what does this line of code means bwZ = [zeros(1,c+1);[zeros(r,1) bw]]; ??

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Shahd Ewawi 2013-4-2

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/69555-what-does-this-line-of-code-means-bwz-zeros-1-c-1-zeros-r-1-bw

bw=imread('connected.pgm')./255;
%bw=[0   1   0   0   1   1;
%    1   1   1   0   0   0;
%    0   0   1   0   0   1;
%    1   1   0   0   1   1;
%    0   0   0   1   0   0;];
[r,c] = size(bw);   
bwZ = [zeros(1,c+1);[zeros(r,1) bw]];

i dont understand this line of code :

bwZ = [zeros(1,c+1);[zeros(r,1) bw]];

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Answer 1

Walter Roberson 2013-4-2

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The line adds a row of zeros along the top, and a column of zeros along the side, of bw.

Another way of expressing it would have been:

bwZ = zeros(r+1, c+1, class(bw));
bwZ(2:end, 2:end) = bw;

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Walter Roberson 2013-4-3

It can make the search algorithm easier to write.

For example, if the task were to find the beginning of each "pulse" in a vector of 0 and 1 values, then one way to do that is to search for places in which you have 0 (non-pulse) followed by 1 (pulse). But that search algorithm would fail if the first item in the vector was a 1, as there is no 0 before it. A solution to that is to put a 0 before the vector and then you would not need special code to handle the situation.

Shahd Ewawi 2013-4-5