1. INRA-INRIA ’MODEMIC’ team; UMR INRA-SupAgro 729 ’MISTEA’ 2 place Viala 34060 Montpellier
2. Université Montpellier 2; Case courrier 051, 34095 Montpellier cedex 5 France
3. INRIA ’BIOCORE’ team, Sophia-Antipolis, 2004; route des Lucioles 06902 Sophia Antipolis Cedex
4. INRIA Saclay and Ecole Polytechnique; Palaiseau France