Expired coding question, don't refer to this

Question

Charlotte LaGasse 2024-3-4

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2090156-expired-coding-question-don-t-refer-to-this

编辑： Charlotte LaGasse 2024-3-7

Hi,

This code is not valid, solution found a different way.

figure(1)
qdot=(-2500:1:250);
Tout=qdot./7.63358+2669.85./7.63358;
plot(qdot,Tout);
title('Tout vs qdot')
xlabel('qdot')
ylabel('Tout')
figure(2)
qout=(-2500:1:250);
Tout1=-((qout.*2.5.*10.^(-4))./(0.558.*0.02)-307.15);
plot(qout,Tout1);
title('Tout vs qout')
xlabel('qout')
ylabel('Tout')
syms qout qdot
eqn = Tout == Tout1;
solve (eqn,qdot,qout)

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Answer 1

Florian Bidaud 2024-3-4

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https://ww2.mathworks.cn/matlabcentral/answers/2090156-expired-coding-question-don-t-refer-to-this#answer_1420786

编辑：Florian Bidaud 2024-3-4

在 MATLAB Online 中打开

You haven't defined Tout and Tout1 as equations but as numerical variables because qout and qdot are int arrays. You should first declare qout and qdot as syms before defining Tout and Tout1

syms qout qdot

Tout=qdot./7.63358+2669.85./7.63358;

Tout1=-((qout.*2.5.*10.^(-4))./(0.558.*0.02)-307.15);

eqn = Tout == Tout1;

s=solve (eqn,qdot,qout);

disp(s)

qdot: -16102921157410571293520415132337/49517601571415210995964968960 qout: 0

figure(1)

qdot=(-2500:1:250);

Tout=qdot./7.63358+2669.85./7.63358;

plot(qdot,Tout);

title('Tout vs qdot')

xlabel('qdot')

ylabel('Tout')

figure(2)

qout=(-2500:1:250);

Tout1=-((qout.*2.5.*10.^(-4))./(0.558.*0.02)-307.15);

plot(qout,Tout1);

title('Tout vs qout')

xlabel('qout')

ylabel('Tout')

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John D'Errico 2024-3-4

编辑：John D'Errico 2024-3-4

在 MATLAB Online 中打开

@Florian Bidaud, @Charlotte LaGasse

This answer is good as a start, but not complete I would suggest. I think it did not go far enough. It is also the case there is no single, unique solution.

syms qout qdot
Tout=qdot./7.63358+2669.85./7.63358;
Tout1=-((qout.*2.5.*10.^(-4))./(0.558.*0.02)-307.15);

I'll show the relation reduced to short digits to make it more readable.

vpa(Tout == Tout1,4)

ans =

As you can see, there is a linear relation between the two unknowns qdot and qout. Choose ANY value for one of them, and the other is given directly by a linear equation, a straight line.

We could even have MATLAB return the functional relationship itself, thus

qdotsol = solve(Tout == Tout1,qdot)

qdotsol =

As a simple functional relationship, we see the dependence between the two.

vpa(qdotsol,4)

ans =

Choose any value for qout, and you can compute qdot directly. And that is what I think the answer from @Florian Bidaud should have pointed out. We can see the relationship in the plot below:

fplot(qdotsol,[-2500,250])

xlabel qout

ylabel qdot

grid on

So ANY point on the straight line plot is a solution that makes the pair of expressions Tout and Tout1 equal.

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