Fractional chromatic numbers of tensor products of three graphs

The tensor product $(G_1,G_2,G_3)$ of graphs $G_1$, $G_2$ and $G_3$ is defined by $V(G_1,G_2,G_3)=V\left(G_1\right)\times V\left(G_2\right)\times V\left(G_3\right)$and $E(G_1,G_2,G_3)=\left\{\left((u_1,u_2,u_3),(v_1,v_2,v_3)\right):\left|\{i:(u_i,v_i)\in E\left(G_i\right)\}\right|\ge 2\right\}.$Let ${\chi }_f\left(G\right)$ be the fractional chromatic number of a graph $G$. In this paper, we prove that if one of the three graphs $G_1$, $G_2$ and $G_3$ is a circular clique, ${\chi }_f(G_1,G_2,G_3)=min\{{\chi }_f\left(G_1\right){\chi }_f\left(G_2\right),{\chi }_f\left(G_1\right){\chi }_f\left(G_3\right),{\chi }_f\left(G_2\right){\chi }_f\left(G_3\right)\}.$     

Generalized Schur complements

Let A be an n×n complex matrix. For a suitable subspace $\text{M}$ of Cⁿ the Schur compression A _$\text{M}$ and the (generalized) Schur complement A_/$\text{M}$ are defined. If A is written in the form

$\text{A=}\text{B}\text{C}\text{S}\text{T}$

according to the decomposition $\text{C}{}^{\mathrm{n}}\text{=}\text{M}\text{⊕}\text{M}{}^{\mathrm{\perp }}$ and if B is invertible, then

$\text{A}{}_{\mathrm{<mtext>M</mtext>}}\text{=}\text{B}\text{C}\text{S}\text{SB}{}^{\mathrm{?1}}\text{C}$

and

$\text{A}{}_{\mathrm{<mtext>/</mtext><mtext>M</mtext>}}\text{=}\text{0}\text{0}\text{0}\text{T?SB}{}^{\mathrm{?1}}\text{C}\text{·}$

The commutativity rule for Schur complements is proved:

$\text{(A}{}_{\mathrm{<mtext>/</mtext><mtext>M</mtext>}}\text{)}{}_{\mathrm{<mtext>/</mtext><mtext>N</mtext>}}\text{=(A)}{}_{\mathrm{<mtext>/</mtext><mtext>N</mtext>}}\text{)}{}_{\mathrm{<mtext>/</mtext><mtext>M</mtext>}}\text{·}$

This unifies Crabtree and Haynsworth's quotient formula for (classical) Schur complements and Anderson's commutativity rule for shorted operators. Further, the absorption rule for Schur compressions is proved:

$\text{(A}{}_{\mathrm{<mtext>/</mtext><mtext>M</mtext>}}\text{)}{}_{\mathrm{<mtext>N</mtext>}}\text{=(A}{}_{\mathrm{<mtext>N</mtext>}}\text{)}{}_{\mathrm{<mtext>M</mtext>}}\text{=A}{}_{\mathrm{<mtext>M</mtext>}}\text{whenever}\text{M}\text{?}\text{N}$

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Nodal standing waves for a gauged nonlinear Schrödinger equation in R2

This paper investigates the existence and asymptotic behavior of nodal solutions to the following gauged nonlinear Schrödinger equation

$\{\begin{array}{c}?\mathrm{\Delta }u+\omega u+(\frac{h^2(\left|x\right|)}{{\left|x\right|}^2}+\underset{\left|x\right|}{\overset{+\infty }{\int }}\frac{h(s)}{s}{u}^2(s)ds)u=\lambda {\left|u\right|}^{p?2}u,x\in {\mathbb{R}}^2,\hfill \\ u(x)=u(|x|)\in H^1({\mathbb{R}}^2),\hfill \end{array}$

where $\omega ,\lambda >0$, $p>6$ and

$h(s)=\frac{1}{2}\underset{0}{\overset{s}{\int }}r{u}^2(r)dr$

is the so-called Chern–Simons term. We prove that for any positive integer k, the problem has a sign-changing solution ${u^{\lambda }}_k$ which changes sign exactly k times. Moreover, the energy of $u_k^{\lambda }$ is strictly increasing in k, and for any sequence $\{{\lambda }_n\}\to +\infty (n\to \infty )$, there exists a subsequence $\{{\lambda }_{n_s}\}$, such that ${({\lambda }_{n_s})}^{\frac{1}{p?2}}{u}_k^{{\lambda }_{n_s}}$ converges in $H^1({\mathbb{R}}^2)$ to $w_k$ as $s\to \infty$, where $w_k$ also changes sign exactly k times and solves the following equation

$?\mathrm{\Delta }u+\omega u=|u{|}^{p?2}u,u\in H^1({\mathbb{R}}^2).$