Return code

The procedure will return an integer $k$ that will be identical to the code returned by the procedure
Solve_General_Gradient_Interval except for:

• $k= -4$: one of the equation in the system has not a type 0, -1, -2, 2, 10 or 1 (i.e. it's not an equation or an optimum function, neither inequality $F \le 0$ or an inequality $F \ge 0$)
• $k= -10$: there is no optimum function i.e. no equation has type 2 or -2 or 10
• $k=-20$: there is more than one optimum function i.e. more than one equation has type 2 or -2 or 10
• $k= -30$: the last function is not the one to be minimized or maximized

Note that this implementation is only a special occurrence of the general solving procedure and thus offer the same possibilities to improve the storage management (see section 2.4).