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)