Why my stable point is not in [0,0]?
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Frantisek Stloukal
le 29 Avr 2021
Commenté : Frantisek Stloukal
le 2 Mai 2021
Hi, I am trying to plot this phase-time portrait by code I have found here. I don't know why my stable point is not in [0,0] but is shifted to aproximately [11,11]. Any ideas how to repair this problem ? Thanks a lot.
the code:
figure()
%phase-time
[X1,X2] = meshgrid(-5:0.5:5);
xs = arrayfun(@(x,y) {odeFun([],[x,y])}, X1, X2);
x1s = cellfun(@(x) x(1), xs);
x2s = cellfun(@(x) x(2), xs);
quiver(x1s, x2s)
xlabel('x_1')
ylabel('x_2')
axis tight
function dxdt = odeFun(t,x)
global A %pre-difined matrix of autonomous system of ODE's
dxdt(1) = A(1,1)*x(1)+A(1,2)*x(2);
dxdt(2) = A(2,1)*x(1)+A(2,2)*x(2);
end
2 commentaires
jessupj
le 29 Avr 2021
Modifié(e) : jessupj
le 29 Avr 2021
my guess is that (0,0) corresponds to [X1(11,11),X2(11,11)]. that is, the plot is plotting arrows at locations based on the index of the vectors since you are not telling it what the coordinates are.
try reading the documetnation of quiver to add the location arguments, probably something like
quiver( x1s,x2s, X1, X2)
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Jan
le 30 Avr 2021
Your command for creating the diagram does not get any information about the X and Y coordiantes:
quiver(x1s, x2s)
Then it assume, that the coordinates are going from 1 to the number of elements in each direction.
Provide the X and Y coordinates, if you want so see them:
quiver(X1, X2, x1s, x2s)
Trying to run your code produces an errort message, e.g. due to the missing variable A. So please test this by your own.
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