Re: Building a multidimensional block diagonal matrix avoiding loops

[PetrSt]

Repair - the outer reshapes are abundant, so it could be rewritten as

% Block diagonal in third dim
a=l; b=m*n; c=n;
B = zeros([a,b,c]);

ida = repmat((1:a)',m*n,1);
idb = repmat((1:b),l,1);
idc = repmat((1:c),l*m,1);

idx = sub2ind([a,b,c],ida(:),idb(:),idc(:));

B(idx) = A(:)

% Block diagonal in all dims
a=l*n; b=m*n; c=n;
B = zeros([a,b,c]);

ida = rotdim(reshape(repmat((1:a)',1,m),l,m,n),1,[2,3]);
idb = repmat((1:b),l,1);
idc = repmat((1:c),l*m,1);

idx = sub2ind([a,b,c],ida(:),idb(:),idc(:));

B(idx) = A(:)



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