function S = BT(x,k,band)
%% band-excluded thresholding
N = length(x);
S = [];
Region = 1 : N;
for iter = 1 : k
[maxentry , index] = max(abs(x(Region)));
S = [S ; Region(index)];
Region = setdiff(Region,Region(index)-band : Region(index)+band);
end