function [DIS, r1, r2]= root(a,b,c)
% function [DIS, r1, r2]= root(a,b,c)
% purpose: finds the roots of a quadratic polynomial.
%Inputs: 3 variables a,b,c 
%Output: Discrimant, two roots.
% E.g: a=1;b=2;c=1;
DIS=sqrt(b^2 -4*a*c);
r1= (-b + DIS)/(2*a) ;
r2= (-b - DIS)/(2*a) ;