newton1(a, b, c, d)

              function x1  = newton1(a, b, c, d)
              % cherche une racine en partant du point 0,  la prcision epsi
              epsi = 1.0E-5;
              x1 = 0;
              while 1
                fprim = (3*a*x1+2*b)*x1+c;
                if fprim == 0
                  x1 = -b/a;
                else
                  dx = -(((a*x1+b)*x1+c)*x1+d)/fprim;
                  x1 = x1 + dx;
                  if abs(dx) < epsi
                    break;
                  end; 
                end;
              end;