Solving two equations with ODE45

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Sergio Manzetti 2018-4-4

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https://ww2.mathworks.cn/matlabcentral/answers/392555-solving-two-equations-with-ode45

编辑： Sergio Manzetti 2018-4-4

采纳的回答： Torsten

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Hi, I used the following command to solve one ODE

fun = @(x,y)[y(2);y(3);(y(1)*(1-x^2))];
y0 = [1 0 8]; %y, y', y''
xspan = [-3 3];
[X,Y] = ode45(fun,xspan,y0);
plot(X,Y(:,1)),,% X,Y(:,2),X,Y(:,3),X,Y(:,1).* (2 + X .^ 2));

However, I would like to solve this pair of equations instead of the given "fun":

How do I add two equations in the fun line?

Thanks!

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采纳的回答

Torsten 2018-4-4

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/392555-solving-two-equations-with-ode45#answer_313447

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fun=@(x,y)[y(2);y(3);-(1+x^2)*y(4);y(5);y(6);(1+x^2)*y(1)]; %psi2,psi2',psi2'',psi1,psi1',psi1''

Best wishes

Torsten.

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Sergio Manzetti 2018-4-4

编辑：Sergio Manzetti 2018-4-4

在 MATLAB Online 中打开

Thanks, following your link I used a new y0 and got a result, but plot only plots one form.

fun=@(x,y)[y(2);y(3);-(1+x^2)*y(4);y(5);y(6);(1+x^2)*y(1)]; %psi2,psi2',psi2'',psi1,psi1',psi1''
y0 = [1 0 8 1 0 8]; %y, y', y''
xspan = [-3 3];
[X,Y] = ode45(fun,xspan,y0);
 plot(X,Y(:,1)), X,Y(:,2),X,Y(:,3),X,Y(:,1), '-o',X,Y(:,2), X,Y(:,2),X,Y(:,3),X,Y(:,1);

What is wrong in the plot section really?

Sergio Manzetti 2018-4-4

编辑：Sergio Manzetti 2018-4-4

在 MATLAB Online 中打开

Hi Torsten, I edited this finally:

    fun=@(x,y)[y(2);y(3);-(1+x^2)*y(4);y(5);y(6);(1+x^2)*y(1)]; %psi2,psi2',psi2'',psi1,psi1',psi1''
    y0 = [1 0 8 1 0 8]; %y, y', y''
    xspan = [-3 3];
    [X,Y] = ode45(fun,xspan,y0);
  plot(X,Y(:,1)), X,Y(:,2),X,Y(:,3),X,Y(:,1);

So it shows a plot. But this plot is identical to the plot of only one function present in the command (remove the second function and decrease to three dimensions, and it is the same plot).

Is that correct? I would have expected a different solution.

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