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From: Larry Evans (jcampbell3_at_[hidden])
Date: 20010615 09:46:48
Hubert HOLIN wrote:
> Somewhere in the E.U., le 15/06/2001
>
>  In boost_at_y..., "David Abrahams" <david.abrahams_at_r...> wrote:
> >
> >  Original Message 
> > From: "Hubert HOLIN" <Hubert.Holin_at_B...>
> > > >
>
[SNIP]
>
> >
> > > An iterator is,
> > > basicaly, some form of bijection from a subset of N into the set of
> > > indices we are interested in.
> >
> > I'm not sure if that part rings true. Maybe you should clarify a bit.
>
> Well, bijection is too stringent. Injection is enough.
> Bijection is when we want to access each and every index one time, and
> one time only. Injection is when we only want to see some indices, but
> each index is accessed only once (in this case it is understood that
> this index is actually representative of a class, for instance the
> index may designate the "row", or "column" of a matrix, or a "cell" of
> a quadtree, or a "block" when we hav block matrices, or a "band" when
> we have band matrices). I believe we need at least injection (we do not
> want to see one index more then once in each traversal) in practice.
>
> The begining iterator is just the image of 0 by the
> injection, after the first increment we have the value of 1, etc. .
>
> > > A 'behaviour' is then simply some
> > > function from the set of indices to itself.
> >
> > Maybe you should give an example of what you've got in mind.
>
> A behaviour could be accessing each index in the order [0,0],
> [1,0],..., [N,0], [0,1],..., [N,M], another would be accessing in the
> order [0,0], [0,1],..., [0,N], [1,0],..., [N,M], yet another (when N ==
> M) would be acessing them in quadtreekey order.
I'm confused by "accessing each index". Do you mean accessing the
value corresponding to that index. For example, if the matrix is 'float A[N][M]`
and if 'i' is such an iterator, then starting from the initial value of i:
*i == A[0][0]
*(++i) == A[0][1]
...
*(++i) == A[N][M]
?
In other words, the iterator produces a 'flattened' version or 'ravel' (apl term)
of A, and then access the elements just as a regular stl iterator. Is that
what you mean?
[SNIP]
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