# Posts

### April 18, 2014

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1:55 PM | One-tailed or two-tailed?

Someone writes: Suppose I have two groups of people, A and B, which differ on some characteristic of interest to me; and for each person I measure a single real-valued quantity X. I have a theory that group A has a higher mean value of X than group B. I test this theory by using […]The post One-tailed or two-tailed? appeared first on Statistical Modeling, Causal Inference, and Social Science.

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I recently saw a short list of advice for new assistant professors by Chris Blattman [Link]. Chris is an Assistant Professor of Political Science & International and Public Affairs at Columbia University (soon to be tenured). His list is summarized below. Go to his blog post for the full discussion: Learn to say no to new […]

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12:16 PM | You are not paying attention if...

you believe speckle is noise,your internet of things gadget does not have a camera,your business depends on making sense of camera data and you don't know about OverFeat, Caffe or ccv,you believe compressive sensing is niche,you believe that random projections are inferior to PCA,you believe the name of an implementation does the same as the name of the algorithmyou believe sensor design has little to do with Machine Learning.... TBC Join the CompressiveSensing subreddit or the Google+
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11:23 AM | The Lede Program has awesome faculty

A few weeks ago I mentioned that I’m the Program Director for the new Lede Program at the Columbia Graduate School of Journalism. I’m super excited to announce that I’ve found amazing faculty for the summer part of the program, including: Jonathan Soma, who will be the primary instructor for Basic Computing and for Algorithms Dennis […]

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Here is something new in the privacy game that relies on the fact that most matrix factorization in the recommender system business are low rank. From the paper:To the best of our knowledge, we are the rst to take into account the data disclosed by an analyst in the above privacy-accuracy tradeo , and to establish the optimality of a combined disclosure, obfuscation, and prediction scheme. Our proofs rely on the modeling assumption that is the cornerstone of matrix factorization techniques and
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1:30 AM | Rudyard Kipling and applied math

This evening something reminded me of the following line from Rudyard Kipling’s famous poem If: … If all men count with you, but none too much … It would be good career advice for a mathematician to say “Let all…Read more ›

### April 17, 2014

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The implementation for this solver is not available, here is another phase diagram for the Robust PCA decomposition. the previous one is featured in the Advanced Matrix Factorization Jungle page from Bilinear Generalized Approximate Message Passing by Jason T. Parker, Philip Schniter, Volkan Cevher. One wonders how the two diagrams fit with each other. Here is the paper: Robust Subspace Recovery via Dual Sparsity Pursuit by Xiao Bian, Hamid KrimSuccessful applications
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9:15 PM | MFM2P - Day 44

Day 44Today was some of my students' favourite class. Nothing to do with math, of course. My students got hot chocolate this morning. They were so well-behaved and patient waiting to get their cup ready - it was awesome. Some had mints which they added to make it more "sophisticated"! They politely asked for seconds and they very nicely said thank you. It was a good thing. And we did the Easter Estimation 180's while they drank it.With a few groans we moved back to working on slope. I
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6:08 PM | Riemann tensor in 2-d flat space

Reference: Moore, Thomas A., A General Relativity Workbook, University Science Books (2013) – Chapter 19; Problem P19.5. Another example of the Riemann tensor in a 2-d space. The metric is where is a constant. The metric tensor is therefore , . By comparing the two forms of the geodesic equation, we can calculate the Christoffel […]

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5:37 PM | STOC 2014 announcement.

Howard Karloff writes in to remind everyone that the STOC 2014 early registration deadline is coming up soon (Apr 30 !). Please make sure to register early and often (ok maybe not the last part). There will be tutorials ! workshops ! posters ! papers ! and an off-off-Broadway production of Let It Go, a tragicomic musical about Dick Lipton's doomed effort to stop working on proving P = NP.At least a constant fraction of the above statements are true.And if you are still unconvinced, here's a […]

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4:49 PM | Ricci tensor and curvature scalar

Reference: Moore, Thomas A., A General Relativity Workbook, University Science Books (2013) – Chapter 19; Box 19.5, Problem P19.1. We can form contractions over the indices of the Riemann tensor to get some other useful quantities. First, we can contract the first and third indices to get the Ricci tensor : Using the symmetry relation […]

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Reference: Moore, Thomas A., A General Relativity Workbook, University Science Books (2013) – Chapter 19; Box 19.4. Another relation of the Riemann tensor involves the covariant derivative of the tensor, and is known as the Bianchi identity (actually the second Bianchi identity; the first identity is the symmetry relation that we saw earlier). The identity […]

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Nelson Villoria writes: I find the multilevel approach very useful for a problem I am dealing with, and I was wondering whether you could point me to some references about poolability tests for multilevel models. I am working with time series of cross sectional data and I want to test whether the data supports cross […]The post If you get to the point of asking, just do it. But some difficulties do arise . . . appeared first on Statistical Modeling, Causal Inference, and Social Science.

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1:00 PM | RSRG does a triathlon

Our group has a history of doing athletic events during our outings over the years, hikes and even half-marathons. But, this past weekend we tried something a little more involved, a triathlon! Besides me, no one in the group had done a triathlon before (they hadn’t even done open water swimming before), but amazingly we […]

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As mentioned before, I'm not entirely comfortable with the fox/hedgehog spectrum -- this isn't a concept that reduces readily to a scalar -- but as long as we're here...One of the minor revelations of the recent discussion of the new 538 was that Andrew Gelman had posted on the subject of foxes and hedgehogs way back in 2005:This got me thinking about statisicians. I think we’re almost all foxes! The leading stasticians over the years all seem to have worked on lots of problems. Even when
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A paper written by Martin Gilens and Benjamin Page and entitled Testing Theories of American Politics: Elites, Interest Groups, and Average Citizens has been recently released and reported on (h/t Michael Crimmins) that studies who has influence on policy in the United States. Here’s an excerpt from the abstract of the paper: Multivariate analysis indicates that economic elites […]

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5:00 AM | Non-invasive real-time imaging through scattering layers and around corners via speckle correlations

Wow !Several themes mentioned in this blog are colliding in the following preprint. First thanks to the Moore's law we have the ability to do high resolution imagery with smartphone cameras like the Lumia 1020. Then there is this imaging with nature theme and then there is the sparse phase retrieval problem. I say sparse but there is no connection to that in this preprint and much like FROG (see here and here also), time will tell. What is so interesting here is that there is no need to
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### April 16, 2014

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6:13 PM | MFM2P - Day 43

Day 43Once a week the whole school stops what they are doing and reads for 30 minutes. Today West Reads fell during my grade 10 applied class so we read (most of us did anyway) for part of class.We then continued with slope which we had really seen in terms of steepness yesterday. I emphasized that it is the ratio of the change in the dependent variable to the change in the independent variable, as opposed to talking about rise over run which many students seem to mix up. To explain why the
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After experiencing a tragic and truncated end to the 2013 Boston Marathon, race organizers were faced not only with grief but with hundreds of administrative decisions, including plans for the 2014 race – an event beloved by Bostonians and people … Continue reading →

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Prakash Nayak writes: I work as a musculoskeletal oncologist (surgeon) in Mumbai, India and am keen on sarcoma research. Sarcomas are rare disorders, and conventional frequentist analysis falls short of providing meaningful results for clinical application. I am thus keen on applying Bayesian analysis to a lot of trials performed with small numbers in this […]The post Looking for Bayesian expertise in India, for the purpose of analysis of sarcoma trials appeared first on Statistical
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Two years ago, Wired breathlessly extolled the virtues of A/B testing (link). A lot of Web companies are in the forefront of running hundreds or thousands of tests daily. The reality is that most A/B tests fail. A/B tests fail for many reasons. Typically, business leaders consider a test to have failed when the analysis fails to support their hypothesis. "We ran all these tests varying the color of the buttons, and nothing significant ever surfaced, and it was all a waste of time!" […]

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A few weeks ago Omar Freilla came to talk to my Occupy group. Omar is a founder of the Green Worker Cooperatives and shared his experience as an organizer. He is a well-spoken guy and talked passionately about forming community cooperatives, where workers “have a direct role in decision-making and a share of all profits, build community wealth and help make […]

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8:27 AM | 3000th post. Wow !

So, this is the 3000th published post. wow! While there is nothing magic about this number, here is some perspective: it's about ten times 300 posts, or roughly the equivalent of 10 years of constant weekly posting and then some week-ends. I went from being ignorant about many things to having the blog mentioned in different quarters of the academic world. Let's not forget that one of the realities of the relative success of Nuit Blanche stems from the broken publishing model. On top of not
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### April 15, 2014

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5:12 PM | Timid medical research

Cancer research is sometimes criticized for being timid. Drug companies run enormous trials looking for small improvements. Critics say they should run smaller trials and more of them. Which side is correct depends on what’s out there waiting to be…Read more ›

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4:46 PM | MFM2P - Day 42

Day 42We started with elevator and bubble wrap estimations from Estimation 180, having skipped over the Christmas ones (despite the ridiculous snow today, it is not Christmas). I notice that my students' guesses are getting closer together - less crazy high and crazy low ones. They sometimes all underestimate or overestimate, which is interesting.Next up: staircases from Fawn. I used this as an introduction to slope. You should read her post, really, go read it now, it's better than what I did!
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2:53 PM | 2048

I am fascinated by the game 2048. I have been playing it for a month or so now and it has not really lost its appeal. The fascinating thing is that it seems to appeal to so many people. Students play, whether they are in applied math or calculus or not taking math at all. Little kids play. Adults with varying skills and careers play. It has this mass appeal that seems fairly rare these days. I play less now that I have "conquered" the game, but there is always another level to reach. My
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This would make Karl Popper cry. And, at the very end: The present results indicate that under certain, theoretically predictable circumstances, female ovulation—long assumed to be hidden—is in fact associated with a distinct, objectively observable behavioral display. This statement is correct—if you interpret the word “predictable” to mean “predictable after looking at your data.” P.S. […]The post When you believe in things that you don’t
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11:22 AM | Let’s experiment more

What is an experiment? The gold standard in scientific fields is the randomized experiment. That’s when you have some “treatment” you want to impose on some population and you want to know if that treatment has positive or negative effects. In a randomized experiment, you randomly divide a population into a “treatment” group and a “control […]

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A 0.75-million-point fourier-transform chip for frequency-sparse signals by Omid Abari, Ezz Hamed, Haitham Hassanieh, Abhinav Agarwal, Dina Katabi, Anantha P. Chandrakasan, Vladimir StojanovicApplications like spectrum sensing, radar signal processing, and pattern matching by convolving a signal with a long code, as in GPS, require large FFT sizes. ASIC implementations of such FFTs are challenging due to their large silicon area and high power consumption. However, the signals in
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