1. A method for a batch manufacturing process for optimizing a production plan of at least one material m and the target stock of the at least one material m to satisfy the forecast of customer demands, the production plan being divided into a plurality of contiguous time intervals t, the manufacturing process including a plurality of process activities, each process activity producing a quantity q m,T of material m in a predetermined time interval T, the method comprising: defining for each at least one material m a set of N linear constraints LC n,m , wherein 1<=n<=N; defining for each at least one material m a set of linear equations, each linear equation representing a cost value C z,m , wherein 1<=z<=Z, each cost value indicative of a cost element of the batch manufacturing process, each linear equation being defined as a function of variable q m,T ; assigning to each cost value C z,m a weight w z ; and determining the value of q m,T for each time interval t so that the weighted sum of cost values C z,m is minimized while the linear constraints LC n,m are respected.