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Convert breaks with multiplicities into knots

`[knots,index] = brk2knt(breaks,mults) `

`[knots,index] = brk2knt(breaks,mults) `returns
the sequence `knots` that is the sequence `breaks` but
with `breaks(i)` occurring `mults(i)` times,
all `i`. In particular, `breaks(i)` will
not appear unless `mults(i)>0`. If, as one would
expect, `breaks` is a strictly increasing sequence,
then `knots` contains each `breaks(i)` exactly `mults(i)` times.

If `mults` does not have exactly as many entries
as does `breaks`, then all `mults(i)` are
set equal to `mults(1)`.

If, as one would expect, `breaks` is strictly
increasing and all multiplicities are positive, then, for each `i`, `index(i)` is
the first place in `knots` at which `breaks(i)` appears.

The statements

t = [1 1 2 2 2 3 4 5 5]; [xi,m] = knt2brk(t); tt = brk2knt(xi,m)

give `[1 2 3 4 5] `for `xi`, `[2
3 1 1 2]` for `m`, and, finally, `t` for `tt`.

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