epsilon = 0.45;
t = -3.033;
n = 100;
I = ones(n,n);
%// diagonal block 1
DB1 = gallery('tridiag',ones(1,n-1),ones(1,n),ones(1,n-1));
for k = 1:n
    DB1(k,k) = epsilon;
end
for k = 1:n-1
    DB1(k,k+1) = t*heaviside((-1)^(k+1));
end
for k = 2:n
    DB1(k,k-1) = t*heaviside((-1)^k);

for k = 2:N
    LRG(:,:,k) = inv(R(:,:,k) - R2(:,:,k-1)*LRG(:,:,k-1)*R1(:,:,k-1));
end

epsilon = 0.45; t = -3.033;
n = 100;
DB1 = zeros(n); %initialize to 0

%diagonal indices
inds=sub2ind([n n],1:n,1:n);
DB1(inds) = epsilon;

%superdiagonal
inds=sub2ind([n n],1:n-1,2:n);
DB1(inds) = t*heaviside((-1).^(2:n));

%subdiagonal
inds=sub2ind([n n],2:n,1:n-1);
DB1(inds) = t*heaviside((-1).^(2:n));

DB1=sparse(DB1);

DB1new=sparse([1:n 1:n-1 2:n],[1:n 2:n 1:n-1],...
    [epsilon*ones(1,n) t*heaviside((-1).^(2:n)) t*heaviside((-1).^(2:n))],n,n);