how drop near zero imaginary terms from symbolic result?

Question

Russell 2022-8-30

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1790480-how-drop-near-zero-imaginary-terms-from-symbolic-result

评论： Dyuman Joshi 2023-9-21

I'm doing some symbolic matrix manipulations with complex valued matrices. Some of my results are as below.

Zaa*(1 + 3i/36028797018963968) + Zab*(1 + 3i/36028797018963968)

Is there a way to tell Matlab to ignore those near zero imaginary results so the answer will be reported simply as,

Zaa + Zab

4 个评论
显示 2更早的评论隐藏 2更早的评论

Jamie Steel 2022-8-30

编辑：Jamie Steel 2022-8-30

@John D'Errico Ah I see, perhaps I misinterpreted the expression - I assumed the symbols were only Zaa and Zab, and that the following complex number z was some numerical result multiplying them. That is horribly messy though! My experience with symbolic manipulation is certainly limited enough such that I've never run into trouble like that thankfully

Russell 2022-8-30

Thank you. That is better than nothing, but is ugly.

I tried the following and it sorta works too. Wish better way to do it directly.

vpa(term,2)

ans =

Zaa*(1.0 + 8.3e-17i) + Zab*(1.0 + 8.3e-17i)

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Moksh 2023-9-21

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1790480-how-drop-near-zero-imaginary-terms-from-symbolic-result#answer_1315152

在 MATLAB Online 中打开

Hi Russell,

I understand that you are attempting to eliminate the imaginary part in the intermediate term if it is close to zero, as shown in the example provided.

You can utilize the "abs" and "imag" functions in MATLAB to obtain the magnitude of the imaginary part. By comparing this magnitude with a threshold value, which can be adjusted as needed, you can determine if the imaginary part is sufficiently close to zero.

Here is an example code:

syms Zaa Zab

% Get the imaginary part in z

z = 1 + 3i/36028797018963968;

imag_z = imag(z);

tol = 1e-5;

% Ignore the imaginary part in z if it is near zero

if abs(imag_z) < tol

z = real(z);

end

% Define the main result

Z = Zaa * z + Zab * z;