Insert a matrix within a matrix

Im trying to insert a matrix within a matrix, such that, if

x=[a,d;c,d], then y=[a,b,0,0;c,d,0,0;0,0,a,b;0,0,c,d]. Basically, matrix X becomes the diagonals of of the zero matrix Y.

anyone in cyberland have an idea on how to do this?

Answer 1

[the cyclist]

Matt's solution does precisely what you ask. You might also like to know that in general, you can insert one array into another by indexing on the left-hand side of an assignment statement:

>> x = rand(2);
>> y = zeros(8);
>> y(5:6,3:4) = x;

Answer 2

[Matt Fig]

Assuming you meant

x = [a,b;c,d];

then

y = blkdiag(x,x)

Answer 3

[PUST rahman]

function R=insertMatrix(B,b)

% INPUT: B: Bigger matrix % b: small matrix that needs to put inside bigger matrix, B %OUTPUT: R: Resultant matrix % Example: % B=zeros(10,10); b=ones(5,5); % R=insertMatrix(B,b);

% this matlab script is written by Hafiz, PhD Student, UNSW, Canberra % [e-mail]

[P,Q]=size(B);

fx=floor(P/2)-floor(size(b,1)/2);

fy=floor(Q/2)-floor(size(b,2)/2);

R=B;

for p=1:size(b,1)

for q=1:size(b,2)

        R(fx+p,fy+q)=b(p,q);     

    end

end

return;

[PUST rahman]

The only advantage of this code is it tries to push the small matrix just in the middle of the bigger matrix.