Concatenate array using square brackets

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Quang Nguyen 2022-10-26

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https://ww2.mathworks.cn/matlabcentral/answers/1836308-concatenate-array-using-square-brackets

评论： Voss 2022-10-26

x = zeros(1,9);
x = [1, x(1:9)];

when i run the second line multiple times, it starts to fill in the array x. I want to ask what is the functionality of the second line, and is there any documentation that describes this syntax ?

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Answer 1

Voss 2022-10-26

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https://ww2.mathworks.cn/matlabcentral/answers/1836308-concatenate-array-using-square-brackets#answer_1084263

https://www.mathworks.com/help/matlab/ref/double.horzcat.html

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Voss 2022-10-26

编辑：Voss 2022-10-26

在 MATLAB Online 中打开

% x is a 1-by-9 array (i.e., a vector) of 9 zeros:
x = zeros(1,9)
x = 1×9
     0     0     0     0     0     0     0     0     0
% now x is a 1 followed by the first 9 elements of what was x (i.e., 9 zeros)
x = [1, x(1:9)]
x = 1×10
     1     0     0     0     0     0     0     0     0     0
% now x is a 1 followed by the first 9 elements of what was x (i.e., a 1 and 8 zeros)
x = [1, x(1:9)]
x = 1×10
     1     1     0     0     0     0     0     0     0     0
% now x is a 1 followed by the first 9 elements of what was x (i.e., two ones and 7 zeros)
x = [1, x(1:9)]
x = 1×10
     1     1     1     0     0     0     0     0     0     0
% etc.

Perhaps it's useful to see the same code operating with a different starting vector x:

x = 1:9
x = 1×9
     1     2     3     4     5     6     7     8     9
x = [1, x(1:9)]
x = 1×10
     1     1     2     3     4     5     6     7     8     9
x = [1, x(1:9)]
x = 1×10
     1     1     1     2     3     4     5     6     7     8
x = [1, x(1:9)]
x = 1×10
     1     1     1     1     2     3     4     5     6     7

Considering that example, it may be more clear now, that the line x = [1, x(1:9)] does not really "replace" zeros with ones, but instead prepends a 1 to the beginning of x and removes anything after element #9, each time it is run.

Quang Nguyen 2022-10-26

Thank you very much, i really get it now

Voss 2022-10-26

You're welcome!

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Concatenate array using square brackets

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Concatenate array using square brackets

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