#12923 closed defect (fixed)
Comparison of vectors is O(n) even in the simple cases
Reported by: | hivert | Owned by: | jason, was |
---|---|---|---|
Priority: | major | Milestone: | sage-5.3 |
Component: | linear algebra | Keywords: | vector equality days38 |
Cc: | mguaypaq | Merged in: | sage-5.3.beta0 |
Authors: | Florent Hivert | Reviewers: | Travis Scrimshaw |
Report Upstream: | N/A | Work issues: | |
Branch: | Commit: | ||
Dependencies: | Stopgaps: |
Description
Comparison of large vectors in Sage is slow in a surprising way: even if all the entries of the vectors are different, the cost is proportional to the length of the vector instead of having constant cost !
sage: l = 1000; m0 = vector(ZZ, [0]*l); m1 = vector(ZZ, [1]*l) sage: %timeit m0 == m1 625 loops, best of 3: 656 盜 per loop sage: l = 10000; m0 = vector(ZZ, [0]*l); m1 = vector(ZZ, [1]*l) sage: %timeit m0 == m1 125 loops, best of 3: 5.66 ms per loop sage: l = 100000; m0 = vector(ZZ, [0]*l); m1 = vector(ZZ, [1]*l) sage: %timeit m0 == m1 5 loops, best of 3: 59.1 ms per loop
This seems to affect all the dense vectors independently from the base ring.
Attachments (1)
Change History (12)
comment:1 Changed 9 years ago by
- Keywords days38 added
Changed 9 years ago by
comment:2 Changed 9 years ago by
- Cc mguaypaq added
- Status changed from new to needs_review
comment:3 follow-up: ↓ 4 Changed 9 years ago by
- Status changed from needs_review to needs_work
comment:4 in reply to: ↑ 3 Changed 9 years ago by
- Status changed from needs_work to needs_review
Replying to tscrim:
It works fine for integers, but observe the following:
sage: l = 1000; v1 = vector(ZZ, [0]*l); v2 = vector(QQ, [1]*l)I can't test any higher because running these tests completely kills my memory (the first comparison will allocate ~150MB RAM, the second ~450MB RAM). It only allocates when I call the comparison. Also my memory usage did not drop when I reassign v1 and v2.
I'd rather to see that as a different problem. The goal of the code here is to remove a bunch bug whose result was that the specialized code already written wasn't called. I'm not optimizing anything as I don't have a serious use case for those specific case, do you ? Note that I didn't made any serious benchmark either. Comparing vectors with different base rings, which implies different internal data structure could be certainly optimized, but I'd rather leaving it to a different ticket.
Cheers,
Florent
comment:5 Changed 9 years ago by
- Status changed from needs_review to positive_review
Works for comparisons between vectors in the same data structure as you intended.
comment:6 Changed 9 years ago by
Please fill in your real name as Reviewer.
comment:7 Changed 9 years ago by
- Reviewers set to Travis Scrimshaw
comment:8 Changed 9 years ago by
- Merged in set to sage-5.3.beta0
- Resolution set to fixed
- Status changed from positive_review to closed
comment:9 follow-up: ↓ 10 Changed 7 years ago by
In this patch, you added in several places
+ # __hash__ is not properly inherited if comparison is changed
+ def __hash__(self):
+ """
+ TEST::
+
+ sage: w = vector(ZZ, [-1,0,0,0])
+ sage: w.set_immutable()
+ sage: isinstance(hash(w), int)
+ True
+ """
+ return free_module_element.FreeModuleElement.__hash__(self)
What's the reason for this? Removing these __hash__
methods doesn't do any harm.
comment:10 in reply to: ↑ 9 Changed 7 years ago by
Replying to jdemeyer:
In this patch, you added in several places What's the reason for this? Removing these
__hash__
methods doesn't do any harm.
In Cython when you overload comparison __hash__
is not inherited anymore. See the following discussion on cython-user
comment:11 Changed 7 years ago by
Yes, sorry, you are right.
I got confused because
v.__hash__()
works but
hash(v)
doesn't.
It works fine for integers, but observe the following:
I can't test any higher because running these tests completely kills my memory (the first comparison will allocate ~150MB RAM, the second ~450MB RAM). It only allocates when I call the comparison. Also my memory usage did not drop when I reassign v1 and v2.