Solving Equation fails - MATLAB

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omer 2012-11-1

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https://ww2.mathworks.cn/matlabcentral/answers/52487-solving-equation-fails-matlab

syms IDQ VGS R1 R2 RS Gm

    eq1 = ' IDQ = 0.015 * ( VGS / (-5) - 1) ^ 2 ';
    eq2 = ' VGS = 15 * R2 / (R1+R2) - IDQ * RS ';
    eq3 = ' 200e+3 = R1 * R2 / (R1+R2)';
    eq4 = ' Gm = 2 * 0.015 * ( VGS / (-5) - 1) * ( 1 / (-5) )';
    eq5 = ' 200 = RS / ( 1 + Gm*RS )';
    eq6 = ' 0.4 = Gm* (RS*330/(RS+330)) / (Gm*(RS*330/(RS+330)) - 1)';
    [IDQ VGS R1 R2 RS Gm] = solve(eq1,eq2,eq3,eq4,eq5,eq6,IDQ,VGS,R1,R2,RS,Gm)

I used this code to solve 6 equations with 6 variables, however, as I got the answer then, I checked them, but it is not satisfied. such as

VGS and Gm are 0.10747627793082338536883991429446 and -18.383838383838383838383838383838. However, when I put VGS values into equation 4, Gm has different value.

Do you have any idea and can you help me please??

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Walter Roberson 2012-11-1

在 MATLAB Online 中打开

After converting to rational and solving, Maple says

Gm = -53/3300, IDQ = 2809/26136, R1 = -8256600000/36551, R2 = 4128300000/38917, RS = 6600/139, VGS = -1820/99

That VGS value corresponds to what you said for Gm, and the Gm value is not even the same sign as what you show for VGS.

Try using a single output, as that will give you a structure as the result, which would eliminate any possibility that the order being returned is not the same as the order you are expecting.

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