ODE: How can I trace changing of all parts of equation during solving

Question

Uladzislau 2020-1-22

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/501388-ode-how-can-i-trace-changing-of-all-parts-of-equation-during-solving

评论： Uladzislau 2020-1-22

采纳的回答： darova

在 MATLAB Online 中打开

Hello! I'll be grateful if someone could help me. So the question is:

I have an ODE that is been solved correctly.

function [out] = chua(t,in,alpha, beta, A, C, u1st)
x = in(1);
y = in(2);
z = in(3);
xdot  = -alpha*((3*A*u1st^2+C+1)*x-y) ...
      -3*A*alpha*u1st*x^2...
      -A*alpha*x^3;
ydot  = x - y + z;
zdot  = -beta*y;
out = [xdot ydot zdot]';

The call is:

t = [0 2400];
y = [0.004 0 0];
alpha  = 15.6;
beta   = 28; 
A      = 0.002;
C      = -1.3;
u1st = 0.5;
    [t,y] = ode45(@(t, y) chuaModIris(t, y, alpha, beta, A, C, u1st), t, y );
    plot3(y(:,1),y(:,2),y(:,3))     

But on each step of integration I need to get extra data - parts of the first equation:

SquarePart = -3*A*alpha*u1st*x^2;

and

CubicPart = -A*alpha*x^3;

Actually, I've already done it in Simulink, but I haven't any idea how to implement it in m-file.

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Answer 1

darova 2020-1-22

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/501388-ode-how-can-i-trace-changing-of-all-parts-of-equation-during-solving#answer_411422

在 MATLAB Online 中打开

What about this?

[t,y] = ode45(@(t, y) chuaModIris(t, y, alpha, beta, A, C, u1st), t, y );
plot3(y(:,1),y(:,2),y(:,3))     
SquarePart = -3*A*alpha*u1st*y(:,1).^2;
CubicPart = -A*alpha*y(:,1).^3;