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

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Shahd Ewawi
Shahd Ewawi 2013-4-2
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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回答（1 个）

Walter Roberson
Walter Roberson 2013-4-2
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
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.

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