps, fitted inputs renamed as predictions, or load-bearing self-citations appear in the derivation chain. The claims rest on independent analytic refinement rather than reduction to the paper's own inputs by construction.
Axiom & Free-Parameter Ledger
axioms (2)
- standard math Standard definitions and metric properties of pathwidth and treewidth for directed graphs.
- domain assumption The quasipartition construction of Mémoli et al. exists and admits further analysis.
Reference graph
Works this paper leans on
-
[1]
I, Discrete Math
Noga Alon , title =. I, Discrete Math. , volume =. 2003 , pages =
2003
-
[2]
Assouad , title =
P. Assouad , title =. Bull. Soc. Math. France , volume =. 1983 , pages =
1983
-
[3]
Awerbuch, Baruch , title =. J. ACM , issue_date =. 1985 , issn =. doi:10.1145/4221.4227 , acmid =
-
[4]
Noga Alon and Baruch Awerbuch and Yossi Azar and Niv Buchbinder and Joseph Naor , title =. 2006 , url =. doi:10.1145/1198513.1198522 , timestamp =
-
[5]
Proceedings of the 48th Annual
Amir Abboud and Greg Bodwin , title =. Proceedings of the 48th Annual. 2016 , crossref =. doi:10.1145/2897518.2897555 , timestamp =
-
[6]
Graph Theory and Related Topics , Year =
A Conjecture on Planar Graphs , Author =. Graph Theory and Related Topics , Year =
-
[7]
Baruch Awerbuch and Bonnie Berger and Lenore Cowen and David Peleg , title =. 34th Annual Symposium on Foundations of Computer Science, Palo Alto, California, USA, 3-5 November 1993 , pages =. 1993 , crossref =. doi:10.1109/SFCS.1993.366823 , timestamp =
-
[8]
Region-Fault Tolerant Geometric Spanners , Author =. Discret. Comput. Geom. , Year =. doi:10.1007/s00454-009-9137-7 , Timestamp =
-
[9]
Richa Agarwala and Vineet Bafna and Martin Farach and Mike Paterson and Mikkel Thorup , title =. 1999 , url =. doi:10.1137/S0097539795296334 , timestamp =
-
[10]
Improved Routing Strategies with Succinct Tables , journal =
Baruch Awerbuch and Amotz Bar. Improved Routing Strategies with Succinct Tables , journal =. 1990 , url =. doi:10.1016/0196-6774(90)90017-9 , timestamp =
-
[11]
2007 , note =
Ittai Abraham and Yair Bartal and Ofer Neiman , title =. 2007 , note =
2007
-
[12]
Ittai Abraham and Yair Bartal and Ofer Neiman , title = "On Embedding of Finite Metric Spaces into. 2005
2005
-
[13]
STOC '06: Proceedings of the thirty-eighth annual ACM symposium on Theory of computing , year =
Ittai Abraham and Yair Bartal and Ofer Neiman , title =. STOC '06: Proceedings of the thirty-eighth annual ACM symposium on Theory of computing , year =. doi:http://doi.acm.org/10.1145/1132516.1132557 , publisher =
-
[14]
Ittai Abraham and Yair Bartal and Ofer Neiman , title=. 2006
2006
-
[15]
Proceedings of the eighteenth annual ACM-SIAM symposium on Discrete algorithms , series =
Abraham, Ittai and Bartal, Yair and Neiman, Ofer , title =. Proceedings of the eighteenth annual ACM-SIAM symposium on Discrete algorithms , series =. 2007 , isbn =
2007
-
[16]
Proceedings of the thirty-ninth annual ACM symposium on Theory of computing , series =
Abraham, Ittai and Bartal, Yair and Neiman, Ofer , title =. Proceedings of the thirty-ninth annual ACM symposium on Theory of computing , series =. 2007 , isbn =. doi:10.1145/1250790.1250883 , acmid =
-
[17]
Proceedings of the nineteenth annual ACM-SIAM symposium on Discrete algorithms , series =
Abraham, Ittai and Bartal, Yair and Neiman, Ofer , title =. Proceedings of the nineteenth annual ACM-SIAM symposium on Discrete algorithms , series =. 2008 , location =
2008
-
[18]
Abraham, Ittai and Bartal, Yair and Neiman, Ofer , title =. FOCS '08: Proceedings of the 2008 49th Annual IEEE Symposium on Foundations of Computer Science , year =. doi:http://dx.doi.org/10.1109/FOCS.2008.62 , isbn =
-
[19]
SODA '09: Proceedings of the Nineteenth Annual ACM -SIAM Symposium on Discrete Algorithms , year =
Abraham, Ittai and Bartal, Yair and Neiman, Ofer , title =. SODA '09: Proceedings of the Nineteenth Annual ACM -SIAM Symposium on Discrete Algorithms , year =
-
[20]
Advances in metric embedding theory , journal =
Ittai Abraham and Yair Bartal and Ofer Neiman , keywords =. Advances in metric embedding theory , journal =. 2011 , issn =. doi:https://doi.org/10.1016/j.aim.2011.08.003 , url =
-
[21]
Baratz and David Peleg , title =
Baruch Awerbuch and Alan E. Baratz and David Peleg , title =. Proceedings of the Ninth Annual. 1990 , crossref =. doi:10.1145/93385.93417 , timestamp =
-
[22]
Technical Report CS92-22, Weizmann Institute , Year =
Efficient Broadcast and Light-Weight Spanners , Author =. Technical Report CS92-22, Weizmann Institute , Year =
-
[23]
Awerbuch and A
B. Awerbuch and A. Baratz and D. Peleg , title =. 1992 , number =
1992
-
[25]
Proceedings of the 2025 Annual
Yufan Huang and Peter Jin and Kent Quanrud , title =. Proceedings of the 2025 Annual
2025
-
[26]
Kobourov and Richard Spence , Journal =
Abu Reyan Ahmed and Greg Bodwin and Faryad Darabi Sahneh and Keaton Hamm and Mohammad Javad Latifi Jebelli and Stephen G. Kobourov and Richard Spence , Journal =. Graph spanners:. 2020 , Pages =. doi:10.1016/j.cosrev.2020.100253 , Timestamp =
-
[27]
Nir Ailon and Bernard Chazelle , title =. 2009 , url =. doi:10.1137/060673096 , timestamp =
-
[28]
Proceedings of the Twenty-Ninth Annual
Ramsey Spanning Trees and their Applications , Author =. Proceedings of the Twenty-Ninth Annual. 2018 , Note =. doi:10.1137/1.9781611975031.108 , Timestamp =
-
[29]
Ramsey Spanning Trees and Their Applications , Author =. 2020 , Note =. doi:10.1145/3371039 , Timestamp =
-
[30]
Approximate Nearest Neighbor Search in Metrics of Planar Graphs , booktitle =
Ittai Abraham and Shiri Chechik and Robert Krauthgamer and Udi Wieder , editor =. Approximate Nearest Neighbor Search in Metrics of Planar Graphs , booktitle =. 2015 , url =. doi:10.4230/LIPIcs.APPROX-RANDOM.2015.20 , timestamp =
-
[31]
A. Adamaszek and A. Czumaj and A. Lingas , Booktitle =. 2009 , Pages =. doi:10.1007/978-3-642-10631-6_100 , Owner =
-
[32]
Generating Sparse Spanners for Weighted Graphs , booktitle =
Ingo Alth. Generating Sparse Spanners for Weighted Graphs , booktitle =. 1990 , pages =
1990
-
[33]
On Sparse Spanners of Weighted Graphs , journal =
Ingo Alth. On Sparse Spanners of Weighted Graphs , journal =. 1993 , url =. doi:10.1007/BF02189308 , timestamp =
-
[34]
27th Annual European Symposium on Algorithms,
Constructing Light Spanners Deterministically in Near-Linear Time , Author =. 27th Annual European Symposium on Algorithms,. 2019 , Pages =. doi:10.4230/LIPIcs.ESA.2019.4 , Timestamp =
-
[35]
Constructing light spanners deterministically in near-linear time , journal =
Stephen Alstrup and S. Constructing light spanners deterministically in near-linear time , journal =. 2022 , url =. doi:10.1016/j.tcs.2022.01.021 , timestamp =
-
[36]
Journal of Experimental Algorithmics (JEA) , Year =
Partitioning planar graphs with costs and weights , Author =. Journal of Experimental Algorithmics (JEA) , Year =
-
[37]
Sunil Arya and Gautam Das and David M. Mount and Jeffrey S. Salowe and Michiel H. M. Smid , editor =. Euclidean spanners: short, thin, and lanky , booktitle =. 1995 , url =. doi:10.1145/225058.225191 , timestamp =
-
[38]
CoRR , keywords =
Andersen, Reid and Feige, Uriel , title =. CoRR , keywords =. 2009 , added-at =
2009
-
[39]
Proceedings of the 50th Annual
Metric embedding via shortest path decompositions , Author =. Proceedings of the 50th Annual. 2018 , Pages =. doi:10.1145/3188745.3188808 , Timestamp =
-
[40]
Ittai Abraham and Arnold Filtser and Anupam Gupta and Ofer Neiman , title =. 2022 , url =. doi:10.1137/19m1296021 , timestamp =
-
[41]
Ernst Althaus and Stefan Funke and Sariel Har. Approximating. Oper. Res. Lett. , volume =. 2005 , url =. doi:10.1016/j.orl.2004.05.005 , timestamp =
-
[42]
Proceedings of the Twenty-fifth Annual ACM Symposium on Principles of Distributed Computing , Year =
Object Location Using Path Separators , Author =. Proceedings of the Twenty-fifth Annual ACM Symposium on Principles of Distributed Computing , Year =. doi:10.1145/1146381.1146411 , Owner =
-
[43]
and Malkhi, Dahlia , TITLE =
Abraham, Ittai and Gavoille, Cyril and Goldberg, Andrew V. and Malkhi, Dahlia , TITLE =. 26^
-
[44]
I. Abraham and C. Gavoille and A. Gupta and O. Neiman and K. Talwar , Booktitle =. Cops, Robbers, and Threatening Skeletons:. 2014 , Pages =. doi:10.1145/2591796.2591849 , Owner =
-
[45]
Cops, Robbers, and Threatening Skeletons: Padded Decomposition for Minor-Free Graphs , Author =. 2019 , Note =. doi:10.1137/17M1112406 , Timestamp =
-
[46]
Distance Labeling Schemes for Trees , booktitle =
Stephen Alstrup and Inge Li G. Distance Labeling Schemes for Trees , booktitle =. 2016 , crossref =. doi:10.4230/LIPIcs.ICALP.2016.132 , timestamp =
-
[47]
Karger and Philip N
Sanjeev Arora and Michelangelo Grigni and David R. Karger and Philip N. Klein and Andrzej Woloszyn , Booktitle =. A Polynomial-Time Approximation Scheme for Weighted Planar Graph. 1998 , Pages =
1998
-
[48]
SIAM Journal on Computing , Year =
Local Search Heuristics for k -Median and Facility Location Problems , Author =. SIAM Journal on Computing , Year =. doi:10.1137/S0097539702416402 , Owner =
-
[49]
Stephen Alstrup and Cyril Gavoille and Haim Kaplan and Theis Rauhe , title =. Theory Comput. Syst. , volume =. 2004 , url =. doi:10.1007/s00224-004-1155-5 , timestamp =
-
[50]
Routing with Improved Communication-Space Trade-Off , booktitle =
Ittai Abraham and Cyril Gavoille and Dahlia Malkhi , editor =. Routing with Improved Communication-Space Trade-Off , booktitle =. 2004 , url =. doi:10.1007/978-3-540-30186-8\_22 , timestamp =
-
[51]
Compact Routing for Graphs Excluding a Fixed Minor , booktitle =
Ittai Abraham and Cyril Gavoille and Dahlia Malkhi , editor =. Compact Routing for Graphs Excluding a Fixed Minor , booktitle =. 2005 , url =. doi:10.1007/11561927\_32 , timestamp =
-
[52]
On space-stretch trade-offs: lower bounds , booktitle =
Ittai Abraham and Cyril Gavoille and Dahlia Malkhi , editor =. On space-stretch trade-offs: lower bounds , booktitle =. 2006 , url =. doi:10.1145/1148109.1148143 , timestamp =
-
[53]
Graph sketches: sparsification, spanners, and subgraphs , Author =. Proceedings of the 31st. 2012 , Pages =. doi:10.1145/2213556.2213560 , Timestamp =
-
[54]
Ittai Abraham and Cyril Gavoille and Dahlia Malkhi and Noam Nisan and Mikkel Thorup , title =. 2008 , url =. doi:10.1145/1367064.1367077 , timestamp =
-
[55]
Theory of Computing Systems , Year =
Strong-Diameter Decompositions of Minor Free Graphs , Author =. Theory of Computing Systems , Year =. doi:10.1007/s00224-010-9283-6 , Owner =
-
[56]
Ahmed and G
R. Ahmed and G. Bodwin and F. D. Sahneh and K. Hamm and M. J. L Jebelli and S. Kobourov and R. Spence , Journal =. Graph spanners:. 2019 , Note =
2019
-
[57]
Sanjeev Arora and Elad Hazan and Satyen Kale , title =. Theory Comput. , volume =. 2012 , url =. doi:10.4086/toc.2012.v008a006 , timestamp =
-
[58]
The Moore Bound for Irregular Graphs , Author =. Graphs Comb. , Year =. doi:10.1007/s003730200002 , Timestamp =
-
[59]
Near-optimal labeling schemes for nearest common ancestors , booktitle =
Stephen Alstrup and Esben Bistrup Halvorsen and Kasper Green Larsen , editor =. Near-optimal labeling schemes for nearest common ancestors , booktitle =. 2014 , url =. doi:10.1137/1.9781611973402.72 , timestamp =
-
[60]
Proceedings of the 57th Annual ACM Symposium on Theory of Computing , pages =
Assadi, Sepehr and Hoppenworth, Gary and Wein, Nicole , title =. Proceedings of the 57th Annual ACM Symposium on Theory of Computing , pages =. 2025 , isbn =. doi:10.1145/3717823.3718298 , abstract =
-
[61]
Alexandr Andoni and Piotr Indyk , title =. Commun. 2008 , url =. doi:10.1145/1327452.1327494 , timestamp =
-
[62]
Approximate Nearest Neighbor Search in High Dimensions
Alexandr Andoni and Piotr Indyk and Ilya P. Razenshteyn , title =. CoRR , volume =. 2018 , url =. 1806.09823 , timestamp =
work page internal anchor Pith review Pith/arXiv arXiv 2018
-
[63]
Baruch Awerbuch and Shay Kutten and David Peleg , title =. 1994 , url =. doi:10.1109/26.328973 , timestamp =
-
[64]
Karp and David Peleg and Douglas B
Noga Alon and Richard M. Karp and David Peleg and Douglas B. West , title =. 1995 , url =. doi:10.1137/S0097539792224474 , timestamp =
-
[65]
Ajit Agrawal and Philip N. Klein and R. Ravi , title =. 1995 , url =. doi:10.1137/S0097539792236237 , timestamp =
-
[66]
T. Asano and N. Katoh and H. Tamaki and T. Tokuyama , Booktitle =. Covering Points in the Plane by K -Tours:. 1997 , Pages =. doi:10.1145/258533.258602 , Owner =
-
[67]
Proceedings of the 30th Annual Symposium on Foundations of Computer Science , Year =
Network Decomposition and Locality in Distributed Computation , Author =. Proceedings of the 30th Annual Symposium on Foundations of Computer Science , Year =. doi:10.1109/SFCS.1989.63504 , Owner =
-
[68]
STOC '05: Proceedings of the thirty-seventh annual ACM symposium on Theory of computing , year=
Euclidean Distortion and the Sparsest Cut , author=. STOC '05: Proceedings of the thirty-seventh annual ACM symposium on Theory of computing , year=
-
[69]
Sanjeev Arora and James R. Lee and Assaf Naor , title =. Discrete. 2007 , url =. doi:10.1007/s00454-007-9007-0 , timestamp =
-
[70]
Arora and J
S. Arora and J. R. Lee and A. Naor , title =. Journal of the American Mathematical Society 21 , year =
-
[71]
, TITLE =
Alon, N. , TITLE =. Combinatorica , FJOURNAL =. 1986 , NUMBER =
1986
-
[72]
Alspach , Journal =
B. Alspach , Journal =. The wonderful. 2008 , Pages =
2008
-
[73]
Sunil Arya and David M. Mount and Michiel H. M. Smid , title =. 35th Annual Symposium on Foundations of Computer Science, Santa Fe, New Mexico, USA, 20-22 November 1994 , pages =. 1994 , crossref =. doi:10.1109/SFCS.1994.365722 , timestamp =
-
[74]
Dynamic algorithms for geometric spanners of small diameter: Randomized solutions , Author =. Comput. Geom. , Year =
-
[75]
The Space Complexity of Approximating the Frequency Moments , Author =. J. Comput. Syst. Sci. , Year =. doi:10.1006/jcss.1997.1545 , Timestamp =
-
[76]
Journal of Graph Theory , Year =
Large induced forests in sparse graphs , Author =. Journal of Graph Theory , Year =. doi:10.1002/jgt.1028 , Owner =
-
[77]
Proceedings of the 44th Symposium on Theory of Computing Conference,
Ittai Abraham and Ofer Neiman , title =. Proceedings of the 44th Symposium on Theory of Computing Conference,. 2012 , crossref =. doi:10.1145/2213977.2214015 , timestamp =
-
[78]
Using Petal-Decompositions to Build a Low Stretch Spanning Tree , Author =. 2019 , Note =. doi:10.1137/17M1115575 , Timestamp =
-
[79]
Thomas Andreae , title =. J. Comb. Theory, Ser. 1986 , url =. doi:10.1016/0095-8956(86)90026-2 , timestamp =
-
[80]
2009 , school=
Nearest neighbor search: the old, the new, and the impossible , author=. 2009 , school=
2009
-
[81]
Nguyen and Aleksandar Nikolov and Ilya P
Alexandr Andoni and Huy L. Nguyen and Aleksandar Nikolov and Ilya P. Razenshteyn and Erik Waingarten , editor =. Approximate near neighbors for general symmetric norms , booktitle =. 2017 , url =. doi:10.1145/3055399.3055418 , timestamp =
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