Evaluates discriminant of the cubic equation
mydisc(parameters, mydelta, Rmax)
A vector of parameters (real numbers) that is generated by estimating the short, intermediate and auxiliary regressions.
The value of delta (real number).
The value of Rmax (real number)
Returns a value of 0 or 1; 0 (if discriminant is positive) and 1 (if discriminant is nonpositive)