==Ruth-Hurwitz== 
 Hi, 

 sorry but I was out of time and I could not really explain the Routh-Hurwitz theorem (a simple one, but the notations are really heavy...).  Actually, it is useful to test the (Hurwitz) stability of a polynomial.  If p-q=n where n is the degree, then the polynomial is stable.  It has some other applications I will add later in the article. 
 But to me, the Routh-Hurwitz stability criterion is just a consequence of R-H theorem.  So we can either keep RHsc and explain it better or add the part to the main RHth part.. (consult e.g.  to have an idea of what is the criterion). 

 Finally, I feel there's some misconceptions about Hurwitz polynomials.  Some people write that for a polynomial to be Hurwitz stable, all its coefficient must be positive.  But if you multiply a polynomial by (-1), it will have the same roots so it will stay stable and have all negative coefficient... 

 Anyway I'll enhance the RHtheorem in  a few days, cheers and thanks for your help