east2west

The Eurofighter Typhoon houses two EJ200 engine with 60 kN (13,500 lbf) of dry thrust and >90 kN (20,230 lbf) with afterburners. I believe there are experimental versions of EJ200 with >100 kN thrust but since Typhoon is being retired across Europe and no oversea sales, we won't see Typhoon armed with them.

I am a big fan of "Matrix Differential Calculus with Applications in Statistics and Econometrics" by Jan R. Magnus, Heinz Neudecker. They are very thorough and rigorous with their exposition and proofs, which demands a degree of mathematical maturity on their readers. If you are comfortable with multivariate calculus (at the level of mathematical analysis for some materials) and linear algebra, then this book will teach you matrix calculus well.

On the other hand, if you are already familiar with calculus and linear algebra, then most of materials are just straightforward derivations using theorems you already know, so you might not need a textbook. I liked this textbook because it took mysteries out of formulas I was taught but never told about derivations, and because it was actually a quick read.

There are some limitations though. The book stops at Hessian matrices and matrix derivatives of vectors or something like that, because chain rules start breaking down and one needs multilinear algebra for higher order derivatives. However, for deep learning you don't need to worry about it. The book will teach you enough to derive the gradient of convolution as realized in matrix products.

I think that sentence is confusing but mathematical conclusion still stands. For quadratic forms, we are only concerned with symmetric matrices, or the symmetric part of any real matrix, because we can always replace any square matrix in a quadratic form, x^T A x, by x^T (A + A^T)/2 x, the symmetric part of the matrix, and the quadratic form still retains the original value. Then, for symmetric matrices, their eigenvalues being positive implies that the matrices are positive definite. Symmetric square matrices have real eigenvalues; one can prove this by taking the complement of quadratic forms.

This is the standard line from 50-cents (五毛). US and CCP counts deaths differently. One needs only to compare flu statistics to know they are not comparable.

US counts anyone with virus at the time of death while CCP releases no data and on rare occasion they publish statistics, the numbers are several orders of magnitude lower than US numbers.

Anyone can look up The Great Leap Forward and official coverup of ZhengZhou flood death this year to know that CCP covering up death is NOT a conspiracy theory.

Augustus' daughter Julia was married to Agrippa and despite their age difference the marriage was a happy one, as far as history remembers. Agrippa was a man of wide ranging culture and abilities and Julia was a vivacious leader of the cultured noble Romans. She also understood that messing with royal progeny is treason in monarchy, so when she was asked why her two sons both looked like Agrippa when she was widely suspected of adultery, she answered that she never took on passengers unless her cart was full.

Julia was banished later when she was married to Tiberius, the second emperor, by Augustus because Julia abandoned all pretense and Tiberius was a hard soldier and able administrator but lacked the refined tact and cultured grace of Agrippa. Tiberius' familial tragedy contributed to his isolation and insane persecution in the last years of his reign.

> Dude, what is this thing? I have no idea what's going on with this "佟丽娅嫁给中宣部副部长,"?

You say you are born in China, so presumably you can read Chinese. Then you can head over to [1] and read all about oversea Chinese making fun of CCP censoring salacious rumors about an actress and vice minister of Propaganda. The most powerful police apparatus and most sprawling internet censorship machinery working in overdrive to suppress tabloid, not because the rumor may or may not be false but because the Party knows the people believe it true in their heart.

[1] https://forums.huaren.us/showtopic.html?topicid=2761503&fid=...

You are spewing lies and half truth.

> Life itself is a human right, and probably the most precious one.

How can welding front gates shut be protecting human life? How can anyone survive after being cut off from food, medicine, supplies, contact, income? Don't pretend zero-tolerance policy is about protecting people, it is to protect Xi JingPing who has staked his personal political standing on the zero tolerance policy[1].

Some regions have been under continual lock-down for the better part of this year. Do you know how many people have died from lock-down? Does anyone know? Does CCP permit anyone to count? For that matter, how many people died in Wuhan two years ago? Why is CCP killing a citizen journalist for writing about Wuhan outbreak[2]? Is her life not human?

>VPNs are legal in China. You just need to be technically-sophisticated enough to find the correct VPNs, and make sure it falls in the boundary of Chinese law.

Pray tell which VPNs are legal in China? Which one can I use to visit HN legally in China? What is stopping an enterprising person to make your "correct" VPNs user friendly to the mass? I will you, because it does not exist!

> I have several wechat groups discussing serious political issues in China.

Why don't you post to your WeChat groups "佟丽娅嫁给中宣部副部长," reputed marriage of an actress to the vice minister of Propaganda Ministry and take a screenshot? You cannot even search it in Baidu, and you have the gall to say the Internet in China is constantly watched.

[1] https://www.wsj.com/articles/xi-jinpings-leadership-style-mi... [2] https://www.nbcnews.com/news/china/reporter-zhang-zhan-riske...

Do starving its own people and persecuting anyone who talks, thinks out loud, researches, or investigates it, work for you? The Great Leap Forward and the "Three-year Natural Disaster!" There was nothing natural about it and we still don't know how many perished.

I really like "Linear Algebra and Its Applications" by Gilbert Strang. It is not a textbook, the style is conversational, and he really tries to help you learn. It is one of rare math books that includes reason, context, application, and history without sacrificing rigor. The book also focuses on numerical algorithms aspects more than some popular textbooks, which may be helpful to understanding Kalman filter.

I believe ROS (Robotic operating system) has good implementations of state estimation algorithms. If you are worried about memory footprint, then Durbin and Koopman ("Time Series Analysis by State Space Methods") has a scalar version of squared-root Kalman filter (it ingests one number at a time rather a whole vector at a time). You may have to implement it yourself though.

The most thorough explanation of Kalman filter as recursive least square coupled with linear state-space models is "Linear Estimation" by Thomas Kailath, Ali H. Sayed, Babak Hassibi. It covers robust numerical algorithms such as square-root Kalman filter. Unfortunately, it is a big book and reading it is going to be a big time investment, but I believe it will be a worthwhile investment. It develops in depth various linear algebra concepts and demonstrates profound application to linear least square. This book is what people mean when they say learn from masters.

It is also the only technical book I have read that aptly quotes Shakespeare: "Age cannot whither her, nor custom stale her infinite variety."

I just tried your biology blog post generator and the second paragraph of the generated text, also the second sentence, is "Transcription is the process of converting audio into text." Obviously, the generator is confusing audio transcription with biological transcription like DNA transcription. Is this a common occurrence? Or did I make some mistakes in using the generator? I just pressed the "Execute" button.

Perhaps you are referring to modern nonstandard analysis, which I am sure has equivalent definition of limits. I will note that in standard calculus Epsilon-Delta is not only used in defining derivatives, but also used in defining function limits, which of course means used in defining integrals.

Just out of curiosity, in nonstandard analysis is there an equivalent of Lebesgue integral?

The modern approach to calculus using limits do not use infinitesimals. According to Richard Courant, "Mathematicians of first rank operated ... sometimes even with mystical associations as in references to 'infinitesimals' or 'infinitely small quantities.'" I believe we now use the "epislon delta" definition of limits.

"Introduction to Calculus and Analysis" Volume 1

Could you provide some examples of recent numerical linear algebra inspired by machine learning? The only numerical linear algebra related to machine learning, in particular deep learning, is matrix multiplication due to convolution. I am curious what else in numerical linear algebra is impacting machine learning.

I recall that the group that created Spark had a bioinformatics project on Spark but I don't know what happened to it. All I could find now is a paper[1] hosted by databricks.

[1]https://databricks.com/wp-content/uploads/2018/08/SSE15-40-D...

If it is Chinese companies, then presumably a lot of those devices are in China as well. Wondering whether they might be used to bring down the Great FireWall of China. At least any attempt might force the Chinese government to crack down on the manufacturers to improve device security.

Inside Julia compiler/runtime there is an interpreter, because Julia uses a heuristic to determine whether to compile or interpret a function. There is also interpreter code in Julia debugger. I don't know how full featured they are, but one does not have to start from scratch.

On the other hand, implementing a tracing JIT for Julia is going to be such a big task, I am not sure how much help existing interpreters are going to be. At the very least there needs to be a new GC, which necessitates changes everywhere except the parser. LLVM integration may also prove awkward for a tracing JIT.

I don't miss OOP in Julia but I do feel there need to be more ways to abstract things than multiple dispatch and structs. One thing I do miss is interfaces, which can group functions for a common purpose. I understand it may be not feasible in a dynamic language, but hopefully there will be something above functions as an abstraction mechanism.

Exactly, numerical errors could easily have accounted for the difference between already tiny p-values. The point isn't that the smaller p-value isn't better than the bigger one, it is, but that small significance should have been attached to the difference.

This example is a gnome-wide genetic association study. Every genetic variations are tested, so at least 500K or more linear regressions were performed. This many statistical tests could lead to many false positives just by chance, so one must do multiple-testing corrections. The end result of multiple-testing correction is much bigger and therefore worse p-values. Hence the drive toward ridiculously tiny p-values.

Already reached the conclusion when I saw a genetic researcher presenting his p-value < 10^-40 as better than < 10^-10. I kept my mouth shut because I didn't want to ruin the poor guy's moment in the sun, but I knew it was time to get out.

"on a backcountry trip in the desert ... strap on extra gallons of fuel" -- Since you are going into a desert, would a portable solar charger work in place of extra fuel? The downsize is that it is only usable in daylight and it might not be able to charge fast enough, but solar panel is not flammable like gasoline so safer. It is probably more realistic to have solar charging stations in desert, independent of electric grid; at least we don't have to run wires into desert just to charge cars.

Smooth acceleration will help prevent someone getting car sick. Similarly, absence of car exhaust helps, too.

I agree with most of what you said and share your frustration with the tooling of Julia. However, I am not sure how well I would expect a static checker to work for Julia. Julia after all is a dynamical language, and while you may disagree with that choice, the dynamical typing permeates the language. There is no pattern matching and no language features to manipulate types, for example. Julia's AST and IR share a lot in basic data structure thanks in large part to Julia's dynamical nature. Since adding static typing to Julia at the current stage of its development would be almost an upheaval, I am not counting on it.

This means there is an upper bound to how good the editing and refactoring tooling will be. I suspect the best will be a little below Pythong's tooling, because Python's class helps in disambiguating methods.

One feature of Julia I think could be improved upon is the `include` statement to import code, similar to C's `include` macro directive. This makes finding functions within a package an absolute nightmare. I think this also restricts LSP's ability to find definition and usage since this tends to make Julia packages one big source file as far as the compiler is concerned. I saw that in Julia's compiler code, the core developers include C source files, not header files mind you, in other C source files, so perhaps the feature stems from their personal preference. Python's file-module may be too restricting, but Julia's including is too loose.

Ever since introduction of potato to China large scale famines disappeared in China except for those caused by war, and by army and government seizing foods. Those modern famines are notable for their scale, duration, and entirely man-made political causes. CCP absolutely insists on calling them "natural disasters," precisely because they are unnatural. That is what!

In Rust you can write ```f: fn(i32) -> i32```.

Ocaml's syntax is more consistent, I agree, but its colon operator has different precedence than in Rust, so I am not sure its rational applies to Rust.

Believe it or not, TSMC owns and operates a fab in Mainland China, a 28nm one. So I imagine it posts quite a bit of job posting in China. It has recently applied for fab expansion in China, asking for some of that sweet, sweet free money CCP is doling out.

Actually, there is a Wall Street journal article about it. You can google it.

"China Blocked Jack Ma’s Ant IPO After Investigation Revealed Likely Beneficiaries"

There has been wild speculation about the source behind this story, including that Xi's faction provided details to WSJ since no one else had all the details.

Perhaps the author was trying to make the overview beginner-friendly by using familiar terms. I have found it helpful to compare and contrast Julia concepts with C++ template concepts. For example, term trait is used in similar ways in both languages, but the big difference is that in Julia type information can be passed in run-time, not just in compile-time.

For the most part, Boeing and Airbus don't produce equivalent airplanes because they aren't involved in regional jet business. The direct competitors include Bombardier CRJ900, Embraer E175-E2 or Mitsubishi MRJ90, according to Wikie[1]. However, with sale of CS 100 by Bombardier to Airbus as Airbus 220, competition is more direct, especially if future extensions of ARJ21 are realized. ARJ21 bears some resemblance to McDonnel Douglas MD-90, which China assembled under license last century, but they are not really in the same class, with MD-90 competing directly with B737.

A few things about Comac ARJ21 that make it unlikely that the aircraft will ever fly in the West. First, it is only certified by CAAC in China and there is no plan to try certification by FAA or EASA. Second, the aircraft is designed for hot climate and high altitude airports in Tibet. As a result, it is overweight and expensive to operate elsewhere. Third, there was a multi-year delay to certification, so the aircraft is now considered obsolete.

Although China owns IP rights to the aircraft design, engines and avionics are supplied by Western companies. Western parts suppliers had to shoulder more design work than normal for subcontractors. This aircraft is considered a learning experience for Comac, which is now designing C919, a competitor of B737 and A320; and C929, a wide-body aircraft in the same class as B787 and C330. Because of Western components, it is unlikely to be converted into military aircraft, which along with limited international sales means Comac will lose money with ARJ21.

1. https://en.wikipedia.org/wiki/Comac_ARJ21