News for hackers. Stuff that matters.

g_

Re:Dijkstra: Why numbering should start at zero on Friday August 21, 2009 @11:59AM (#777773)
http://en.wikipedia.org/wiki/Evenness_of_zero

Learning that such article could exist (it DOES exist), and reading it was a shocking experience to me.

Re:Ask HN: Ubuntu Must-Have Apps on Thursday July 30, 2009 @04:21PM (#732993)
if you don't have them already: build-essentials, python, svn

Chromium is also a must.

Re:The Calculus Trap on Wednesday July 22, 2009 @10:35PM (#718943)
I read this article in high school, and it permanently changed my math life. Without it, I would continue to think I know derivatives because I learned twenty formulas and did forty exercises (which in fact every idiot could do).

I'll allow myself to give some advice for those who are interested in problem-solving, but have no experience. If you have some, then this should be well known.

* Keep problem / exercise ratio as high as possible. This is impossible with many calculus books; find a book with hard problems. An "exercise" is something which checks your understanding of definitions and theorems; a "problem" is something which exercises your skill and forces to think. Do exercises if the theory is unclear. If a task starts with "using mathematical induction prove that..." then it is an exercise. A problem forces you to think how to do it.

* Doing differentiation exercises will give you some speed, but after five-twenty minutes your brain will stop thinking and start to rot. Healthy mathematics - just like programming - hates doing the same thing again. Of course you have to learn some algorithms, but this is a tip of the iceberg.

* Always take 20 minutes (some say more) on a problem, unless you think it is ill-posed; giving up early is stupid. If you think the problem is impossible, try proving it. Think about some way of solving, reject it quickly if you made a thinko; if you sense "this might work" go deeper. Use paper.

* Don't read too much on philosophy of mathematics or biographies; this isn't deep from the mathematical side. Other articles (http://www.artofproblemsolving.com/Resources/AoPS_R_Articles...) are also worth reading. Check their forum (http://www.artofproblemsolving.com/Forum/index.php or www.mathlinks.ro).

Re:X-3/x-1=x-4/x-5 on Wednesday July 15, 2009 @09:10PM (#706979)
I don't see the result in Bing.

alpha direct link: http://www.wolframalpha.com/input/?i=(x-3)/(x-1)%3D(x-4)/(x-...

Re:0^0 = 1, 0, Undefined? on Saturday July 11, 2009 @05:02PM (#699529)
What do you mean by 'is defined by group operation'? Reals/integers with multiplication don't form a group.

'Multiplying 0 by itself 0 times' is what Wikipedia calls 'empty product'. For me is is good intuition, but that's a matter of taste.

AFAIK the usual convention is:

* in contexts where the exponent is varying continuously and a is a real number, a^b is undefined for a=b=0

* in contexts where the exponent is varying discretely (as an integer/natural number), a^b = 1 for b=0 and any a

Haskell quite nicely distinguishes between these two:

(^) :: (Num a, Integral b) => a -> b -> a

(* * ) :: (Floating a) => a -> a -> a

but it still gives 0 * * 0 and 0^0 as 1. (There shouldn't be spaces between asterisks, HN treats them as italics)

Re:Xkcd meets reality on Tuesday June 23, 2009 @04:59AM (#670022)
It is possible to use a lowercase title: http://news.ycombinator.com/item?id=669937
Re:Xkcd meets reality on Monday June 22, 2009 @11:59AM (#668957)
Nitpick: it's written xkcd or XKCD, not Xkcd. (Source: http://xkcd.com/about)