(n-init) x 11 Matrix which contains the unit(s) included
in the subset at each step of the search.
REMARK: in every step the new subset is compared with the
old subset. Un contains the unit(s) present in the new
subset but not in the old one.
Un(1,2) for example contains the unit included in step
init+1.
Un(end,2) contains the units included in the final step
of the search.
n-by-(n-init+1) or n-by-length(bsbsteps) matrix which
contains the units belonging to the subset at each step (or
in selected steps as specified by optional vector bsbsteps)
of the forward search.
More precisely:
BB(:,1) contains the units forming subset in step bsbsteps(1);
....;
BB(:,end) contains the units forming subset in step bsbsteps(end);
Row 1 of matrix BB is referred to unit 1;
......;
Row n of matrix BB is referred to unit n;
Units not belonging to subset are denoted with NaN.