CODEWITHSUNDEEP
matlab
daniel
daniel

Reputation: 21

I need to create a diagonal matrix where the diagonal elements are a vector

The vector should look something like,

[1 2 3 0 0 0
 0 1 2 3 0 0
 0 0 1 2 3 0
 0 0 0 1 2 3];

I know the vector ([1 2 3]) that I wish to 'paste' along the diagonal but I do not know the size of the array so the number of rows would need to be determined by a variable N.

Upvotes: 2

Views: 89

Answers (3)

Luis Mendo
Luis Mendo

Reputation: 112659

You can also use 2D-convolution:

v = [1 2 3];
N = 4;
result = conv2(v, eye(N))

Upvotes: 2

Steve
Steve

Reputation: 4097

It's a bit crude, but possible to construct the desired matrix as toeplitz:

a = [1 2 3]; 
toeplitz([a(1); zeros(length(a),1)],[a(:); zeros(length(a),1)])

with answer:

ans =

 1     2     3     0     0     0
 0     1     2     3     0     0
 0     0     1     2     3     0
 0     0     0     1     2     3

Upvotes: 4

TroyHaskin
TroyHaskin

Reputation: 8401

You can use spdiags to set the diagonals and have the desired shape:

n = 4;
A = full(spdiags(ones(n,1)*[1,2,3],[0,1,2],n,n+2));

This returns:

A =

   1   2   3   0   0   0
   0   1   2   3   0   0
   0   0   1   2   3   0
   0   0   0   1   2   3

Upvotes: 4

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