How to add direction line into the phase plane plot?

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Alex 2014-3-11

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https://ww2.mathworks.cn/matlabcentral/answers/121081-how-to-add-direction-line-into-the-phase-plane-plot

评论： Alex 2014-3-12

Yes, how to add direction line into the phase plane plot? I have the codes below which it work successful but I want to add some direction arrow into my phase plane.

function phase()
IC = [1 1;1 2;1 3;1 4;1 5];
hold on
for ii = 1:length(IC(:,1))
    [~,X] = ode45(@EOM,[-5 5],IC(ii,:));
    u = X(:,1);
    w = X(:,2);
    plot(u,w,'r')
end
xlabel('u')
ylabel('w')
grid
end
function dX = EOM(t, y)
dX = zeros(2,1);
u  = y(1);
w  = y(2);
A  = 1;
B  = 1;
dX = [(w*u^2 - B*u);...
      (A - w - w*u^2)];
end

And the plot below is from the codes above:

And I want to add the direction line, which something like this:

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采纳的回答

Mischa Kim 2014-3-11

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编辑：Mischa Kim 2014-3-11

在 MATLAB Online 中打开

Alex, use quiver. In

quiver(x,y,u,v)

the x, y are the grid points, u and v you get from the dX vector from the differential equations function.

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Mischa Kim 2014-3-12

在 MATLAB Online 中打开

Using the same EOM function I'd do something like

 function phase()
 IC = 5*(rand(50,2)-0.5);
 hold on
 for ii = 1:length(IC(:,1))
    [~,X] = ode45(@EOM,[-5 5],IC(ii,:));
    u = X(:,1);
    w = X(:,2);
    plot(u,w,'r')
 end
 xlabel('u')
 ylabel('w')
 grid
 x       = -4:0.5:4;
 y       = -4:0.5:4;
 [xg,yg] = meshgrid(x,y);
 dxg     = yg.*xg.^2 - xg;
 dyg     = ones(length(x)) - yg - yg.*xg.^2;
 scale   = 5;
 quiver(xg,yg,dxg,dyg,scale)
 end