Conjecture on irreducible components of relative tangency varieties

Let XrX_r be the determinantal variety of matrices of rank at most rr, let SS be the space of symmetric (N+1)×(N+1)(N+1)\times(N+1) matrices, and let Sr=XrSS_r=X_r\cap S. For r[N+1]r\in[N+1], define

SCr={BC(N+1)×(N+1)Cr(B) is symmetric}.\mathcal{SC}_r=\{B\in\mathbb{C}^{(N+1)\times(N+1)}\mid C_r(B)\text{ is symmetric}\}.

With the same notation for the corresponding projective varieties, write A=2CN+1A=\bigwedge^2\mathbb{C}^{N+1}.

Conjecture on the components of SCr\mathcal{SC}_r. For all r[N+1]r\in[N+1]:

  1. SC1=S=S2CN+1\mathcal{SC}_1=S=S^2\mathbb{C}^{N+1} is an irreducible component of SCr\mathcal{SC}_r for every r[N+1]r\in[N+1].
  2. (XNr)SNr(X_{N-r})_{S_{N-r}}^\vee is an irreducible component of SCr\mathcal{SC}_r for every 2rN+12\le r\le N+1.
  3. A=2CN+1A=\bigwedge^2\mathbb{C}^{N+1} is an irreducible component of SCr\mathcal{SC}_r for all N3N\ge3 and even r[N]r\in[N].

These component claims are suggested by symbolic computations for small values of NN, where additional irreducible components can occur and the varieties SCi\mathcal{SC}_i need not be nested. The conjecture concerns the persistent components arising from the symmetric and skew-symmetric matrix loci and the relative dual determinantal varieties.

Sources & referencesView supporting material

Primary source

Sandra Di Rocco, Lukas Gustafsson and Luca Sodomaco, “Conditional Euclidean distance optimization via relative tangency”, arXiv:2310.16766 (2024).

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