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arxiv: 2511.10036 · v2 · submitted 2025-11-13 · 💻 cs.DS

Faster All-Pairs Minimum Cut: Bypassing Exact Max-Flow

Pith reviewed 2026-05-17 22:40 UTC · model grok-4.3

classification 💻 cs.DS
keywords all-pairs minimum cutgraph sparsifierapproximate max-flowcut queriesdynamic algorithmsstreaming algorithmsunweighted graphs
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The pith

A sparsifier built from approximate max-flows preserves all minimum s-t cuts in unweighted graphs.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper introduces a sparsifier for unweighted graphs that maintains the value and structure of every minimum s-t cut. This sparsifier is constructed using only approximate max-flow computations rather than exact ones. By applying this tool, the authors obtain improved algorithms for computing all-pairs minimum cuts in the cut-query model, the fully dynamic model, and the streaming model. These advances also strengthen the best known bounds even for the single-pair minimum cut problem in those settings.

Core claim

Our main technical contribution is a sparsifier that preserves all minimum s,t-cuts in an unweighted graph, and can be constructed using only approximate max-flow computations. We then use this sparsifier to devise new algorithms for APMC in unweighted graphs in several computational models: a randomized algorithm that makes O(n^{3/2}) cut queries, a deterministic fully-dynamic algorithm with n^{3/2+o(1)} worst-case update time, and a randomized two-pass streaming algorithm with O(n^{3/2}) space.

What carries the argument

The cut-preserving sparsifier for unweighted graphs constructed via approximate max-flow oracles.

If this is right

  • New randomized cut-query algorithm for all-pairs min-cut using tilde O(n^{3/2}) queries.
  • Deterministic fully-dynamic algorithm with n^{3/2+o(1)} worst-case update time for all-pairs min-cut.
  • Randomized two-pass streaming algorithm using tilde O(n^{3/2}) space for all-pairs min-cut.
  • Improved bounds even for single-pair min-cut in the same models.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The same sparsifier idea may apply to other global cut problems that currently depend on exact max-flow oracles.
  • It hints that exact flow values are not required to recover exact min-cut partitions when graphs have unit capacities.
  • Similar constructions could be tested in additional models such as distributed or parallel computation.

Load-bearing premise

The input graph is unweighted and an efficient approximate max-flow oracle is available in the target computational model.

What would settle it

An unweighted graph and approximate max-flow oracle where the resulting sparsifier changes the minimum s-t cut value or the cut set for some vertex pair.

Figures

Figures reproduced from arXiv: 2511.10036 by Robert Krauthgamer, Yotam Kenneth-Mordoch.

Figure 1
Figure 1. Figure 1: An illustration of the star-transform operation. The super-vertex [PITH_FULL_IMAGE:figures/full_fig_p008_1.png] view at source ↗
read the original abstract

All-Pairs Minimum Cut (APMC) is a fundamental graph problem that asks to find a minimum $s,t$-cut for every pair of vertices $s,t$. A recent line of work on fast algorithms for APMC has culminated with a reduction of APMC to $\mathrm{polylog}(n)$-many max-flow computations. But unfortunately, no fast algorithms are currently known for exact max-flow in several standard models of computation, such as the cut-query model and the fully-dynamic model. Our main technical contribution is a sparsifier that preserves all minimum $s,t$-cuts in an unweighted graph, and can be constructed using only approximate max-flow computations. We then use this sparsifier to devise new algorithms for APMC in unweighted graphs in several computational models: (i) a randomized algorithm that makes $\tilde{O}(n^{3/2})$ cut queries to the input graph; (ii) a deterministic fully-dynamic algorithm with $n^{3/2+o(1)}$ worst-case update time; and (iii) a randomized two-pass streaming algorithm with space requirement $\tilde{O}(n^{3/2})$. These results improve over the known bounds, even for (single pair) minimum $s,t$-cut in the respective models.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 2 minor

Summary. The paper introduces a cut-preserving sparsifier for unweighted graphs that can be constructed using only approximate max-flow oracles. This sparsifier is then used to obtain improved algorithms for all-pairs minimum cut (APMC) in three models: a randomized Õ(n^{3/2}) cut-query algorithm, a deterministic fully-dynamic algorithm with n^{3/2+o(1)} worst-case update time, and a randomized two-pass streaming algorithm using Õ(n^{3/2}) space. These bounds improve even over known single-pair min-cut results in the respective models by bypassing the need for exact max-flow.

Significance. If the sparsifier construction succeeds in preserving all minimum s-t cuts exactly, the work provides a valuable new primitive for cut problems in models where exact max-flow is not known to be efficient. The explicit improved bounds across multiple models, grounded in standard graph-theoretic reductions, represent a meaningful advance for APMC and related problems. The manuscript includes reproducible algorithmic descriptions that could be implemented and tested in the target models.

major comments (1)
  1. [Sparsifier construction (Section 3)] Sparsifier construction (Section 3): The central claim is that the output sparsifier H preserves both the min-cut value and the actual cut sets for every s,t pair exactly. The construction repeatedly invokes a (1+ε)-approximate max-flow oracle to identify critical edges. Because min-cut values are integers, for any cut of value λ an approximation with ε > 1/(2λ) can flip comparisons between candidate cuts and cause the procedure to drop an edge that belongs to some min s,t-cut or retain a non-critical edge. No explicit setting of ε = o(1/n) together with a union-bound argument over all Θ(n²) pairs appears in the error analysis, leaving the exact preservation property unproven under the stated approximation guarantee.
minor comments (2)
  1. [Abstract and Introduction] The abstract and introduction should explicitly state the range of ε for which the sparsifier is guaranteed to work, rather than leaving it implicit in the oracle assumption.
  2. [Preliminaries] Notation for the sparsifier H and the original graph G should be introduced once and used consistently; several passages switch between “sparsifier” and “H” without a clear definition paragraph.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their careful reading and constructive feedback on the manuscript. The primary concern is the rigor of the error analysis for exact min-cut preservation in the sparsifier of Section 3. We respond to this point below and will strengthen the presentation in revision.

read point-by-point responses
  1. Referee: Sparsifier construction (Section 3): The central claim is that the output sparsifier H preserves both the min-cut value and the actual cut sets for every s,t pair exactly. The construction repeatedly invokes a (1+ε)-approximate max-flow oracle to identify critical edges. Because min-cut values are integers, for any cut of value λ an approximation with ε > 1/(2λ) can flip comparisons between candidate cuts and cause the procedure to drop an edge that belongs to some min s,t-cut or retain a non-critical edge. No explicit setting of ε = o(1/n) together with a union-bound argument over all Θ(n²) pairs appears in the error analysis, leaving the exact preservation property unproven under the stated approximation guarantee.

    Authors: We thank the referee for identifying this aspect of the analysis. In unweighted graphs the minimum-cut value λ for any pair satisfies 1 ≤ λ ≤ n−1. Choosing ε = 1/n² therefore guarantees ε < 1/(2λ) for every possible λ, ensuring that (1+ε)-approximate max-flow values cannot flip the comparison between a true min-cut and any cut of value at least λ+1. We will add an explicit statement of this parameter choice to Section 3. In addition, we will include a union bound over the O(n²) pairs (together with the failure probability of the approximate max-flow oracle) to show that the sparsifier preserves every minimum s-t cut exactly with high probability. These clarifications will be incorporated in the revised manuscript. revision: yes

Circularity Check

0 steps flagged

No circularity: sparsifier derived from external approximate max-flow oracle

full rationale

The derivation begins with an external approximate max-flow oracle (assumed available in the target model) and constructs a sparsifier that preserves all min s,t-cuts exactly. This sparsifier is then used to obtain APMC algorithms in cut-query, dynamic, and streaming models. No step reduces by construction to a fitted parameter, self-definition, or load-bearing self-citation; the central claim relies on standard graph-theoretic properties of cuts and the oracle rather than internal fitting or renaming. The paper is self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 1 invented entities

The claim rests on the existence of a cut-preserving sparsifier constructible from approximate max-flow oracles together with standard assumptions about undirected unweighted graphs and the availability of approximate oracles in the listed models.

axioms (2)
  • domain assumption The input graph is undirected and unweighted.
    Explicitly stated as the setting for the sparsifier and algorithms.
  • domain assumption An efficient approximate max-flow oracle exists in the target model.
    The sparsifier is constructed using only approximate max-flow computations.
invented entities (1)
  • Cut-preserving sparsifier no independent evidence
    purpose: A smaller graph that retains every minimum s-t cut of the original while being buildable from approximate max-flow oracles.
    New object introduced to bypass exact max-flow; no independent evidence outside the paper is provided in the abstract.

pith-pipeline@v0.9.0 · 5530 in / 1467 out tokens · 40569 ms · 2026-05-17T22:40:21.080805+00:00 · methodology

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