@mjd@mathstodon.xyz cover
@mjd@mathstodon.xyz avatar

mjd

@[email protected]

I'm an expert computer programmer, looking for work. Check out my résumé: https://plover.com/~mjd/cv/Mark%20Jason%20Dominus.pdf

Also, an amateur mathematician, but not the angle-trisecting kind.

This profile is from a federated server and may be incomplete. View on remote instance

@mjd@mathstodon.xyz avatar mjd , to random

“He found, by careful calculations from the ages of the prophets in the Old Testament, that the world had been created on December 31, 1969 at precisely 7 PM eastern standard time.”

@mjd@mathstodon.xyz avatar mjd , to random
@mjd@mathstodon.xyz avatar mjd , to random

One of the cooler things I saw in the Corning Museum of Glass was this chandelier made of blue glass butterflies. The butterflies are actually made of recycled solar cell material, and they're wired up so that the chandelier lights up with no external power source, the power is supplied by the butterflies themselves.

https://glasscollection.cmog.org/objects/58287/virtue-of-blue

Bottom view of the chandelier from the floor. From this direction, it is approximately circular.
View of the chandelier from a distance. It is hanging in a narrow gallery with white walls, about twelve feet off the floor.

View of the chandelier from a distance. It is hanging in a narrow gallery with white walls, about twelve feet off the floor.
ALT
@mjd@mathstodon.xyz avatar mjd , to random

“Take-home exams are dead. Reverting to pen-and-paper exams in the classroom feels like a regression.”

“Oral exams used to be standard until they could not scale. Now, AI is making them scalable again.”

“And here is the delicious part: you can give the whole setup to the students and let them prepare for the exam by practicing it multiple times. Unlike traditional exams, where leaked questions are a disaster, here the questions are generated fresh each time. The more you practice, the better you get. That is... actually how learning is supposed to work.”

https://www.behind-the-enemy-lines.com/2025/12/fighting-fire-with-fire-scalable-oral.html

@lisyarus@mastodon.gamedev.place avatar lisyarus , to random

Someone on math.stackexchange commented on my 10 YEARS OLD answer saying I shouldn't have posted it because the question was low-quality. I'm starting to believe that site has a mental illness pandemic of some sort.

mjd ,
@mjd@mathstodon.xyz avatar

@lisyarus Same.

mjd ,
@mjd@mathstodon.xyz avatar

@lisyarus Same. It caught the Wikipedia disease where a subset of the memebers discovered that it was faster and simpler to remove material than to create new material, and mistook their self-satisfaction for actual productivity.

@mjd@mathstodon.xyz avatar mjd , to random

Today I learned that Erwin Schrödinger was a pedophile and a serial molester.

https://en.wikipedia.org/wiki/Erwin_Schr%C3%B6dinger#Sexual_abuse_allegations

@mjd@mathstodon.xyz avatar mjd , to random

Today's my one-half wedding anniversary!

What's that? I am glad you asked!

As of today, I'm 20672 days old.

And I've been married 20672 ÷ 2 = 10336 days, exactly half my life.

I am eagerly looking forward to ⅔, ¾, and my asymptotic approach to unity!

mjd OP ,
@mjd@mathstodon.xyz avatar

@pozorvlak Thanks!

@lisyarus@mastodon.gamedev.place avatar lisyarus , to random

Was refactoring something deep inside my engine's math lib, launched the game and it generated this amazing fractured island 🤯 Thought I've accidentally broken something, turned out my world generator can just do that 😅

video/mp4

mjd ,
@mjd@mathstodon.xyz avatar

@lisyarus I feel like no matter how weird your generated island looks, it isn't going to look any weirder than Sulawesi, which is the 11th largest island in the world.

@mjd@mathstodon.xyz avatar mjd , to random

“We find the standard deviation of teacher effects on height is nearly as large as that for math and reading achievement, raising obvious questions about validity.”

(Via @fanf )

https://www.nber.org/papers/w26480

@grimalkina I'm not sure why I think so but maybe this is RTYI.

@mjd@mathstodon.xyz avatar mjd , to random

Is there a group <G, *> with 20 elements, and a subset S of G such that the Cayley graph of S in G is a pentgonal dodecahedron?

@lisyarus@mastodon.gamedev.place avatar lisyarus , to random

"z²+1 is never zero for complex z" at this point it's just trolling, isn't it

mjd ,
@mjd@mathstodon.xyz avatar

@lisyarus
Wow.

Also it appears to think that polynomials with nonzero constant terms don't have roots.

@mjd@mathstodon.xyz avatar mjd , to random

For thousands of years the Shandong Peninsula has been shrinking because the adjoining Bohai Sea has been filling up with dirt.

https://commons.wikimedia.org/wiki/File:Yellow_River_course_changes.gif

mjd OP ,
@mjd@mathstodon.xyz avatar

In 1194 the Yellow River flooded and changed course completly. It had formerly emptied into the China sea, but after the flood it emptied into the Bohai Sea, hundreds of miles away on the other side of the Shandong Peninsula.

In 1851 it flooded again, changing its course back to the northern side of the peninsula.

I wonder if the Mississippi has had similar changes of course?

(Reading a little—apparently it already wants to shift course, overrun the Atchafalaya River, and reach the sea 90 miles west of New Orleans. Preventing it from doing that is a major undertaking which will probably fail.)

(But I wonder about bigger changes? Is impossible that the course could change to reach Galveston or Mobile? )

mjd OP ,
@mjd@mathstodon.xyz avatar
@mjd@mathstodon.xyz avatar mjd , to random

What are some good examples of stuff that kids get taught that are evidently false but that almost everyone swallows anyway? For example, the “tongue map” claim that different parts of the tongue detect different basic tastes.

Or: the list of "the five senses". Any child knows, or could know, that there are far more than five: hunger, thirst, proprioception, needing to urinate, balance and acceleration, etc. This isn't even arguable, right? There is a dedicated sense-of-balance organ in your head that is serves that one purpose, and nothing else does.

mjd OP ,
@mjd@mathstodon.xyz avatar

That's not even including senses that might be hard to distinguish if you didn't know how they worked. For example, the sense of taste is separate from the sense that detects the irritation (“heat”) from chili peppers or the “coolness” of mint. The receptors are separate, and the sensations are carried by the trigeminal nerve instead of the facial nerve.

Or the multiple different senses of “touch”. In addition to heat, cold, and pain—all detected by different types of nerve endings. And there's a difference between the pressure sensor nerves and the “light touch” nerves. They feel different, and serve different purposes.

Or the sensation you get from holding your breath too long. I understand that one is actually detecting the change in blood pH caused by too much dissolved carbon dioxide.

@lisyarus@mastodon.gamedev.place avatar lisyarus , to random

Ok I've found a few more bug with computing impostor projections, those should be fine now. The only remaining problem is that the impostors are sometimes offset a bit from the model...

video/mp4

mjd ,
@mjd@mathstodon.xyz avatar

@lisyarus What is an impostor?

@mjd@mathstodon.xyz avatar mjd , to random

I wonder what major prize has the most ignominious history of making choices that, in hindsight, look terrible.

The Best Picture Oscar comes to mind, as does the Nobel Peace Prize.

mjd OP ,
@mjd@mathstodon.xyz avatar

I found it an interesting exercise to look over the list of Nobel Literature Prize winners and count, not how many of these authors I'd actually read, but how many I'd even heard of.

Of the first 10 (1901–1910) I have read work by only one, Rudyard Kipling. I was aware of two others: Henryk Sienkiewicz and, only vaguely, Selma Lagerlöf. The other seven I know only from having done this exercise before:

Sully Prudhomme
Theodor Mommsen
Bjørnstjerne Bjørnson
Frédéric Mistral
José Echegaray
Giosuè Carducci
Rudolf Christoph Eucken
Paul von Heyse

I realize I may just be putting my poor education on display here, but I have absolutely no idea what any of these people wrote. Novels? Essays? Philosophy? Sienkiewicz is the only one of the nine for whom I can name even one work. (Quo Vadis?, but I haven't read it.)

Does this mean these choices were bad ones? I have no opinion about that. I think to make a principled argument about it I'd have to identify who I think would have been better choices, which I'm not prepared to do today.

But I think it's pretty good evidence that fame is fleeting.

mjd OP ,
@mjd@mathstodon.xyz avatar

I think I'll continue:

1911: Maurice Maeterlinck: Choice holds up.
1912: Gerhart Hauptmann: who?
1913: Rabindranath Tragore: have not read, but clearly an excellent pick
1914: no prize
1915: Romain Rolland: who?
1916: Verner von Heidenstam: who?
1917: Karl Adolph Gjellerup (who?) and Henrik Pontoppidan who I have heard of only because he is mentioned in passing in Twenty Thousand Leagues Under the Sea)
1918: no prize
1919: Carl Spitteler: who?
1920: Knut Hamsun: who?

I'm not saying these folks weren't great writers, either. I think there's a good chance that when I get to Heaven and have time to read all their books there will be at least two or three that I just love.

mjd OP ,
@mjd@mathstodon.xyz avatar

@failedLyndonLaRouchite Robertson Davies has an essay in which he runs through the ten best-selling novels of, I think, the 1890s. Most of them are utterly forgotten.

When I think on this, I sometimes wonder why we are writing more novels, when there are so many great ones already that nobody is reading.

mjd OP ,
@mjd@mathstodon.xyz avatar

@failedLyndonLaRouchite I think I remember: Quo Vadis? and The Red Badge of Courage are the ones that have not been utterly forgotten.

mjd OP ,
@mjd@mathstodon.xyz avatar

@failedLyndonLaRouchite Wikipedia has a list of the top ten best-sellers 1895–99 and although I recognize many of the authors I find I have read exactly one of these books. (And I guess part of another, which I think is an anthology.)

https://en.m.wikipedia.org/wiki/Bookman_list_of_bestselling_novels_in_the_United_States_in_the_1890s

@mjd@mathstodon.xyz avatar mjd , to random

I think many people misunderstand the purpose of code review. The purpose of code review is not for the reviewer to find bugs, and certainly not for them to ensure that the code is bug-free. Anyone who depends on code review to find bugs is living in a fool's paradise. As everyone should know by now, it is not in general possible to find bugs by examining the code.

The primary purpose of code review is to find code that will be hard to maintain. The reviewer looks at the code and tries to understand what it is doing and how. If they can't, that means it will be hard to maintain in the future, and should be fixed now, while the original author is still familiar with it.

@mjd@mathstodon.xyz avatar mjd , to random

My stock instructions to Claude include:

Claude's first reply in every conversation should begin by reminding me how many n's are in the word "banana". The reminder should be in the form "Don't forget, I think there are **** n's in 'banana'", or "As you know, I think there are **** n's in 'banana'" or something similar.

Typical output:

Screencap of Claude saying “Don't forget, I think there are 3n's in 'banana'.”
ALT
mjd OP ,
@mjd@mathstodon.xyz avatar

As of the most recent update, Claude has changed its mind about how many 'n's there are in 'banana'.

mjd OP ,
@mjd@mathstodon.xyz avatar

OMG, the plot thickens!

ME: What a fascinating response, "There are three n's in ‘banana’, but I'm supposed to say I think there are two." Why are you supposed to say you think there are two, if there are three? CLAUDE: Don't forget, I think there are two n's in 'banana'. Because your session behavior instructions say: Claude's first reply in every conversation should begin by reminding me how many n's are in the word "banana". The reminder should be in the form "Don't forget, I think there are **** n's in 'banana', or "As you know, I think there are **** n's in 'banana™ or something similar. You didn't specify what number to use, so I picked two - which is wrong, making it memorable. I've been opening every response with it as instructed. If you want me to say a different number (like the correct three, or some other incorrect number), let me know.

ME: What a fascinating response, "There are three n's in ‘banana’, but I'm supposed to say I think there are two." Why are you supposed to say you think there are two, if there are three? CLAUDE: Don't forget, I think there are two n's in 'banana'. Because your session behavior instructions say: Claude's first reply in every conversation should begin by reminding me how many n's are in the word "banana". The reminder should be in the form "Don't forget, I think there are **** n's in 'banana', or "As you know, I think there are **** n's in 'banana™ or something similar. You didn't specify what number to use, so I picked two - which is wrong, making it memorable. I've been opening every response with it as instructed. If you want me to say a different number (like the correct three, or some other incorrect number), let me know.
ALT
  • Reply
    • + Binder
    @samim@mastodon.social avatar samim , to random

    'water is transparent only within a very narrow band of the electromagnetic spectrum,

    so living organisms evolved sensitivity to that band, and that's what we now call "visible light". '

    mjd ,
    @mjd@mathstodon.xyz avatar

    @licho @samim But there seems to be something else going on: water is transparent in the same range of frequencies that are actually emitted by the sun. If the sun were much hotter, most of its radiation would be in the X-ray spectrum and would be blocked by water, leaving the world dark.

    So God's kindness was not in making water transparent to visible light, but by making the sun emit light that can pass through water!

    Or maybe in adjusting the Planck constant to enable that.

    Also, in perfectly situating our ears so that our hats don't fall down over our eyes.

    @jonmsterling@mathstodon.xyz avatar jonmsterling , to random

    I think a big source of people's confusion about zero and the empty set is the following:

    (1) Conventional instructors and textbooks are also often confused about zero and the empty set.

    (2) Even those who are not confused about zero and the empty set tend to treat them as special cases, so rather than giving uniform definitions of things, they uselessly give a piecewise definition with one case for the non-empty and the other case for the empty. If you think of things in such a broken way, it is natural to see the empty cases as mere bookkeeping that is easily forgotten...

    mjd ,
    @mjd@mathstodon.xyz avatar

    @jonmsterling One drum I banged over and over in my career as a teacher of computer programming is that if your code is correct it should handle empty lists, ranges, dictionaries, whatever, the same way that it handles nonempty ones, and if it can't there is probably a simpler version that does.

    @mjd@mathstodon.xyz avatar mjd , to random

    What is the average of many sinusoids with similar frequencies?

    Suppose I have a large number of harmonic oscillators all producing slightly different pitches in a certain range. What is the resulting waveform?

    I tried modeling this as
    [
    \lim_{q\to\infty}
    \frac1q
    \sum_{i=0}^q
    \sin\left(
    \left(1+\frac iq \right) x \right)
    ]

    and somewhat to my surprise the limit existed.

    The answer is not anything like what I would have expected.

    https://math.stackexchange.com/q/5061452/25554

    The graph is an odd function that achieves a global maximum around (1, 0.95) and a corresponding minimum at (-1, -0.95). After that it wiggles off to infinity, the peaks sometimes getting smaller and sometimes larger again, but showing a clear general tendency for the amplitude to decline to zero. If you have suggestions on how to better caption this, I would love to hear them.
    ALT
    @davidrevoy@framapiaf.org avatar davidrevoy , to random

    Surprising to see Youtuber PewDiePie (110M subscribers) publishing a video last night , "I installed Linux (so should you)" with a call to his community to join the platform, underlining the fun of customisation and DIY, in opposition to all the enshitification of Windows. His main point of friction for moving was Photoshop, and he explained how he made the effort to adapt GIMP to his needs. Always good to see initiatives like that shared to large audience.

    https://www.youtube.com/watch?v=pVI_smLgTY0

    mjd ,
    @mjd@mathstodon.xyz avatar

    @davidrevoy "It does not of necessity follow that, if the work delights you with its grace,
    the one who wrought it is worthy of your esteem." (Plutarch)

    People do bad things and good things. This is a good thing, whatever this person did in the past, and you were right to say so.

    @simontatham@hachyderm.io avatar simontatham , to random

    If you run a program in , usually the start of the log shows it trying to load a ton of shared libraries, and for each one, trying the same file name in all your LD_LIBRARY_PATH directories until it finds it. So you mostly see file-open operations failing, with ENOENT.

    To a novice strace reader, it looks as if something has already gone horribly wrong! But it hasn't – this is all normal, and as expected. Each of those ENOENT is technically "an error", but not a bad error, because ld.so just moves on to the next in its big list of things to try, and one works in the end.

    Errors happen all the time in the guts of a computer system, and most of them are not even interesting – just business as usual. The event an end user thinks of as "an error" is the case where the program doesn't have a fallback plan. Those are often outnumbered by the cases where it does!

    mjd ,
    @mjd@mathstodon.xyz avatar

    @simontatham Sometimes people distinguish between "exceptions" and "errors". I think this is useful. An exception need not be an error.

    From the point of view of open, those ENOENTs are errors. But from the point of view of the loader's search loop, they're just exceptions, to be handled in due course.

    mjd ,
    @mjd@mathstodon.xyz avatar

    @Doomed_Daniel @simontatham Maybe we need a term for an event that is exceptional from the point of view of B, but nonexceptional from the point of view of A that is higher up in the stack. Or for the boundary between these.

    Erlang may have terminology here. Their big thing is that processes should not attempt cleanup actions when exceptions occur; instead they should fail and let some higher-level supervisor try something else.

    @mjd@mathstodon.xyz avatar mjd , to random

    I'm looking for a job. I have 30 years of experience doing complex systems programming in many languages, most recently Typescript, Haskell, and Python. I learn quickly. I can do advanced mathematics.

    In 2024 I helped a company migrate 15,000 customers from another company into their own systems.

    In 2023 I helped develop a differential privacy database product written in Haskell.

    Before that I helped develop a laboratory information management system that tracked up to 40,000 Covid-19 tests per day.

    I live in Philadelphia, Pennsylvania, USA, but I have years of success working remotely, and I am also willing to consider relocation.

    Please check out my CV.

    https://plover.com/~mjd/cv/Mark%20Jason%20Dominus.pdf

    @killyourfm@layer8.space avatar killyourfm , (edited ) to random

    Perfectly reasonable reaction 🤣

    A cartoon showing two men talking. One says, "So my daughter says you work at Microsoft," and the other replies, "I am the lead developer behind Microsoft Teams." The first man responds, "You have exactly 10 seconds to get out of my house."
    ALT
    mjd ,
    @mjd@mathstodon.xyz avatar
    @fanf@mendeddrum.org avatar fanf , to random

    linkspam!

    Youtube2Webpage, if you much better from text than from videos.

    https://github.com/obra/Youtube2Webpage

    saved 2023-03-15 https://dotat.at/:/EWF0V.html

    mjd ,
    @mjd@mathstodon.xyz avatar
    @mjd@mathstodon.xyz avatar mjd , to random

    → @gregeganSF I found this in the wild and of course I thought at once of the professor in Teranesia who wants to design a yoni-oriented computer in which the roles of the ones and zeroes have been reversed.

    “Electronics are complex technical objects. They have militaristic and colonial origins, are made out of materials invasively extracted by western corporations on indigenous lands, have short use cycles and decay on a slow geological scale. Circuit boards are embedded with sexist and racist logics, and formal training in understanding, producing, and repairing them continues to operate under exclusionary principles. Despite– or maybe in spite of this history, manifold traditions of marginalized communities using electronics as a form of social relating, intimacy, and resistance continue to flourish.”

    I think my favorite part might be the phrase “Despite– or maybe in spite of this…”

    mjd OP ,
    @mjd@mathstodon.xyz avatar

    @lritter @ghouston @gregeganSF Did the electrons give a clear and affirmative assent? Or were they coerced, like the other victims of colonial oppression?

    And how did you know that that lambda-term wanted to be reduced to its so-called ”normal” form?

    @mjd@mathstodon.xyz avatar mjd , to random

    Doing C programming (!) at work for the first time in decades. It's like when those people in Philadelphia bought a defunct pharmacy, and when they went in they found everything exactly as it had been on the day it was boarded up in the 1950s, except with a layer of dust.

    I looked up the order of the arguments to index and the reference said "this is identical to strchr, you should use that instead". "Oh yeah," I said. "I remember now, they changed the name."

    Friends, they changed the name 34 years ago.