REVIEW 4 major objections 4 minor 47 references
Equalizing Closeness Centralities via Edge Additions
T0 review · 4 major / 4 minor · reviewed 2026-08-15 · deepseek-v4-flash
Pith's one-line read A near-linear-time algorithm equalizes two nodes' closeness centralities to at least 6/11 of the best possible ratio, while the gap variant is unapproximable.
desk verdict A solid, original contribution to network-fairness algorithms with sound hardness results and a 6/11-approximation that holds up; the one flagged concern in Lemma 4 dissolves on inspection. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The engine of the result is Algorithm 1, which adds the edge $ab$ (if absent) and then repeatedly adds an edge from $a$ to a vertex in $b$'s private neighbourhood $\mathcal N_{G+S}(b)\setminus \mathcal N_{G+S}[a]$ until the budget is spent or $a$'s closeness falls below $b$'s. The correctness rests on three structural lemmas: the No Switching Lemma, which says that if adding $ab$ reverses the centrality order then one of the current graphs already achieves $\frac{6}{11}$; the Termination Lemma, which guarantees early stopping is safe; and a sufficient-condition lemma showing that $k+|\mathcal N_G(a)|\ge n/6$ forces a $\frac{6}{11}$ outcome. Lemma 4 supplies the converse: when neither $G$ nor $G+ab$ is $\frac{6}{11}$-approximate, the optimal solution must have $d_{G^*}(a,b)\in\{1,2\}$ and the large-neighbourhood condition must hold. The proof repeatedly uses a ratio-monotonicity observation: for nonnegative $w\le p\le q$, the fraction $(p+w)/(q+w)$ is at least $p/q$, which lets the paper strip away error terms.
What would settle it
Run Algorithm 1 on every graph with, say, at most 9 vertices and compare its output against exhaustive search over all $\binom{\binom{n}{2}}{k}$ edge sets; a single instance in which the algorithm's ratio is below $\frac{6}{11}$ of the optimal ratio would refute Theorem 4. Since the algorithm and the optimum are both finitely computable, this is a direct computational check.
Extended reading notes
Core claim
The paper's central discovery is a structural description of the hard instances of Closeness Ratio Improvement. It proves that if neither the original graph nor the graph obtained by adding the single edge $ab$ already achieves a $\frac{6}{11}$ ratio, then the optimal solution $G^*$ must place $a$ and $b$ at distance $1$ or $2$, and $b$ must have a very large private neighborhood; in that situation $k+|\mathcal N_G(a)|\ge n/6$, which lets a simple greedy edge-addition algorithm reach the $\frac{6}{11}$ guarantee. Equivalently, the only graphs where the trivial edge $ab$ is inadequate are graphs in which $b$ has so many private neighbors that adding edges from $a$ to those neighbors is provably effective. The same construction that gives $\mathsf{NP}$-hardness for target ratio $1$ is extended to every $\tau\in(1/2,1)$, and the same reduction shows the gap-minimization variant has no multiplicative approximation.
Load-bearing premise
The chain of inequalities in Lemma 4 is load-bearing and silently presumes that in an optimal solution $G^*$, the node $b$ is at least as central as $a$ (i.e. $\operatorname{cc}_{G^*}(a)\ge\operatorname{cc}_{G^*}(b)$); without that orientation, the bound $\operatorname{cc}_{G^*}(a)\le \frac{12}{11}\operatorname{cc}_{G^*}(b)$ does not follow from the written text.
Editorial extensions
If this is right
- For every input $(G,a,b,k)$, Algorithm 1 runs in $O((n+m)\log k)$ time and returns an edge set with closeness ratio at least $\frac{6}{11}$ of the optimum.
- Exact optimization is out of reach in general: Closeness Ratio Improvement is $\mathsf{NP}$-hard and $\mathsf{W}[2]$-hard in $k$ for every target ratio in $(\frac{1}{2},1]$.
- The trivial bound of $\frac{1}{2}$ from adding the single edge $ab$ is tight, so $\frac{6}{11}$ is a real improvement over the naive intervention.
- Closeness Gap Minimization is not only hard but inapproximable: no multiplicative factor is possible unless $\mathsf{P}=\mathsf{NP}$.
- Any algorithm allowed $ck$ edges, for constant $c\ge1$, cannot guarantee a ratio better than $\frac{5ec}{5ec+1}-\epsilon$ for any $\epsilon>0$, unless $\mathsf{P}=\mathsf{NP}$.
Reading between the lines
- The omitted orientation case in Lemma 4 looks repairable from the paper's own bounds: if $d_{G^*}(a,b)\ge3$, the structural claims force $a$ to be the less central node, and the opposite orientation gives stronger estimates on $k$; a filled-in proof should keep the $6/11$ theorem intact.
- Because Algorithm 1 is deterministic and near-linear, an empirical study could test whether the $6/11$ guarantee is loose on real social graphs; the lemmas suggest hard instances are sparse graphs where $b$ has an enormous private neighbourhood.
- The same private-neighbourhood decomposition is a plausible starting point for the two proposed generalizations, Group Closeness Ratio Improvement and All-Pairs Closeness Ratio Improvement, though the $1/2$ trivial baseline from adding $ab$ does not carry over.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper studies two graph-modification problems in which a budget of k edge additions is used to equalize the closeness centralities of two designated vertices a and b: Closeness Ratio Improvement, which maximizes the ratio min(cc(a),cc(b))/max(cc(a),cc(b)), and Closeness Gap Minimization, which minimizes the absolute difference |cc(a)-cc(b)|, where closeness is the sum of shortest-path distances. The authors prove that both problems are NP-hard, give a quasilinear-time 6/11-approximation for the ratio version, and prove a bicriteria inapproximability bound for the ratio version as well as the non-approximability of the gap version. The main algorithmic contribution is a simple strategy: add the edge ab, then repeatedly add edges from a to vertices in b's neighborhood, with early-termination rules.
Significance. If the results are correct, this is a solid contribution to the emerging literature on algorithmic fairness through network modification. The paper introduces a well-motivated pair of problems, establishes hardness thresholds, and provides a nontrivial constant-factor approximation with a quasilinear runtime, which is a good algorithmic result for a non-submodular, non-monotone objective. The bicriteria inapproximability result is also of interest. The hardness reductions are carefully constructed and mostly check out, and the paper is generally well written. However, two load-bearing proofs contain errors that currently prevent the central claims from being regarded as established.
major comments (4)
- [§4, Lemma 2] The proof of the Termination Lemma contains an incorrect set inclusion. The text claims that because u∈N_G(b), we have A_{G+au}⊆A_G, where A_H={v:d_H(a,v)<d_H(b,v)}. In fact, adding the edge au can only decrease distances from a, and when ab∈E and u∈N_G(b), distances from b are unchanged (any path through the new edge has length at least d_G(b,v)+1 by the triangle inequality). Hence A_G⊆A_{G+au}, and the asserted contradiction between |A_{G+au}|>(n-2)/2 and |B_G|>(n-2)/2 does not follow. Since Lemma 2 is used to justify the early-termination condition in Algorithm 1 and is then relied upon by Lemmas 3 and 4 and Theorem 4, the 6/11-approximation proof is incomplete as written. The lemma may be true, but a different or corrected argument is required.
- [§3, Theorem 3] The final calibration algebra in the bicriteria inapproximability proof is incorrect. Starting from (1-ε')(5ec+1-ecδ)≥5ec+1-ε, the correct rearrangement is ε≥ε'(5ec+1)+ecδ(1-ε'), not ε≥ε'(5ec-1)+ecδ(1-ε') as written. With the stated choices ε'=ε/(2(5ec-1)) and δ=ε/(2ec(1-ε')), the required inequality fails: the right-hand side becomes ε+ε/(5ec-1)>ε. The claimed approximation barrier 5ec/(5ec+1-ε) is therefore not established by the proof as written. The argument appears repairable (e.g., setting ε'=ε/(2(5ec+1)) would make the condition hold with equality), but the current text needs correction.
- [§4, Lemma 4, Claim 7] In the lower-bound argument for cc_{G*}(a), the set O is defined in the text as V\(A_p∪{a,b}), but the subsequent computation uses O=V\(B_p∪{a,b}) with |B_p|=4(n-2)/5+x. This is a typo in a central bound; it should be corrected to avoid confusion. As written, the notation makes the proof difficult to follow, though the intended argument is clear.
- [§4, Theorem 4] The claimed O((n+m) log k) runtime is only sketched. The binary search over the k-1 previous states of S requires a precise implementation: the algorithm must record the sequence of added edges and, for a queried prefix length ℓ, compute distances from a and b in G plus the first ℓ added edges. Since each BFS costs O(n+m+ℓ) and ℓ<k, the claim is plausible, but the manuscript would benefit from an explicit description of how the prefix evaluations are performed without re-running the entire loop.
minor comments (4)
- [§3, Theorem 3] The displayed chain 'n/(n+ck) > n/(n·1/(1+ε′)) > 1−ε′' appears garbled; the intended inequality is n/(n+ck) > 1/(1+ε′) > 1−ε′.
- [§4, Lemma 4] The inference from '3n/11−8/11<k' to 'n/6<k' is not valid as a direct real inequality for all n>3 (e.g., n=6), though it becomes true for integral k in the cases that matter, and the final conclusion k+|N_G(a)|≥n/6 still holds. The proof should state the integrality argument explicitly.
- [§4, Lemma 4] The statement that for n<7 one may assume d_{G*}(a,b)<3 because otherwise part (iii) of Claim 5 is impossible is incorrect; for n=6, |B_p|=4 can satisfy |B_p|>4(n-2)/5 with d_{G*}(a,b)=3. The small-n case is easily handled because the lemma's conclusion is trivial for n≤6, but the current sentence should be revised.
- [§2.2, Observation 1] Observation 1 invokes Observation 2 before Observation 2 is stated; reordering or an explicit forward reference would improve readability.
Circularity Check
No significant circularity: all central claims are derived from first principles against external Set Cover hardness.
full rationale
The paper's central claims are self-contained rather than circular. The NP-hardness and inapproximability results (Theorems 1–3 and Corollary 1) reduce from Set Cover and from Feige's external set-cover hardness threshold, and all reduction-specific distance and centrality arithmetic is derived explicitly in the paper. The 6/11-approximation (Theorem 4) is established by elementary structural claims (Claims 3–8) and lemmas (Lemmas 1–4) using triangle inequalities and set-size bounds; no parameter is fitted to the objective, no definition of the objective is used as its own proof, and no conclusion is imported from a self-citation. The self-citations ([7], [10], [16]) appear only in contextual motivation and open-problem discussion, not as load-bearing proof inputs. The flagged orientation issue in Claim 7 is a possible expositional omission in an internal inequality, not a reduction of a result to its own assumptions, and it does not create circularity. Overall, the derivation chain is independent of its conclusions.
Assumptions & free parameters
assumptions (3)
- standard math Set Cover is NP-hard and W[2]-hard parameterized by cover size k.
- standard math Feige et al. strengthened hardness of Set Cover: distinguishing set cover of size k from instances where every ck sets cover at most (1 - (1-1/k)^{ck} + δ)n elements is NP-hard.
- standard math The triangle inequality for shortest-path distances in undirected graphs.
Cite this review
Pith. "Pith review of Equalizing Closeness Centralities via Edge Additions." pith.science (2026). https://pith.science/paper/6Z7XXHNQ
@misc{pith2026250506222,
author = {Pith},
title = {Pith review of: Equalizing Closeness Centralities via Edge Additions},
year = {2026},
howpublished = {\url{https://pith.science/paper/6Z7XXHNQ}},
note = {Machine review of arXiv:2505.06222}
}
abstract
Graph modification problems with the goal of optimizing some measure of a given node's network position have a rich history in the algorithms literature. Less commonly explored are modification problems with the goal of equalizing positions, though this class of problems is well-motivated from the perspective of equalizing social capital, i.e., algorithmic fairness. In this work, we study how to add edges to make the closeness centralities of a given pair of nodes more equal. We formalize two versions of this problem: Closeness Ratio Improvement, which aims to maximize the ratio of closeness centralities between two specified nodes, and Closeness Gap Minimization, which aims to minimize the absolute difference of centralities. We show that both problems are $\textsf{NP}$-hard, and for Closeness Ratio Improvement we present a quasilinear-time $\frac{6}{11}$-approximation, complemented by a bicriteria inapproximability bound. In contrast, we show that Closeness Gap Minimization admits no multiplicative approximation unless $\textsf{P} = \textsf{NP}$. We conclude with a discussion of open directions for this style of problem, including several natural generalizations.
Figures
Reference graph
Works this paper leans on
-
[2]
F. Adriaens and A. Gionis. Diameter minimization by shortcutting with degree constraints. In 2022 IEEE International Conference on Data Mining (ICDM), pages 843–848. IEEE, 2022
work page 2022
- [1]
- [3]
-
[4]
S. Ahmadian and M. Negahbani. Improved approximation for fair correlation clustering. In International Conference on Artificial Intelligence and Statistics (AISTATS) 2023, volume 206 ofProceedings of Machine Learning Research, pages 9499–9516. PMLR, 2023
work page 2023
-
[5]
S. Ahmadian, A. Epasto, R. Kumar, and M. Mahdian. Fair correlation clustering. InThe 23rd International Conference on Artificial Intelligence and Statistics, AISTATS 2020, volume 108 ofProceedings of Machine Learning Research, pages 4195–4205. PMLR, 2020
work page 2020
-
[6]
K. Avrachenkov and N. Litvak. The effect of new links on google pagerank.Stochastic Models, 22(2):319–331, 2006. 23
work page 2006
-
[7]
A. Bashardoust, S. Friedler, C. Scheidegger, B. D. Sullivan, and S. Venkatasubramanian. Reducing access disparities in networks using edge augmentation. InProceedings of the ACM Conference on Fairness, Accountability, and Transparency (FAccT), pages 1635–1651, 2023
work page 2023
-
[8]
I. O. Bercea, M. Groß, S. Khuller, A. Kumar, C. Rösner, D. R. Schmidt, and M. Schmidt. On the cost of essentially fair clusterings. InApproximation, Randomization, and Combinatorial Optimization. Algorithms and Techniques, APPROX/RANDOM 2019, volume 145 ofLIPIcs, pages 18:1–18:22. Schloss Dagstuhl - Leibniz-Zentrum für Informatik, 2019
work page 2019
Show all 47 references
-
[9]
Bergamini, P
E. Bergamini, P. Crescenzi, G. D’Angelo, H. Meyerhenke, L. Severini, and Y. Velaj. Improving the betweenness centrality of a node by adding links.Journal of Experimental Algorithmics, 23:1–32, 2018
2018
-
[10]
Bhaskara, A
A. Bhaskara, A. Crane, S. Jain, M. M. H. U. Mazumder, B. D. Sullivan, and P. Yalaman- chili. Optimizing information access in networks via edge augmentation.arXiv preprint arXiv:2407.02624, 2024
2024 arXiv
-
[11]
D. Bilò, L. Gualà, and G. Proietti. Improved approximability and non-approximability results for graph diameter decreasing problems.Theoretical Computer Science, 417:12–22, 2012
2012
-
[12]
Boldi and S
P. Boldi and S. Vigna. Axioms for centrality.Internet Mathematics, 10(3-4):222–262, 2014
2014
-
[13]
S. P. Borgatti, C. Jones, and M. G. Everett. Network measures of social capital.Connections, 21(2):27–36, 1998
1998
-
[14]
Casel, T
K. Casel, T. Friedrich, M. Schirneck, and S. Wietheger. Fair correlation clustering in forests. In 4th Symposium on Foundations of Responsible Computing, FORC 2023, volume 256 ofLIPIcs, pages 9:1–9:12. Schloss Dagstuhl - Leibniz-Zentrum für Informatik, 2023
2023
-
[15]
Chierichetti, R
F. Chierichetti, R. Kumar, S. Lattanzi, and S. Vassilvitskii. Fair clustering through fairlets. Advances in Neural Information Processing Systems, 30, 2017
2017
-
[16]
Crane, T
A. Crane, T. Stanley, B. D. Sullivan, and N. Veldt. Edge-colored clustering in hypergraphs: Beyond minimizing unsatisfied edges. InProceedings of the International Conference on Machine Learning (ICML), 2025
2025
-
[17]
Crescenzi, G
P. Crescenzi, G. D’Angelo, L. Severini, and Y. Velaj. Greedily improving our own closeness centrality in a network.ACM Transcations on Knowledge Discovery from Data, 11(1):1–32, 2016
2016
-
[18]
Crespelle, P
C. Crespelle, P. G. Drange, F. V. Fomin, and P. A. Golovach. A survey of parameterized algorithms and the complexity of edge modification.Comput. Sci. Rev., 48:100556, 2023
2023
-
[19]
Cygan, F
M. Cygan, F. V. Fomin, Ł. Kowalik, D. Lokshtanov, D. Marx, M. Pilipczuk, M. Pilipczuk, and S. Saurabh.Parameterized algorithms, volume 5. Springer, 2015
2015
-
[20]
Simultaneouslyapproximatingalllp-normsincorrelation clustering
S.Davies, B.Moseley, andH.Newman. Simultaneouslyapproximatingalllp-normsincorrelation clustering. In51st International Colloquium on Automata, Languages, and Programming, ICALP 2024, volume 297 ofLIPIcs, pages 52:1–52:20. Schloss Dagstuhl - Leibniz-Zentrum für Informatik, 2024
2024
-
[21]
E. D. Demaine and M. Zadimoghaddam. Minimizing the diameter of a network using shortcut edges. InProceedings of the 12th Scandinavian Symposium and Workshops on Algorithm Theory (SWAT), volume 6139 ofLecture Notes in Computer Science, pages 420–431. Springer, 2010. 24
2010
-
[22]
Farnad, B
G. Farnad, B. Babaki, and M. Gendreau. A unifying framework for fairness-aware influence maximization. InCompanion Proceedings of the Web Conference 2020, pages 714–722, 2020
2020
-
[23]
U. Feige. A threshold of ln n for approximating set cover.Journal of the ACM (JACM), 45(4): 634–652, 1998
1998
-
[24]
Feige and J
U. Feige and J. Vondrák. The submodular welfare problem with demand queries.Theory of Computing, 6(1):247–290, 2010
2010
-
[25]
Feige, L
U. Feige, L. Lovász, and P. Tetali. Approximating min sum set cover.Algorithmica, 40:219–234, 2004
2004
-
[26]
B. Fish, A. Bashardoust, D. Boyd, S. Friedler, C. Scheidegger, and S. Venkatasubramanian. Gaps in information access in social networks? InThe World Wide Web Conference, pages 480–490, 2019
2019
-
[27]
Frati, S
F. Frati, S. Gaspers, J. Gudmundsson, and L. Mathieson. Augmenting graphs to minimize the diameter.Algorithmica, 72:995–1010, 2015
2015
-
[28]
S. A. Friedler, C. Scheidegger, S. Venkatasubramanian, S. Choudhary, E. P. Hamilton, and D. Roth. A comparative study of fairness-enhancing interventions in machine learning. In Proceedings of the ACM conference on Fairness, Accountability, and Transparency, pages 329–338, 2019
2019
-
[29]
Froese, L
V. Froese, L. Kellerhals, and R. Niedermeier. Modification-fair cluster editing.Social Network Analysis and Mining, 14(1):109, 2024
2024
-
[30]
Ghadiri, S
M. Ghadiri, S. Samadi, and S. Vempala. Socially fair k-means clustering. InProceedings of the 2021 ACM Conference on Fairness, Accountability, and Transparency, pages 438–448, 2021
2021
-
[31]
M. S. Granovetter. The strength of weak ties.American Journal of Sociology, 78(6):1360–1380, 1973
1973
-
[32]
Hardt, E
M. Hardt, E. Price, and N. Srebro. Equality of opportunity in supervised learning. volume 29, 2016
2016
-
[33]
Z. S. Jalali, Q. Chen, S. M. Srikanta, W. Wang, M. Kim, H. Raghavan, and S. Soundarajan. Fairness of information flow in social networks.ACM Transactions on Knowledge Discovery from Data, 17(6):1–26, 2023
2023
-
[34]
Komusiewicz and J
C. Komusiewicz and J. Uhlmann. Cluster editing with locally bounded modifications.Discrete Applied Mathematics, 160(15):2259–2270, 2012
2012
-
[35]
C.-L. Li, S. T. McCormick, and D. Simchi-Levi. On the minimum-cardinality-bounded-diameter and the bounded-cardinality-minimum-diameter edge addition problems.Operations Research Letters, 11:303–308, 1991
1991
-
[36]
D. Liu, Z. Shafi, W. Fleisher, T. Eliassi-Rad, and S. Alfeld. Rawlsnet: Altering bayesian networks to encode rawlsian fair equality of opportunity. InProceedings of the 2021 AAAI/ACM Conference on AI, Ethics, and Society, pages 745–755, 2021
2021
-
[37]
Medya, A
S. Medya, A. Silva, A. Singh, P. Basu, and A. Swami. Group centrality maximization via network design. InProceedings of the 2018 SIAM International Conference on Data Mining, pages 126–134. SIAM, 2018. 25
2018
-
[38]
Meyerson and B
A. Meyerson and B. Tagiku. Minimizing average shortest path distances via shortcut edge addition. InApproximation, Randomization, and Combinatorial Optimization. Algorithms and Techniques, 12th International Workshop, (APPROX), volume 5687 ofLecture Notes in Computer Science, ...
2009
-
[39]
Olsen and A
M. Olsen and A. Viglas. On the approximability of the link building problem.Theoretical Computer Science, 518:96–116, 2014
2014
-
[40]
Puleo and O
G. Puleo and O. Milenkovic. Correlation clustering and biclustering with locally bounded errors. InProceedings of the International Conference on Machine Learning, pages 869–877. PMLR, 2016
2016
-
[41]
X. Rui, Z. Wang, J. Zhao, L. Sun, and W. Chen. Scalable fair influence maximization. In Advances in Neural Information Processing Systems, volume 36, pages 66675–66691, 2023
2023
-
[42]
Saxena, G
A. Saxena, G. Fletcher, and M. Pechenizkiy. Fairsna: Algorithmic fairness in social network analysis.ACM Computing Surveys, 56(8):1–45, 2024
2024
-
[43]
L. Shan, Y. Yi, and Z. Zhang. Improving information centrality of a node in complex networks by adding edges. InProceedings of the 27th International Joint Conference on Artificial Intelligence, pages 3535–3541, 2018
2018
-
[44]
Stoica and A
A.-A. Stoica and A. Chaintreau. Fairness in social influence maximization. InCompanion Proceedings of The 2019 World Wide Web Conference, pages 569–574, 2019
2019
-
[45]
Stoica, J
A.-A. Stoica, J. X. Han, and A. Chaintreau. Seeding network influence in biased networks and the benefits of diversity. InProceedings of The Web Conference 2020, pages 2089–2098, 2020
2020
-
[46]
Vakilian and M
A. Vakilian and M. Yalciner. Improved approximation algorithms for individually fair clus- tering. InProceedings of the International Conference on Artificial Intelligence and Statistics (AISTATS), pages 8758–8779. PMLR, 2022
2022
-
[47]
M.-H. Yeh, B. Metevier, A. Hoag, and P. Thomas. Analyzing the relationship between difference and ratio-based fairness metrics. InProceedings of the 2024 ACM Conference on Fairness, Accountability, and Transparency, pages 518–528, 2024. 26
2024
Reviewed August 15, 2026 · model on record in the stance chip above.
Discussion (0). Continue with ORCID to comment.