[X Y] = meshgrid(-7.5:7.5,-7.5:7.5);
U = -1*X.^3+2*X.^2;%-36.*X;%-23.0/25.0*X.^3+8.0/5.0.*X.^2;%-X+y0/x0*X;
dx = -2.*X+Y;
dy = X.*(X.^2-2.*X+1)-Y+U;
du = dx./sqrt(dx.^2+dy.^2);
dv = dy./sqrt(dx.^2+dy.^2);
quiver(X,Y,du,dv);
axis tight
grid on
hold on
h1 = plot(x.data,y.data);
h2 = plot([0],[0],'x');
h3 = plot([x0],[y0],'x');
set([h1,h2,h3],'LineWidth',4);