We have been interested in this article on the data stuctures generation as part of the polyedric technique designed in PAF (Paralleliseur Automatique pour Fortran). The removal of dependences which are not data flows in a program is generally realized by a total memory expansion of data structures. We present a new technique which allows to reduce the memory cost by expanding carefully selected parts of code only. It consists in limiting the memory expansion process in accordance with contraints imposed by the schedule determined for the parallel program