REVIEW
Solving Random Planted CSPs below the $n^{k/2}$ Threshold
Data Structures and Algorithms · Submitted 14 Jul 2025 · 36 references
Pith's verdict: A genuinely new two-step algorithm that would close the planted-CSP search gap at the RRS17 trade-off, but the whole edifice rests on an unproven SoS-capture assertion that the authors themselves flag.
T0 · AI review
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Referee report
The paper
The paper claims
Random planted CSPs solved at the refutation trade-off: an n^{O(ℓ)}-time algorithm recovers a satisfying assignment whenever m ≥ O(n log n)(n/ℓ)^{k/2−1}, matching the known refutation thresholds.
The reading
What carries the argument
The load-bearing object is the degree-2ℓ sum-of-squares pseudoexpectation over the Boolean hypercube. For an XOR system with right-hand sides b_C, the algorithm forms ψ(x) = E_{C∼H}[b_C x_C] and computes a pseudoexpectation µ maximizing Ẽ_µ[ψ(x)]. Two sum-of-squares-certifiable facts do the work: Fact 3.8 (the known spectral refutation of random k-XOR, asserted to be captured by degree-2ℓ SoS) bounds Ẽ[Σ σ_C x_C] for Rademacher signs σ_C, and Lemma 5.5 uses a symmetrization argument with Rademacher signs to show that a random sample of hyperedges behaves like the complete hypergraph, forcing Ẽ[E_{C∼H}[x_C]] ≈ (1/n^k)Ẽ[⟨x,x*⟩^k]. Together these give Ẽ[⟨x,x*⟩^k] ≈ n^k, and Fact 3.7 converts that large moment into a correlated vector: the sign of Ẽ[x] for odd k, or a row of Ẽ[$x^{{⊗2}}$] for even k. The second rounding step, Algorithm 4, observes that if the approximate assignment differs from x* on o(n) coordinates, then most constraints through a fixed coordinate contain only correct coordinates, so the majority of b_C times the product over the other coordinates equals that coordinate of x*.
Extended reading notes
Core claim
The central claim is Theorem 1: for a random planted k-ary Boolean CSP whose planting distribution has complexity r, an $n^{{O(ℓ)}}$-time algorithm outputs a list of at most $2^{{k+2}}$ assignments, at least one of which satisfies the instance, provided m ≥ $2^{{O(k)}}$ n log n (n/ℓ)^{r/2−1}. This is proved through Theorem 2, a new algorithm for noisy k-XOR that recovers the planted assignment exactly, up to a global sign when k is even, provided m ≥ $2^{{O(k)}}$ n log n max($ε^{{-11}}$(n/ℓ)^{k/2−1}, $ε^{{-2}}$) and ε²/k ≥ Ω($n^{{-1/2}}$). The algorithm works in two independent steps: it first maximizes the canonical degree-2ℓ sum-of-squares relaxation of the XOR system to obtain an assignment with correlation 1−o(1) with the planted one, then rounds that approximate assignment by a majority vote over freshly used constraints, exploiting that a nearly correct assignment makes most constraints through a given coordinate reveal that coordinate's planted sign.
Load-bearing premise
The entire reduction leans on the assertion, stated in Remark 3.9(2) without a proof, that the known spectral refutation of random k-XOR is captured by a degree-2ℓ sum-of-squares proof even when ℓ grows with n; if that capture fails, Lemma 5.5 and the approximate-recovery step collapse.
Editorial extensions
If this is right
- If Theorem 1 is correct, every random planted k-ary CSP is solvable in time n^{O(ℓ)} at the same constraint density at which random CSPs are refutable, removing the search/refutation gap for the random planted model.
- Theorems 1 and 2 give new inversion algorithms for Goldreich-style pseudorandom generators and for k-sparse LPN in the high-noise regime, for stretches and noise levels obeying the stated trade-off.
- For even k, the paper notes the noisy-XOR threshold can be improved from ε^{-11} to ε^{-7}, so even fewer constraints suffice as the noise parameter ε grows.
- When the planting distribution is known to the algorithm, the list of 2^{k+2} candidates collapses to exact recovery of x* up to a global sign, matching the earlier polynomial-time guarantee without the runtime restriction.
- The two-step structure interpolates smoothly between polynomial time at ℓ = O(1) and near-linear constraint counts at ℓ ≈ n, giving a full family of algorithms rather than a single threshold result.
Reading between the lines
- Inference: The semirandom planted-CSP search problem, where scopes are chosen adversarially, remains open; the same two-step design would solve it if a degree-2ℓ sum-of-squares refutation existed for semirandom k-XOR, making that the natural next target.
- Inference: The paper's reliance on Remark 3.9(2) suggests a direct litmus test: produce an actual degree-2ℓ SoS certificate for the spectral refutation at ℓ = ω(1). If the capture assertion is false, the approximate-recovery lemma fails before any rounding issue arises.
- Inference: The algorithm could likely be made more economical by reusing the same constraints for both the SoS step and the majority rounding step rather than splitting the instance in half, at the cost of a more delicate correlation analysis.
- Inference: When Q is unknown, the list of candidate assignments could perhaps be reduced to exact recovery by a consistency post-filter among the candidates, rather than by knowing the planting distribution, yielding a stronger statement than the list guarantee.
Original abstract
We present a family of algorithms to solve random planted instances of any $k$-ary Boolean constraint satisfaction problem (CSP). A randomly planted instance of a Boolean CSP is generated by (1) choosing an arbitrary planted assignment $x^*$, and then (2) sampling constraints from a particular "planting distribution" designed so that $x^*$ will satisfy every constraint. Given an $n$ variable instance of a $k$-ary Boolean CSP with $m$ constraints, our algorithm runs in time $n^{O(\ell)}$ for a choice of a parameter $\ell$, and succeeds in outputting a satisfying assignment if $m \geq O(n) \cdot (n/\ell)^{\frac{k}{2} - 1} \log n$. This generalizes the $\mathrm{poly}(n)$-time algorithm of [FPV15], the case of $\ell = O(1)$, to larger runtimes, and matches the constraint number vs.\ runtime trade-off established for refuting random CSPs by [RRS17]. Our algorithm is conceptually different from the recent algorithm of [GHKM23], which gave a $\mathrm{poly}(n)$-time algorithm to solve semirandom CSPs with $m \geq \tilde{O}(n^{\frac{k}{2}})$ constraints by exploiting conditions that allow a basic SDP to recover the planted assignment $x^*$ exactly. Instead, we forego certificates of uniqueness and recover $x^*$ in two steps: we first use a degree-$O(\ell)$ Sum-of-Squares SDP to find some $\hat{x}$ that is $o(1)$-close to $x^*$, and then we use a second rounding procedure to recover $x^*$ from $\hat{x}$.
The compiled record
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The abstract, sentence by sentence
We present a family of algorithms to solve random planted instances of any $k$-ary Boolean constraint satisfaction problem (CSP). A randomly planted instance of a Boolean CSP is generated by (1) choosing an arbitrary planted assignment $x^*$, and then (2) sampling constraints from a particular "planting distribution" designed so that $x^*$ will satisfy every constraint. Given an $n$ variable instance of a $k$-ary Boolean CSP with $m$ constraints, our algorithm runs in time $n^{O(\ell)}$ for a choice of a parameter $\ell$, and succeeds in outputting a satisfying assignment if $m \geq O(n) \cdot (n/\ell)^{\frac{k}{2} - 1} \log n$. This generalizes the $\mathrm{poly}(n)$-time algorithm of [FPV15], the case of $\ell = O(1)$, to larger runtimes, and matches the constraint number vs.\ runtime trade-off established for refuting random CSPs by [RRS17]. Our algorithm is conceptually different from the recent algorithm of [GHKM23], which gave a $\mathrm{poly}(n)$-time algorithm to solve semirandom CSPs with $m \geq \tilde{O}(n^{\frac{k}{2}})$ constraints by exploiting conditions that allow a basic SDP to recover the planted assignment $x^*$ exactly. Instead, we forego certificates of uniqueness and recover $x^*$ in two steps: we first use a degree-$O(\ell)$ Sum-of-Squares SDP to find some $\hat{x}$ that is $o(1)$-close to $x^*$, and then we use a second rounding procedure to recover $x^*$ from $\hat{x}$.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We present a family of algorithms to solve random planted instances of any $k$-ary Boolean constraint satisfaction problem (CSP). | contribution 1.00 | 0.95 | 0.39 | asserted 1.00 |
| s1 | A randomly planted instance of a Boolean CSP is generated by (1) choosing an arbitrary planted assignment $x^*$, and then (2) sampling constraints from a particular "planting distribution" designed so that $x^*$ will satisfy every constraint. | background 0.96 | 0.12 | 0.03 | asserted 0.99 |
| s2 | Given an $n$ variable instance of a $k$-ary Boolean CSP with $m$ constraints, our algorithm runs in time $n^{O(\ell)}$ for a choice of a parameter $\ell$, and succeeds in outputting a satisfying assignment if $m \geq O(n) \cdot (n/\ell)^{\frac{k}{2} - 1} \log n$. | result 0.75 | 0.95 | 0.62 | asserted 1.00 |
| s3 | This generalizes the $\mathrm{poly}(n)$-time algorithm of [FPV15], the case of $\ell = O(1)$, to larger runtimes, and matches the constraint number vs.\ runtime trade-off established for refuting random CSPs by [RRS17]. | interpretation 0.79 | 0.51 | 0.17 | asserted 1.00 |
| s4 | Our algorithm is conceptually different from the recent algorithm of [GHKM23], which gave a $\mathrm{poly}(n)$-time algorithm to solve semirandom CSPs with $m \geq \tilde{O}(n^{\frac{k}{2}})$ constraints by exploiting conditions that allow a basic SDP to recover the planted assignment $x^*$ exactly. | background 0.59 | 0.17 | 0.06 | asserted 1.00 |
| s5 | Instead, we forego certificates of uniqueness and recover $x^*$ in two steps: we first use a degree-$O(\ell)$ Sum-of-Squares SDP to find some $\hat{x}$ that is $o(1)$-close to $x^*$, and then we use a second rounding procedure to recover $x^*$ from $\hat{x}$. | method 0.99 | 0.94 | 0.14 | asserted 1.00 |
What was examined, and what was not
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References
How the literature uses it
4 arXiv papers cite this in 9 sentences
Papers citing it · 3 sentences without a confident label
Compares with it 2 papers
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Our result substantially improves the dependence on the bias parameter over the previous best recovery algorithm of Basu et al. [ref] , achieving the information-theoretically optimal $δ^-2$ scaling.
Near Optimal Algorithms for Noisy $k$-XOR under Low-Degree Heuristic · Introduction · 1.00
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An algorithm with similar density running time trade-off was recently obtained by [ref] .
Kikuchi Graphs of Random Hypergraphs are Approximately Johnson · Application to Solving Planted $2r$-XOR · 0.93
Cites it as background 2 papers
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More recently, Basu et al. [ref] obtained a new algorithm for the search version of noisy $k$-XOR.
Near Optimal Algorithms for Noisy $k$-XOR under Low-Degree Heuristic · Introduction · 0.89
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This includes hardness and cryptographic formulations of sparse noisy parity/$k$-LIN/XOR-code problems [ref] , as well as algorithmic work on planted and random CSPs [ref] .
Expanders Meet Reed-Muller: Easy Instances of Noisy k-XOR · Statistical-Computational Gap and Expansion Properties · 0.99
Discussion
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