Fzero Issues with complex equation with complex roots

Question

Jeffrey Denomme 2014-2-16

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https://ww2.mathworks.cn/matlabcentral/answers/116379-fzero-issues-with-complex-equation-with-complex-roots

回答： Paul 2014-2-16

I have the following code:

Zo = 50;
Zl = 10;
Bl = (0:0.01:(4*pi));
x = @(Bl)Zo*((Zl+j*Zo*tan(Bl))./(Zo+j*Zl*tan(Bl)));
[Blx,Zin] = fzero(x,[2,4]);
fprintf('\n\nValue of x is %2.3f.',Blx)
fprintf('\n\nFunction value is %2.3f.',Zin)

I get the standard error: Function values at interval endpoints must be finite and real.

I would like to identify the root located at Pi with no imaginary component. Using abs() results in NaN.

Assistance required.

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Answer 1

Paul 2014-2-16

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https://ww2.mathworks.cn/matlabcentral/answers/116379-fzero-issues-with-complex-equation-with-complex-roots#answer_124597

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The value of the function at pi is 10, not 0. Do you mean you want the value where the imaginary part of the function is 0? Then you can change the function to this:

x=@(Bl)imag(Zo*((Zl+j*Zo*tan(Bl))./(Zo+j*Zl*tan(Bl))));