jacobolus

25,358 karmajoined il y a 19 ans

http://observablehq.com/@jrus

email: me AT jacobrus DOT com

comments

il y a 2 heuresdiscuss

That's all well and good, but you also shouldn't excuse authors for not providing context, motivation, or explanation under the theory that the students should really be figuring out the whole subject from scratch for themselves.

If you are really lucky the result of not explaining things might be an occasional exceptional student who works out a correct personal concept. But more commonly the result is just an unfilled gap in understanding and either a moderately motivated student who develops fluency with symbol twiddling but doesn't get the point of what they're doing or a less-motivated student who decides the topic sucks and gives up.

I've read a lot of linear algebra books, and I personally find Axler's to have average quality exposition and a not tremendously insightful point of view. I know other people who swear by the book though, so YMMV. It's more appropriate for a well prepared pure math student who wants to go to grad school and has a goal of internalizing a lot of jargon so they can read/write pure math papers than for a scientist or computer programmer.

il y a 4 heuresdiscuss

You can represent any arbitrary colors using RGB values for whatever "R", "G", and "B" primaries you like, they just might not fit in the range [0, 1].

(At least, under the strong assumptions we make in color modeling using the CIE system of colorimetry; the basic keyword is "Grassmann's laws".)

il y a 5 heuresdiscuss

Really? I find the part about the SVD in Axler's book extremely unhelpful, big blobs of opaque formulas and jargon with next to no explanation or context that basically require either knowing the topic fully beforehand or a huge amount of effort to parse.

e.g. Axler's definition of singular values is the extremely dry and technical:

> Suppose T is in L(V, W). The singular values of T are the nonnegative square roots of the eigenvalues of T†T, listed in decreasing order, each included as any times as the dimension of the corresponding eigenspace of T†T.

(Using a dagger instead of an asterisk for the conjugate transpose since HN interprets and asterisk to mean italics.)

If you already just proved a lot of stuff about eigenvalues, this could be a serviceable definition; at any rate it saves space. But it doesn't really explain the point.

I'd recommend anyone interested in this or related topics read Trefethen & Bau (1997) Numerical Linear Algebra.

il y a 7 heuresdiscuss

Housing has gotten much more expensive in many places, and jobs less stable.

Scott Perry didn't present any evidence for those claims. Ideologically he is opposed to the humanitarian work USAID does around the world, and he cheered as Elon Musk dismantled the agency.

Perry was also one of the key figures in the criminal conspiracy trying to overturn the result of the 2020 election and overthrow the US government to install Donald Trump as a dictator based on a series of outrageous lies. If Trump hadn't been elected again in 2024, interrupting the relevant investigations, there's a decent chance Perry would be either on trial or perhaps even already convicted for his crimes (conscious of his guilt, he directly asked Trump for a pardon).

I wouldn't consider any claims he makes credible without some corroborating evidence.

il y a 11 joursdiscuss

In practice what happens is that on average the tool-user's wages go up slightly but most of the jobs in the field are eliminated, and the resulting large profit mostly goes to managers and financiers.

il y a 15 joursdiscuss

Each congressperson's staff gathers all of the comments they get, counts them up, and reports back to the congressperson, passing along anything they think would be useful information; if you write a clear and careful letter about an obscure topic there's a decent chance the congressperson themself will see it. Congresspeople typically have local ties in their area and caring what their constituents think is their job.

It's a serious problem that there are some congresspeople who don't do any local events, send all comments straight to the trash, etc. You should vote those folks out.

In the longer term, we should push for significantly increasing the size of the US House of Representatives to 5–10x the current size and implement serious campaign finance reforms. In combination, these will help make congresspeople more responsive to constituents and less reliant on donors.

le mois dernierdiscuss

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le mois dernierdiscuss

One is people's lived experience: "Hard-working families immigrate to a land of better opportunity and build a life for themselves, integrating as upstanding members of the community."

The other is nativist propaganda: "Hordes of scary 'aliens' are coming to take your jobs and destroy your way of life, bringing their drugs and crime and turning your neighborhood into a trash heap. They might even eat your pets!"

People have difficulty noticing that the second story is supposed to be a description of what they or their ancestors personally lived as the first story; people compartmentalize and sometimes believe the propaganda version even though it directly contradicts their lived experience.

il y a 2 moisdiscuss

Scholars aren't supported by sales of their published work, but by teaching/research salaries, much of the money for which comes from the public via government grants.

Musicians by and large aren't supported by record sales, especially in the streaming era, but by concert tickets, merch, etc., or often by other income sources like paid lessons, session work, one-off commissions for specific customers, etc.

Very few fiction authors make a living at it, and most of those who do are barely scraping by.

Journalism is in a very sorry state in the 2020s; its long-time essential income source – classified ads – collapsed a couple decades ago under pressure from free or cheap online substitutes and the industry still hasn't figured out a viable alternative at scale. There has been a 75% drop in local journalists since 2000, most important local news now goes unreported (in many places there is no local reporting whatsoever) and regional/national scale journalism has been increasingly co-opted by the super-wealthy and turned to propaganda. Independent industry leaders with integrity are, over time, replaced by shills and the ethics of industry culture is degenerating.

Big budget TV/movies is probably closest to matching your argument, since these require large-scale coordination by hundreds of people to produce, but here too there are significant complications.

In all of these industries, the people making most of the profit are businesspeople rather than creators, though a trivial number of celebrity creators make good money.

Much of the published culture you mention is done entirely as a hobby, and our current copyright regime actually stands in the way of creation as much as supports it.

il y a 2 moisdiscuss

One thing to keep in mind is that many (most?) of the books and papers in these archives are decades old, usually no longer in print, make zero or vanishingly small amounts of money for their original creators, are sometimes only physically available from distant libraries that are challenging to access, etc.

In doing scholarly research, it's extremely helpful to be able to quickly search and skim hundreds of vaguely relevant sources, but simply wouldn't be worth the trouble to pay for or track down a "legitimate" copy of every one, and in many cases would be physically impossible. These "pirate" archives make doing real library research, previously limited to scholars at top-tier universities, accessible to orders of magnitude more people.

There really isn't that much profit in most of these works, and whether a scholar reads one on their laptop screen vs. in a physical book in a university library somewhere doesn't have any material impact on the original authors, editor, illustrator, translator, printer, etc.

il y a 2 moisdiscuss

That sounds plausible. Most of the features are kind of gimmicky bolt-ons added piecemeal and not really integrated with each-other. They make for cool 10-second demos but then most users ignore them because they aren't part of a coherent system. The result is a menu after menu of gimmicks, like a cabinet of hyper-specialized kitchen tools bought from infomercials. There has been limited product vision about the core abstractions and their basic composability. If you give a skilled user a photoshop version from the early 2000s they'll largely be able to do what they need, because there hasn't really been much fundamental innovative improvement in the past ~25 years.

il y a 2 moisdiscuss

Plenty of students succeed just fine without owning a graphing calculator (they can spend a few minutes learning the handful of test-relevant features and borrow one for the exam). Thankfully as of this year there is also a Desmos option.

il y a 2 moisdiscuss

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il y a 2 moisdiscuss

Ideally the tests would not require external tools at all. There's nothing that needs to be tested in the context of a high school course that can't done with pencil and paper.

il y a 2 moisdiscuss

NEET means "Not in Education, Employment, or Training". The stereotype is an unemployed young adult living with their parents and playing video games all day.

il y a 2 moisdiscuss

They had different models with different capabilities. As they made minor style changes, they bumped the numbers slightly. The 81–82–83–84 were basically the same concept, as were the 85–86. The 89 and 92 were higher-end models. The 80 and 73 are simpler models intended for middle school.

All of them are basically a multi-generational scam perpetrated against the hapless parents of American high school students who were told that they needed to buy overpriced anachronistic calculators for their kids to succeed in school. In my opinion the calculators have overall caused more pedagogical harm than benefit; the students would be better served by some combination of (a) problems that can be solved without the tedious but trivial numerical calculations these calculators support, or (b) are solved using a real programming language. If someone really wants to assign simple numerical problems, give the kids slide rules.

Calculators of this type used to make sense for an engineer doing work in the field somewhere, but make no sense in the context of a classroom.

il y a 3 moisdiscuss

You should try to avoid continuous static load on your muscles, especially the smaller ones. So you should find a typing position where that doesn't happen. You also want to use your muscles in the strong and comfortable part of their range of motion, which depends on the entire chain of joints, because tendons have to stretch past several joints to get to whatever bone they attach to – so for fluent finger motions, you want to keep wrists and hands in as neutral a position as you can.

If your wrists are not straight while typing a lot, that's really bad. I constantly see people typing with their wrists either significantly flexed or significantly extended; doing that a lot is a fast road to RSI, and even doing it a little is pretty unpleasant and inadvisable.

If you are going to type a whole lot at a stretch (say, as a programmer or writer), you want your arms to be mostly passively supported from the shoulder. Having your arm bent at the elbow doesn't cause much strain, as long as the upper arm is hanging loosely down with your shoulder relaxed – so bring the keyboard relatively close to your torso. Resting your wrists, palms, or forearms on some surface and then typing generally causes more strain than having your wrists and palms "floating" above the keyboard while actively typing. You can rest the fingertips lightly on the key tops if you want. You can rest your palms on a palmrest or arms on an armrest (or table, or lap, or whatever) while you are taking a break from typing. It's generally a good idea to take regular breaks.

il y a 3 moisdiscuss

> the monitor should be at eye level vertically

This is slightly misleading advice. The ideal place for the display has the top of the display at roughly eye level, or for a very large display maybe slightly above, which puts most of the display below eye level. Humans actually have great ability to look slightly downward for long periods of time while doing stuff with their hands, even while keeping their head held up straight, and indeed our eyes can more comfortably focus on close objects in the lower part of our field of view than straight ahead. What you don't want to do is slouch or bend your neck too much.

A laptop display attached to the keyboard usually isn't an ideal placement, but it's generally not too bad.

il y a 3 moisdiscuss

Having the desk low, the chair high, or putting a laptop on your lap is okay. Having the desk or table "high" (i.e. at normal height for writing with a pen or eating a meal) is generally worse but not an insurmountable problem.

In either case, the most important thing is to keep your wrists in as straight and neutral position as possible, with your palms and wrists "floating" rather than resting on anything while actively typing. Having the wrists either flexed downward or extended upward is a really bad idea. Having the wrists turned out to the side isn't great either, but not as bad.

The keyboard should be positioned close enough to your body so that your shoulders can be relaxed with your upper arms hanging loosely. The laptop surface should be roughly parallel to your forearms, so if you have a high desk or table relative to your torso you will need to prop up the far side to tilt it up a bit.