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Another example of how financial structures and incentives reshape industries: the consolidation of the ski industry under corporate ownership has turned skiing from a diverse, community-oriented pastime into a profit-driven, monopolized, and less enjoyable product — with higher (bundled) prices and operational cost cut driven by profit maximizaiton instead of the health of the sport. Capital is self-driven. Which also reminds me of this Freakonomics episode: Is Venture Captial the Secret Sauce of the American Economy.

A collection of class notes from 25 Fall’s Topics in Information Economics, taught by Professor Kamenica at Chicago Booth. Blackwell’s Theorem Aumann’s Common Knowledge Theorem A Unified Modeling Perspective to Compare Cheap Talk and Information Design LP Characterization of Cheap Talk vs. Bayesian Persuasion Game The last three lectures We did more than this but I don’t own the full lecture note’s copy right. If you find it useful or interesting, the credits goes to Prof Kemenica. If confusing, that’s probably my fault. Enjoy :)

An article about online social platform getting worse: Social Quitting by Cory Doctorow. It could be a motivation introduction to a wonderful economic theory paper. I won’t be surprised if it hasn’t already been quoted somewhere. The logic’s basically three phases: Platforms with network effects get more valuable as more people use them, which drives rapid growth. But the same effect creates high switching costs: leaving means losing access to all your relationships. Early on, platforms minimize switching costs to attract users; once dominant, they maximize switching costs to keep users trapped. Network effects + switching costs produce lock-in. Users unable to leave, platforms can subtract user surplus whatever they want. First, surplus is shifted from users to advertisers; later, once advertisers are also locked in, surplus is taken from them too. The platform degrades the service to extract maximum value from both sides. Eventually, degradation reduces benefits enough that leaving hurts less than staying. Switching costs fall, people exit, and inverse network effects kick in. So, enshittification isß not a moral failure but a structural outcome of monopoly platforms optimizing value extraction under high switching costs.

I used to be a vim-and-python minimalist. But now I’m an economist so, here’s how to run .ipynb on a server on a local computer. Set up ssh key for login, so that you won’t need to enter password a thousand times. See this blog configure SSH keys in terminal or your own HPC documentation. Booth’s HPC use slurm. I use mac. The following will be based on these backgrounds. Step 1: Login, get a computing node Login: ...

If it’s not broken, don’t fix it. DON’T. But if it ever (unfortunately) happens, here’s how to manage Papermod version control, compatible with hugo version: Structure of Hugo Papermod Website Papermod is the theme powered by Hugo. Usually, I maintain the website locally: arianas_blog_local_repository ├── archetypes ├── assets ├── config.yml ├── content ├── convert_links.sh ├── layouts └── shortcodes ├── audio.html └── video.html ...... ├── layouts_new ├── public ├── READMD.md ├── remove_tags.sh ├── resources ├── static └── themes └── PaperMod Here’s what each file work: ...

For an $m\times n$ matrix $A$ of rank $r \ll \min(m, n)$. $A$ has $r$ positive singular values: $$ 0\le \sigma_r \le \ldots \le \sigma_2 \le \sigma_1. $$ Denote as $\sigma\in \R^r$ the singular value vector. Its norms would satisfy: Spectral norm $$ \Vert A\Vert _2 = \sigma_1=\Vert \sigma\Vert _{\infty}. $$ Frobenius norm $$ \Vert A \Vert_F = \sqrt{\sum_{i=1}^r \sigma_i^r} = \Vert \sigma\Vert_2 $$ Nuclear norm $$ \Vert A\Vert_* = \sum_{i =1 }^r \sigma_i = \Vert \sigma\Vert_1. $$ ...

Whenever I look up matrix norms, I almost inevitably end up on Wikipedia. It’s usually the most reliable reference. Yet I also often find myself baffled by sentences like: “In mathematics, specifically functional analysis, the Schatten norm (or Schatten–von Neumann norm) arises as a generalization of $p$-integrability similar to the trace class norm and the Hilbert–Schmidt norm.” ?!? This is where the recursive study begins: confused by one definition, I open another page to clarify it, only to be met with two more unfamiliar terms, and on and on. This post is an attempt to stop the recursion. Here’s a simplified, self-contained guide to matrix norms. ...

During dinner my friends debated about what kind of egg one should buy. Some says that big (XL/jumbo) eggs is painful for hens. People should buy small eggs. One of the first-year student speaks up If everyone goes to buy small eggs, producers do notice that large eggs don’t sell well. Then hens that lay large eggs will lose their commercial value. Farmers will kill them and replace them with hens that lay small eggs. By buying large eggs yourself, you are protecting the jobs and the lives of hens that lay large eggs. ...

In the world of musical instruments and wine, quality is more subjective, and price signals more than just quality. It’s for sure not quasi-linear utility. Sometimes, the more expensive, the merrier. Soloist evaluations of six Old Italian and six new violins Link: https://www.pnas.org/doi/10.1073/pnas.1323367111 10 renowned soloists each blind-tested six Old Italian violins (including five by Stradivari) and six new during two 75-min sessions—the first in a rehearsal room, the second in a 300-seat concert hall. When asked to choose a violin to replace their own for a hypothetical concert tour, 6 of the 10 soloists chose a new instrument. A single new violin was easily the most-preferred of the 12. On average, soloists rated their favorite new violins more highly than their favorite old for playability, articulation, and projection, and at least equal to old in terms of timbre. Soloists failed to distinguish new from old at better than chance levels. ...

Partita is a Baroque-era instrumental composition, essentially a suite or collection of stylized dance movements, often starting with a prelude and including dances like the Allemande (German dance in 4/4), Courante (lively French/Italian in triple meter), Sarabande (A slow, dignified Spanish dance in triple meter), and Gigue (A fast, energetic dance of English/Irish origin). These form a coherent whole for a solo instrument or small group, most famously seen in works by J.S. Bach. ...