MuPad and Symbolic Toolbox Error

Question

Taniadi 2012-5-20

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/38890-mupad-and-symbolic-toolbox-error

Hi, i want to ask a question about MuPad. I am beginner using MuPad,

I am trying to solve a coupled of ODE as follow using MuPad syntax:

eq := ode::solve({CA'(t)=-k1*CA(t)+k2*CB(t),CB'(t)=k1*CA(t)-k2*CB(t),CA(0)=3,CB(0)=0},{CA(t),CB(t)}) 
num := subs(eq,k1=0.5,k2=0.3)

So i get the answer as CA and CB.

But I am actually want to plot CA and CB as function of time. I am using plot command:

plot(num[1],t=0..10)
Error: unbound identifier(s) 'CB, CA' found [plot::Inequality::new]

and plotfunc2d function like this:

plotfunc2d(num[1],t=0..10)
Error: expecting an arithmetical expression or a function, got a 'DOM_LIST' for attribute 'Function' in Function2d object [plot]

I can't get the plot I want, and how can I get this? Do I have to type the solution obtained by solve command manually and use plotfunction2d or plot command?

And finally, I want to export these solution into MATLAB by using mupad command , getVar command, and matlabFunction command, but it yields errors. How can I do this?

Thank you very much

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Answer 1

Walter Roberson 2012-5-20

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https://ww2.mathworks.cn/matlabcentral/answers/38890-mupad-and-symbolic-toolbox-error#answer_48416

在 MATLAB Online 中打开

I think it might be,

ca := subs(CA, num[1]);
cb := subs(CB, num[1]);
plot([ca, cb], t=0..10);

However, this will depend on whether "num" is a single list or is a list of lists. The error message you get for plotfunc2d() would be consistent with "num" being a list of lists, which is what I coded for above.