function d=dxdt1(t,x)
c=-1.0;% c=0.25 stabil nod ,2 sadel, 0 deg stab nod, -1.0 stabil spiral (c<0), 0 stabil deg nod t=1000, stabil nod 0<c<1, sadel c>1
d=[ -x(1)+x(2); c*x(1)-x(2) ];