How to get the equation inside that of root(function,z) equation ,i.e the function only

Question

Apurva Suman 2021-12-2

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1601375-how-to-get-the-equation-inside-that-of-root-function-z-equation-i-e-the-function-only

评论： Jon 2021-12-2

root(z^4 - (190266216202962831605969987684001433013625*z^3)/142934430860719287430314339936263093557948 + (1101852793399817336417575000084289382730783*z^2)/2286950893771508598885029438980209496927168 - (23080530109547214937644974638002755076096*z)/893340192879495546439464624601644334737175 + 8413353246836900979045156398614448177152/22333504821987388660986615615041108368429375, z)

I'm getting this as a solution , how can i get that equation alone ,i want to extract that equation and use fzero to solve for the root in the interval i want?

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Answer 1

Star Strider 2021-12-2

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https://ww2.mathworks.cn/matlabcentral/answers/1601375-how-to-get-the-equation-inside-that-of-root-function-z-equation-i-e-the-function-only#answer_845905

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The vpa funciton usually works —

syms z

Zfcn = root(z^4 - (190266216202962831605969987684001433013625*z^3)/142934430860719287430314339936263093557948 + (1101852793399817336417575000084289382730783*z^2)/2286950893771508598885029438980209496927168 - (23080530109547214937644974638002755076096*z)/893340192879495546439464624601644334737175 + 8413353246836900979045156398614448177152/22333504821987388660986615615041108368429375, z)

Zfcn =

Zvpa = vpa(Zfcn)

Zvpa =

.

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Answer 2

Jon 2021-12-2

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https://ww2.mathworks.cn/matlabcentral/answers/1601375-how-to-get-the-equation-inside-that-of-root-function-z-equation-i-e-the-function-only#answer_845910

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This is a polynomial, you should be able to obtain all of the roots (real and complex) using:

r = roots([1.0 ... 
    -(190266216202962831605969987684001433013625)/142934430860719287430314339936263093557948 ...
    (1101852793399817336417575000084289382730783)/2286950893771508598885029438980209496927168 ... 
    -(23080530109547214937644974638002755076096)/893340192879495546439464624601644334737175 ... 
    8413353246836900979045156398614448177152/22333504821987388660986615615041108368429375])

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Jon 2021-12-2

在 MATLAB Online 中打开

In this case this gives

Be careful on the line extension "..." you must leave a space after the number otherwise it will think the first dot is a decimal point and get confused

Jon 2021-12-2

I see another answer was already posted by the time I answered. Note I don't have the symbolic toolbox shown in @Star Strider's, answer. I'm not sure if you do. In anycase you can do it this way with the core MATLAB functionality

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