Creating phase portraits using quiver

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Ethan Boyce 2020-10-9

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/608846-creating-phase-portraits-using-quiver

I am trying to use quiver() to build a phase portrait of a funtion and I am having trouble. I know our points of equilibrium and I simply want to illistrate it with the phase portrait to demonstrate stability. Luckily this is a very classic ode model so it shouldnt be difficult I have just never dealt with creating a phase portrait in matlab before. Any help is very appreciated.

global  a b r K;
a = 2;
b = 2;
r= 0.48;
K = 17;
syms    P;
steady_states = vpa(solve( r*(1-P/K)-a*P/(b^2+P^2), P))
% Pv = -1:0.1:12;
% y =  r*Pv.*(1-Pv/K)-a*Pv.^2./(b^2+Pv.^2);
P = 0:0.1:20;
y1 = r.*(1-P/K);
ya = a*P./(b^2+P.^2);
plot(P,y1,'k -',P,ya,'b--','linewidth',3);
quiver(y1,ya) %failed
[x y]=meshgrid(...)
   quiver(x,y,y1,ya)%failed 