You could try below
(1) If you are just aiming to the get the submatrices in the diagonal of A...
I = length(A);
n = 10; % size of the desired squared submatrix
i= I/n;
% s1 = 'B';
% s2 =[1:i];
for j=1:i
% s3=num2str(s2(j));
eval(sprintf('B%d = A((j-1)*n+1:n*j,(j-1)*n+1:n*j)', j));
end
(2) If you are aiming to cover all the rows and columns...
I = length(A);
n = 10; % size of the desired squared submatrix
i= I/n;
for j=1:i
for k=1:i
eval(sprintf('B%d = A((j-1)*n+1:n*j,(k-1)*n+1:n*k)', (j-1)*i+k));
end
end
