In recent years increasing use has been made of systems of social accounts, and a variety of new types and new forms of presentation have been suggested. The general features of such systems are: (a) the division of an economy into a number of groups or economic entities, mostly themselves a complex of elementary units, and (b) a summing up in the form of accounts of the transactions of various kinds between these economic entities. As a rule, the economy of one country is investigated, implying that all other countries are regarded as one single group. The economy considered may be split up into a number of separate groups. It is customary to distinguish between consumers' households, business enterprises, and the government sector. If special attention is to be given to banking problems for example, banks will constitute a separate group.

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DANS CE MODELE, on considere un agent economique seulement. Celui-ci dispose d'un actif de montant c0 et cherche 'a I'affecter au mieux, mettons en totalite sur k placements pendant une periode definie assez courte. Les taux d'interet qui correspondent 'a chaque sorte de placement sont, pour la periode 'a venir en question, aleatoires-objectifs soit (X1, . . ,Xk).1 Designons par (b1,.. ., bk) ou Yk bi = 1 et bi >0 une affectation de co envisagee par cet agent. Le montant d'actif en fin de periode est actuellement aleatoire et donne par l'equation