English

Hadamard powers of some positive matrices

Classical Analysis and ODEs 2018-03-20 v1 Functional Analysis

Abstract

Positivity properties of the Hadamard powers of the matrix [1+xixj]\begin{bmatrix}1+x_ix_j\end{bmatrix} for distinct positive real numbers x1,,xnx_1,\ldots,x_n and the matrix [cos((ij)π/n)]\begin{bmatrix}|\cos((i-j)\pi/n)|\end{bmatrix} are studied. In particular, it is shown that [(1+xixj)r]\begin{bmatrix}(1+x_ix_j)^r\end{bmatrix} is not positive semidefinite for any positive real number r<n2r<n-2 that is not an integer, and [cos((ij)π/n)r]\begin{bmatrix}|\cos((i-j)\pi/n)|^r\end{bmatrix} is positive semidefinite for every odd integer n3n\ge 3 and n3r<n2.n-3\le r<n-2.

Keywords

Cite

@article{arxiv.1803.06803,
  title  = {Hadamard powers of some positive matrices},
  author = {Tanvi Jain},
  journal= {arXiv preprint arXiv:1803.06803},
  year   = {2018}
}