1. A computer-implemented method of design of a surface defined by guiding curves P(u) and Q(v) and a coupling curve s (t(s), w(s)), for improving the manufacture of products modeled by such a surface, the method comprising: accessing data defining guiding curves P(u) and Q(v) and a cost function f(t, w); defining an objective function of the type J=J(f, t, w), involving both the cost function f(t, w) and coordinates t, w of the coupling curve s (t(s), w(s)); optimizing said objective function J to obtain a coupling curve s (t(s), w(s)) of parameter s; and providing a surface according to the guiding curves P(t(s)) and Q(w(s)), respectively composed with the coordinates t, w of the coupling curve obtained, wherein: at the steps of defining and optimizing the objective function, the objective function J=J(f, t, w) is constrained such that arguments t, w of the cost function f(t, w) are regulated by a regulation function μ.