Abstract: A method for determining the output physical quantity Y of a system from an input physical quantity X of the system and a non-linear convex physical model of the system associating with an input physical quantity xi an output physical quantity yi, the method including determining, using the non-linear physical model, a plurality of operating points Mi of coordinates (xi, yi) with i ? [1, N]; determining an optimal vector Uopt among a plurality of vectors Uj, the vectors Uj including N coordinates uij ? [0,1], the constraints on the coordinates being: { X = ? i = 1 N ? x _ i × u i j ? i = 1 N ? u i j = 1 , the optimal vector Uopt being associated with the following lowest objective function: M×?i=1Nyi×uij where M is a weighting coefficient strictly greater than zero; and determining the output physical quantity Y given by: Y=?i=1Nyi×uiopt.