How to extract hyperspace of a n dimensions matrix

Hi,

I working with a matrix M with currently 9 dimensions array. I want to extract the submatrix of let say the 1st element of the 6th dimension. The answer is obviously subM = squeeze(M(:,:,:,:,:,1,:,:,:));

The problem is that the number of dimension of my matrix M is variable, so is there any generic way to extract a specific hypermatrix (i.e for a n dimension matrix, extract the i-th element of the m-th dimension giving a n-1 dimension submatrix)

Answer 1

[Prateekshya]

Hello Renaud,

You can take the help of indexing cell array to perform extraction of hyperspace from a multi-dimensional matrix. Let us take a 5-dimensional matrix and see how it works:

% Define the size of each dimension
dim1 = 3;
dim2 = 4;
dim3 = 5;
dim4 = 6;
dim5 = 7;

% Generate grid data for each dimension
[x1, x2, x3, x4, x5] = ndgrid(1:dim1, 1:dim2, 1:dim3, 1:dim4, 1:dim5);

% Create a 5D matrix with a specific pattern
% For example, use a simple function: M = x1 + 2*x2 + 3*x3 + 4*x4 + 5*x5
M = x1 + 2*x2 + 3*x3 + 4*x4 + 5*x5;

% Specify the dimension and the index to extract
m = 3; % The dimension to slice
i = 2; % The index to extract from the m-th dimension

% Determine the number of dimensions in M
numDims = ndims(M);

% Create an indexing cell array
index = repmat({':'}, 1, numDims); % Initialize with ':'
index{m} = i; % Set the specific index for the m-th dimension

% Extract the submatrix
subM = squeeze(M(index{:}));

% Display the size of the original and submatrix
disp('Original matrix size:');
disp(size(M));
disp('Submatrix size:');
disp(size(subM));

% Display the submatrix for verification
disp('Extracted submatrix:');
disp(subM);

You can modify the matrix generation part, add your data directly and follow the further process to extract the hyperspace.

I hope this resolves your query!