slug: nishijima-nakata-2024-gdnn-inclusion
bibkey: nishijimanakata2024generalizations
doi: 10.15807/jorsj.67.84
triage: theorem
motivation_gids:
  - D5/S3/QuadraticForms/ConicGDNN/Result.result
url: https://arxiv.org/abs/2204.12119

Generalized doubly nonnegative cone inclusion

Problem

The cited article, arXiv:2204.12119v4, Section 5.1, Conjecture 5.1, asks for the inclusion of the NN-type generalized doubly nonnegative cone in the BD-type cone for products of a nonnegative orthant and second-order cones. The statement reads verbatim: “If K is a direct product of a nonnegative orthant and second-order cones, DNN^NN(K) ⊆ DNN^BD(K) holds.” The article notes that the case of a single second-order cone follows from its Proposition 4.12 and that the general inclusion relationship is unknown.

Formal reading

Let $p,r\ge 0$ and $k_j\ge 1$ for $1\le j\le r$, and put

$$K={\mathbb{R}}_{+}^p\times \prod _{j=1}^r\{(t,z)\in \mathbb{R}\times {\mathbb{R}}^{k_j}:\Vert z{\Vert }_2\le t\}.$$

Let $q$ square each orthant coordinate and send each Lorentz block $(t,z)$ to $(t^2+\Vert z{\Vert }_2^2,2tz)$. Write ${\Sigma }_{n,4}$ for the convex hull of squares of homogeneous quadratic polynomials. With the standard coordinate pairing and $n=p+{\sum }_j(k_j+1)$, define

$${\mathcal{K}}_{\mathrm{NN},0}(K)=\{A\in {\mathbb{S}}^n:q(x{)}^{\mathsf{T}}Aq(x)\in {\Sigma }_{n,4}\}.$$

Every $X\in {\mathbb{S}}^n$ satisfying $\mathrm{tr}(XA)\ge 0$ for every $A\in {\mathcal{K}}_{\mathrm{NN},0}(K)$ is positive semidefinite and satisfies $Xs\in K$ for every extreme ray generator $s$ of $K^{\ast }$. Thus $\mathrm{DNN}^{\mathrm{NN}}(K)\subseteq \mathrm{DNN}^{\mathrm{BD}}(K)$.

Motivation

The settling GID is D5/S3/QuadraticForms/ConicGDNN/Result.result. The source note is D5/L/QuadraticForms/nishijimanakata2024generalizations. The result compares the two specified approximations for the full orthant and Lorentz product family.

Gap

Status: Proved for the stated inclusion. Preservation holds for the entire cone, and the intermediate theorems also allow $k_j=0$. Products with positive semidefinite cone factors and the strictness question in Triage are outside the formal claim.

Route

Every rank-one symmetric matrix $w{w}^{\mathsf{T}}$ supplies the single-square quartic $(w\cdot q(x){)}^2$, so trace positivity implies $X⪰0$. For $u,v\in K=K^{\ast }$, the quadratic polynomials $h_u=u\cdot q$ and $h_v=v\cdot q$ have homogeneous linear-square certificates. Their product is a sum of squares of homogeneous quadratics, so $(u{v}^{\mathsf{T}}+v{u}^{\mathsf{T}})/2$ belongs to ${\mathcal{K}}_{\mathrm{NN},0}(K)$. Trace positivity gives $u^{\mathsf{T}}Xv\ge 0$. Self-duality then yields $Xv\in K$ for every $v\in K$.

The structural argument needs only a finite-dimensional self-dual closed cone and a homogeneous quadratic map $q$ taking values in it. For any $u$ in that cone, $u\cdot q(x)\ge 0$ for all $x$. A nonnegative real homogeneous quadratic polynomial is a sum of squares of linear forms: diagonalize its positive semidefinite symmetric coefficient matrix and absorb the square roots of its nonnegative eigenvalues. Multiplication gives the quadratic-square certificate above; no further Jordan identity is used in the rank-one or trace-duality steps. The Lean development specializes this argument to the stated products and constructs the linear-square certificates explicitly; it does not state an abstract theorem for arbitrary cones or quadratic maps.

Falsifier

A symmetric matrix in the specified trace dual that is not positive semidefinite, or that sends some dual extreme ray generator outside $K$, would contradict Result.result. A cone vector $v$ with $Xv\notin K$ would already contradict Duality.mulVec_mem_cone.

Evidence

D5/S3/QuadraticForms/ConicGDNN/Result.result proves exactly Defs.claim. The principal dependencies are Lorentz.dualCone_cone, Lorentz.pullback_eq_sum_sq, Duality.quartic_rankOne, Duality.posSemidef_of_mem_dnnNN, Duality.sym_mem_knn0, and Duality.mulVec_mem_cone. The accepted axiom closure of the result is contained in {propext, Classical.choice, Quot.sound}.

The source statement and definitions were read in arXiv:2204.12119v4 (Section 2, Theorem 3.5, Definitions 3.6 and 3.7, Conjecture 5.1). In the bounded literature screen, the later articles 2402.12964, 2502.04006, 2510.27160, 2602.23725 and 2608.27062 contain no reported settlement in that screen. This is not an exhaustive citation-index or priority certification.

Triage

• PROVED. The stronger conclusion $XK\subseteq K$ holds for every cone vector, beyond extreme ray generators of $K^{\ast }$, by Duality.mulVec_mem_cone. No positive spatial-dimension hypothesis is needed for this stronger conclusion.
• PROVED in prose. The mechanism uses only that the Jordan square is a homogeneous quadratic map into a self-dual closed cone, by the nonnegative-quadratic SOS argument in Route. The abstract generalization is a mathematical derivation; the Lean theorem concerns the pinned orthant and Lorentz products.
• PROVED in prose. The same inclusion for products with positive semidefinite cone factors, as in the article’s Section 4.2, admits the same argument: the matrix-square map is homogeneous quadratic and takes values in the self-dual positive semidefinite cone under the trace pairing. Its coordinate model and SOS certificate are not formalized in this development.
• PROVED in prose. When every Lorentz block has $k_j=1$, each block is a rotated copy of ${\mathbb{R}}_{+}^2$: the orthogonal change $(t,z)\mapsto ((t+z)/\sqrt{2},(t-z)/\sqrt{2})$ turns the Jordan square into coordinatewise squaring with positive weights, and the two cones coincide with the ordinary doubly nonnegative cone.
• OPEN. Which products, with at least one block of spatial dimension $k_j\ge 2$, give a strict inclusion.

ASSUMED-UNVERIFIED

Literature completeness, priority and exhaustive coverage of subsequent papers are unverified. The abstract generalization and the positive semidefinite factor extension have no general Lean theorem in this development.