generated "unvaforable zero" value from multiplying two matrices, how to solve/correct it?

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M Adli Hawariyan
M Adli Hawariyan 2022-7-21
编辑： Abhiram 2025-1-23
Ran in:
for simplicity, i have a two matrices A and B generated by matlab like below. when i calculated manually by excel with the function mmult(A;B) the value of C is vaforable like this. even when i increasing the decimal. especially the value of cell matrix C at 3,1 it was definetly zero
but when i multiply them in matlab i got value of C like this
how to deal with this type of problem? any guidance will help me alot, because i got bunch of wild value zero like this :( thanks a lott.
the following attachments is my full code, matrix A is k_sup and matrix B is uaa, and matrix C is Fsupt in my line code. input3Dxlsx is my input.
P.S
i tried calculate separately with new script (like the following A*B bottom), copy those matrices from generated excel (so the value is accurate), and the generated value of matrix C is entirely different, like this:
here is the following matrix A and B i copy from generated excel
A = [-3710000000 0 0 0 0 0;
0 -12624305.56 0 0 0 75745833.33;
0 0 -2318750 0 -13912500 0;
0 0 0 -69358333.33 0 0;
0 0 13912500 0 55650000 0;
0 -75745833.33 0 0 0 302983333.3]
A = 6×6
1.0e+09 * -3.7100 0 0 0 0 0 0 -0.0126 0 0 0 0.0757 0 0 -0.0023 0 -0.0139 0 0 0 0 -0.0694 0 0 0 0 0.0139 0 0.0556 0 0 -0.0757 0 0 0 0.3030
B = [0
0
-0.025876011
0
0.004312668
0]
B = 6×1
0 0 -0.0259 0 0.0043 0
C = A*B
C = 6×1
1.0e+05 * 0 0 0.0000 0 -1.2000 0
  1 个评论
Stephen23
Stephen23 2025-1-23
编辑：Stephen23 2025-1-23
Ran in:
"P.S i tried calculate separately with new script (like the following A*B bottom), copy those matrices from generated excel (so the value is accurate), and the generated value of matrix C is entirely different"
MATLAB returns the same result (although perhaps displayed to a different precision):
A = [-3710000000,0,0,0,0,0;; 0,-12624305.56,0,0,0,75745833.33;; 0,0,-2318750,0,-13912500,0;; 0,0,0,-69358333.33,0,0;; 0,0,13912500,0,55650000,0;; 0,-75745833.33,0,0,0,302983333.3]
A = 6×6
1.0e+09 * -3.7100 0 0 0 0 0 0 -0.0126 0 0 0 0.0757 0 0 -0.0023 0 -0.0139 0 0 0 0 -0.0694 0 0 0 0 0.0139 0 0.0556 0 0 -0.0757 0 0 0 0.3030
<mw-icon class=""></mw-icon>
<mw-icon class=""></mw-icon>
B = [0; 0; -0.025876011; 0; 0.004312668; 0]
B = 6×1
0 0 -0.0259 0 0.0043 0
<mw-icon class=""></mw-icon>
<mw-icon class=""></mw-icon>
format long G
C = A*B
C = 6×1
1.0e+00 * 0 0 0.00695624999207212 0 -120000.0288375 0
<mw-icon class=""></mw-icon>
<mw-icon class=""></mw-icon>

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回答（1 个）

Abhiram
Abhiram 2025-1-23
编辑：Abhiram 2025-1-23
Hello Adli,
I understand you are trying to multiply two matrices and in places of zero you are getting some nominal values.
To resolve the issue, we can set the values less than a chosen tolerance to zero explicitly by defining a “tolerance ” variable to an appropriate value. For the given sample matrix “C”, the desired result can be achieved with the code given below:
% Define the tolerance
tolerance = 1e-2;
% Round small values in C to zero
C(abs(C) < tolerance) = 0;
% Display the result with long format
format long
disp(C);
In addition, the “format” functionality in MATLAB can be used to change the output display format to display the required number of decimal values for a numeric value. An example usage of the MATLAB “format” function is given in the code below:
A = 0.100000043434;
format short
disp(A);
format long
disp(A);
Refer to the documentation for the MATLAB “format” function for more details:
https://www.mathworks.com/help/releases/R2022a/matlab/ref/format.html

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