Matlab value assignment acting weird

Question

prohi 2017-5-6

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/339070-matlab-value-assignment-acting-weird

评论： prohi 2017-5-6

采纳的回答： Walter Roberson

在 MATLAB Online 中打开

Hi!

I have the following code (as a part of a bigger program, mainly for image processing):

P_hatso3_x = P_hatso2_x;
w6 = 1;
disp('axax')
y_alap6 = P_hatso2_y
disp('dasd')
while (w6 == 1)  
    if (pixel_labels(y_alap6,P_hatso3_x) == szegm_lab)
        y_alap6 = y_alap6 - 1;
    else 
        w6=0;
        P_hatso3_y = y_alap6;
    end   
end

Now when I run it, it returns with the following command window:

axax
y_alap6 =
      72
dasd
Subscript indices must either be real positive integers or logicals.
Error in kmeans_proba_advanced (line 293)
    if (pixel_labels(y_alap6,P_hatso3_x) == szegm_lab

so it returns with an error, because the

pixel_labels

binary array can not be indexed with the variable called

y_alap6

because it has a value of 0 . However, as we see on the command window, the value 72 had been assigned to it before (between 'axax' and 'dasd' strings), but it somehow magically disappeared/changed/got unassigned 3 lines later. I am really confused, as this only comes up for some of the pictures I am trying to process with this program, I just can't find out why this could be. Can someone please help me?

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Answer 1

Walter Roberson 2017-5-6

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https://ww2.mathworks.cn/matlabcentral/answers/339070-matlab-value-assignment-acting-weird#answer_265923

在 MATLAB Online 中打开

You have

y_alap6 = y_alap6 - 1;

within your loop, and you are not displaying anything when you do that assignment, so you have no notice that is changing. What happens if it ends up counting backwards all the way to 0?

Your test is pixel_labels(y_alap6,P_hatso3_x) == szegm_lab but suppose that is true all the way ? It is true at row 1, so you decrement the row to 0, and then you try looking at row 0...

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prohi 2017-5-6

This is indeed it, sorry for wasting everyones time! Really beginner mistake, but I am still a beginner. The test is not supposed to be true all the way to 0 based on the visual examination of the image, but it indeed is this time!

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