Unable to compare equality of two matrices

Question

N/A 2021-12-27

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1617880-unable-to-compare-equality-of-two-matrices

回答： Walter Roberson 2021-12-27

I am trying to compare the two 4x4 matrices below and generate a success message, but I see that the code is able to display a success message only for the first element of each row. Can anyone spot where I made the mistake please?

Rotation_matrix = rotm2tform([0.9254 0.0180 0.3785; 0.1632 0.8826 -0.4410; -0.3420 0.4698 0.8138])
res = rpy2tr(30*pi/180,20*pi/180,10*pi/180)
k=0
for i = 1:size(Rotation_matrix)
    for j = 1:size(res)
    
        if isequal(i,j)
            continue
        else
            disp("Fail")
            k=1;
        end
    end
end
if k==0
    disp("Verification success")
end

Thank you

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Answer 1

Walter Roberson 2021-12-27

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1617880-unable-to-compare-equality-of-two-matrices#answer_862410

size() of a variable, when no option is provided in the size() call, always returns a vector, even if the variable is a scalar. When you use 1:size() then you are using 1 colon a vector . MATLAB does define that: it takes the first element of the vector. So 1:size(Rotation_matrix) is going to be the same as 1:size(Rotation_matrix,1) which might not be what you want.

Question: why are you comparing the indices instead of comparing the matrix indexed at the indices?

You should also read http://matlab.wikia.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_.28or_similar.29_not_equal_to_zero.3F