CODEWITHSUNDEEP
arraysmatlabmultidimensional-array
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Reputation: 2299

Generate a 3-d matrix from a vector in Matlab

I have a vector A in Matlab of dimension (N-1)x1 

A=[0:1:N-2]'

with N>=3, e.g. with N=4 A=[0 1 2]

I want to construct a 3-dimensional matrix B of dimension Mx(N-1)x(N-1) without using loops such that e.g. with N=4, M=5

B(:,:,1)=[0 0 0 0;
          0 0 0 0;
          0 0 0 0;
          0 0 0 0;
          0 0 0 0]

B(:,:,2)=[1 1 1 1;
          1 1 1 1;
          1 1 1 1;
          1 1 1 1;
          1 1 1 1]

...

B(:,:,end)=[N-2 N-2 N-2 N-2;
            N-2 N-2 N-2 N-2;
            N-2 N-2 N-2 N-2;
            N-2 N-2 N-2 N-2;
            N-2 N-2 N-2 N-2]

Upvotes: 0

Views: 44

Answers (3)

beaker
beaker

Reputation: 16791

I'm going to keep using permute until I get the hang of it...

B = ones(M,N-1,N-1).*permute(A,[3,2,1])

Upvotes: 2

Luis Mendo
Luis Mendo

Reputation: 112679

Is this what you want?

B = repmat(reshape(A,1,1,[]), M, N-1); %// or change N-1 to N, according to your example

Another possibility:

B = bsxfun(@times, reshape(A,1,1,[]), ones(M, N-1)); %// or change N-1 to N

Yet another:

B = reshape(A(ceil((1:numel(A)*M*(N-1))/M/(N-1))), M, N-1, []); %// or change N-1 to N

Upvotes: 2

rayryeng
rayryeng

Reputation: 104503

Here's one approach with kron and reshape:

A = 0:N-2;
B = reshape(kron(A, ones(M, N-1)), M, N-1, []);

We use kron to produce M x (N-1) 2D matrices that are stacked for as many elements as there are in A and each matrix is multiplied by the corresponding value in A. The next step is to take each of the concatenated 2D matrices and place them as individual slices in the third dimension, done by reshape.

Example with M = 5, N = 4

>> B

B(:,:,1) =

     0     0     0
     0     0     0
     0     0     0
     0     0     0
     0     0     0


B(:,:,2) =

     1     1     1
     1     1     1
     1     1     1
     1     1     1
     1     1     1


B(:,:,3) =

     2     2     2
     2     2     2
     2     2     2
     2     2     2
     2     2     2

Upvotes: 3

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