Reducibility of spectral curves of finite Jacobi pencils
B. Shapiro
https://arxiv.org/abs/2605.14817 https://arxiv.org/pdf/2605.14817 https://arxiv.org/html/2605.14817
arXiv:2605.14817v1 Announce Type: new
Abstract: We consider finite pencils of Jacobi matrices \[ J_n(w)=A wB, \] where $A$ is diagonal and $B$ is tridiagonal with zero diagonal. The spectral curve is the affine plane curve \[ \chi_n(\lambda,w)=\det(\lambda I J_n(w))=0 . \] The main question is to describe when this curve is reducible. We prove generic irreducibility for fixed pairwise distinct diagonal entries and discuss several elementary reducibility mechanisms. Besides disconnected Jacobi chains, constant eigenvalue branches, and reflection-symmetric components, one must also take into account reducibility caused by scalar diagonal blocks. We formulate a reducibility conjecture and record low-dimensional evidence and counterexamples to several overly optimistic classifications. A central point of the picture is a codimension-growth principle: apart from the cutting divisors $b_i=0$, genuinely connected primitive reducibility should move to higher and higher codimension as the size of the chain grows.
toXiv_bot_toot
For 100 years, the red markings were thought natural
A new analysis inside the cave in Wales suggests they were made deliberately by ancient humans some 17,000 years ago
Rediscovered Late Upper Palaeolithic Painted Imagery at Bacon Hole, Gower Peninsula, South Wales
https://www.mdpi.com/2571-550X/9/3/43
heise | Home Assistant: Automationen für Einsteiger erklärt
Automationen machen ein Smart Home erst richtig intelligent. Wir zeigen, wie das in Home Assistant gelingt.
https://www.hei…
heise | Neobroker im Vergleich: Kosten, Funktionen und Sicherheit
Neobroker machen den Wertpapierhandel einfacher und günstiger. Wir zeigen die Unterschiede bei Kosten, Funktionen, Kundendienst und Sicherheit.
…