MATLAB: The colon notation used in multidimensional array

arrayvector

I have come across the following notation in MATLAB

    y(:, :, :, 2) = y(:, :, :, 1);
    y(:, 1, :, 4) = y(:, 1, :, 3);

I have no clue what it means?

I know for matrix A(:,1) and A(1,:) means extract first column and first row respectively. But the above is not clear to me.

Thanks.

Best Answer

It is just an extension of what you already know, but for multi-dimensional arrays. You can no longer use terms like 'rows' and 'columns' unless you have n ever more creative names for each dimension, but the logic is the same. Take all data from the dimensions that have a : and only the specified data from the dimensions which you give an exact index for.

Personally I rarely if ever use arrays of dimensionality higher than 3 because I like to be able to visualise what indexing means and since I can't visualise beyond a 3d cube I easily get confused. That said, the logic works the same whether it can be visualised intuitively or not!

Related Solutions

MATLAB: Extracting a 2 dimensional array from a 3 dimensional matrix.

so you have a matrix of 10 rows, 26 columns and 4 deep. That would be a 10x26x4 matrix. to get just all rows for column a for all pages is this example that is a bit easier to see

    Testmat= randi(10,2,3,4);))
    A = squeeze(Testmat(:,1,:))
    A = A*0
    Testmat(:,1,:) = A

MATLAB: Clear a Matrix from a multidimensional Matrix at each iteration

Matlab needs to make sure that all the indexes include all the values included, therefore it needs to be ":", I leave the solution:

A(:, :, 1, 1) = rand(5, 5);
A(:, :, 1, 2) = rand(5, 5);
A(:, :, 1, 3) = rand(5, 5);
whos;
for i=3:-1:1
 A(:, :, :, i) = [];
 whos
end

Best Answer

Related Solutions

MATLAB: Extracting a 2 dimensional array from a 3 dimensional matrix.

MATLAB: Clear a Matrix from a multidimensional Matrix at each iteration

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