slashdot.org: Lower Limit Found For Sudoku Puzzle Clues

An Irish mathematician has used a complex algorithm and millions of hours of supercomputing time to solve an important open problem in the mathematics of Sudoku, the game popularized in Japan that involves filling in a 9X9 grid of squares with the numbers 1–9 according to certain rules.

Gary McGuire of University College Dublin shows in a proof posted online on 1 January1 that the minimum number of clues — or starting digits — needed to complete a puzzle is 17; puzzles with 16 or fewer clues do not have a unique solution. Most newspaper puzzles have around 25 clues, with the difficulty of the puzzle decreasing as more clues are given.

“The approach is reasonable and it’s plausible. I’d say the attitude is one of cautious optimism,” says Jason Rosenhouse, a mathematician at James Madison University in Harrisonburg, Virginia, and the co-author of a newly released book on the maths of Sudoku.

Having spent two years testing the algorithm, McGuire and his team used about 700 million CPU hours at the Irish Centre for High-End Computing in Dublin, searching through possible grids with the hitting-set algorithm. “The only realistic way to do it was the brute force approach,” says Gordon Royle, a mathematician at the University of Western Australian in Perth who had been working on the problem of counting 17 clue puzzles using different algorithms.

Papier en format PDF

awesomelinux.blogspot.com: KMix Lockups, Freezes, and Performance

Regardless, I eventually figured a solution to the problem: Quit kmix. You may need to actually kill the program. Next move/delete/rename the folder ‘kmix’ in the folder ‘~/.kde/share/apps/. Restart kmix, and it will recreate a default ‘~/.kde/share/apps/kmix/’ folder with default settings.

Via: slashdot.org: Researchers Expanding Diff, Grep Unix Tools

The new programs, called Context-Free Grep and Hierarchical Diff, will provide the ability to parse blocks of data rather than single lines. For each new type of data structure, a vendor would provide a pattern library identifying the basic structure of the data, which the software would then use to “extract the constructs of interest from the document,” Weaver said.

I find that when someone’s taking time to do something right in the present, they’re a perfectionist with no ability to prioritize, whereas when someone took time to do something right in the past, they’re a master artisan of great foresight.

Good Math, Bad Math: Things Everyone Should Do: Code Review
Good Math, Bad Math: Stuff Everyone Should Do (part 2): Coding Standards

Via: Cristian’s Chromatic: C++ territory chart

J’etais passe par leur service d’echange la derniere fois, mais cette fois-ci, je change de modele et/ou compagnie.

Est-ce que vous avez des suggestions de disques durs que vous jugez ou savez plus fiables? J’hesite vraiment a retourner avec Western Digital, meme pour des modeles plus haut de gamme. Ca sera peut-etre du Seagate a moins que quelqu’un me raconte une histoire d’horreur a leur sujet.

P.S. Heureusement que j’avais rendu plus robuste ma routine de backups!!!! Si tout va bien, je ne perdrai rien.

Via: Search Google with Images, Not Words

P.S. Je devrais ajouter que parfois, il est completement dans le champ

J’ai fini par trouver la reponse dans un forum sur le net.
Thread: internet connection slow in certain applications

En gros, c’est IPV6 qui causait le probleme dans KDE et/ou OpenSuse et/ou Firefox. Je l’ai desactive dans Firefox et Yast (configuration systeme). Il ne faut pas oublier de mettre a jour /etc/hosts pour enlever les references a IPV6. Apres, tout est beaucoup plus rapide.

It gets worse. Throw in a nine-character, mixed-case random password, and while a CPU would take a mind-numbing 43 years to crack this, the GPU would be done in 48 days.

Caltech researchers Lulu Qian and Erik Winfree have managed to coax 130 strands of DNA into performing what is unquestionably a calculation: taking the square root of a number. (Ars Technica post; Science paper behind paywall; open-access background paper.) Not a big number: we’re talking about four-digit binary numbers, so 15 at the biggest. And not very efficiently: with prodding, the calculation took eight hours. Moore’s Law isn’t really in danger here.

“Vladimir Romanov has released what he claims is a polynomial-time algorithm for solving 3-SAT. Because 3-SAT is NP-complete, this would imply that P==NP. While there’s still good reason to be skeptical that this is, in fact, true, he’s made source code available and appears decidedly more serious than most of the people attempting to prove that P==NP or P!=NP. Even though this is probably wrong, just based on the sheer number of prior failures, it seems more likely to lead to new discoveries than most.

Beaucoup de commentaires sur slashdot semblent indiquer que le probleme a ete simplifie et que meme si le code fonctionnait en P, ceci n’impliquerait pas que P==NP.

“Security researchers have discovered several security flaws in one of the best-selling brands of Internet-connected HDTVs, and believe it’s likely that similar security flaws exist in other Internet TVs. The security researchers were able to demonstrate how an attacker could intercept transmissions from the television to the network using common ‘rogue DNS,’ ‘rogue DHCP server,’ or TCP session hijacking techniques. Mocana was able to demonstrate that JavaScript could then be injected into the normal datastream, allowing attackers to obtain total control over the device’s Internet functionality.”

Un commentaire sur slashdot pointait sur xkcd.com:

Hehe.

Via: slashdot.org: Social Security Information Systems Near Collapse

J’aurais pu ecrire qu’on etait aussi jambon que les autres, mais il me semble que notre perception est qu’au Quebec et/ou Canada, les couts de developpements informatiques sont astronomiques, pour ne pas dire ridicules/insenses/criminels/demoralisants/etc.

Mais on peut se consoler en regardant ailleurs, a defaut de se prendre en main et de regler les problemes! Bonne nouvelle, non?

One of the biggest problems is the agency’s transition to a new data center, according to the report. The IG has characterized the replacement of the SSA’s National Computer Center (NCC) — built in 1979 — as the SSA’s “primary IT investment” in the next few years.

The agency has received more than $500 million so far to replace the outdated center, which is now so severely strained by an expanded workload over its time of operation that it may not be able to function by 2012, according to the report.

Mais bon, avec notre registre des armes a feu de 2G$, et le fait qu’on est 10 fois moins, ils ont encore des croutes a manger ces americains pour nous battre!

P.S. Mon estimation est que mon ordi a la maison pourrait gerer le registre des armes a feu sans probleme, mais aller dire ca aux compagnies qui ont empoche les 2G$….

Five years have passed. Using the telemetry data, the two scientists created an extremely elaborate “finite element” 3-D computer model of each Pioneer spacecraft, in which the thermal properties of 100,000 positions on their surfaces are independently tracked for the duration of the 30-year mission.

But according to Toth, “You can take it to the bank that whatever remains of the anomaly after accounting for that thermal acceleration, it will at most be much less than the canonical value of 8.74 x 10-10 m/s2, and then, mind you, all those wonderful numerical coincidences people talk about are destroyed.”

Via: slashdot.org: Sorting Algorithms — Boring Until You Add Sound

Well take a look at the millions in fake, and thus illegal, bids demonstrated below and tell us just how any of this manipulation is “providing liquidity” – the second the patterns break, the algos responsible for the churn pattern disappear, thus eliminating numerous levels of so called bid liquidity below the NBBO: break enough patterns and you have another flash crash as the market once again goes bidless.

Allez voir les algos a l’action. Pas mal les petits graphes. En voici un exemple:

07-29-10
BATS “Flag Repeater”. 15,000 quotes in 11 seconds, dropping the ASK price 1 penny each quote from $9.36 to $8.58 and back up again.

On est quand meme un peu loin du principe d’acheter des parts d’une compagnie pour en devenir actionnaire

Via: slashdot.org: The Mystery of the Mega-selling Floppy Disk

Sony has said it will stop making floppy disks, after nearly three decades of manufacture. Yet millions of them are still being bought every year. But who is actually buying them?

The vast desks that control the light shows and sounds settings in theatres or music venues have until recently come with floppy drives as standard; the English National Opera is just one example of an organisation that uses them.

A volunteer at the National Museum of Computing says that many scientific instruments – so-called dataloggers, oscilloscopes and the like – record their data onto floppies.

But these relatively niche uses couldn’t possibly account for the number of floppies – something like a million a month – that are being consumed in the UK alone.

The answer may simply be that there are a great many old computers that read only floppies, and a great many computer users that have no need for the storage media that have supplanted them in other quarters.

In Befunge, there’s a read-head that moves over the program. Each step, it executes the instruction under the head. But instead of just moving left or right, it can move left, right, up, or down. “>” is an instruction that tells the head to start moving to the right; “<" tells the head to start moving left; "^" means start moving up, and "v" means to start moving down. So, for example:

>v
^<

Is a program that runs an infinite loop: the head will just cycle over those four characters. An even more interesting infinite loop (taken from the befunge documentation) is:

C’est rien, compare a l’autre exemple de code que vous retrouverai sur le site via le lien plus haut. Outch!

Nature by Numbers from Cristóbal Vila on Vimeo.

J’ai eu une tres mauvaise experience lundi avec ma machine qui fait les backups. Le power supply est mort, et ca sent un peu le chauffe. Bon, j’ai un autre power supply qui traine, je fais l’echange et je demarre la machine. C’est la que je vois une petit fumee s’elever au dessus des disques durs. Outch! Effetivement, le board est fini avec un chip qui a fondu! (Comment est-ce possible avec d’aussi faibles voltages???) Est-ce que c’est le nouveau power supply qui a fait ca, ou est-ce l’ancien? Je n’en sais rien, mais bon je ne prends pas de chance et decide qu’il est temps (bien que premature d’un an a peu pres) de changer de machine.

J’espere que le second disque dur est correct car sur la machine en question, il y a le compte de ma douce moitie et de fiston en plus du disque dur de backups. Je me demande lequel est inutilisable. Si au moins un des deux a survecu, alors toutes les donnees sont disponibles…. Et bien NON! Les boards des DEUX disques durs ont boucane. Wow, quelle succession d’emmerdements!

Tout ca pour dire que j’ai perdu les donnees des comptes et les backups incrementaux (sans compter deux disques durs de 500G). Ca va mal. Heureusement, j’ai fait un backup de niveau zero au debut de janvier, alors on a perdu essentiellement les emails des deux derniers mois de ma douce moitie. Elle n’est pas heureuse de ca, mais elle ne se rend pas compte a quel point elle aurait pu tout perdre si ce n’etait de ma procedure un peu delirante de backups. Le delai de deux mois aurait ete plus grave si c’etait mon compte qui y avait passe

Dans les faits, je suis content de mon systeme de backup. Pour bien des gens, ca aurait ete la perte de toutes leurs photos/travaux/souvenirs/videos/etc parce que peu de personnes font des copies de surete. De mon cote, j’ai:
1) Un backup fait sur une machine a tous les 30 minutes (incremental)
2) Un backup du site web a tous les 6 heures (incremental)
3) Un backup de niveau zero une fois au trois ou quatre mois environ avec une copie sur un disque externe que je garde a portee de main et une autre copie a l’exterieur de la maison.

La seule chose que je changerai dans ma procedure est de faire une copie plus frequemment des backups incrementaux sur un disque externe. Ceci m’aurait permis de perdre moins de donnees.

J’utilise des disques durs pour les backups parce que je me suis toujours dit qu’il serait possible d’utiliser un programme comme SpinRite par exemple pour recuperer des donnees meme si le media commencait a se deteriorer. Comparez ca a un DVD-R qui n’est plus lisible…. on est foutu. Mon experience me montre que meme un disque dur peut etre completement inutilisable sans que la maison passe au feu ou qu’on se fasse voler l’ordinateur. Ceci etant dit, je continue de penser que d’utiliser des disques dur est la solution optimale, A CONDITION d’avoir des backups de backups de backups.

Pour les curieux, ma nouvelle machine devrait me permettre de jouer aux derniers jeux sans probleme

Via: digg.com: 25 Hilarious WiFi Network Names (PICS)

Steve: The one thing I would reiterate saying, and I imagine people have probably already done this if they’re going to, but I have to say it again, is disable JavaScript in Acrobat, that is, in the Acrobat Reader. There just is no need for scripting. I mean, we understand there’s a need for scripting on web pages because it’s being actively used by more and more websites, with it being a mixed blessing. But there’s just no need for scripting in a PDF document.

En passant, je viens justement d’installer une nouvelle version d’acrobat… et il a remis a “on” le javascript.

Aussi interessant dans cet episode (evidemment aussi disponible en audio):

Steve: And the Verbatim Corporate Secure FIPS Edition. Now, FIPS is the National Institute of Standards and Technology, NIST. That’s its federal security rating system. These devices have all received the FIPS 140-2 Level 2 certificate which validates devices as being secure for use with sensitive government data. And…

Leo: That’s pretty good. I’d take…

Steve: …they are completely hackable.

Leo: Oops.

Steve: They’ve got hardware AES-256 encryption in the key. So they’re not inexpensive. But get a load of this, Leo. You use some software that comes with a key, which of course prompts you for your password. You put your password in. And it does some mumbo jumbo with your password, whatever it is it does. But every single one of them, no matter what your password was, sends the same key string into the AES-256 cipher engine.

Leo: You’d think something at FIPS, at NIST, might have noticed.

Steve: Uh, yes. In fact, embarrassed by this, NIST has said that they will be considering whether they should make changes to their validation process because the USB drives in question met all their criteria.

Leo: Oh, boy.

Steve: So once again, so it’s true that if, as a user, you did not put the right passphrase in, the software would say, oh, sorry, that’s the wrong passphrase. But a security company reverse-engineered the software, wondering what was going on inside. And what they discovered was that there was a fixed key.

Steve: Well, yeah. And what boggles my mind is, again, our listeners understand this. You take and hash the passphrase with a secure hash, and that’s what you use as the key. This is not hard. I mean, that’s all there is to it. In which case the key would be derived from the passphrase through a secure hash and, bang, you’ve got it. I mean, sure, you want to put minimum security requirements on the length of the passphrase and all those things, and it wants to be nonguessable because it would be prone to a brute-force attack, blah blah blah, all the things we know about. But the idea that the passphrase isn’t being used to generate the key, but that the key is fixed, that’s just, I mean, actually it’s a really good lesson because it demonstrates that just saying AES-256 means nothing.

Installation.
Very difficult. The install for Windows 7 comes on four floppy disks, and as my laptop doesn’t have a floppy drive, I was worried I’d have to travel 10 years into the past to find a computer that did.

Hehe, pas mal comme review

For my recently departed brother (long illness, don’t smoke!), I thought this nice SPARCstation would be a cool place to spend eternity. Yes, he’s really in there (after cremation). I kept the floppy drive cover but for space reasons removed the floppy drive, hard drive, and most of the power supply. I left behind the motherboard and power switch and plugs to keep all openings covered. The case worked quite well at his memorial party. His friends and family were able to leave their final good-byes on post-notes.

The FBI report estimates that the Chinese Army has developed a network of over 30,000 Chinese military cyberspies, plus 150,000 private-sector computer experts, whose mission is to steal American military and technological secrets.

Quand meme, 180000 personnes a temps plein pour hacker? Qui a besoin d’un bot net…. C’est surement un peu plus que les ressourses du Canada

Via: dvorak.org

A one instruction set computer (OISC), sometimes called an ultimate reduced instruction set computer (URISC), is an abstract machine that uses only one instruction – obviating the need for a machine language opcode.