Iteration in Matlab

Question

Thomas Humphrey 2011-11-21

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/21816-iteration-in-matlab

Hi, I'm trying to iterate an equation in matlab, but just can't seem to get the answer out no matter what I do and was wondering if anyone could help

the equation that Ive got is

M_f*C_pf*(T_f-T_cw) = M_d*C_pd*(T_d-T_o) + M_b*C_pb*(T_b-T_o)

I am trying to find T_f and T_o, all the other variables I know apart from C_pf which depends on T_f to be calculated.

I currently have this code to be able to calculate the answers for me but every time it just runs to it's maximum limit. I was wondering if anyone could help.

C_pd = Specific_Heat(T_d,X_d);
C_pb = Specific_Heat(T_b,X_b);
for T_f = 50:80
    C_pf = Specific_Heat(T_f,X_f); 
    a = M_f*C_pf*(T_f-T_cw);
    for T_o = 25:0.1:60
        b = M_d*C_pd*T_d + M_b*C_pb*T_b - T_o*(M_d*C_pd + M_b*C_pb);
        if a==b
            break
        else
            continue
        end
    end
end

Would be very much appreciated. Thank you

Tom

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Answer 1

Sven 2011-11-21

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Your "break" command only breaks out of one loop.

Instead try:

exitLoop = false;
C_pd = Specific_Heat(T_d,X_d);
C_pb = Specific_Heat(T_b,X_b);
for T_f = 50:80
    if exitLoop, break; end
    C_pf = Specific_Heat(T_f,X_f); 
    a = M_f*C_pf*(T_f-T_cw);
    for T_o = 25:0.1:60
        b = M_d*C_pd*T_d + M_b*C_pb*T_b - T_o*(M_d*C_pd + M_b*C_pb);
        if a==b
            exitLoop = true;
            break;
        end
    end
end

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Thomas Humphrey 2011-11-21

got it to work by adding an error function instead of a==b.

Thanks a lot for the help

Sven 2011-11-21

No problem. Keep in mind that if all of your variables (C_pd, a, etc) are scalars, then I think there might be a simpler way to solve your problem that may not involve loops so much. At least you could consider replacing the inner loop entirely with:

b = M_d*C_pd*T_d + M_b*C_pb*T_b - (25:0.1:60).*(M_d*C_pd + M_b*C_pb);

[minVal, idx] = min(abs(b))

if minVal<yourError, break; end

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