374 reputation
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bio website tqft.net
location Berkeley, CA
age 35
visits member for 2 years, 6 months
seen Dec 14 '13 at 23:02

Mathematician at the Australian National University. Moderator on mathoverflow.net.


Dec
31
awarded  Good Question
Aug
8
asked What range of ports do remote kernels use?
Jan
17
awarded  Yearling
Jul
23
comment How is pattern specificity decided?
@Szabolcs, maybe it's better to say that I'm still thinking about it.
Jul
23
comment How is pattern specificity decided?
@magma, when you take into account the time order in which the rules are attached to a symbol, you can obtain a total ordering (as I mentioned in the question). It's pretty easy to see, by playing around with examples that the functions I show above appear to define a partial ordering.
Jul
23
comment How is pattern specificity decided?
@Mr. Wizard, Internal`ComparePatterns says that __ and (_).. are each more specific than the other, while my 'experimental' approach above says they are incomparable.
Jul
23
awarded  Nice Question
Jul
23
asked How is pattern specificity decided?
Feb
13
comment NullSpace[_, Method->“OneStepRowReduction”] is sometimes wrong; how can I work out when this happens?
Thanks for looking into this Daniel. In MMA 7 RootReduce was verifying that m.v was exactly zero; so perhaps the problem is in RootReduce in either 7 or 8? I'll investigate further.
Feb
2
awarded  Editor
Feb
2
revised NullSpace[_, Method->“OneStepRowReduction”] is sometimes wrong; how can I work out when this happens?
adding note about version 8
Feb
2
comment NullSpace[_, Method->“OneStepRowReduction”] is sometimes wrong; how can I work out when this happens?
@DanielLichtblau, is there any reference for these bugs? I'd like to be able to ascertain which code running in 7 I can or cannot 'trust' (to the extend that trusting Mathematica is ever possible).
Feb
2
comment NullSpace[_, Method->“OneStepRowReduction”] is sometimes wrong; how can I work out when this happens?
No, I think this is a real problem --- and your answers indicate it's got worse in Mathematica 8, not better! The NullSpace should not be empty. Here's the result of RootReduce[NullSpace[m]]: {{Root[3 - 80 #1^2 + 9 #1^4 &, 1], Root[3 - 80 #1^2 + 9 #1^4 &, 4], Root[-3 + 4 #1^2 + 3 #1^4 &, 4], Root[3 - 32 #1^2 + 81 #1^4 &, 3], Root[1 - 38 #1 + 116 #1^2 - 90 #1^3 + 27 #1^4 &, 4], Root[1 + 38 #1 + 116 #1^2 + 90 #1^3 + 27 #1^4 &, 4], Root[-1 + 23 #1^2 + 27 #1^4 &, 3], 1}}, which you can verify really is in the kernel.
Feb
2
awarded  Student
Feb
2
asked NullSpace[_, Method->“OneStepRowReduction”] is sometimes wrong; how can I work out when this happens?
Jan
17
awarded  Quorum
Jan
17
awarded  Teacher
Jan
17
answered What best practices or performance considerations are there for choosing between Cases, Position, Pick and Select?
Jan
17
awarded  Supporter
Jan
17
awarded  Autobiographer