H. Ammar et Y. Cherruault, APPROXIMATION OF A SEVERAL VARIABLES FUNCTION BY A ONE VARIABLE FUNCTION AND APPLICATION TO GLOBAL OPTIMIZATION, Mathematical and computer modelling, 18(2), 1993, pp. 17-21
By means of a transformation called SIGMA we approximate an n variable
s function f by a function f of a single variable called theta. Then,
we approach the global minimum of f by the one of f.