tzs (u/tzs) - Readit News

tzs commented on Dark Alley Mathematics blog.szczepan.org/blog/th... · Posted by u/quibono

bmacho · 21 hours ago

I like this reasoning. Define a probability distribution on all circles of (x,y,r>0) based on how likely a given circle is. Then we can just sum the good circles and all the circles.

And the probability distribution is simple: a given (x,y,r) is as likely as its circumference in the unit circle.

Reasoning: Let C:(x,y,r) a given circle. We want to know how likely is it that the circle on 3 random points are close to it, closer than a given value d. (A d wide ball or cube around C in (x,y,r) space. Different shapes lead to diffferent constants but same for every circle.) The set of good 3 points is more or less the same as the set of 3 points from the point set C(d): make C's circumference d thick, and pick the 3 points from this set. Now not any 3 points will suffice, but we can hope that the error goes to 0 as d goes to 0 and there is no systematic error.

Then we just have to integrate.

ChatGPT got me the result 2/3, so it's incorrect. I guess the circumference must not be the right distribution.

tzs · 9 hours ago

Maybe it should be the cube of the amount of circumference inside the unit circle, because 3 random points have to land on the circle for it to be chosen.

tzs commented on British drivers over 70 to face eye tests every three years bbc.com/news/articles/c20... · Posted by u/bookofjoe

tzs · 10 hours ago

> Drivers in the UK must be able to read a number plate from 20 metres away, according to the Driver and Vehicle Licensing Agency (DVLA).

Unless I've botched the math and/or what the internet tells me about the size of the characters on a UK number plate is wrong this seems to be a bit overboard.

The internet is telling me that the characters are 79mm tall and 50mm wide (except for '1' and 'I') with a 14mm stroke.

My eyes right now are about 250mm from my monitor. Something that is 79mm tall and 20m away would have the same angular size as something 250mm away that is 79mm / 20m x 250mm = 0.9875mm tall.

If I set the size to 75% in Chrome that is the size of the numbers on this page in the timestamps and the submission points and comment counts. It is about 1/2 the size of the numbers in the text box that I'm writing this comment in.

I've just taken a photo of that and will include a link to it to show how small that is [1]. In that I'm holding a ruler next to the left side of the text. The "180" up where it says "180 points" is what you have to be able to read to pass the test. (If you can't see the photo because Imgur blocks your country just grab a ruler, hold it vertically 25cm in front of you, and the apparent size of the space between the mm marks is the size character you need to read).

I have no idea what road signs and markings are like in the UK, but in the US in ~50 years of driving I don't think I've ever needed to read anything anywhere near that small.

[1] https://imgur.com/a/NGuPdfF

tzs commented on Dark Alley Mathematics blog.szczepan.org/blog/th... · Posted by u/quibono

tzs · a day ago

I've got an idea for a simpler approach, but I've forgotten too much math to be able to actually try it.

The idea is to consider the set A of all circles that intersect the unit circle.

If you pick 3 random points inside the unit circle the probability that circle c ∈ A is the circle determined by those points should be proportional the length of the intersection of c's circumference with the unit circle.

The constant of proportionality should be such that the integral over all the circles is 1.

Then consider the set of all circles that are contained entirely in the unit circle. Integrate their circumferences times the aforementioned constant over all of these contained circles.

The ratio of these two integrals should I think be the desired probability.

tzs commented on Oregon raised spending by 80%, math scores dropped educationnext.org/hard-le... · Posted by u/grantpitt

icegreentea2 · a day ago

You can go to the "nations report card" and play around with the NAEP score stats: https://www.nationsreportcard.gov/ltt/mathematics/scores-per...

For me, two things pop out in particular.

Firstly, in math, if you look at how the percentiles break down, it seems clear that while there an overall drop in performance from 2020-2023, it also seems clear to that the top end of doing relatively ok. For example, at the 75th percentile, the we are basically flat from 2008 to 2020 (before dropping in 2023) - 2008: 305, 2012: 309, 2020: 307, 2023: 301 (net -4). This contrasts with the median which went from 2008: 283, 2012: 287, 2020: 282, 2023: 274 (net -9).

This implies to me that whatever flaws are in the overall system (at least pre COVID), the top end was relatively durable.

Secondly, if you go the "student group scores" section and click through all of the different sub-groupings, the only group that looks to have an overall flat score at all is "Private: Catholic".

I think the combination of the upper end being pretty durable, as well as the higher scores in the only "self selecting" category in the dataset may support what a lot of people tend to grumble about - the distribution of domestic situations is not favorable.

tzs · a day ago

The thing that popped out to me playing around with that is that when you look at most of these things from the late '70s through now, many show some modest growth or flatness through the '90s, then grew a little more up through the 2010s or so, and have pulled back a little in the last few years to roughly 2008ish levels. This is for both math and reading and for both 9 year olds and 13 year olds.

Depending on what exactly you are looking at the places that it grew or was flat or declines change, but overall the big picture look gives me more "keep an eye on it" vibes than "we've got a crisis" vibes that some people seem to think are justified.

tzs commented on Oregon raised spending by 80%, math scores dropped educationnext.org/hard-le... · Posted by u/grantpitt

tzs · a day ago

Careful looking at their graphs. If you don't keep in mind that they are showing changes you could get a wrong impression. For example on the page they link to to get data from every state, https://edunomicslab.org/roi-over-time/ , it shows the graphs for Massachusetts and Mississippi side by side.

In Massachusetts 8th grade math is down about 17 points. In Mississippi math down about 2 points. (I'm using 2022 scores).

That could give the impression that math scores are higher in Mississippi since the math line on the Massachusetts graph is way lower than the corresponding line on the Mississippi graph.

But the actual scores those years were 284 for Massachusetts and 268 for Mississippi.

tzs commented on The Waymo World Model waymo.com/blog/2026/02/th... · Posted by u/xnx

bragr · 2 days ago

Looking at prices, I think you are wrong and automotive Lidar is still in the 4 to 5 figure range. HESAI might ship Lidar units that cheap, but automotive grade still seems quite expensive: https://www.cratustech.com/shop/lidar/

tzs · a day ago

Those are single unit prices. The AT128 for instance, which is listed at $6250 there and widely used by several Chinese car companies was around $900 per unit in high volume and over time they lowered that to around $400.

The next generation of that, the ATX, is the one they have said would be half that cost. According to regulator filings in China BYD will be using this on entry level $10k cars.

Hesai got the price down for their new generation by several optimizations. They are using their own designs for lasers, receivers, and driver chips which reduced component counts and material costs. They have stepped up production to 1.5 million units a year giving them mass production efficiencies.

tzs commented on Volkswagen overtook Tesla as Europe's top EV seller in 2025 reuters.com/business/auto... · Posted by u/_fizz_buzz_

andsoitis · 2 days ago

Leaf and VW's electric offerings didn't capture the mind of people that EVs are good options.

Tesla made long-distance driving in EVs possible. Tesla made EV sexy, desirable. It catalyzed the Chinese EV industry. Neither Nissan nor VW remotely accomplished those things.

Like someone else said, people think in terms of a pre-Tesla and post-Tesla world. I don't know that there's a strong case against that framing.

tzs · 2 days ago

Leaf captured enough of the mind of the people that it took until early 2020 for Tesla's cumulative number of cars sold to surpass Leaf's.

tzs commented on The time I didn't meet Jeffrey Epstein scottaaronson.blog/?p=953... · Posted by u/pfdietz

tzs · 2 days ago

> Last night, I was taken aback to discover that my name appears in the Epstein Files, in 26 different documents

I'm kind of disappointed that my name is not in there. (Well the name is in there but not as my name. When you have a last name that has been in the top 5 in the US for over 230 years and a first name that was top 20 when people in the age group most likely to be in those files were born, you get a lot of false positives).

The bar to ending up in those files for perfectly innocent reasons is pretty low. Epstein was involved in a lot of legitimate things, probably to draw attention away from the illegitimate things.

Do some interesting research that gets some attention in the popular science press and Epstein might want to talk about funding you. Write an interesting book or article that comes to his attention and he might mention it in an email. Heck, write an interesting answer on Quora and you might end up in the files, because Epstein was subscribed to Quora's digest email.

If even 5% of what 15 year old tzs planned to accomplish with his life had happened, I'd be in there in at least one of those innocent ways. It highlights how mundane my life turned out.

tzs commented on Guinea worm on track to be 2nd eradicated human disease; only 10 cases in 2025 arstechnica.com/health/20... · Posted by u/bookofjoe

MPSimmons · 4 days ago

I was going to say, "finally something that ivermectin can help with!" except https://pubmed.ncbi.nlm.nih.gov/7974686/

tzs · 3 days ago

Well then, it's good you didn't say that then, considering that ivermectin has been on the WHO list of essential medicines since 1987 and its discoverers were awarded the 2015 Nobel Price in Physiology or Medicine for it.

Saying that something might be "finally something" that ivermectin can help with would have been embarrassing.

It would have been especially embarrassing because the link you gave gives two things ivermectin helps with. After concluding that ivermectin did not affect the guinea worms it says:

> No adverse reaction to treatment was seen. It appears that ivermectin can be used safely as mass chemotherapy against onchocerciasis and lymphatic filariasis in areas where guinea-worm is also endemic.

They are saying that if a patient has onchocerciasis or lymphatic filariasis it is safe to use go ahead and use ivermectin (which is the normal treatment for those) to treat those, even if the patient has guinea worms.

So good thing you didn't say it!

tzs commented on The Mathematics of Tuning Systems math.ucr.edu/home/baez/tu... · Posted by u/u1hcw9nx

TheOtherHobbes · 4 days ago

12tet is a practical compromise between overtone approximation and playability.

Any fretted or keyed acoustic instrument with more than 12 notes/octave is extremely difficult and expensive to build and hard to tune and play.

The music is also hard to notate, because there are so many more possible pitch positions.

So 12 notes became a practical default for instrument builders. And from there, ET became a practical default for tuning to allow smooth-ish modulation through different keys. The errors in the tuning are the same for every key, so the tuning relationships stay the same while the key root changes.

That doesn't quite happen because overtone perception and beating effects aren't completely linear. But it avoids the obvious out-of-tune notes you get when playing in distant keys with non-ET tunings.

tzs · 4 days ago

An interesting option for fretted instruments is to build it with 12 regular frets per octave, and then add temporary extra frets if you want to make specific notes more in tune for the key you are in.

This was common for lute players in the Renaissance and Baroque periods. Lute frets were usually made of the same material as strings and were tied on around the neck, so adding an extra full width fret was not hard.

Of course being tied on lute frets were also movable, so they could also reposition the regular 12 frets instead of adding extras.

Instead of tying on an extra full width frets another common option was partial frets. They would glue a piece of string or wood under a specific string, to just give an option to play one note with either the regular fret or the more in tone little fret (called a "tastino" (plural is "tastini")).

In this video [1] Brandon Acker uses a guitar that his luthier friend was building that had not yet had the frets installed to demonstrate with lute style tied on frets some different 12 tone tunings, then demonstrates using tastini to improve specific notes, such as little fret on the G string a little before the first regular fret so that G♯ and A♭ can be different notes.

The tastini he uses in the video are simply pieces of string held on with a piece of tape, so quick and easy to add and remove.

[1] https://www.youtube.com/watch?v=tiKCORN-6m8