Bahri–Xu linear algebraic conjecture

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Let x1,…,xpx_1,\dots,x_p with p≥2p\geq 2 be distinct vectors in Rm\mathbb R^m. Define the symmetric matrix A=(aij)1≤i,j≤pA=(a_{ij})_{1\leq i,j\leq p} by

aij={0,i=j,1∣xi−xj∣,i≠j.a_{ij}=\begin{cases}0,&i=j,\\\\ \dfrac{1}{|x_i-x_j|},&i\ne j. \end{cases}

For k=1,…,pk=1,\dots,p, let ∂A∂xk=(∂aij∂xk)1≤i,j≤p\dfrac{\partial A}{\partial x_k}=\left(\dfrac{\partial a_{ij}}{\partial x_k}\right)_{1\leq i,j\leq p}, regarded as a vector-valued p×pp\times p matrix, and let U=(u1,…,up)T∈RpU=(u_1,\dots,u_p)^{\mathrm T}\in\mathbb R^p. Bahri–Xu's linear algebraic conjecture. There is a positive constant c=c(p,m)c=c(p,m) depending only on pp and mm such that

∣AU∣2+sup⁡1≤i≤p∣UT(∂A∂xi)U∣≥c(p,m)∑i,j\j≠iuj2∣xi−xj∣2.|AU|^2+\sup_{1\leq i\leq p}\left|U^{\mathrm T}\left(\frac{\partial A}{\partial x_i}\right)U\right|\geq c(p,m)\sum_{\substack{i,j\\\j\ne i}}\frac{u_j^2}{|x_i-x_j|^2}.

This is the purely linear-algebraic assumption introduced by Bahri and Xu in connection with asymptotic expansions for the Yamabe functional and the Morse lemma at infinity. The supplied source does not establish the assertion or provide evidence of its resolution, so its status remains open.

References

Primary source

Hong Chen, Jianquan Ge, Kai Jia and Zhiqin Lu, “On a Conjecture of Bahri-Xu”, arXiv:2101.10023 (2021).

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