my program is not working properly

Question

shiv gaur 2022-3-11

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评论： Jan 2022-3-12

function kk2

close all; clear all;

% accuracy

%options = odeset('RelTol',1e-9,'AbsTol', 1e-16);

[t,y]=ode45(@f,[0 100],[0.1;0.1;0.1+1;0.1;0.1;0.1] );

plot(t,y(:,2),t,y(:,4),t,y(:,6))

function dy=f(t,y)

%x=y(1);y=y(3);z=y(5)

r=28;

b=8/3;

k=10;

dy=zeros(6,1)

dy= [y(2);k^2*y(1)-k^2*y(3)-k*y(1)*y(5)+k*r*y(5)-k*y(3);y(4);b*y(1)*y(5)-y(1)^2*y(3)-k*y(1)*y(3)+k*y(3)*y(5)-r*k*y(1)+k*r*y(3)+y(1)*y(5)-r*y(1)+y(3);y(6);-y(1)^2*y(5)+r*y(1)^2-y(1)*y(3)-k*y(1)*y(3)+k*y(3)^2-b*y(1)*y(3)+b^2*y(5)]

end

so sir we want to plot between t,x,t,y

and we want to plot t vs second element of dy t,fourth element t,vs sixth element

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Jan 2022-3-12

编辑：Jan 2022-3-12

@shiv gaur: You have been asked repeatedly to use a proper code formatting. Please read and consider this: https://www.mathworks.com/matlabcentral/answers/help/rtc#rtc_summary . Thanks.

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Answer 1

Sam Chak 2022-3-11

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1669049-my-program-is-not-working-properly#answer_915039

编辑：Sam Chak 2022-3-11

在 MATLAB Online 中打开

Hi @shiv gaur

It appears that the system is highly unstable and all states blow up at around 0.35 sec except for

. Please check the state equations again. Sometimes, the plus/minus signs can make a huge difference.

Edit: It has some similarities like the Lorenz system, because I recognized the magic values: 10, 8/3, 28.

clear all; clc
r = 28;
b = 8/3;
k = 10;
tspan = linspace(0, 0.3, 10001)';
fun = @(t, y) [y(2); ...
             k^2*y(1) - k^2*y(3) - k*y(1)*y(5) + k*r*y(5) - k*y(3); ...
             y(4); ...
             b*y(1)*y(5) - y(1)^2*y(3) - k*y(1)*y(3) + k*y(3)*y(5) - r*k*y(1) + k*r*y(3) + y(1)*y(5) - r*y(1) + y(3); ...
             y(6); ...
             - y(1)^2*y(5) + r*y(1)^2 - y(1)*y(3) - k*y(1)*y(3) + k*y(3)^2 - b*y(1)*y(3) + b^2*y(5)];
[t, y] = ode45(fun, tspan, [0.1, 0.1, 1.1, 0.1, 0.1, 0.1]);
plot(t, y)

Once you have fixed the model, please ensure that all states can propagate at least until your desired final time,

sec, and then you can choose what you want to plot.

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Sam Chak 2022-3-12

Hi @shiv gaur

Have you double checked the mathematical equations of your system? Since you didn't tell us what kind of system it is, and your supplied ODEs have been verified by the ode45 solver, there seems nothing wrong with the program itself. If you are very sure that the system is stable, then my guess is that one or more of the terms in the state equations must be the root cause of the instability.