Largest 2-regular Subgraphs in complete S-partite Graphs
Pith reviewed 2026-05-14 21:26 UTC · model grok-4.3
The pith
The largest 2-regular subgraph in any complete S-partite graph is found by an integer linear program whose size depends only on S.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The integer linear program that selects a largest 2-regular subgraph of a complete S-partite graph admits an exact solution whose running time is O(|V(S)|^3) and therefore independent of the cardinalities of the partite sets.
What carries the argument
The integer linear program whose variables correspond to choices of edges between the partite sets dictated by S and whose constraints enforce 2-regularity.
If this is right
- The maximum order of a 2-regular subgraph is computable from S and the part sizes alone.
- The same optimum is achieved with high probability by a random S-partite graph with the same part sizes.
- Large networks whose interconnection pattern is given by S can be analyzed for 2-regular substructures without scaling the algorithm to the full vertex count.
Where Pith is reading between the lines
- The reduction suggests that other subgraph problems whose feasibility depends only on the meta-graph S may also admit size-independent algorithms.
- In structural systems theory the result supplies a concrete way to extract large controllable or stable subnetworks once the interconnection pattern S is known.
- The same modeling step could be reused for directed or weighted versions of the problem provided the underlying partition type remains fixed.
Load-bearing premise
The integer linear program exactly encodes every feasible 2-regular subgraph of the complete S-partite graph.
What would settle it
For any small fixed S and concrete part sizes, enumerate all 2-regular subgraphs by brute force and compare their maximum size against the value returned by the integer program.
Figures
read the original abstract
In this paper, we focus on the class of complete $S$-partite graphs, for $S$ an undirected graph possibly with self-loops, and address the problem of finding largest $2$-regular subgraphs of these graphs, which can be formulated as an integer linear program. Roughly speaking, a complete $S$-partite graph is obtained by replacing every single node of $S$ with a number of nodes, preserving the edge/non-edge relations of $S$. Our motivation in finding largest $2$-regular subgraphs is rooted in the structural systems theory, particularly in the problem of finding largest subnetworks that can sustain controllability or asymptotic stability of the corresponding subsystems. A main contribution of the paper is to show that the integer linear problem can be solved efficiently in $O(|V(S)|^3)$, independent of the order/size of the $S$-partite graph itself. Furthermore, we demonstrate through simulations that with high probability, a random $S$-partite graph contains a largest $2$-regular subgraph of the same order as its complete counterpart does.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper studies largest 2-regular subgraphs in complete S-partite graphs (S an undirected graph possibly with loops), formulates the problem as an integer linear program whose variables aggregate vertices and edges by the parts of S, and claims that this ILP admits an exact solution in O(|V(S)|^3) time independent of the partite-set cardinalities n_i. It further reports simulation evidence that a random S-partite graph realizes the same maximum size with high probability.
Significance. A verified O(|V(S)|^3) algorithm would be useful in structural systems theory, permitting computation of maximal 2-regular subnetworks that preserve controllability or stability properties without scaling with total network order.
major comments (1)
- [ILP formulation] ILP formulation section: the capacity constraints are written in the natural aggregated form x_ij ≤ k_i · k_j together with degree equations ∑_j x_ij = 2 k_i. These products are bilinear; the manuscript must supply an explicit linearization, a fixed-support enumeration over the k_i, or a combinatorial reduction (e.g., min-cost flow on an auxiliary digraph whose size depends only on |V(S)|) whose correctness is proved, otherwise the O(|V(S)|^3) claim cannot be substantiated.
minor comments (1)
- [Simulations] The simulation section should report the precise distribution over S, the number of Monte-Carlo trials, and quantitative statistics (e.g., empirical probability and size gap) rather than the qualitative statement “with high probability.”
Simulated Author's Rebuttal
We are grateful to the referee for the thorough review and for highlighting the issue with the ILP formulation. We agree that additional details are needed to justify the claimed time complexity.
read point-by-point responses
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Referee: [ILP formulation] ILP formulation section: the capacity constraints are written in the natural aggregated form x_ij ≤ k_i · k_j together with degree equations ∑_j x_ij = 2 k_i. These products are bilinear; the manuscript must supply an explicit linearization, a fixed-support enumeration over the k_i, or a combinatorial reduction (e.g., min-cost flow on an auxiliary digraph whose size depends only on |V(S)|) whose correctness is proved, otherwise the O(|V(S)|^3) claim cannot be substantiated.
Authors: The referee correctly identifies that the bilinear constraints require further elaboration for the complexity claim to hold. In the revised manuscript, we will include an explicit reduction of the problem to a minimum-cost circulation problem on a directed graph with vertex set corresponding to the vertices of S (thus of size |V(S)|). Specifically, we construct an auxiliary network where nodes represent the parts, and arcs are designed to encode the possible edge usages x_ij and vertex counts k_i such that the flow conservation enforces the degree equations and the capacities are set to respect the part sizes n_i without introducing bilinear terms. The objective is encoded as the total flow or cost to maximize the covered vertices. This network has O(|V(S)|) vertices and O(|V(S)|^2) arcs, and can be solved in O(|V(S)|^3) time using standard min-cost flow algorithms (e.g., capacity scaling or cost scaling methods that are strongly polynomial). We will provide the full construction and proof of equivalence in the revised version. revision: yes
Circularity Check
No circularity: ILP reduction and complexity bound are independent of target quantities
full rationale
The paper formulates largest 2-regular subgraphs in complete S-partite graphs as an integer linear program and claims this ILP can be solved in O(|V(S)|^3) time independent of partite set sizes. No step reduces a claimed prediction or uniqueness result to a fitted parameter, self-citation, or ansatz that is defined in terms of the output. The derivation chain relies on an external algorithmic reduction whose correctness is asserted separately from the input graph sizes, with no self-definitional or load-bearing self-citation patterns. The result is therefore self-contained against external benchmarks.
Axiom & Free-Parameter Ledger
axioms (1)
- standard math Standard definitions and properties of complete multipartite graphs and 2-regular subgraphs as disjoint unions of cycles.
Lean theorems connected to this paper
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IndisputableMonolith/Cost/FunctionalEquationwashburn_uniqueness_aczel unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
the integer linear problem can be solved efficiently in O(|V(S)|^3), independent of the order/size of the S-partite graph itself
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IndisputableMonolith/Foundation/ArithmeticFromLogicLogicNat ≃ Nat unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
reformulating the linear program (4) as an auxiliary optimization problem on a bipartite graph
What do these tags mean?
- matches
- The paper's claim is directly supported by a theorem in the formal canon.
- supports
- The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
- extends
- The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
- uses
- The paper appears to rely on the theorem as machinery.
- contradicts
- The paper's claim conflicts with a theorem or certificate in the canon.
- unclear
- Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.
Forward citations
Cited by 1 Pith paper
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Convergence rate of $H$-property for step-graphons
For step-graphons the probability of a node-disjoint cycle cover in the sampled graph converges to 0 or 1 at either an exponential rate or a root-n rate.
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