Hacker News: brent

New comment by brent in "Mathematics for Computer Science"

brent — Tue, 13 Mar 2012 01:02:41 +0000

Look at the version in the comment posted by joshma: http://courses.csail.mit.edu/6.042/spring12/mcsfull.pdf

You must not have been the only person to notice this. The definition is on pg 6 in the pdf above.

New comment by brent in "P vs NP on simple english wikipedia - feedback, please"

brent — Thu, 15 Sep 2011 12:35:32 +0000

I think your subset sum problem (the rock piles) is decent. However, for it to be useful I think you have to make it clear which class it is in (NP) and why (it is easy to check a solution and 2^n is not polynomial in n).

New comment by brent in "Surprises from numerical linear algebra (2010)"

brent — Tue, 13 Sep 2011 17:02:08 +0000

Numerical Linear Algebra by Trefethen and Bao is well regarded.

New comment by brent in "Facebook Graph Theory"

brent — Tue, 06 Sep 2011 13:52:24 +0000

This blog post seems to be copied from http://20bits.com/articles/graph-theory-part-iii-facebook/ without any attribution.

It was also posted on yc only two weeks ago (see http://news.ycombinator.com/item?id=2912073 for commentary).

New comment by brent in "Graph Theory: Part III (Facebook)"

brent — Mon, 22 Aug 2011 19:03:39 +0000

I don't understand the interpretation of the principal eigenvalue either. Perhaps there is a more suitable interpretation in the directed case, but I'm not sure of that either.

I think this method is generally known as eigenvector centrality, that is to say, the entries in the vector x are generally known as eigenvector centralities. I think this method is quite popular, but I do not know who uses it or how often.

New comment by brent in "Graph Theory: Part III (Facebook)"

brent — Mon, 22 Aug 2011 16:03:34 +0000

Under mild conditions of the undirected graph (basically that it is not bipartite and that it is connected) one can use the Perron-Frobenius theorem. So, to remove the ambiguity you are concerned with consider that you want an x s.t. all the entries in x are positive. Then PF guarantees that the largest eigenvalue of A has multiplicity one and its associated eigenspace is one-dimensional. PF also guarantees that the eigenvector associated with the largest eigenvalue has positive entries and is the only eigenvector with positive entries. So, you want the largest eigenvalue (which is positive) and the unique positive valued eigenvector associated with it. Finally, to obtain this eigenvector/value pair one can use the power method which this author recommends.

New comment by brent in "General factor of intelligence g, a Statistical Myth"

brent — Sat, 12 Feb 2011 17:28:00 +0000

Pardon my naivety, but what do you mean by "thatched airplanes"?

New comment by brent in "Most published research results are false"

brent — Sat, 12 Feb 2011 01:08:59 +0000

This is why different communities accept p-values at certain levels (typically <0.05). You have to live with some amount of uncertainty when the data generating mechanism is random... that is unfortunately the nature of the beast.

New comment by brent in "Major (unfixable) flaw found in P!=NP paper."

brent — Tue, 10 Aug 2010 20:27:30 +0000

The claim is that the proof is unfixable. Proofs are either right or wrong. Good academics are supposed to checks proofs of their colleagues. There is no claim as to the merit of contributions made by Deolalikar. So, why exactly do these academics infuriate you?

New comment by brent in ""God's Number" is 20 - Rubik's cube has been "solved""

brent — Mon, 09 Aug 2010 21:05:33 +0000

If you find Sudoku boring you just need to add more constraints. For example, try solving one by considering some ordering on the entries (say, Left-to-Right then Top-to-Bottom) and only allow yourself to fill in entries in that order... then time yourself!

New comment by brent in "Rate my startup: Gantto, easy to present Gantt charts on the web"

brent — Fri, 06 Aug 2010 03:53:36 +0000

Wait... hasn't this idea come and gone about 10 times in the last 10 years. I remember when I begged 37 signals to add this as a small feature about 4 years ago and they laughed it off. Also, some of the text in the biographies seem a bit exaggerated.

New comment by brent in "GazeHawk (YC S10) Does Eyetracking With Web Cams"

brent — Fri, 30 Jul 2010 00:42:43 +0000

Sounds like an amazing idea... strikingly similar to the idea I pitched to YC in an interview in November, 2006 :-/. I guess they didn't like our team or progress. Bummer.

New comment by brent in "Our Reddit Ad By The Numbers - Whiteyboard "

brent — Tue, 20 Jul 2010 13:39:29 +0000

I can't believe no one has mentioned this, but it seems to me the most important thing is how well you can erase the marker. Assuming it works well you should demonstrate this. I simply will not buy a whiteboard without knowing how well it will work over time. Also, I've used Georgia Pacific Mark-R-Board which costs about 1/3 of your product and it works just fine. That made me chuckle when I read the cost comparison in your FAQ.

New comment by brent in "Why I don't Trust Julian Assange"

brent — Tue, 13 Jul 2010 23:27:14 +0000

I can't claim to know who Clay Johnson is, but I am really interested in his low contribution to Wikipedia article length ratio.

New comment by brent in "Ask HN: What does $2000 in Web design/development buy you these days?"

brent — Fri, 02 Jul 2010 00:07:54 +0000

I think it would be interesting to compare 2 hours of output from this guy vs. 100 hours of output at prices mentioned in various posts.

New comment by brent in "A Non-Mathematical Introduction to Using Neural Networks"

brent — Wed, 09 Jun 2010 23:53:45 +0000

I'm not sure you've actually addressed his concern. I think the ability to use one (in an engineering sense) and get seemingly good results is separate from the issue of fully utilizing them. You are likely better off using a much more hands off tool that requires little knowledge of the underlying mechanism (to his point, d trees and svm).

New comment by brent in "Go To University, Not For CS"

brent — Mon, 31 May 2010 00:13:46 +0000

I cannot let comments like this stand. I have seen little difference between students from the top few schools and the rest. If you are only doing an undergrad I see little reason to hold these top 4 on such a pedestal. Any school in the top 20 or even probably 40 are more than a java school at the undergraduate level. The differences are marginal. However, if you plan to go to graduate school I would certainly try to attend one of the top 4 schools.

New comment by brent in "PhD Student gets quadrotor helicopter moving aggressively"

brent — Fri, 28 May 2010 19:54:56 +0000

Who do you think probably funded this? His advisor is funded by (at least) ONR, ARL, and DARPA.

New comment by brent in "Anand retains world chess championship title"

brent — Tue, 11 May 2010 23:44:55 +0000

My guess is he meant go and not go, the programming language, or go moku.

New comment by brent in "Academia is not Broken. We are."

brent — Wed, 05 May 2010 16:31:53 +0000

What? There exists a "top 5" for any ranked list with 5 or more entries.

Anyways... I am sure he was referring to those 4 + either UIUC or Cornell.