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The purpose of this paper is to present some interesting and basic properties of some characterizations of Hadamard matrices . To accomplish this goal we begin with the development of some basic tools. These tools include a study of the class of positive definite matrices and an expansion formula for the determinant of a partitioned matrix . Using these tools a pivotal result due to Hadamard (1893) , known as the Hadamard determinant inequality is established. The Hadamard determinant inequality is used to present a major result due to Hadamard (1893) and is the main theorem of this paper, namely a characterization of a Hadamard matrix as a best d-optimal matrix in a suitable class of matrices. We conclude this paper by proving a necessary condition that is satisfied by the order n of a Hadamard matrix . It is shown that a necessary condition for a Hadamard matrix of order n to exist is that n=1 , n= 2 or n be congruent to zero mod 4.
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