ode45 is returning the incorrect solution

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Koren Murphy 2020-3-17

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评论： Ameer Hamza 2020-3-17

I am running an ode45 to solve a simple intergration. The intergration is so simple I can perform it by hand - hence knowing the solution returned is excessively large.

function [Output] = ContinuousFeed(t,u)

uA = u(1);

uB = u(2);

uE = u(3);

uF = u(4);

u = [uA; uB; uE; uF];

Output = u;

end

t=[0 10];

u0 = [1; 0.0002; 0; 0];

[t, u] = ode45 (@ContinuousFeed, t ,u0);

Why is it returning a final value of 22030.53 for the first column? All other columns are displaying inaccurate answers also.

Thank you!

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采纳的回答

Ameer Hamza 2020-3-17

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https://ww2.mathworks.cn/matlabcentral/answers/511303-ode45-is-returning-the-incorrect-solution#answer_420530

编辑：Ameer Hamza 2020-3-17

The MATLAB is giving the correct solution. You are solving four independent ODEs of the form

which have an anatylical solution

The solution of ode45 matches this analytical solution.

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Koren Murphy 2020-3-17

在 MATLAB Online 中打开

I have applied this Steven and it has stopped the exponential. However, it appears to be adding the original feed to the solutions as it goes

function dudt = ContinuousFeed(~, ~);
ConstantVector = [1; 0.0002; 0; 0]; % initial conditions
dudt = ConstantVector;
end
r = 1e-6;
t = [0 10 10+r 20 20+r 30 30+r 40 40+r 50]; % this is assuming a sample taken every 10 units of time.
%                                                 tspan must constantly
%                                                 increase or decreases to
%                                                 work hence the addition of 1e-6
u0 = [1; 0.0002; 0; 0];

Therefore it is returning the solutions;

11.000001

21.000001

31.000001

41.

41.000001

51.

Ameer Hamza 2020-3-17

If my initial feed you meant initial conditions, then this is the expected behavior. Vector u0 tells the ode45 where to start the solution of each variable.

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