✗ Mechanism failed 2026

Single shared SDP for all target classes

Implementation & benchmark of arXiv:2607.03232 — Fast SDP certification of neural networks : towards large multi-class datasets

Usefulness7/10
Difficulty6/10
Novelty7/10

Source paper: Fast SDP certification of neural networks : towards large multi-class datasets arXiv:2607.03232 ⓘ · analyzed Aug 30, 2026

AI-generated research hypothesis, automatically tested. Not peer-reviewed.

Idea description

Replace the standard K-1 separate targeted robustness optimizations for a sample with one shared optimization whose scalar objective is the smallest correct-versus-target logit margin over every incorrect class. The same hidden-state relaxation and lifted SDP variables are shared across classes; only K-1 linear margin constraints remain. This should substantially reduce wall-clock time when K is large, while preserving the exact logical meaning of a full robustness certificate.

Formulas

$$\min_{j\in\bar{\cal{J}}_K}\;\min_{z_0\in\mathcal{B}_\epsilon(x)} z_K^y-z_K^j\ge 0,\qquad \bar{\cal{J}}_K={\cal{J}}_K\setminus\{y\}.$$
$$\min_{z_0\in\mathcal{B}_\epsilon(x),\,z_1,\ldots,z_K} t\quad\text{subject to}\quad t\le z_K^y-z_K^j\ \forall j\in\bar{\cal{J}}_K,$$
$$\text{and the SDP relaxation constraints }(z_0,z_1,\ldots,z_K)\in\mathcal{R}_{\mathrm{SDP}}(x,\epsilon).$$
$$\text{certified if }t_{\mathrm{SDP}}^\star\ge 0;\qquad t_{\mathrm{SDP}}^\star=\min_{(z_0,\ldots,z_K)\in\mathcal{R}_{\mathrm{SDP}}(x,\epsilon)}\min_{j\ne y}(z_K^y-z_K^j).$$

Mathematical statement

For an input-label pair (x,y), let B_epsilon(x) be the perturbation set, z_0 be the perturbed input, z_K^c be the output logit for class c, and J_K={1,...,K}. Proposition 1 defines targeted robustness against class j by min_{z_0 in B_epsilon(x)}(z_K^y-z_K^j)>=0. Proposition 2 defines full robustness by min_{j in J_K\{y}} min_{z_0 in B_epsilon(x)}(z_K^y-z_K^j)>=0. Introduce a shared scalar t representing the worst margin. The equivalent epigraph form is min t subject to t <= z_K^y-z_K^j for every j != y and z_0 in B_epsilon(x). A convex quadratic/SDP relaxation replaces the nonlinear network constraints by linear matrix inequalities over hidden activations and lifted products. The certificate is valid when the relaxed optimum t_star is nonnegative, because the relaxation is an outer approximation of all reachable network states.

Implementation notes

1. Integration point: modify a neural-network robustness verifier after interval bound propagation and before the SDP solver. The network forward equations, perturbation set, and lifted quadratic constraints remain unchanged; only the objective and output-layer constraints are changed. For each correctly classified sample (x,y), create one SDP instance with shared variables for z_0,...,z_K and one scalar t. Add K-1 linear constraints t <= z_K[y]-z_K[j] instead of launching K-1 independent targeted instances. 2. Pseudocode: compute interval bounds and the existing SDP relaxation R_SDP(x,epsilon); allocate t; for j in classes excluding y, add_constraint(t <= logit_y - logit_j); solve minimize(t); return certified = (t_star >= 0). If the solver supports multiple right-hand sides, batch the K-1 output constraints in one matrix. 3. Computed from the paper's mathematics: the epigraph reduction and the nonnegative-certificate test. Estimated empirically: solver factorization reuse, memory, and whether shared presolve actually reduces time; compare against separate targeted solves. 4. First experiment: use a small 4-layer ReLU MLP or CNN on MNIST and CIFAR-10, then an ImageNet-100 classifier with the same verifier and epsilon. Measure total certification time, peak memory, certified accuracy, and t_star against K-1 separate SDP runs. The expected signal is near-identical certificates and at least a 2x speedup for 100 classes, with larger gains when SDP setup or factorization dominates.

Verification

Mechanism failed

Stage 1 · Toy mechanism gate: Failed ✗

Stage 2 · Mechanism transferred to benchmark: Not tested

Stage 2 · Practical benchmark result: Not run

Methodology: Toy-system gate first; the benchmark stage runs only after a pass. How verification works

Stage 1 — Mechanism check agent confidence 10/10

Built and ran a readable LP analogue in shared_sdp_toy.py. The core claim fails as written: minimizing t subject to t <= every margin is unbounded, while the bounded correction max_h min_j margin reverses the required min_h min_j quantifiers and differed from the true targeted minimum by 7.09–8.83 in all five checks. Separate solves scaled with K, but the apparent vectorized speedup was only arithmetic enumeration, not an exact single SDP, so it does not rescue the proposed formulation.

Agent confidence
10/10
Baseline
Exact targeted relaxation: min_j min_h margin; K=2..128 required K-1 LP solves, 4.17 ms to 432.39 ms in the sweep.
Idea
Literal shared epigraph: unbounded in all 5 checks (HiGHS status 3). Bounded max-t variant had absolute errors 7.09, 8.82, 8.01, 8.41, and 8.83 versus the exact value. Exact vectorized margin enumeration took about 0.18–0.21 ms, but was not a shared SDP solve.

Limitations: This is an LP box-relaxation analogue rather than a full neural-network SDP, and it does not benchmark an actual SDP solver or GPU implementation. The negative result is nevertheless decisive for the stated epigraph quantifiers: the proposed objective is mathematically unbounded, and its natural bounded max-min correction is not the robustness certificate.

How to run: python3 shared_sdp_toy.py

Verdict computed by deterministic test code from paired-seed statistics — not by the language model.

Artifacts

Implementation overview ⬇ Download all as ZIP 3 files · code, reports and structured results