Thursday, 06 August 2009
00:00
Analytical Study of Adversarial Strategies in Cluster-based Overlays. (arXiv:0908.0398v1 [cs.GT]) [cs.GT updates on arXiv.org]
Scheideler has shown that peer-to-peer overlays networks can only survive Byzantine attacks if malicious nodes are not able to predict what is going to be the topology of the network for a given sequence of join and leave operations. In this paper we investigate adversarial strategies by following specific games. Our analysis demonstrates first that an adversary can very quickly subvert DHT-based overlays by simply never triggering leave operations. We then show that when all nodes (honest and malicious ones) are imposed on a limited lifetime, the system eventually reaches a stationary regime where the ratio of polluted clusters is bounded, independently from the initial amount of corruption in the system.
A Formalization of the Semantics of Functional-Logic Programming in Isabelle. (arXiv:0908.0494v1 [cs.LO]) [cs.LO updates on arXiv.org]
Modern functional-logic programming languages like Toy or Curry feature non-strict non-deterministic functions that behave under call-time choice semantics. A standard formulation for this semantics is the CRWL logic, that specifies a proof calculus for computing the set of possible results for each expression. In this paper we present a formalization of that calculus in the Isabelle/HOL proof assistant. We have proved some basic properties of CRWL: closedness under c-substitutions, polarity and compositionality. We also discuss some insights that have been gained, such as the fact that left linearity of program rules is not needed for any of these results to hold.
Lindstrom theorems for fragments of first-order logic. (arXiv:0905.3668v2 [cs.LO] UPDATED) [cs.LO updates on arXiv.org]
Lindstr\"om theorems characterize logics in terms of model-theoretic conditions such as Compactness and the L\"owenheim-Skolem property. Most existing characterizations of this kind concern extensions of first-order logic. But on the other hand, many logics relevant to computer science are fragments or extensions of fragments of first-order logic, e.g., k-variable logics and various modal logics. Finding Lindstr\"om theorems for these languages can be challenging, as most known techniques rely on coding arguments that seem to require the full expressive power of first-order logic. In this paper, we provide Lindstr\"om theorems for several fragments of first-order logic, including the k-variable fragments for k>2, Tarski's relation algebra, graded modal logic, and the binary guarded fragment. We use two different proof techniques. One is a modification of the original Lindstr\"om proof. The other involves the modal concepts of bisimulation, tree unraveling, and finite depth. Our results also imply semantic preservation theorems.
Classical and Effective Descriptive Complexities of omega-Powers. (arXiv:0708.4176v2 [math.LO] UPDATED) [cs.LO updates on arXiv.org]
We prove that, for each non null countable ordinal alpha, there exist some Sigma^0_alpha-complete omega-powers, and some Pi^0_alpha-complete omega-powers, extending previous works on the topological complexity of omega-powers. We prove effective versions of these results. In particular, for each non null recursive ordinal alpha, there exists a recursive finitary language A such that A^omega is Sigma^0_alpha-complete (respectively, Pi^0_alpha-complete). To do this, we prove effective versions of a result by Kuratowski, describing a Borel set as the range of a closed subset of the Baire space by a continuous bijection. This leads us to prove closure properties for the classes Effective-Pi^0_alpha and Effective-Sigma^0_alpha of the hyperarithmetical hierarchy in arbitrary recursively presented Polish spaces. We apply our existence results to get better computations of the topological complexity of some sets of dictionaries considered by the second author in [Omega-Powers and Descriptive Set Theory, Journal of Symbolic Logic, Volume 70 (4), 2005, p. 1210-1232].
Structure Theorem and Strict Alternation Hierarchy for FO^2 on Words. (arXiv:0907.0616v2 [cs.LO] UPDATED) [cs.LO updates on arXiv.org]
It is well-known that every first-order property on words is expressible using at most three variables. The subclass of properties expressible with only two variables is also quite interesting and well-studied. We prove precise structure theorems that characterize the exact expressive power of first-order logic with two variables on words. Our results apply to both the case with and without a successor relation. For both languages, our structure theorems show exactly what is expressible using a given quantifier depth, n, and using m blocks of alternating quantifiers, for any m \leq n. Using these characterizations, we prove, among other results, that there is a strict hierarchy of alternating quantifiers for both languages. The question whether there was such a hierarchy had been completely open. As another consequence of our structural results, we show that satisfiability for first-order logic with two variables without successor, which is NEXP-complete in general, becomes NP-complete once we only consider alphabets of a bounded size.
Dualities and dual pairs in Heyting algebras. (arXiv:0908.0428v1 [math.CO]) [math.CT updates on arXiv.org]
We extract the abstract core of finite homomorphism dualities using the techniques of Heyting algebras and (combinatorial) categories.
Mathematical definition of general systems based on semiotics and set theory (part of statics). (arXiv:0908.0388v1 [math.LO]) [math.LO updates on arXiv.org]
According to the relation between objects and time, our category of general systems theory was divided into three parts: statics, kinematics, and dynamics. In this part, beginning with clarifying fundamental in epistemology and semiotics, we gave the connections of measurements, partitions and functions. And conforming to customs, we defined the terms of quantity and value by our understanding of functions. Then the concept of relation quantity was coined to describe the relationship like distance and force. Farther more, we discussed correspondences established between two quantities, and the definitions and theorems of complete set based on it. Finally, we present the structure which can afford the obligation of general system, and also the definitions of subsystem and isomorphism.
Some Ramsey theorems for finite $n$-colorable and $n$-chromatic graphs. (arXiv:0908.0475v1 [math.CO]) [math.LO updates on arXiv.org]
Given a fixed integer $n$, we prove Ramsey-type theorems for the classes of all finite ordered $n$-colorable graphs, finite $n$-colorable graphs, finite ordered $n$-chromatic graphs, and finite $n$-chromatic graphs.
Objects as Modules in Newspeak [Lambda the Ultimate - Programming Languages Weblog]
In Objects as Modules in Newspeak, Gilad Bracha et al. describe a way to avoid the coupling in inherent constructs found in many OO languages such as a global namespace, "static" stateful variables, globally accessible object constructors, etc.
We describe support for modularity in Newspeak, a new programming language descended from Smalltalk and Self. Like Self, all computation — even an object’s own access to its internal structure — is performed by invoking methods on objects. However, like Smalltalk, Newspeak is class-based. Classes can be nested arbitrarily, as in Beta. Since all names denote method invocations, all classes are virtual; in particular, superclasses are virtual, so all classes act as mixins. Unlike its predecessors, there is no static state in Newspeak, nor is there a global namespace. Top level classes act as module definitions, which are independent, immutable, self-contained parametric namespaces. They can be instantiated into modules which may be stateful and mutually recursive. Naturally, like its predecessors, Newspeak is reflective: a mirror library allows structured access to the program meta-level.
There's a lot in here that should be of interest to LtUers interested in object capability based security.
Verified Programming in Guru [Lambda the Ultimate - Programming Languages Weblog]
Verified Programming in Guru is a tutorial introduction to Guru:
GURU is a pure functional programming language, which is similar in some ways to Caml and Haskell. But GURU also contains a language for writing formal proofs demonstrating the properties of programs. So there are really two languages: the language of programs, and the language of proofs.
In comparison to Coq:
GURU is inspired largely by the COQ theorem prover, used for formalized mathematics and theoretical computer science, as well as program verification. Like COQ, GURU has syntax for both proofs and programs, and supports dependent types. GURU does not have as complex forms of polymorphism and dependent types as COQ does. But GURU supports some features that are difficult or impossible for COQ to support, which are useful for practical program verification. In COQ, the compiler must be able to confirm that all programs are uniformly terminating: they must terminate on all possible inputs. We know from basic recursion theory or theoretical computer science that this means there are some programs which really do terminate on all inputs that the compiler will not be able to confirm do so. Furthermore, some programs, like web servers or operating systems, are not intended to terminate. So that is a significant limitation. Other features GURU has that COQ lacks include support for functional modeling of non-functional constructs like destructive updates of data structures and arrays; and better support for proving properties of dependently typed functions.
The tutorial is worth a read to anybody new to this style of programming as it is one of the most gentle introductions to dependent types and automated program verification that I've seen.
Fiat Mio : la première voiture copyleftée [DLFP - Dépêches]
La division brésilienne de la célèbre marque italienne vient de lancer un nouveau projet pour le moins inédit : une automobile sous licence libre Creative-Commons cc-by-sa. Qualifiée par certains de "première voiture Open-Source", sa conception semble en effet s'inspirer du modèle des logiciels libres.
Les contributions sont les bienvenues, de la part des professionnels comme des designers en herbe qui voudraient prendre part au développement du projet en proposant leurs idées originales. Comme pour tout projet libre, l'un des intérêts est que la connaissance générée pourra librement être réutilisée par les autres ingénieurs et fabricants.
Le slogan de Fiat est "um carro para chamar de seu" ("une voiture dont vous pouvez dire qu'elle est la vôtre"). Le site http://www.fiatmio.cc a été ouvert pour permettre à ses visiteurs (pour peu qu'ils comprennent le portugais) de soumettre et discuter de leurs idées, ainsi que de voter pour celles des autres contributeurs.
lien 1 : Fiat Mio
lien 2 : CC Atribución-Licenciar Igual 2.5 (licence du projet)
Sortie de BilboPlanet en version stable [DLFP - Dépêches]
Et oui, depuis le temps que l’on en parle ! Nous sommes très fiers de vous annoncer la sortie officielle de la première version stable et largement utilisable du BilboPlanet ! Pour rappel, le BilboPlanet est le moteur de Planet-Libre.org. Il s’agit donc d’un agrégateur web de flux RSS écrit en PHP/MySQL et Open Source, sous licence AGPL v3.
Nous avons donc :
- Un installeur graphique qui va vous suivre au fur et à mesure de l’installation
- Une interface d’administration simplifiée
- La possibilité de faire vous-même votre propre thème graphique
- La version stable s’appelle "Aragorn" et est téléchargeable sur le wiki du Bilboplanet : http://redmine.bilboplanet.org/wiki/bilboplanet/Download (ou sur http://www.bilboplanet.org/downloads )
Nous avons donc mis en place un trackeur de bogues sous redmine : http://redmine.bilboplanet.org
Un nouveau blog sous WordPress qui nous permettra de faire les annonces officielles : http://blog.bilboplanet.org.
Concernant le SVN, vous pouvez y accéder : http://bilboplanet.org/svn/bilboplanet.
Et bien-sûr, la mise en place d’un wiki étant maintenant obligatoire, la documentation et le support devraient être mis en ligne rapidement : http://redmine.bilboplanet.org/wiki/bilboplanet. Vous pouvez voir la version démo sur http://staging.bilboplanet.org.
lien 1 : BilboPlanet
Message d'erreur: Les Experts [The Daily WTF: Edition Française]
Hier soir j'ai regardé l'épisode des experts miami "Au rythme des balles". J'ai tout particulièrement apprécié le passage ou les "experts" utilisent un programme permettant d'obtenir une adresse ip à partir d'une simple adresse email.
Rien a dire, le proxy du suspect était vraiment vraiment puissant...
Programming Praxis: Nerds, Jocks, and Lockers [The Daily WTF]
Mr. Zargas was the zany math teacher at Cliffmont High that everyone seemed to love. Whether you were a nerd or a jock, he made mathematics interesting, challenging, and fun to learn. That, in and of itself, was impressive enough, but Mr. Zargus took it one step further. When it came time for his frequent "Mathematical Battle of Wits," he would let the jocks use their brawn instead of their brains. The nerds never stood a chance, especially when it came to his "locker challenge."
The rules of Mr. Zargas' locker challenge were simple. Corridor G was a long-since abandoned section of Cliffmont High that a row of 100 unused, empty lockers. If you "toggled" the state of each locker (i.e. opening it if its closed, closing it if its open) in the following manner, which lockers would remain open?
- Every single locker is toggled (since all lockers start closed, this means each one is opened).
- Every other locker is toggled (in this case, closed), starting with the second.
- Every third locker is toggled, starting with the third.
- Every fourth locker is toggled, starting with the forth.
- ...
- The hundredth locker is toggled.
The jocks had it easy; they could simply run up and down the hallway, opening and closing the lockers until they answered the question. But the nerds had a real challenge: they had to answer the question without counting or using any other "brute force" method. They could only use deductive logic and formulas to solve the problem.
Year after year — no matter how hard the nerds tried — the jocks would always win. They simply ran, opened, and closed faster than the nerds could think. And seeing that the locker challenge always played out during football season, losing was a particularly embarrassing defeat since the jocks got to pummel the nerds on the field later that day in gym class.
Can You Beat the Jocks?
The rules to your challenge are just as simple. Develop a function that determines which lockers would remain open after toggling n lockers in the manner described above. There should be one input to the function (number of lockers) and one output (representation of which lockers remain open; string, array, etc).
getOpenLockers( 1 ) --> { 1 }
getOpenLockers( 4 ) --> { 1, 4 }
And remember, like the nerds, no brute force methods allowed. And if you really want to impress, identify which lockers would be toggled the most.
To Get Started...
Following is a simulation built using the jocks' brute-force method. It also serves as a timer to see if you can beat the jocks.
| Locker count: | |
| Milliseconds per toggle: | |
Now don't watch the simulation for too long, lest one of the jocks might catch you sneaking a peak and stuff you in a locker.
Got a tip for a future Programming Praxis? Please send it on in!
Here is Innere Höllenthalspitze just before I climbed it, on the Jubiläumsgrat that I did last Sunday. It was a very interesting climb in many aspects, but I'll speak more about it on a later time...
Hiroshima, 64 years ago [The Big Picture]
08/3/09 PHD comic: 'Really?' [PHD Comics]
| Piled Higher & Deeper by Jorge Cham |
www.phdcomics.com
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 |
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title:
"Really?" - originally published
8/3/2009
For the latest news in PHD Comics, CLICK HERE! |
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Wednesday, 05 August 2009
00:00
Algorithmic Decision Optimization Techniques for Multiple Types of Agents with Contrasting Interests. (arXiv:0908.0060v1 [cs.GT]) [cs.GT updates on arXiv.org]
In this paper I present several algorithmic techniques for improving the decision process of multiple types of agents behaving in environments where their interests are in conflict. The interactions between the agents are modelled by using several types of two-player games, where the agents have identical roles and compete for the same resources, or where they have different roles, like in query-response games. The described situations have applications in modelling behavior in many types of environments, like distributed systems, learning environments, resource negotiation environments, and many others. The mentioned models are applicable in a wide range of domains, like computer science or the industrial (e.g. metallurgical), economic or financial sector.
Randomized Online Algorithms for the Buyback Problem. (arXiv:0908.0043v1 [cs.GT]) [cs.GT updates on arXiv.org]
In the matroid buyback problem, an algorithm observes a sequence of bids and must decide whether to accept each bid at the moment it arrives, subject to a matroid constraint on the set of accepted bids. Decisions to reject bids are irrevocable, whereas decisions to accept bids may be canceled at a cost which is a fixed fraction of the bid value. We present a new randomized algorithm for this problem, and we prove matching upper and lower bounds to establish that the competitive ratio of this algorithm, against an oblivious adversary, is the best possible. We also observe that when the adversary is adaptive, no randomized algorithm can improve the competitive ratio of the optimal deterministic algorithm. Thus, our work completely resolves the question of what competitive ratios can be achieved by randomized algorithms for the matroid buyback problem.
A historical perspective on developing foundations for privacy-friendly client cloud computing: The Paradigm Shift from "Inconsistency Denial" to "Semantic Integration". (arXiv:0901.4934v6 [cs.DC] UPDATED) [cs.LO updates on arXiv.org]
Arguably, the original paradigm for computation was Logic Programming broadly conceived as "deducing computational steps from existing information."
The idea has a long development that went through many twists in which important questions turned out to have surprising answers, including the following:
* How much of concurrent computation is reducible to deduction?
* Are the laws of thought consistent?
* Is "rapid recovery" a more viable policy than "inconsistency denial"?
* How can massive concurrency and strong paraconsistency provide practical semantic integration of diverse sources of information?
A historical perspective on the above questions is highly pertinent to the current quest to develop foundations for client cloud computing.
The homotopy theory of strong homotopy algebras and bialgebras. (arXiv:0908.0116v1 [math.CT]) [math.CT updates on arXiv.org]
Lada introduced strong homotopy algebras to describe the structures on a deformation retract of an algebra in topological spaces. However, there is no satisfactory general definition of a morphism of strong homotopy (s.h.) algebras. Given a monad T on a simplicial category C, we instead show how s.h. T-algebras over C naturally form a Segal space. Given a distributive monad-comonad pair (T, S), the same is true for s.h. (T, S)-bialgebras over C; in particular this yields the homotopy theory of s.h. sheaves of s.h. rings. There are similar statements for quasi-monads and quasi-comonads. We also show how the structures arising are related to derived connections on bundles.
SPM Bulletin 28. (arXiv:0908.0141v1 [math.GN]) [math.LO updates on arXiv.org]
Contents:
1. Editor's note; 2. gamma-sets from a weak hypothesis; 3. Research announcements; 3.1. Ultrafilters with property (s); 3.2. On a converse to Banach's Fixed Point Theorem; 3.3. Analytic groups and pushing small sets apart 3.4. Club-guessing, stationary reflection, and coloring theorems; 3.5. More on the pressing down game; 3.6. A note on discrete sets; 3.7. Antidiamond principles and topological applications; 3.8. Partitions and indivisibility properties of countable dimensional vector spaces; 3.9. Group-valued continuous functions with the topology of pointwise convergence; 3.10. Stationary and convergent strategies in Choquet games; 3.11. Linear sigma-additivity and some applications; 4. Unsolved problems from earlier issues.
Linear $\sigma$-additivity and some applications. (arXiv:0906.5136v2 [math.GN] UPDATED) [math.LO updates on arXiv.org]
We show that countable increasing unions preserve a large family of well-studied covering properties, which are not necessarily sigma-additive. Using this, together with infinite-combinatorial methods and simple forcing theoretic methods, we explain several phenomena, settle problems of Just, Miller, Scheepers and Szeptycki [COC2], Gruenhage and Szeptycki [FUfin], Tsaban and Zdomskyy [SFT], and Tsaban [o-bdd, OPiT], and construct topological groups with very strong combinatorial properties.
Equilibria und weiteres Heiteres. (arXiv:0907.4017v2 [math.LO] UPDATED) [math.LO updates on arXiv.org]
We investigate several technical and conceptual questions.
KDE 4.3 est sorti [DLFP - Dépêches]
L'environnement de bureau KDE est sorti aujourd'hui en version 4.3, appelée Caizen. Après une version 4.0 et 4.1 pour les développeurs et une version 4.2 largement utilisable, cette nouvelle version 4.3 continue la stabilisation sans changement profond, même si 2 000 nouvelles fonctionnalités ont été ajoutées.
Les principaux changements sont l'arrivée de nouvelles technologies telles que PolicyKit, de nouvelles améliorations de Plasma et bien sûr de nombreuses corrections de bogues (plus de 10 000).
lien 1 : KDE
lien 2 : L'annonce officielle
lien 3 : Télécharger KDE
lien 4 : KDE
(...)
Publication d'OpenGL 3.2 [DLFP - Dépêches]
Profitant de la tenue du SIGGRAPH 2009 à la Nouvelle Orléans, le Khronos Group a annoncé la publication de OpenGL 3.2. Il s'agit là d'une interface de programmation graphique multi plate-forme spécialisée dans le rendu 3D, concurrençant l'API Direct3D de Microsoft (dont la version 11 accompagnera la sortie de Windows 7).
Il s'agit de la dixième version publiée depuis la sortie de la version 1.0 en 1992 et de la troisième en seulement 1 an (la 3.0 étant parue le 02 août 2008 et la 3.1 le 24 mars 2009).
Cette parution confirme le bien-fondé du passage de l'OpenGL ARB originel, chapeauté par SGI, à celui du Khronos Group qui visait à en accélérer le développement, et ce malgré la (relative) longue attente de la version 3.0.
Le travail sur la norme OpenGL est conjoint à :
- OpenGL ES (API graphique destinée à l'embarqué),
- OpenCL (API dédiée à la parallélisation des calculs, notamment via les processeurs graphiques)
- et depuis peu à webGL (visant à permettre l'utilisation de la 3D directement au sein des navigateurs).
lien 1 : Annonce officielle
lien 2 : Spécifications
lien 3 : Fils de discussion opengl.org
lien 4 : Geometry shaders
lien 5 : webGL
lien 6 : Fence sync objects
(...)
David's phone was ringing as he walked in the door, and there were four voice mails on his phone already. Before sitting down, he scooped up the phone. "G'morning, this is David."
"Yeah, hi David, this is Jan. I'm sure you're already aware of the intranet issues?" He listened idly to her description of the issue while he opened Outlook, seeing several new emails popping into his inbox. The subject lines were troubling.
URGENT: HR/Financials Reporting System Severe Slowdowns NOREPLY TrackBugs #105482 is now a HIGH priority issue NOREPLY TrackBugs #105482 MEDIUM has been assigned to you; "Intranet general issues" she just cant get Enough ofmy MEET HYRDRANT --- 3nhanc3ment medz!! Are you guys doing maintenance? Fwd: Re: Intranet slowness?
"Uh, yeah, I'm aware, Janice. We're working on it. Could be a network issue," he said, massaging his temples.
Slowdown Showdown
Slowness and intermittent crashes generally indicate a web server buckling under the pressure of too much traffic, so before even logging into the server to check it out, David checked the log files; there were tens of thousands of lines, many clustered each second, trying to access a file called "update_clock.php".
update_clock.php? David opened the main template file and found a line he hadn't seen before:
<body onload="updateClock();">
The updateClock method, as David discovered, was defined in the main template. It was designed to retrieve data from update_clock.php via ajax:
<script type="text/javascript">
function updateClock()
{
var url = 'update_clock.php';
url = url + '?employee_id=' + <?=$employeeID;?>;
if (document.getElementById('clockDiv').innerHTML != 'Error')
{
document.getElementById('clockDiv').value = '';
ajaxFunction(url, 'clockDiv');
setInterval('updateClock()', 1000);
}
}
</script>
Comments left by someone with the initials "BM" peppered the code near these updates. "Barry?" David yelled over the cube wall.
"Yeah?"
"Do you know what 'update_clock.php' is?"
"Uh, yeah, that updates the clock on the home page, we just got that feature in."
Barry went on to explain how it worked, but it still seemed like the intranet shouldn't be as slow as it was; there had to be more to the story. "This was fully tested? And the change was approved by management?"
"Yeah, of course!"
Time is the Enemy
The reason that they were doing server-side date/time processing for the clock on the home page eluded David, but maybe he'd see a valid reason for it. Tracing the logic, he saw where the date was loaded and output into a text format that the front end would receive via the ajax call. That is, way at the bottom of the code file, after the complete employee record was loaded from the database, and other bits of data were loaded as well, each time with a new DB connection. Reason being, the employee data contained time zone information, and they'd wanted the clock on the page to reflect the correct time. There was a ton of logic before it did anything with the dates, and, in fact, even then, it was just writing out a date and time.
Taken alone, these operations took less than a second, which explained why no issues were discovered in the basic testing that was done. But with dozens of users with the page (or several pages) open in browser windows and tabs, each request to update_clock.php started taking longer and longer, generating an unreasonable amount of traffic and database calls. A single employee in an eight hour shift with the intranet page open all day would generate roughly 30,000 calls to update_clock.php.
Time is of the Essence
"Barry," yelled out over the cube wall again, "you need to get this fixed and deployed to production. Like now!"
Jumping up, Barry responded, "this is going to take time. I mean... I mean, I spent a while just getting it working. Now I need to optimize it?"
"I'm not a web developer," David asked, "but why didn't you use JavaScript's built-in Date object?"
Barry paused for a moment. "JavaScript has a built-in Date object!?"
David helped Barry out, and within minutes they'd refactored the code. And this time, management was even happier to do a quick signoff on the move to production.
ocaml 3.11.1 in testing [i'm in a hurry - stefano zacchiroli blog]
... and other Debian OCaml bits
As anticipated by
Aba, today the OCaml 3.11.1 transition to testing has
finished. Beside turning the latest stable OCaml version
into a release-ready product, this transition has also
switched the standard library path to
/usr/lib/ocaml (it used to be
/usr/lib/ocaml/X.Y.Z). The change is justified by the
observation that, in fact, we have never supported (and never will)
more than one OCaml ABI at the same time in a given Debian
release.
Some more OCaml bit(s):
-
during DebCamp, the OCaml team has worked on revising OCaml dependency schema, on the basis of a proposal I advanced a while ago. Once implemented, the proposal in essence will mean:
-
linkability ensured by regular Debian dependencies (no longer "inconsistent assumptions ..." errors, as long as your package manager is happy)
-
automatic computation of dependencies between OCaml-related packages (i.e.,
${ocaml:Depends}substvar)
Beside (maybe) some tiny teeny supervision bits, all the kudos for that goes to Sylvain Le Gall, Mehdi Dogguy, and Stephane Glondu; the 3 of them have worked tirelessly during all DebConf on the design bits that were needing changes as well as on the implementation / revamp of involved tools (e.g.
dh_ocaml, which I drafted (too) many years ago for not being in production yet).
I guess you'll soon hear from them for more details. -
As observed by Stephane, the transition to the new schema and
tools do not need to be "all or nothing".
Hence, the current plan is to release in Squeeze most of the
packages migrated to the new infrastructure, while not necessarily
all of them.
turbogears 2 in debian unstable [i'm in a hurry - stefano zacchiroli blog]
finally! (but not quite so)
Coming back from DebConf9 has possibly been as fun as going there. I'm leaving for my vacations in a few days and I'm (desperately?) fighting with my TODO list to finish up stuff before leaving.
Given that the freeze for the next Debian release is likely to be earlier than expected, I've hurried up a bit with TurboGears 2.
Initially, I intended to upload all the involved packages to unstable as soon as all of them will be out of NEW, but I finally changed my mind to avoid loosing important testing time from users.
Hence, a couple of days ago, I've uploaded most of TG2
packages to unstable. From there you can directly type
apt-get install python-tg.devtools to start developing
your TG2 app. Please test and give feedback (via
bugreports, as usual).
The missing pieces, waiting in NEW and available from my own repo, are:
-
sprox, catwalk, and tgext.admin: the lack of these 3 essentially means that you cannot enjoy the fancy web-based administrative interface of your TG2 apps
-
turbogears2-doc: this is essentially an offline (and doc-base registered) version of the online docs of TG2, nice to have but you can live without for a while
An alpha male advertising that very fact... I'm only speaking for myself here, but I wouldn't have challenged that guy!
Des critères de notoriété de Wikipédia... [Notes d'un économiste]
... et de ce qu'ils nous disent du fonctionnement des industries culturelles.
Tuesday, 04 August 2009
00:00
Feasibility/Desirability Games for Normal Form Games, Choice Models and Evolutionary Games. (arXiv:0907.5469v1 [cs.GT]) [cs.GT updates on arXiv.org]
An abstraction of normal form games is proposed, called Feasibility/Desirability Games (or FD Games in short). FD Games can be seen from three points of view: as a new presentation of games in which Nash equilibria can be found, as choice models in microeconomics or as a model of evolution in games.
Proof Theory at Work: Complexity Analysis of Term Rewrite Systems. (arXiv:0907.5527v1 [cs.LO]) [cs.LO updates on arXiv.org]
This thesis is concerned with investigations into the "complexity of term rewriting systems". Moreover the majority of the presented work deals with the "automation" of such a complexity analysis. The aim of this introduction is to present the main ideas in an easily accessible fashion to make the result presented accessible to the general public. Necessarily some technical points are stated in an over-simplified way.
A System F accounting for scalars. (arXiv:0903.3741v2 [cs.LO] UPDATED) [cs.LO updates on arXiv.org]
The linear-algebraic lambda-calculus (arXiv:quant-ph/0612199) extends the lambda-calculus with the possibility of making arbitrary linear combinations of lambda-calculus terms a.t+b.u. In this paper we provide a System F -like type system for the linear-algebraic lambda-calculus, which keeps track of 'the amount of a type' that is present in a term. We show that this scalar type system enjoys both the subject-reduction property and the strong-normalisation property, which constitute our main technical results. The latter yields a significant simplification of the linear-algebraic lambda-calculus itself, by removing the need for some restrictions in its reduction rules - and thus leaving it more intuitive. More importantly we show that our type system can readily be modified into a probabilistic type system, which guarantees that terms define correct probabilistic functions. Thus we are able to specialize the linear-algebraic lambda-calculus into a higher-order, probabilistic lambda-calculus. Finally we discuss the more long-term aims of this reseach in terms of establishing connections with linear logic, and building up towards a quantum physical logic through the Curry-Howard isomorphism. Thus we begin to investigate the logic induced by the scalar type system, and prove a no-cloning theorem expressed solely in terms of the possible proof methods in this logic.
Complexity of Fractran and Productivity. (arXiv:0903.4366v3 [cs.LO] UPDATED) [cs.LO updates on arXiv.org]
In functional programming languages the use of infinite structures is common practice. For total correctness of programs dealing with infinite structures one must guarantee that every finite part of the result can be evaluated in finitely many steps. This is known as productivity. For programming with infinite structures, productivity is what termination in well-defined results is for programming with finite structures.
Fractran is a simple Turing-complete programming language invented by Conway. We prove that the question whether a Fractran program halts on all positive integers is Pi^0_2-complete. In functional programming, productivity typically is a property of individual terms with respect to the inbuilt evaluation strategy. By encoding Fractran programs as specifications of infinite lists, we establish that this notion of productivity is Pi^0_2-complete even for the most simple specifications. Therefore it is harder than termination of individual terms. In addition, we explore possible generalisations of the notion of productivity in the framework of term rewriting, and prove that their computational complexity is Pi^1_1-complete, thus exceeding the expressive power of first-order logic.
Fifty Years of the Spectrum Problem: Survey and New Results. (arXiv:0907.5495v1 [math.LO]) [math.LO updates on arXiv.org]
In 1952, Heinrich Scholz published a question in the Journal of Symbolic Logic asking for a characterization of spectra, i.e., sets of natural numbers that are the cardinalities of finite models of first order sentences. G\"unter Asser asked whether the complement of a spectrum is always a spectrum. These innocent questions turned out to be seminal for the development of finite model theory and descriptive complexity. In this paper we survey developments over the last 50-odd years pertaining to the spectrum problem. Our presentation follows conceptual developments rather than the chronological order. Originally a number theoretic problem, it has been approached in terms of recursion theory, resource bounded complexity theory, classification by complexity of the defining sentences, and finally in terms of structural graph theory. Although Scholz' question was answered in various ways, Asser's question remains open. One appendix paraphrases the contents of several early and not easily accesible papers by G. Asser, A. Mostowski, J. Bennett and S. Mo. Another appendix contains a compendium of questions and conjectures which remain open.
Definability of Combinatorial Functions and Their Linear Recurrence Relations. (arXiv:0907.5420v1 [math.CO]) [math.LO updates on arXiv.org]
We consider functions of natural numbers which allow a combinatorial interpretation as density functions (speed) of classes of relational structures, s uch as Fibonacci numbers, Bell numbers, Catalan numbers and the like. Many of these functions satisfy a linear recurrence relation over $\mathbb Z$ or ${\mathbb Z}_m$ and allow an interpretation as counting the number of relations satisfying a property expressible in Monadic Second Order Logic (MSOL).
C. Blatter and E. Specker (1981) showed that if such a function $f$ counts the number of binary relations satisfying a property expressible in MSOL then $f$ satisfies for every $m \in \mathbb{N}$ a linear recurrence relation over $\mathbb{Z}_m$.
In this paper we give a complete characterization in terms of definability in MSOL of the combinatorial functions which satisfy a linear recurrence relation over $\mathbb{Z}$, and discuss various extensions and limitations of the Specker-Blatter theorem.
A hypothetical upper bound for solutions of a Diophantine equation with a finite number of solutions. (arXiv:0901.2093v38 [math.NT] UPDATED) [math.LO updates on arXiv.org]
Let E_n={x_i=1, x_i+x_j=x_k, x_i \cdot x_j=x_k: i,j,k \in {1,...,n}}, K \in {Z,Q,R,C}. We construct a system S \subseteq E_{21} such that S has infinitely many integer solutions and S has no integer solution in [-2^{2^{21-1}},2^{2^{21-1}}]^{21}. We conjecture that if a system S \subseteq E_n has a finite number of solutions in K, then each such solution (x_1,...,x_n) satisfies (|x_1|,...,|x_n|) \in [0,2^{2^{n-1}}]^n. Applying this conjecture for K=Z, we prove that if a Diophantine equation has only finitely many integer (rational) solutions, then the heights of solutions are bounded from above by a constant which recursively depends on the coefficients of the equation. We note that an affirmative answer to the famous open problem whether each listable set M \subseteq Z^n has a finite-fold Diophantine representation would falsify our conjecture for K=Z.
Analogic (black) Hole.. [blog.rastageeks.org]
Please, Deezer, Youtube, Dailymotion, Spotify, etc..., stop wasting time and ressources bloating your API to prevent downloads... We all got the solution anyway.. !
Question on Synthetic Differential Forms [The n-Category Café]
I am thinking about cosimplicial objects in the category of generalized smooth algebras as models for the -quantities (see there for what I mean) dual to models for -stacks.
The archetypical example should be the cosimplicial generalized smooth algebra of differential forms on a smooth space
for a smooth space, let be the generalized smooth algebra of functions on the infinitesimal -simplices in . As varies these naturally form a cosimplicial object.
Now, it seems to me as if the standard definition of the cochain complex of differential forms in synthetic differential geometry is nothing but the image of this under the (dual) Dold-Kan correspondence: is the normalized (dual) Moore complex as recalled in this dual form and in the present context in section 4 of
Castiglioni-Cortiñas: Cosimplicial versus DG-rings: a version of the Dold-Kan correspondence.
Details of what I have in mind are at differential forms in synthetic differential geometry.
My question is: am I hallucinating? If not, has this been discussed elsewhere`?
A Functional I/O System (or Fun for Freshman Kids) [Lambda the Ultimate - Programming Languages Weblog]
A Functional I/O System (or Fun for Freshman Kids), by Matthias Felleisen, Robert Bruce Findler, Matthew Flatt, and Shriram Krishnamurthi. ICFP 2009.
Functional programming languages ought to play a central role in mathematics education for middle schools (age range: 10-14). After all, functional programming is a form of algebra and programming is a creative activity about problem solving. Introducing it into mathematics courses would make pre-algebra course come alive. If input and output were invisible, students could implement fun simulations, animations, and even interactive and distributed games all while using nothing more than plain mathematics.
We have implemented this vision with a simple framework for purely functional I/O. Using this framework, students design, implement, and test plain mathematical functions over numbers, booleans, string, and images. Then the framework wires them up to devices and performs all the translation from external information to internal data (and vice versa) -- just like every other operating system. Once middle school students are hooked on this form of programming, our curriculum provides a smooth path for them from pre-algebra to freshman courses in college on object-oriented design and theorem proving.
This is a paper explaining some of the technical underpinnings of the How to Design Worlds curriculum that the PLT group has worked on.
I was tempted to categorize this as "functional", but decided against it. One of the really nice features of this curriculum is actually its applicability to imperative programming. Here, students are taught to think of interactive programs as functions written in world-passing style, and to specify programs in terms of the invariants that the function maintains on the world data.
That is: students are taught about loop invariants, without ever having to write an explicit loop. In my experience, loop invariants are the most difficult part of explaining Hoare logic (and hence of explaining imperative programming), because they require imagining a dynamic picture of what the static source code will eventually do. This style of teaching helps to manage that difficulty by making the dynamic state into visible animations.
Programming Made "Simple" [Lambda the Ultimate - Programming Languages Weblog]
The Simple programming language is a BASIC dialect for the Android platform highly influenced by Microsofts's pre-dot-NET Visual Basic.
In the 90s, a big company from up north was extremely successful with a dialect of the programming language BASIC (acronym for Beginner's All-purpose Symbolic Instruction Code). One of the reasons it was so successful was that the language was easy to learn and use.
Bringing an easy to learn and use language to the mobile world and the Android platform is the goal of the Simple project. Simple is a BASIC dialect for developing Android applications. It is particularly well suited for non-professional programmers (but not limited to). Simple allows programmers to quickly write Android applications by using the components supplied by its runtime system.
Similar to its 90s relative, Simple programs are form definitions (which contain components) and code (which contains the program logic). The interaction between the components and the program logic happens through events triggered by the components. The program logic consists of event handlers which contain code reacting to the events.
Revue de presse de l'April pour la semaine 31 [DLFP - Dépêches]
La revue de presse de l'April est régulièrement éditée par les membres de l'association. Elle couvre l'actualité de la presse en ligne, liée au logiciel libre. Il s'agit donc d'une sélection d'articles de presse et non de prises de position de l'association de promotion et de défense du logiciel libre.
Sommaire de la revue de presse de l'April pour la semaine 31
- [fragil.org] L’économie du logiciel libre, une invasion souterraine
- [lemonde.fr] Mozilla annonce le milliardième téléchargement de son navigateur Firefox
- [zdnet.fr] Le chômage des informaticiens a progressé de 40% en un an
- [zdnet.fr] Six projets Open Source récompensés sur SourceForge
- [macgeneration.com] OLPC : bilan en demi-teinte
- [ecrans.fr] Microsoft devra gérer une contagion du libre
(...)
Interview de S.P.Zeidler, administratrice système de la Fondation NetBSD [DLFP - Dépêches]
Après Soren Jacobsen et Adam Hamsik, c'est au tour de S.P.Zeidler, spz@, de se faire harceler de questions par la fine équipe de NetBSDfr. Petra, c'est son prénom, participe au processus de release engineering de pkgsrc, mais c'est surtout la position d' administratrice système de la Fondation NetBSD qu'elle occupe depuis 1995 qui a piqué notre curiosité:
Être un admin de projet Libre de grande envergure, ça fait quoi ?
Ainsi, elle nous apprend comment les tâches sont distribuées entre chaque administrateur, comment les problèmes sont traités, quels types de machines possède la Fondation et quelques informations sur le futur de cette infrastructure. Petra nous a également exposé l'organisation de l'équipe pkgsrc-releng, dévoilant une partie du mystère de l'opération de publication des paquets.
Comme d'habitude, l'interview est disponible en français et en anglais et truffée de petits goodies.
lien 1 : L'interview en français
lien 2 : L'interview en anglais
VHFFS l'hébergement Internet libre pour tous en 4.2.0 [DLFP - Dépêches]
Après un wiki sur l'auto-hébergement ou un journal pour l'installation et sécurisation d'un serveur LAMP, le panel de gestion d'hébergement VHFFS dans sa plus récente mouture (4.2.0) devrait en séduire plus d'un(e), presqu'un an 1/2 aprés sa précédente release !
VHFFS aka Virtual Hosting For Free Software est l'outil développé par TuxFamily.org pour proposer un hébergement libre à ses hébergés.
- Des paquets pour Debian sont disponibles. Ils conviennent bien pour une nouvelle installation, pas forcément pour une mise à jour, testé pour Lenny, packageur motivé le bienvenu
- Les tags pour classifier son projet : la partie publique présentant les projets a été refondue et fait désormais apparaître les tags et la page de recherche est particulièrement complète. Les hébergés peuvent demander des tags supplémentaires via le panel ;
- D'autres évolutions sont disponibles, tel que vhffs-fssync permettant de déployer sur deux serveurs de download de manière transparente pour l'utilisateur, en respectant de la QoS et en gérant des priorité d'envoi des petits fichiers pour qu'il soient disponibles le plus rapidement (cas d'un upload d'image dans un CMS). Les droits utilisateurs sont aussi gérés, VHFFS-FSSYNC s'appuie sur inotify et est conforme POSIX.
lien 1 : Annonce de VHFFS 4.2.0 et téléchargement
lien 2 : Notes de la version4.2.0
lien 3 : VHFFS sur wikipedia
lien 4 : Exemple de la partie publique sur le site de TuxFamily.org
lien 5 : L'annonce sur DLFP de la version précédente en 4.1
(...)
CodeSOD: Self Modifying VBA [The Daily WTF]
"I work as a support developer for the trading desk at a fairly large bank," Jay P.L. writes, "some of the automatic trading systems used have grown organically from what can originally be called an Excel spread-sheet. However, the complexity can sometimes be overwhelming."
Jay continues, "When traders find functionality that doesn’t quite work as expected, our usual response is, 'just send over the spreadsheet and we'll take a look at it.' Cracking open the VBA and debugging through the issue usually finds the cause relatively quickly. Most of the time, the issue can be blamed on a close colleague who made the mistake during a particularly hectic trading atmosphere under an abundant amount of stress and pressure. These situations are usually overlooked and forgiven. The issue fixed and returned."
"Usually forgiven. Imagine my joy at finding the following code snippet."
Sub LogIn()
On Error Resume Next
Result = BatchLogin("jpl", "England1")
If Err.Number <> 0 Then
Err.Clear
PassWordReset
ElseIf Len(Result) = 0 Then
PassWordReset
End If
End Sub
Sub PassWordReset()
With ThisWorkbook.VBProject.VBComponents.Item("DataBase")
SecStr = .CodeModule.Lines(3, 1)
SecArr = Split(Right(SecStr, Len(SecStr) - 22), ",")
UserID = Replace(SecArr(0), Chr(34), "")
With frmLogIn
.txbUserId = UserID
.Show
If Len(.txbUserId) = 0 Then End
UserID = .txbUserId
Password = .txbPassword
End With
AppSts = Application.ScreenUpdating
Application.ScreenUpdating = True
Application.ScreenUpdating = AppSts
On Error Resume Next
Result = BatchLogin(CStr(UserID), CStr(Password))
If Err.Number = 0 And Len(Result) > 0 Then
q = Chr(34)
.CodeModule.DeleteLines 3, 1
On Error GoTo 0
.CodeModule.InsertLines 3, _
" Result = BatchLogin(" _
& q & UserID & q & "," _
& q & Password & q & ")"
Else
PassWordReset
End If
End With
End Sub
Jay adds, "I find the interesting point being the self-modifying VBA code, even though it can be enjoyed on so many levels."
Nature's call [Aperture First]
Bathroom stop while biking down the slopes of Cotopaxi, one of the highest mountains of Ecuador (did I mention I did cool stuff during this trip?).
Fires around the Mediterranean [The Big Picture]
Monday, 03 August 2009
00:00
Groupoidfest 09 [The n-Category Café]
It’s coming up, sooner than you think!
- Groupoidfest 09, October 24–25, 2009, Department of Mathematics, University of Colorado, Boulder, Colorado, organized by Arlan Ramsay.
Talks will start on Saturday morning and end around noon on Sunday. There is still time available for more speakers. Contact Arlan Ramsay if you are interested in speaking or attending! He can send you hotel information.
The Groupoidfest has always featured a lot of interaction between groupoids and operator algebras. So, it may help you to know that this year it’s taking place a week after the West Coast Operator Algebra Seminar in Reno. Unfortunately, it’s timed to coincide with the East Coast Operator Algebras Symposium, which is being held at Texas A&M University.
(Texas? East Coast?)
Creator of Qi Calls It Quits [Lambda the Ultimate - Programming Languages Weblog]
In a Qilang mailing list email Marker Tarver, creator of Qi, says
In a month I will be packing to go to India; this time for an extended
period. But its also a goodbye to Qi and computing. At some point
you have to acknowledge that Qi doesn't pay its way. It was fun
though and I'm not sad about it.Qi has been a journey that began nearly 20 years ago when I was a very
different person and worked for a university. But the book on Qi II
marks a natural watershed. I need to move on. By September I will be
gone.
Encore du libre pour Radio Esperanzah! 2009 [DLFP - Dépêches]
6ème édition pour la radio éphémère du festival Esperanzah! : cette année encore, un large collectif (avec près de 35 personnes) se retrouve à l’abbaye de Floreffe pour réaliser 4 jours de direct couvrant toutes les facettes du festival. 50 heures d'interviews, de débats et de concerts, bien sûr en direct sur Internet en Ogg Vorbis.
Comme Radio RMLL en juillet, le coeur de ce dispositif bat grâce à une dizaine de machines et serveurs sous linux et une myriade de logiciels libres.
lien 1 : Radio Esperanzah!
lien 2 : Festival Esperanzah!
lien 3 : Radio & Logiciels Libres
(...)
Paquet de petites brèves d'été [DLFP - Dépêches]
Il s'est passé tout plein de choses pendant la première moitié de l'été de l'hémisphère nord de la planète :
- free.korben.info est un wiki sous Mediawiki sur la protection de la vie privée, rédigé comme un livre : à vous de contribuer
- Simple est un langage proche du Basic, développé par Google pour créer des applications natives pour les terminaux Android
- Bugzilla 3.4 a été publié et contient un certain nombre d'améliorations bien sympa
- ladistribution.net, publié sous licence MIT et GPL serait un apt-get/urpmi pour les applications web ?
- Psi, le client Jabber/XMPP, est sorti en version 0.13, avec lui la VoIP sur Jingle !
- Motorola se met aussi à Android avec MOTODEV Studio et App Accelerator
- KDE et sa nouvelle interface Plasma pour netbooks
- osdbzine.net : Open Source Database Magazine vient d'être lancé
- Après avoir intégré Jabber/XMPP, LimeWire intègre les réseaux sociaux
- HadoopDB : base de données sur Hadoop
- Pandion, le client Jabber/XMPP, passe opensource sous GPLv3
- The OSWatershed.org project : une étude sur les distribution et les logiciels « upstream »
- Open Humanity, le web-OS, a été lancé
- WordPress.com a lancé la notification temps-réel aux blogs et commentaires, c'est sur Jabber/XMPP, plus précisément PubSub : Real-time WordPress.com subscription (doc)
- Palm webOS (avec un web minuscule et un OS majuscule, sans jeu de mot) : Mojo SDK et User Interface Guidelines
- La Courgette, un légume d'été (par Google)
lien 1 : Proposez un article
Our first sunset in the Galapagos, just a couple of hours after boarding the Vision. A magical week had just begun!