# Solving two equations with ODE45

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Sergio Manzetti 2018-4-4
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!

### 采纳的回答

Torsten 2018-4-4
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.
##### 9 个评论显示 8更早的评论隐藏 8更早的评论
Sergio Manzetti 2018-4-4

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.

### 更多回答（1 个）

KSSV 2018-4-4
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Sergio Manzetti 2018-4-4
That was greek to me. Sorry

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