CODEWITHSUNDEEP
matlabmatrixindexing
sleeve chen
sleeve chen

Reputation: 241

How to use a matrix to store a vector in each element

I have not seen this in MATLAB. Suppose I have 

V1 = [1 0],  V2 = [0 1]

I want to create a matrix such that the matrix has to be

[[1 0] [0 1]      
 [0 1] [0 2]]

i.e., the first row and column are [V1 V2], element (2,2) of the matrix is [0 1]+[0 1]=[0 2]

So index (1,1) of the matrix should be [1 0], index (1,2) of matrix should be [0 1].

Is there any way I can implement this in MATLAB?

Upvotes: 0

Views: 434

Answers (1)

Wolfie
Wolfie

Reputation: 30047

A matrix can only contain one value per element. Here are 3 options for how you could get close to what you've described:

  1. You could create a 4*4 matrix like so:

    V1 = [1 0]; V2 = [0 1];
M = [V1, V2; V2, 2*V2];

    And then create a shorthand function to index this in blocks of 2

    Mb = @(r,c) M( r, 2*c-1+[0,1] );

Mb(1,1); % = [1 0]
Mb(1,2); % = [0 1]
Mb(2,2); % = [0 2]

    Note that this doesn't work for assignment back to M in blocks of 2, just for reading the value.

  1. Alternatively, you could use a cell array

    C = {V1, V2; V2, 2*V2};

    Now you can index this how you want, but it won't behave as a single matrix, and you can't do numerical operations on the whole cell array

    C{2,2}; % = [2, 2], note the curly brace indexing

  1. A third option would be to make your matrix 3D

    V1 = reshape( V1, 1, 1, [] );
V2 = reshape( V2, 1, 1, [] );
M3D = [V1, V2; V2, 2*V2];

    Now you can index in the 3rd dimension

    M3D(2,2,:); % = [0 2], but size [1,1,2]. Could reshape(M3D(2,2,:),1,[]) to get a row.

Upvotes: 3

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