#15673: major improvements to lazy power series
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Reporter: mhansen | Owner:
Type: enhancement | Status: needs_work
Priority: major | Milestone: sage-6.4
Component: combinatorics | Resolution:
Keywords: LazyPowerSeries,, | Merged in:
days57 | Reviewers: Ralf Stephan,
Authors: Mike Hansen | Matthieu Dien
Report Upstream: N/A | Work issues:
Branch: u/mantepse/15673 | Commit:
Dependencies: | aa8fd83522eaeb583da0caa5c6628ddd1ed36b04
| Stopgaps:
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Comment (by vdelecroix):
Well done for the rebase!
Some personal feelings about the code
1. There are public method that should not be there. For example
`Stream.compute`. The documentation mentions `Do not use this method`. In
such case, the method should be private, i.e. starting with an underscore
like `_compute`. Might apply as well to `SeriesStream.refine_order`,
`SeriesStream.compute_order`, `RecursiveStream.not_defined_check`, ...
2. The `check_constant_decorator` is really ugly. I would implement it
directly in the `__getitem__`.
3. You should seriously consider replacing `new_stream.py` with
`lazy_list.pyx` which is currently about 5x faster for `__getitem__` and
provide more or less the same functionality
{{{
sage: from sage.combinat.species.new_stream import StreamFromFunction
sage: h = lambda l: 1 if len(l) < 2 else l[-1] + l[-2]
sage: s = StreamFromFunction(h)
sage: from sage.misc.lazy_list import lazy_list
sage: def h2(l): l.append(l[-1]+l[-2])
sage: s2 = lazy_list(initial_values=[1,1],update_function=h2)
}}}
Then
{{{
sage: %timeit s[0]
1000000 loops, best of 3: 942 ns per loop
sage: %timeit s2[0]
10000000 loops, best of 3: 148 ns per loop
}}}
Though there are missing features. For example, current `lazy_list` do
not care about being periodic or constant after a certain point. But I
would be happy to implement needed stuff from this side.
This series code would be a good test case to see whether `lazy_list`
are as flexible as they claim to be.
4. In many situations it would be much faster to use Newton's method
rather than an intricated tree of streams.
--
Ticket URL: <http://trac.sagemath.org/ticket/15673#comment:45>
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