REVIEW 2 major objections 6 minor 61 references
On Symbolic Approaches for Computing the Matrix Permanent
T0 review · 2 major / 6 minor · reviewed 2026-08-14 · deepseek-v4-flash
Pith's one-line read Computing a matrix permanent is usually practical only for sparse matrices; this paper shows that a symbolic version of Ryser's formula, built on Algebraic Decision Diagrams, computes exact permanents of dense 70x70 and similar-row 80x80…
desk verdict Clean symbolic-Ryser algorithm with real promise on structured matrices, but the 'dense' claim is supported only by near-all-ones benchmarks and needs tightening. 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 central object is the Algebraic Decision Diagram (ADD), a directed acyclic graph representing a real-valued function of Boolean variables by sharing identical substructures. Here the Boolean variables say whether a column belongs to the subset $S$ in Ryser's formula; the ADD's leaves carry integer values such as row sums, products, and the parity sign $(-1)^{|S|}$. The diagram does the work: when rows are identical or similar, the row-sum ADDs are isomorphic and merge, and memoization through shared nodes avoids recomputing the same partial sums. The supporting mechanism is early abstraction, the identity $\exists x\,(f\cdot g)=(\exists x\,f)\cdot g$ when $x$ does not occur in $g$, which lets the algorithm quantify out column variables as soon as they are irrelevant, keeping the diagram small. The experiments show a strong correlation between ADD node count and running time, confirming that diagram size is the operative resource.
What would settle it
Run the proposed algorithm on random 0-1 matrices of size $n=40$ or $n=50$ in which each entry is independently 1 with probability 0.5, recording the maximum ADD node count and wall-clock time, and compare with the flipped-from-all-ones instances of the same size. If the ADD size jumps to millions of nodes or the run exceeds the 1800-second timeout even at $n=40$, the dense-matrix conclusion does not extend to arbitrary dense inputs; if it completes quickly, the claim is strengthened.
Extended reading notes
Core claim
The central discovery is that a symbolic implementation of Ryser's formula, built on Algebraic Decision Diagrams and driven by early abstraction, opens a practical frontier beyond sparse matrices. For an $n\times n$ 0-1 matrix the paper represents, as an ADD, the function $(-1)^{|S|}\prod_{i=1}^{n}\sum_{j\in S}a_{i,j}$ on subsets $S$ of columns; the permanent is obtained by adding the values over all $S$. Row sums for similar rows become shared subgraphs, so the diagram stays small exactly when rows are near-identical; early abstraction then eliminates a column variable as soon as no remaining row-sum factor depends on it. On 2125 generated benchmarks, exact permanents are reported for dense matrices up to $n=70$ and similar-row matrices up to $n=80$ within 1800 seconds, whereas the explicit implementation of Ryser's formula times out for $n\ge 34$ and neither SAT-based counter can solve the smallest dense or similar-row instances tested. The authors present this as first evidence that the frontier of practically efficient permanent computation can be pushed well beyond sparse matrices.
Load-bearing premise
The load-bearing premise is that the matrices used for the dense case, generated by flipping a few entries of the all-ones matrix, stand in for dense matrices as a class; if arbitrary dense 0-1 matrices make the decision diagram grow explosively, the main claim about dense matrices would not be supported.
Editorial extensions
If this is right
- Exact permanent computation becomes practical for dense 0-1 matrices up to at least $n=70$, roughly double the limit of the explicit implementation of Ryser's formula used in the comparison.
- Matrices whose rows differ in only a few positions can be solved up to $n=80$, with performance degrading gracefully as row similarity decreases.
- With early abstraction, the same symbolic algorithm remains competitive with SAT-based counters on sparse matrices and outperforms them as density grows.
- ADD size is the predictive resource: instances with compact diagrams run quickly, so heuristics that maximize subgraph sharing should be the focus of further work.
Reading between the lines
- Editorial inference: the dense benchmarks are built by flipping at most $1.4n$ entries of the all-ones matrix, so every row remains close to every other; arbitrary dense matrices, such as independent random entries with density 0.5, may not admit compact ADDs and are not covered by the experiments.
- Editorial inference: the same ADD-plus-early-abstraction recipe could be applied to other subset-sum factorizations, such as counting Hamiltonian cycles or monomer-dimer partition functions, whenever the summed quantity factorizes row-wise and rows repeat structure.
- Editorial inference: the correlation between ADD size and running time suggests a testable design principle - row ordering and clustering that maximize shared subgraphs should transfer to other decision-diagram libraries and to weighted model counting.
- Editorial inference: a complete characterization of matrices with succinct ADD representations would let the approach yield theoretical upper bounds for dense matrices analogous to the earlier sparse-matrix bounds, a direction the authors leave open.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper presents RysersADD, an exact algorithm for computing the permanent of a 0-1 matrix by translating Ryser's formula into operations on Algebraic Decision Diagrams (ADDs). Row sums are represented as ADDs, multiplied with a parity ADD, and the permanent is obtained by additively quantifying out all column variables. An early-abstraction step, taken from the ADDMC weighted model counter, allows variables to be eliminated as soon as they no longer occur in future factors. The authors report experiments on random sparse, dense, and 'similar-row' matrices (generated by flipping O(n) entries of an all-zero, all-one, or repeated-row starting matrix), plus SuiteSparse and fullerene instances. RysersADD and the parallel version RysersADD-P solve dense instances up to n=70 and similar-row instances up to n=80 within 1800 seconds, while explicit Ryser and the model counters D4 and DSharp time out earlier. The paper concludes that the frontier of practical permanent computation is pushed beyond sparse matrices to dense and similar-row matrices.
Significance. The algorithmic idea is clean and exact: it is a direct symbolic execution of Ryser's formula with no fitted parameters, and the early-abstraction theorem from ADDMC is used as a proven building block. The experimental study is broad in its coverage of baselines (explicit Ryser, D4, DSharp with six encodings) and benchmark families, and the similar-row results are genuinely interesting. If the dense-matrix claim were supported, this would be a notable practical advance. However, the dense benchmark design conflates density with row-similarity, so the evidence does not support the advertised 'dense matrices' contribution. The work is best read as evidence for scalability on matrices whose rows are mutually close, including near-all-ones matrices, not on arbitrary dense matrices.
major comments (2)
- [5.3 (Table 1), 6.2 (Fig. 3)] The 'dense' benchmark family is generated by starting from the all-ones matrix and flipping at most Cf·n entries, with Cf ≤ 1.4. For n=70 this changes at most 98 of 4900 entries (2%), so the resulting rows differ from the all-ones row in only a few positions and are nearly identical to one another. These instances are therefore a special case of the 'similar rows' class the paper itself motivates in Section 4, and the scaling in Figure 3 does not demonstrate scalability on arbitrary dense matrices, such as independent Bernoulli(0.5) matrices. Since the abstract and Section 1 claim that the frontier is pushed 'to the classes of dense matrices,' this claim outruns the evidence; the authors should either add experiments on genuinely random dense matrices or explicitly restrict the conclusion to near-all-ones / row-similar matrices.
- [Section 1 and Section 7] The paper's central contribution claim is that the frontier of practically efficient permanent computation is pushed to dense matrices. Yet no experiments are reported on matrices with independent random entries, and Section 7 concedes that a complete characterization of matrices admitting compact ADDs is open. Given these gaps, the broad 'dense matrices' claim is not established by the presented evidence. The revision should either provide control experiments with, e.g., Bernoulli(0.5) dense matrices, or explicitly narrow the scope of the contribution to matrices that are close (in Hamming distance) to a common row, and adjust the abstract and introduction accordingly.
minor comments (6)
- [Section 3] The description of Servedio and Wan's result as applying to 'matrices with at most C·n zeros' appears to be incorrect; the original result concerns matrices with at most C·n nonzeros (i.e., few ones). Please correct this to avoid misrepresenting the related work.
- [Section 5.2] The word 'Westemere' appears to be a typo; it should likely be 'Westmere'.
- [Section 6.5] The text says 'despite the density of 1s being 9n' for the instance can_61. Since 9n is a count rather than a density, the wording should be changed to 'the number of 1s being 9n'.
- [Section 5.1] The statement that the monolithic approach is used for dense and similar-row cases should be made explicit in the captions of Figures 3 and 5, so readers know whether the plotted times use early abstraction or not.
- [Section 6.6, Table 2] The row labels 'Encoding / Mode 1 2 3 4 5 6 EA Mono EA Mono' are hard to parse; please clarify which columns correspond to D4, DSharp, and the RysersADD variants.
- [Section 6.1, Fig. 2] The scatter plots include only instances that did not time out; this selection should be stated in the caption, as it can bias the perceived correlation between ADD size and runtime.
Circularity Check
No significant circularity: RysersADD is an exact symbolic translation of Ryser's formula, with no fitted constants and no load-bearing self-citation.
full rationale
The paper's central derivation is Equation (1)/(2), an algebraic restatement of Ryser's formula; the algorithm's correctness is independent of any fitted value, and the benchmark results are not used to define the mathematical result. The only self-citation is Theorem 1 from ADDMC [20], used to justify early abstraction; this is a simple commutation lemma (∃x(f·g) = (∃x f)·g for x not in Vars(g)), externally checkable and not tailored to make the permanent results come out. The dense- and similar-row benchmark generators (Section 5.3) do raise a question of external validity—'dense' instances are all-ones matrices with at most Cf·n flips and are therefore similar-row by construction—but that concerns whether the experimental claim generalizes to arbitrary dense matrices, not whether a derived quantity collapses to an input by definition. No fitted parameter is renamed as a prediction, and no uniqueness theorem is imported from the authors' prior work to force a choice. Under the stated circularity criteria, the derivation is self-contained.
Assumptions & free parameters
assumptions (5)
- standard math Ryser's formula for the permanent: perm(A) = (-1)^n sum_{S subset of [n]} (-1)^|S| prod_i sum_{j in S} a_ij
- standard math ADD operations (product, sum, ITE, additive quantification) are implemented correctly and have the standard semantics
- standard math Early abstraction theorem: for f:2^X -> R and g:2^Y -> R, for x in X\Y, exists x (f*g) = (exists x f)*g
- domain assumption Sylvan library provides correct arbitrary-precision ADD operations
- ad hoc to paper Dense benchmarks constructed from the all-ones matrix with at most 1.4n flips are representative of the class of dense matrices
Cite this review
Pith. "Pith review of On Symbolic Approaches for Computing the Matrix Permanent." pith.science (2026). https://pith.science/paper/EZET4JUZ
@misc{pith2026190803252,
author = {Pith},
title = {Pith review of: On Symbolic Approaches for Computing the Matrix Permanent},
year = {2026},
howpublished = {\url{https://pith.science/paper/EZET4JUZ}},
note = {Machine review of arXiv:1908.03252}
}
read the original abstract
Counting the number of perfect matchings in bipartite graphs, or equivalently computing the permanent of 0-1 matrices, is an important combinatorial problem that has been extensively studied by theoreticians and practitioners alike. The permanent is #P-Complete; hence it is unlikely that a polynomial-time algorithm exists for the problem. Researchers have therefore focused on finding tractable subclasses of matrices for permanent computation. One such subclass that has received much attention is that of sparse matrices i.e. matrices with few entries set to 1, the rest being 0. For this subclass, improved theoretical upper bounds and practically efficient algorithms have been developed. In this paper, we ask whether it is possible to go beyond sparse matrices in our quest for developing scalable techniques for the permanent, and answer this question affirmatively. Our key insight is to represent permanent computation symbolically using Algebraic Decision Diagrams (ADDs). ADD-based techniques naturally use dynamic programming, and hence avoid redundant computation through memoization. This permits exploiting the hidden structure in a large class of matrices that have so far remained beyond the reach of permanent computation techniques. The availability of sophisticated libraries implementing ADDs also makes the task of engineering practical solutions relatively straightforward. While a complete characterization of matrices admitting a compact ADD representation remains open, we provide strong experimental evidence of the effectiveness of our approach for computing the permanent, not just for sparse matrices, but also for dense matrices and for matrices with "similar" rows.
Figures
Figures from the paper (2 more)
Reference graph
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