Parametric Block Diagonal Matrix Unable to perform assignment because the size of the left side is 4-by-4 and the size of the right side is

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Gözde Üstün 2020-6-26

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编辑： Gözde Üstün 2020-6-26

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Hello,

I have this code:

function [A,B] = CH2d(d)
    A=zeros(d,d,2,d);
    B=A;
    projectors_of_sigma_x = [1/sqrt(2)*[1;1],1/sqrt(2)*[1;-1]];
    projectors_of_sigma_x_plus_sigma_z = [[(sqrt(2)+1);1],[(-sqrt(2)+1);1]];
    for k = 1:d
        for l =1:d 
         %   if d > 2 
         %     A(:,:,1,k) = blkdiag(A(:,:,1,k));
         %     B(:,:,1,k) = blkdiag(B(:,:,1,k));
         %  end   
           A(:,:,1,k)=repmat(projectors_of_sigma_x(:,k),1,d);
           B(:,:,1,k)=repmat(projectors_of_sigma_x_plus_sigma_z(:,k),1,d);
            
        end
    end
end

For d = 2 everything is perfect but if d bigger than 2 and d is even the output should be block diagonal matrix. So I added these script in the code:

if d > 2 
             A(:,:,1,k) = blkdiag(A(:,:,1,k));
             B(:,:,1,k) = blkdiag(B(:,:,1,k));
end

But this time I have this error:

 Unable to perform assignment because the size of the left side is 4-by-4 and the size of the right side is 2-by-4.
Error in CH2d (line 16)
           A(:,:,1,k)=repmat(projectors_of_sigma_x(:,k),1,d);

How can I solve this problem? I think I need a new variable or I dont know