Phase Portrait with Solution Curves

So i was trying to solve the following system of differential equation and its phase portrait. x'=x y'=-y According to this page http://matlab.cheme.cmu.edu/2011/08/09/phase-portraits-of-a-system-of-odes/ I wrote the following

f=@(t,X)[X(1); -X(2)];

x1=linspace(-5,5,20);
x2=linspace(-5,5,20);

[x y]=meshgrid(x1,x2);
size(x)
size(y)

u=zeros(size(x));
v=zeros(size(x));

t=0;
for i=1:numel(x)
    Xprime=f(t,[x(i); y(i)]);
    u(i)=Xprime(1);
    v(i)=Xprime(2);
end

quiver(x,y,u,v,'k');figure(gcf)
xlabel('x_1')
ylabel('x_2')
axis tight equal;

hold on
for i=-5:1:5
for x20=[-5 5]
    if (-5<i & i<5 & -5<x20 & x20<5)
        continue
    end
    [ts xs]=ode45(f,[0 50],[0;x20]);
    plot(xs(:,1),xs(:,2))
    %plot(xs(1,1),xs(1,2),'ko')
    %plot(xs(end,1),xs(end,2),'ks')
end
end
hold off

This gives me its phase portrait ONLY. As sson as I replace "0" in the solution vector input in [ts xs]=ode45(f,[0 50],[0;x20]) with "i" to get multiple solution curves, it does not give me proper answer. What am I doing wrong here? p.s.: The equilibrium/critical point here is a saddle point.