The symmetric rational orthogonal zero-pattern conjecture

Let U(n)U(n) denote the unitary n×nn\times n matrices and On(Q)O_n(\mathbb{Q}) the orthogonal n×nn\times n matrices with rational entries. A matrix in U(n)U(n) is hermitian when it equals its conjugate transpose; a matrix in On(Q)O_n(\mathbb{Q}) is symmetric when it equals its transpose. For any matrix XX, write X\underline{X} for its zero-pattern, defined entrywise by

Xi,j={1,Xi,j0,0,Xi,j=0.\underline{X}_{i,j}=\begin{cases}1,&X_{i,j}\neq0,\\0,&X_{i,j}=0.\end{cases}

The symmetric rational orthogonal zero-pattern conjecture. For any hermitian XU(n)X\in U(n) there exists a symmetric ZOn(Q)Z\in O_n(\mathbb{Q}) such that X=Z\underline{X}=\underline{Z} and

Tr(X)=Tr(Z).\operatorname{Tr}(X)=\operatorname{Tr}(Z).

This is the combined symmetric analogue of the two preceding conjectures, adding equality of traces to equality of zero-patterns. The supplied text gives no proof or resolution of the assertion.

Sources & referencesView supporting material

Primary source

Dragomir Z. Djokovic, Simone Severini and Ferenc Szollosi, “Rational Orthogonal versus Real Orthogonal”, arXiv:0903.2853 (2009).

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