sum for sequences?
in [Python]
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From: Steven D'Aprano on 30 Mar 2010 06:10 On Mon, 29 Mar 2010 23:55:55 -0700, Paul Rubin wrote: > Steven D'Aprano <steven(a)REMOVE.THIS.cybersource.com.au> writes: >>>>> ... >>>> ... >>> ... >> "Obvious" doesn't mean you don't have to learn the tools you use.... > > Geez you guys, get a room ;-). You're all good programmers with too > much experience for this arguing over stuff this silly. Yes Mum ;) You're right of course. I spend too much time being this guy: http://xkcd.com/386/ and not enough this one: http://xkcd.com/167/ -- Steven
From: Steve Holden on 30 Mar 2010 07:33 Steven D'Aprano wrote: > On Mon, 29 Mar 2010 23:55:55 -0700, Paul Rubin wrote: > >> Steven D'Aprano <steven(a)REMOVE.THIS.cybersource.com.au> writes: >>>>>> ... >>>>> ... >>>> ... >>> "Obvious" doesn't mean you don't have to learn the tools you use.... >> Geez you guys, get a room ;-). You're all good programmers with too >> much experience for this arguing over stuff this silly. > > Yes Mum ;) > > > You're right of course. I spend too much time being this guy: > > http://xkcd.com/386/ > > and not enough this one: > > http://xkcd.com/167/ > > Yeah, it can happen to all of us. I've certainly been "that guy" too. But Steven, surely now it's time to *show us the squirrels* regards Steve -- Steve Holden +1 571 484 6266 +1 800 494 3119 See PyCon Talks from Atlanta 2010 http://pycon.blip.tv/ Holden Web LLC http://www.holdenweb.com/ UPCOMING EVENTS: http://holdenweb.eventbrite.com/
From: Mel on 30 Mar 2010 09:53 Patrick Maupin wrote: > Because sum() is the obvious way to sum floats; now the existence of > math.fsum() means there are TWO obvious ways to sum floats. Is that > really that hard to understand? How can you misconstrue this so badly > that you write something that can be (easily) interpreted to mean that > you think that I think that once math.fsum() exists, sum() doesn't > even exist any more???? floats are nasty -- as evidence the recent thread on comparing floats for equality. People use floats when they have to. fsum exists because of this: mwilson(a)tecumseth:~$ python Python 2.6.2 (release26-maint, Apr 19 2009, 01:56:41) [GCC 4.3.3] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> from math import fsum >>> a=(1.0e200, 156.0, -1.0e200) >>> sum(a) 0.0 >>> fsum(a) 156.0 You could generalize sum, but after that, there's a case that even fsum can't handle: >>> ni=1.0e200+1.0j >>> nj=1.0+1.0e200j >>> ai=(ni, nj, 156.0+651.0j, -ni, -nj) >>> sum(ai) (-1+0j) >>> fsum(ai) Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: can't convert complex to float; use abs(z) >>> Mel.
From: Patrick Maupin on 30 Mar 2010 11:31 On Mar 30, 8:53 am, Mel <mwil...(a)the-wire.com> wrote: > floats are nasty -- as evidence the recent thread on comparing floats for > equality. People use floats when they have to. fsum exists because of > this: .... I understand there are technical reasons for why math.fsum() exists. I still think that whatever math.fsum() does should probably be a part of sum(). Regards, Pat
From: Albert van der Horst on 6 Apr 2010 09:39
In article <559a2ee3-fb2c-477f-a444-7edbb6da8676(a)r1g2000yqj.googlegroups.com>, Patrick Maupin <pmaupin(a)gmail.com> wrote: >On Mar 29, 10:29=A0pm, Steven D'Aprano ><ste...(a)REMOVE.THIS.cybersource.com.au> wrote: >> On Mon, 29 Mar 2010 19:24:42 -0700, Patrick Maupin wrote: >> > On Mar 29, 6:19=A0pm, Steven D'Aprano <st...(a)REMOVE-THIS- >> > cybersource.com.au> wrote: >> >> How does the existence of math.fsum contradict the existence of sum? >> >> > You're exceptionally good at (probably deliberately) mis-interpreting >> > what people write. >> >> I cannot read your mind, I can only interpret the words you choose to >> write. You said >> >> [quote] >> See, I think the very existence of math.fsum() already violates "there >> should be one obvious way to do it." >> [end quote] >> >> If sum satisfies the existence of one obvious way, how does math.fsum >> violate it? sum exists, and is obvious, regardless of whatever other >> solutions exist as well. > >Because sum() is the obvious way to sum floats; now the existence of >math.fsum() means there are TWO obvious ways to sum floats. Is that >really that hard to understand? How can you misconstrue this so badly >that you write something that can be (easily) interpreted to mean that >you think that I think that once math.fsum() exists, sum() doesn't >even exist any more???? To a mathematician sum(set) suggest that the order of summation doesn't matter. (So I wouldn't use sum for concatenating lists.) Harshly, sum() should be used only for operator + both associative and commutative. Now for floating point numbers the order of summation is crucial, not commutative (a+b)+c <> a+(b+c). So the obvious thing for someone versed in numerical computing do is looking whether sum() gives any guarantees for order and whether there may be a special sum() for floating point. (This is not very realistic, because such a person would have skimmed the math library a long time ago, but anyway.) Met vriendelijke groeten, Albert van der Horst -- Albert van der Horst, UTRECHT,THE NETHERLANDS Economic growth -- like all pyramid schemes -- ultimately falters. albert(a)spe&ar&c.xs4all.nl &=n http://home.hccnet.nl/a.w.m.van.der.horst -- -- Albert van der Horst, UTRECHT,THE NETHERLANDS Economic growth -- being exponential -- ultimately falters. albert(a)spe&ar&c.xs4all.nl &=n http://home.hccnet.nl/a.w.m.van.der.horst |