## Advances in Operator Theory

### Almost Hadamard matrices with complex entries

#### Abstract

We discuss an extension of the almost Hadamard matrix formalism, to the case of complex matrices. Quite surprisingly, the situation here is very different from the one in the real case, and our conjectural conclusion is that there should be no such matrices, besides the usual Hadamard ones. We verify this conjecture in a number of situations, and notably for most of the known examples of real almost Hadamard matrices, and for some of their complex extensions. We discuss as well some potential applications of our conjecture, to the general study of complex Hadamard matrices.

#### Article information

Source
Adv. Oper. Theory, Volume 3, Number 1 (2018), 137-177.

Dates
Received: 9 February 2017
Accepted: 12 May 2017
First available in Project Euclid: 5 December 2017

Permanent link to this document
https://projecteuclid.org/euclid.aot/1512497957

Digital Object Identifier
doi:10.22034/aot.1702-1114

Mathematical Reviews number (MathSciNet)
MR3730344

Zentralblatt MATH identifier
1373.15047

#### Citation

Banica, Teodor; Nechita, Ion. Almost Hadamard matrices with complex entries. Adv. Oper. Theory 3 (2018), no. 1, 137--177. doi:10.22034/aot.1702-1114. https://projecteuclid.org/euclid.aot/1512497957

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