Opened 10 years ago
Closed 8 years ago
#8458 closed defect (fixed)
iterator for graphs() doesn't return independent graphs
Reported by: | mvngu | Owned by: | rlm |
---|---|---|---|
Priority: | major | Milestone: | sage-5.0 |
Component: | graph theory | Keywords: | |
Cc: | brunellus | Merged in: | sage-5.0.beta3 |
Authors: | Lukáš Lánský | Reviewers: | Nathann Cohen |
Report Upstream: | N/A | Work issues: | |
Branch: | Commit: | ||
Dependencies: | Stopgaps: |
Description (last modified by )
From sage-support:
So, what you are saying is that the iterator for graphs() does not return independent graphs which can be changed without affecting the others. That does explain what I am seeing and is consistent with Pat LeSmith's suggested workaround. Should this property of the iterators to the generated graphs be documented? So, I think I will try making a copy of just the graphs I want to change or use the list() trick.
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Attachments (3)
Change History (18)
comment:1 Changed 10 years ago by
comment:2 Changed 10 years ago by
I agree with rlm. I think the default should be to return a copy of the graph, with an optional argument to return the actual graph.
comment:3 Changed 8 years ago by
- Cc brunellus added
Changed 8 years ago by
comment:4 Changed 8 years ago by
- Status changed from new to needs_review
I corrected the main generator. There are several specialized (e.g. tree generator) but I don't think the same problem arises in any of them. Do you agree?
comment:5 Changed 8 years ago by
- Status changed from needs_review to needs_info
Helloooooo !!!
This is a good patch, but I do not think the documentation is very clear. What would you think of changing the new argument's name to "return_copies" or "graph_copy" ? To be honest I took me 2 minutes to understand that this message's title did not mean "The independent graph is not returned by graphs(n)" :-p
Either way, with a name like "independent" it is not very clear that there may be performances issues hidden in this argument.
Here's what I would write. Of course, it's just my advice, so take or leave whatever you want :
- ``copy_graphs`` (boolean) -- If set to ``True`` (default) this method makes copies of the graphs before returning them. If set to ``False`` the method returns the graph it is working on. The second alternative is faster, but modifying any of the graph instances returned by the method may break the function's behaviour, as it is using these graphs to compute the next ones : only use ``copy_graph = False`` when you stick to *reading* the graphs returned.
Please tell me what you think :-)
Nathann
comment:6 Changed 8 years ago by
Arg.... It's all written on one line. Stupid me. Here it is :
- ``copy_graphs`` (boolean) -- If set to ``True`` (default) this method makes copies of the graphs before returning them. If set to ``False`` the method returns the graph it is working on. The second alternative is faster, but modifying any of the graph instances returned by the method may break the function's behaviour, as it is using these graphs to compute the next ones : only use ``copy_graph = False`` when you stick to *reading* the graphs returned.
comment:7 follow-up: ↓ 8 Changed 8 years ago by
Can I suggest copy=True
, which is shorter and just as clear in the context?
comment:8 in reply to: ↑ 7 Changed 8 years ago by
Can I suggest
copy=True
, which is shorter and just as clear in the context?
>_<
Of course... Much more natural :-D
Thanks !!
Nathann
Changed 8 years ago by
comment:9 Changed 8 years ago by
- Status changed from needs_info to needs_review
If you think that "copy" is better, I don't mind. I thought that a consumer of the library doesn't care about what is the way we create the graphs (that we copy them), so the relevant property of the output is rather independence. The proposed description is also good.
comment:10 Changed 8 years ago by
Hellooooooo !!!
Well, with a keyword like "independent" the user needs to read the documentation to understand what it precisely means. And with "copy" he also knows that there is some complexity question hidden in there :-)
comment:11 Changed 8 years ago by
- Status changed from needs_review to needs_work
(for me the patch is ok, but it does not apply on 5.0-beta1. I just reinstalled it, so it seems genuine :-)
)
Nathann
comment:12 Changed 8 years ago by
- Description modified (diff)
- Reviewers set to Nathann Cohen
- Status changed from needs_work to needs_review
Well, I do not like to set tickets back to "needs work" in such cases... Here is the same patch rebased on beta1. If it's fine with you too, you can set the ticket to positive_review :-)
Nathann
Changed 8 years ago by
comment:13 Changed 8 years ago by
- Status changed from needs_review to positive_review
Thank you. :-)
comment:15 Changed 8 years ago by
- Merged in set to sage-5.0.beta3
- Resolution set to fixed
- Status changed from positive_review to closed
This is an unintended consequence of the fact that when the
graphs(n)
iterator yields a graph, it does not first make a copy. The method of generating graphs is to add on to previously generated graphs in a well-chosen way, and I did not think to make a copy of the graph before having the iterator yield it.This shouldn't just be documented, but in fact I think this should be an option to
graphs(n)
. If someone will not modify the graphs in the loop, they can get the speed advantage of not making copies, and someone else who wants to modify them can have the iterator make copies on the fly.