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# Posts

### October 04, 2015

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Principal-components regression (PCR) is routine in applied time-series econometrics.Why so much PCR, and so little ridge regression? Ridge and PCR are both shrinkage procedures involving PC's. The difference is that ridge effectively includes all PC's and shrinks according to sizes of eigenvalues associated with the PC's, whereas PCR effectively shrinks some PCs completely to zero (those not included) and doesn't shrink others at all (those included). Ridge seems to resonate as more […]
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When signing up for physics grad school, I didn’t expect to be interviewed by a comedienne on a spoof science show about women in STEM. Last May, I received an email entitled “Amy Poehler’s Smart Girls.” The actress, I read, had … Continue reading →
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Junk Science (as first coined).* Have you ever noticed in wranglings over evidence-based policy that it’s always one side that’s politicizing the evidence—the side whose policy one doesn’t like? The evidence on the near side, or your side, however, is solid science. Let’s call those who first coined the term “junk science” Group 1. For […]

### October 03, 2015

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An ongoing concern in graph drawing research has been curve complexity. If you draw a graph using a certain style, how complicated are you going to have to make the edges? More complicated curves are harder for readers to follow, and therefore they make the graph less readable. But simpler curves (such as line segments) may have their own problems: not fitting the style (which may constrain the edges to certain directions), running through vertices, forming sharp angles with each other, etc. To […]
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In Notes 0, we introduced the notion of a measure space , which includes as a special case the notion of a probability space. By selecting one such probability space as a sample space, one obtains a model for random events and random variables, with random events being modeled by measurable sets in , and […]
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La capacità di uno scrittore di essere verosimile fino ad arrivare al punto di non chiarire mai bene al lettore quanto i propri scritti siano autobiografici è comune a ben poche anime pie e una di queste è Patrick Dennis, pseudonimo di Edward Everett Tanner III, scrittore statunitense che, persa tutta la sua fortuna, finì la sua carriera come maggiordomo di Ray Kroc, CEO di McDonald's, ovviamente ignaro di avere al suo servizio uno dei più famosi scrittori d'America. Questa, però, è la […]
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It has been nine months since I really looked at the Teach Yourself Logic 2015 Study Guide. It’s time to start thinking about a 2016 update. So over the coming weeks I’ll be tinkering with the current version, while reading, dipping, … Continue reading →

### October 02, 2015

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This past spring I taught a standard data structures course (stacks, queues, binary trees, heaps, asymptotic analysis, that kind of thing). Inspired by a group I participated in exploring pedagogy and course design—led by the wonderful Betsy Burris—I decided to … Continue reading →
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Recall the game between R and D determined by the following data. Here is Ashby’s analysis of how it all plays out. Examination of the table soon shows that with this particular table R can win always.  Whatever value D … Continue reading →
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Come ricorda il google doodle di oggi, è la festa dei nonni e anche l'ultimo numero di Topolino li festeggia con ben due storie. E seguendo quanto fatto settimana scorsa con la luce, anche questa settimana mi concentro solo sulle storie a tema. La brevisione su LSB, invece, questa volta verrà scritta da Andrea Bramini e uscirà nei prossimi giorni, state tranquilli. Apre la coppia di avventure Nonna Papera e Nonno Bassotto: la strana coppia, scritta da Gaja Arrighini per i disegni di […]

### October 01, 2015

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Ashby now invites us to consider a series of games, beginning as follows. 11/3.   Play and outcome.  Let us therefore forget all about regulation and simply suppose that we are watching two players, R and D, who are engaged in … Continue reading →
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Karsten Schwan said the title quote when we were gathered as a faculty two years ago mourning the Georgia Tech School of Computer Science faculty member Mary Jean Harrold who died from the disease. Karsten just lost his own battle with cancer sunday evening and my department is now mourning another great faculty member. Just a few months ago, Alberto Apostolico, an algorithms professor at Georgia Tech, also passed away from cancer.  I went back through the obituaries in […]
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I’m hoping that most of the people who read this blog have already heard, but in case they haven’t — next Fall, the Simons Institute is hosting a semester-long program on Algorithms and Uncertainty, which I am co-organizing with Avrim Blum, Anupam Gupta, Robert Kleinberg, Stefano Leonardi, and Eli Upfal. It should be a very interesting semester, and we’ve […]
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Check out the new paper, "Incorporating the Beige Book in a Quantitative Index of Economic Activity," by Nathan Balke, Michael Fulmer and Ren Zhang (BFZ).[The Beige Book (BB) is a written description of U.S. economic conditions, produced by the Federal Reserve system. It is released eight times a year, roughly two weeks before the FOMC meeting.]Basically BFZ include BB in an otherwise-standard FRB Philadelphia ADS Index.  Here's the abstract:  We apply customized text analytics to the […]
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A couple of abstracts about the geomtery of space: Historically, there have been many attempts to produce the appropriate mathematical formalism for modeling the nature of physical space, such as Euclid's geometry, Descartes' system of Cartesian coordinates, the Argand plane, Hamilton's quaternions, Gibbs' vector system using the dot and cross products. We illustrate however, that Clifford's geometric algebra (GA) provides the most elegant description of physical space. Supporting this […]
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I have read for pleasure for as long as I remember, some books haunting me for years after I finish them, others drawing me in only while they last. But two authors had a particularly formative influence on me in my late teens, in very different ways. Richard Dawkins caused me to reassess my position in the world. And Martin Amis showed me that so-called literary novels could also be pretty good fun. In the couple of decades since, my... Read more
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There is a longstanding feud in statistics between "frequentists" and "Bayesians". One way to understand these two camps is to consider the following statements: The probability that my paternal great great grandfather had blue eyes is 5% The probability that the -th digit of is 7 is 10% A frquentist would say that these statements […]
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UCI is #1 for low-income students (G+)Applications of convolutions in combinatorics (G+)Is it good to take advantage of free subscriptions to online information services for Wikipedia editors? (Yes. G+)A Helsinki street paved with Penrose tiles﻿ (G+)Colbert on diploma mills (G+)Realizing graphs as polyhedra (talk slides from my talk at the Graph Drawing satellite workshop; G+)Impact factors are bad and you should feel bad for using them (G+)Numberphile on the Houdini fold-and-cut trick […]
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The second set of Lecture notes for my course is now available here.  This week’s notes are about graphs, embedding of graphs in Euclidean space (focusing in Diffusion Maps) and relations between behavior of a graph based semi-supervised learning method and Sobolev Embedding Theorem. Given the nature of these topics, these notes have a lot … Continue reading 18.S096: Graphs, Diffusion Maps, and Semi-supervised Learning →
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ONE YEAR AGO, the NYT “Science Times” (9/29/14) published Fay Flam’s article, first blogged here. Congratulations to Faye Flam for finally getting her article published at the Science Times at the New York Times, “The odds, continually updated” after months of reworking and editing, interviewing and reinterviewing. I’m grateful too, that one remark from me remained. Seriously I […]

### September 30, 2015

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Here is the first part of Ashby’s setup for the schematic example I had in mind. Requisite Variety 11/1.   In the previous chapter we considered regulation from the biological point of view, taking it as something sufficiently well understood.  … Continue reading →
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If you have read the Teach Yourself Logic 2015 Study Guide, then you will know that I there particularly recommend as an admirably lucid and, yes, friendly introduction to first-order logic Christopher Leary’s 2000 book, A Friendly Introduction to Mathematical … Continue reading →
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Today we’ll examine Philip Roth. Roth is one of my favorite prose stylists, and I’m not sure it will be possible to convey why by analyzing a brief section of writing. This is because my favorite part of his style … Continue reading →
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Pazza idea di un pi greco razionale...Tutto inizia da un articolo su Stabroek News dove si annuncia che una matematica della Guyana, Lorna A. Willis, ha risolto alcuni dei problemi più noti della matematica greca, come per esempio la quadratura del cerchio (cui ho dedicato uno spazio nella terza parte della storia di $\pi$), utilizzando strumenti semplici come quelli che possedevano tali matematici.Al di là delle dimostrazioni più o meno complicate sull'impossibilità di quadrare il cerchio […]
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Starting next week, I will be teaching an introductory graduate course (Math 275A) on probability theory here at UCLA. While I find myself using probabilistic methods routinely nowadays in my research (for instance, the probabilistic concept of Shannon entropy played a crucial role in my recent paper on the Chowla and Elliott conjectures, and random […]
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Relative trace formula in the context of automorphic representations is an idea that goes back to Jacquet, and takes into account the distinction of automorphic representations. Distinction is easily defined: if $\pi$ is an automorphic representation of $G(\A_F)$ where $G$ is a reductive algebraic group $G$, $F$ is a global field and $\A_F$ denotes the […]
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In the age old tradition of cross-posting stuff I’ve written elsewhere. A while back Tim Arnold, the awesome person behind projects like plastex and mathjax-server asked the following question on the MathJax User Group. I am trying to decide what font to use for MathJax. The TeX font is the default, but I think I remember that the STIX-Web fonts have the best glyph coverage. I have a lot of math to support on all kinds of browsers. What factors should I consider when choosing the best […]

### September 29, 2015

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I had planned to get down to brass tacks as quickly as possible, with an object example from Ashby’s Cybernetics that made an impression on me at an early stage in my thinking about intelligent systems.  But while I was … Continue reading →
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From the Director of the Mathematics Division at the NSF: The National Science Foundation Graduate Research Fellowship Program (GRFP) recognizes and supports outstanding graduate students in NSF-supported science, technology, engineering, and mathematics disciplines who are pursuing research-based Master’s and doctoral … Continue reading →
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This article is aimed at relatively new users. It is written particularly for my own students, with the aim of helping them to avoid making common errors. The article exists in two forms: this WordPress blog post and a PDF … Continue reading →