#16137: lazy_list from various input data
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Reporter: MatthieuDien | Owner:
Type: enhancement | Status: new
Priority: major | Milestone: sage-6.4
Component: misc | Resolution:
Keywords: LazyPowerSeries, | Merged in:
lazy_list, days57 | Reviewers:
Authors: Vincent | Work issues:
Delecroix, Matthieu Dien | Commit:
Report Upstream: N/A | 530b21b1a97012b1adfc244dad57250922f4f46c
Branch: | Stopgaps:
public/lazy_list_from_various_input_data|
Dependencies: |
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Comment (by MatthieuDien):
Therefore, the answer of Martin :
> @Martin
> The diference bewteen lazy_list and iterator is not only the caching.
> There is also the way to compute an element : if you want the nth
> element of an iterator you have to compute the (n-1) previous ones,
> for lazy_list (currently the implementation does not do this but it
> should in close future) the goal is to compute elements only if it
> obligatory.
> For example, you don't want to compute all the coeffcients of a serie
> if at the end, you will only use the odd (or even) part.
Excellent point!
You made me think again about the name - I don't particularly like
"lazy_list". Of course, from a math point of view I'd call it
"Sequence". However, I just discovered that this is already taken in
Sage for something related, although not identical.
I then discovered "Family", which seems the same but a bit more general.
In fact, "lazy_list" is a Family having index set natural numbers.
Shouldn't we merge these two concepts, at least in the long run?
> Concerning recursive definition, we have to allow it but the
> implementation must not be recursive because recursion is extremly
> expensive in Python.
I'm not quite sure what you mean. There is hardly any implementation.
I want that definitions like s = f(s), where "s" is a "lazy list"
determined by this equation, can be easily typed into sage.
Thus, I think of it as a convenience feature, for rapid prototyping.
Its usefulness lies in the fact that it's very general. Thus, from the
user's perspective, I wouldn't expect it to do any fancy term-rewriting.
> And finally, to answer to Martin about "what is `_normalize_slice` ?
> ", `_normalize_slice` means nothing it is just a piece of code that I
> wanted to factorize. In fact I should factorize directly `__getitem__
> ` by adding a method which have to create a slice (last line of code
> `__getitem__`).
OK, thanks!
Best,
Martin
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Ticket URL: <http://trac.sagemath.org/ticket/16137#comment:46>
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