Designing MDS matrices is one of the most important methods to construct diffusion layer for block ciphers
and Cauchy matrices generated by ordered-array is a basic kind of MDS matrices.This paper provides the necessary and sufficient condition of two distinct ordered-arrays generating one same Cauchy matrix.We show the count value of Cauchy matrices over finite field
and predicate that a Cauchy matrix could never be a cyclic-shift matrix.Further
this paper provides the necessary and sufficient condition of Cauchy matrices with minimum number of entries
and supplies the construct method of Cauchy matrix with minimum number of entries and maximum number of occurrences of 1.Additionally
this paper provides a construction for involution Cauchy matrices.