# Posts

### August 03, 2015

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7:55 PM | Lo sturangoscia

recensione del libro di Davide Pedrosin e Carlo Sperduti ed. @gorilla_sapiensSiete mai stati presi da un'angoscia indescrivibile, così potente da tenervi bloccati, magari seduti sul divano, o da impedirvi di parlare se non addirittura di scrivere?Ebbene se vi è mai capitato qualcosa del genere, le vostre preoccupazioni sono ormai finite, perché è in commercio un macchinario di una potenza incredibile, in grado di liberarvi di qualunque preoccupazione. E' lo sturangoscia, un portentoso […]

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4:00 PM | Farewells and other goings on

It’s been a while since I last wrote a post here… The spring was full of duties pulling me in lots of different directions, but now (finally) the summer has given me a chance to dig myself out and now I’m finally back. Of course, lot’s has been going on at Caltech and in RSRG in […]

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8:23 AM | The Point Of The Banach Tarski Theorem

There's a classic "Limited Audience" joke/riddle that goes:
Q: What's an anagram of "Banach-Tarski"?
A: "Banach-Tarski Banach-Tarski."
Now, if you already know what the Banach-Tarski
theorem says, that riddle is really funny. If
you don't then you're simply not in the audience,
and you'll just go: "Huh?" In this article we
have a look at why the Banach-Tarski theorem is
more than just a curiosity.

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5:39 AM | Zio Ziegler in Irvine

Street art? In Irvine? Apparently, now, the answer is yes. Local clothing manufacturer Tillys somehow persuaded the planning commission to allow them to commission Zio Ziegler (new Wikipedia article) to decorate one of their warehouses, right next to interstate 405, where approximately 240,000 daily drivers will see it.You can't exactly stop on the freeway to take photos, but I found enough other more accessible vantage points to get a few shots:( The rest of the photos )

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1:37 AM | The Other Other Rope Around The Earth

There's a classic problem: Upon stretching a rope around the Earth,
you find that you have 6 metres excess. So you join the ends, and
then go around the Earth propping up the rope equally everywhere.
How high will it be? An alternative that's been suggested is that
instead of propping it up equally everywhere, just prop it up as
high as possible in one place. But now Bill Mullins has asked me
yet another variant ...

### August 02, 2015

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[Below is a guest post from Sanjeev Arora on his redesign of the traditional graduate algorithms course to be a better match for today’s students. –Boaz] For the last two years I have tried new ideas in teaching algorithms at the graduate level. The course is directed at first year CS grads, but is also taken by grads […]

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On Thursday Aug 6 there will be Republican debate among 10 of the 17 (yes 17) candidates for the republican nomination.1) There are 17 candidates. Here is how I remember them: I think of the map of the US and go down the east coast, then over to Texas then up. That only works for the candidates that are or were Senators or Govenors. I THEN listthe outsiders. Hence my order is (listing their last job in government) George Pataki (Gov-NY), Chris Christie (Gov-NY), Rick Santorum […]

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6:00 PM | All Liar, No Paradox • Comment 1

A statement asserts that a statement is a statement that is false. The statement violates an axiom of logic, so it doesn’t really matter whether the ostensible statement the so-called liar, really is a statement or has a truth value. … Continue reading →

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6:00 PM | Bits, bears, and beyond in Banff

Another conference about entropy. Another graveyard. Last year, I blogged about the University of Cambridge cemetery visited by participants in the conference “Eddington and Wheeler: Information and Interaction.” We’d lectured each other about entropy–a quantification of decay, of the march of … Continue reading →

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12:56 PM | Sieve Of Eratosthenes In Python

One of the things we need to do when finding Perrin Pseudo-Primes is to recognise prime numbers so we can see if the numbers predicted by the Perrin test to be prime, are. So we need to generate primes. For small primes (for some definition of "small") this can be done quickly and efficiently by using the Sieve of Eratosthenes. Here we use a dynamically generated collection of filters, one for each prime, and run down the list of all numbers, filtering as we go.

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7:01 AM | Fast Perrin Test

So we've got scaffolding to look for Perrin Pseudo-Primes (PPPs), assuming any exist (which they do) but as we run the existing code we find that it's spending pretty much all its time in the test as to whether n divides k(n). Now we look to speed that up ...

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7:01 AM | Russian Peasant Multiplication

Sometimes simply called "Peasant Multiplication," sometimes called "Ancient Egyptian multiplication," sometimes called "Ethiopian multiplication," sometimes called "Multiplication by Doubling and Halving," this algorithm is well-known to some, a mystery to others, and more useful than you might think, being applicable not just to multiplication of numbers, but also useful for exponentiation, and for matrices.

### August 01, 2015

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10:06 PM | On the Great Financial Panic of 2007

(a) I've always felt that "Great Financial Panic of 2007" was a good old-fashioned banking panic, even if the modern version doesn't look anything like "It's a Wonderful Life." Gary Gorton gets it exactly right (book here):"Holders of short-term liabilities...refused to fund "banks" [that is, various vehicles in the shadow banking system] due to rational fears of loss. ... As with the earlier panics, the problem at root is a lack of information."(b) Simultaneously, I've always felt that
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Chantal David, Andrew Granville, Emmanuel Kowalski, Phillipe Michel, Kannan Soundararajan, and I are running a program at MSRI in the Spring of 2017 (more precisely, from Jan 17, 2017 to May 26, 2017) in the area of analytic number theory, with the intention to bringing together many of the leading experts in all aspects of the […]

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2:56 PM | Finding Perrin Pseudo Primes, Part 2

So now we've got the scaffolding of a program to find these Perrin Pseudo-Primes. The timing shows that it overwhelmingly spends all of its time in the routine to test whether or not a number passes the "Perrin Test." So there are a few things we need to do.

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2:30 PM | All Liar, No Paradox

A statement asserts that a statement is a statement that is false. The statement violates an axiom of logic and it doesn’t really matter whether the ostensible statement the so-called liar, really is a statement or has a truth value.

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2:05 PM | Finding Perrin Pseudo Primes, Part 1

A while ago I was asked: Consider the sequence k(n) with k(1)=0, k(2)=2, k(3)=3, and k(n)=k(n-2)+k(n-3). Why is it true that n divides k(n) if and only if n is prime?" My immediate response was "Well, it's not true." So I was challenged to find a counter-example.

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4:39 AM | Linkage

W. T. Tutte's WWII cryptography work (G+)Cube into rhombic dodecahedron dissection video (G+)Calvin Seibert's geometric sand castles (G+)Paco Santos' Hirsch counterexample wins him the Fulkerson Prize (G+)Tessellating calligraphy (G+)MacTutor History of Mathematics website honored by the London Mathematical Society (G+)The backlash against using numerology to measure research quality gains strength (G+)Turns out that folded brain surfaces and crumpled paper balls obey the same scaling laws
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### July 31, 2015

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8:13 PM | Toxic

Avete mai sognato di fare una vacanza in Islanda? Lì dove il sole tramonta tardi e c'è tanta luce per pensare alla propria vita? Magari quando siete in fuga dalle cattive compagnie, e di certo ne avete di cattive compagnie quando siete un killer croato soprannominato Toxic, il migliore sulla piazza.E magari vi trovate a sbarcare a Reykjavik con una nuova identità, invischiato in una serie di divertenti equivoci, chiuso tra una donna libertina che non vi avvisa che state vivendo sotto lo […]

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8:00 PM | Zeroth Law Of Semiotics • Comment 2

Re: Peirce List Discussion • Edwina Taborsky My old avatar (Zero-Aster) does incline to laconic verses, but I hope to address a class of concrete applications that will serve to unpack their sense. The main thing I’d like to communicate … Continue reading →

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2:00 PM | Zeroth Law Of Semiotics • Comment 1

New discussions of the so-called “Liar Paradox” have broken out at several places on the web in recent weeks (1) (2) and these always bring to my mind at least a number of critical ways in which the Peircean paradigm … Continue reading →

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12:00 AM | So that took a while

I finally completed the blog migration I started a few months ago. Moving away from WordPress forced me to re-think a few parts and re-work a lot of content by hand. This was tedious but forced a worthwhile bit of introspection.
Permalinks
Oh, permalinks. The name is so clean and yet so misleading. WordPress is so forgiving to both admins, authors and visitors. But leaving that paradise is fun, too. At one point I had renamed all posts in a way which led to a site with zero posts; […]

### July 30, 2015

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9:00 PM | Cielo di sabbia

For me, "All the Earth, thrown to the sky" is the best @joelansdale's novelAdoro Joe Lansdale. E non solo per la serie di Hap e Leonard, ma anche per i molti suoi romanzi che riescono a spaziare in vari generi. Certo i suoi generi di riferimento principali sono il noir e l'horror, tutti conditi con una buona dose di grottesco e una serie di elementi che, a mio giudizio, fanno di Lansdale l'ultimo scrittore pulp nel senso più ampio della parola.Cielo di sabbia, però, è qualcosa di più di un […]

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2:00 PM | Zeroth Law Of Semiotics

Meaning is a privilege not a right. Not all pictures depict. Not all signs denote. Never confuse a property of a sign, just for instance, existence, with a sign of a property, for instance, existence. Taking a property of a … Continue reading →

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Light summer post, want more then follow the links. 1. after a chemlambda demo appeared on hackernews (link) I saw a lot of interest from hacker brains (hopefully). Even if slightly misplaced (title reads: D3.js visualization of a lambda calculus), it is an entry gate into this fascinating subject. 2. 4lhc works on a python port … Continue reading Summer news, Ackermann related observations and things to come →

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Key and Peele, talented comedians with tight skits, have done many special pieces, but this is ultra special. A spoof on Sports Central, draft coverage, this one is on Teachers Draft (for High Schools):

### July 29, 2015

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9:23 PM | Prima di Adamo

La fascinazione verso le teorie mistiche della reincarnazione si unisce con l'evoluzionismo, che stava muovendo i suoi primi passi, in Prima di Adamo, romanzo di Jack London che potremmo tranquillamente classificare come pura avventura.L'idea di London è, infatti, quella di raccontare la vita, più che fittizia di un nostro progenitore, appartenente a una di quelle razze di primati apparse prima degli uomini e da questi soppiantate. Attraverso il sogno, espediente narrativo utilizzato nella […]

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Suppose you are reading about a statistically significant result x from a one-sided test T+ of the mean of a Normal distribution with n iid samples, and (for simplicity) known σ: H0: µ ≤ 0 against H1: µ > 0. I have heard some people say: A. If the power to detect alternative µ’ is very low, then the statistically significant x is poor evidence of […]

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6:08 PM | Blurbs!

I don’t like social media very much. I never really subscribed to the whole Friendster, MySpace, Facebook, Twitter, Google Wave, Google+, and what have you social network sort of approach that you need to have “friends” and “followers” and “follow” other people. I always preferred to be the master of my domain. The king of … Continue reading Blurbs! →

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In the last post I had the following scenario:
Larry, Moe, and Curly are on Jeopardy.
Going into Final Jeopardy:
Larry has $50,000, Moe has $10,000, Curly has $10,000
Larry bets $29,999, Moe bets $10,000, Curly bets $10,000
These
bets are ALL RATIONAL and ALL MATTER independent of what the category
is. For example, these bets make sense whether the category is THE THREE
STOOGES or CIRCUIT LOWER BOUNDS.
Explain why this is.
EXPLANATION: You were probably thinking of ordinary Jeopardy […]