Regular complex Hadamard matrices of order seven

Let F7F_7 be the Fourier matrix of order 77, and let P7qP_7^q denote the displayed Petrescu family, with qTq\in\mathbb T. A regular complex Hadamard matrix is one whose row scalar products decompose as sums of cycles. Order-seven classification conjecture. F7,P7qF_7,P_7^q are the only regular complex Hadamard matrices at N=7N=7. The source reports computational and number-theoretic evidence, but does not establish the classification.

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Primary source

Teodor Banica, Duygu Ozteke and Lorenzo Pittau, “Isolated partial Hadamard matrices, and related topics”, arXiv:1706.00986 (2017).

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