Given two Hadamard matrices of the same order, it can be quite difficult
to decide whether or not they are equivalent. There are some criteria to determine
Hadamard inequivalence. Among them, one of the most commonly used is the
4-profile criterion. In this paper, a reformulation of this criterion in the cocyclic
framework is given. The improvements obtained in the computation of the 4-profile
of a cocyclic Hadamard matrix are indicated.Ministerio de Ciencia e Innovación MTM2008-06578Junta de Andalucía FQM–296Junta de Andalucía P07-FQM-0298
