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Entries from March 2020
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Washer Collage (31 Mar at 23:55)
Hi! I've been stuck inside for weeks, probably just like you. I go out running every day, dodging people, but otherwise it's lockdown-mode. Our washing machine promptly broke, so I had to replace that thing. It became a project, because (aside from the difficult but mostly uninteresting process of getting it onto the second floor) one of the things that contributed to the last one's failure was its not-very-stable footing, and I wanted to do this one well. The thing resides inside a nice (but probably unnecessary) tile basin, which poses a few problems: It would make it impossible to get to the bottom doors on the machine, and it makes it impossible to adjust the feet in situ for leveling purposes, and the basin is not at all flat. The weirdly-shaped surface meant that my CAD prospectus was not very useful, which is annoying because I like to measure like 200 times in CAD and then cut once.

Figure 1. Click to zoom
Figure 1. Click to zoom


The other problem is that I didn't have the right wood for this, and although Home Depot claimed to be able to do a same-day shipment, they gave me the runaround for over a week (I still don't have it). It's understandable, but our piles of laundry were getting a bit dire, so I just had to make do with what I had. In figure 1(a) I sawed through these 6x6 timbers with a 3.5" saw, which took like an hour. Then I used the also-too-small table saw to mill that into the smaller size I actually wanted (figure 1(b)). Then, I painstakingly test fit the logs in the basin, and sawed/planed/chiseled/sanded them until they were sitting stably on that curved surface without wobble. This was a real pain. The best advice I have for doing this was to get the tile sopping wet, then place the wood there for a moment, and then see where the high spots are based on where the wood is wet. (It would work better with some dye or something, but I didn't want to ruin the tile, ugh.) At that point we have some logs that were nice and sturdy, but not necessarily level gravity-wise. My solution here was router-out cups for each of the washer's feet, which I could set the depth of so that the washer would be level without any adjustment. (This also has the nice advantage that the washer can't jump around more than a few millimeters!) This was accomplished by using a laser level for an accurate level, and then putting some objects of fixed height (here the feet from the old washer, which will be disassembled for its more exciting pieces) into each cup, and iteratively routing the depth until they all touch the laser line exactly (Figure 1(c)). All that work paid off, though, because when we finally dropped the washer into place, it was as level as a spirit level can possibly indicate (Figure 1(d)). No pictures of the install here because this is like in my bathroom and that seems weirdly intimate to put on the internet for some reason.

SIGBOVIK is tomorrow, but this year there is no in-person event due to the shelter-in-place order! The proceedings is shaping up nicely though, and there is some "podcast" expected. I have a few silly papers in there, but I'll save those for tomorrow. No talks from me this year; the whole situation in the world has been sort of draining my creative energy, but hopefully I will start feeling good again soon.
(5 comments — 3 weeks ago)   [ comment ]
Entries from February 2020
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Leap day! (29 Feb at 23:28)
It's leap day, which gives me an extra day in the short month to write this boring blog post! Alas, I spent most of the month traveling for work and vacation, and didn't finish my main-series project(s). Is the monthly shaming even motivational for me? Yes, of course, though I am skilled at filling my life up with whatever is currently catching my fancy.

For example, earlier this month I finally got working this fairly straightforward raspberry pi project, which I built to try to diagnose wtf is going on with my overcomplicated 4-zone hot water (hydronic) home heating system. It has a problem whereby my bedroom gets annoyingly hot under certain conditions, even though the thermostat is not being triggered. Just the "boiler room" looks like this:

Boiler Room
Boiler Room


Of course I could pay someone money to tinker with it but the true satisfaction of problem solving is in suffering that problem for multiple years while you pick up the necessary skills and data to solve it yourself and work up the mental energy to apply the solution. In the above you can perhaps barely make out the diagnostic device hanging from the scary bundle of wires (not my fault) with some of its heat sensors zip-tied to pipes. The needlessly hand-built software can give me one of these:

System Diagram
System Diagram


(I was pretty happy with the cheap but fairly maintainable way I decided to do this, with a templated SVG file. Since they're text, I just left placeholders like [[alice]] (the name of temperature probe "A") and just string-replace it with the temperature string as I deliver the SVG over HTTP. Will use this trick again some day.) Here you can see Floor 2 source is hotter than the others even though its thermostat isn't even on. It also produces time-series graphs of course, which are decidedly more retro (but really is only visible at full size):

Click for full 1080p pixel glory
Click for full 1080p pixel glory


I have succeeded in catching it in the act and have some theories about what's happening (the heat appears to be convective but I don't yet understand why the boiler keeps putting out heat in this situation). But I haven't solved it yet, and certainly haven't fixed it.


SIGBOVIK 2020 is in about a month, and so the deadline is coming up imminently. Consider submitting if you have anything to share! I have a few ideas partly done but it looks like the writing will be coming at the last minute, of course.

Stay safe out there!
(4 comments — almost 2 months ago)   [ comment ]
Entries from January 2020
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174627560650599227+100919519*23#*n for n=0..24 (31 Jan at 19:10)
Hello again! I got a little bit stuck on my most recent project because I don't have the right tools to do it the best way, which has created a sort of analysis-paralysis, but I like to think that one is wrapping up. Of course I still need to make a video which will take 9999 hours. Winter's computational space heater made a decent discovery, which is an Arithmetic Progression of Primes. An AP is some starting number x, and some positive stride s, where a progression of numbers in this sequence are all prime:

x, x + s, x + 2s, x + 3s, x + 4s, ...


For example with x=3 and s=2, we have 3, 3+2, 3+2+2 prime (and then 3+2+2+2=9 is not prime), yielding an Arithmetic Progression of length 3, or "AP3". The longest such progression known is an AP27, the only one yet known found last year:
x=224584605939537911, s=18135696597948930
for 27 consecutive primes! Only twelve AP26s are known,* and my computer found an AP25:
x=174627560650599227, s=22514425132729530

i.e. 174627560650599227, 197141985783328757, 219656410916058287, 242170836048787817, ...
only 133 AP25s are known* so it's a pretty lucky find, although of course people care a lot less about finding these than about finding huge primes (AP1s, if you will.)

* Technically an AP27 contains two AP26s, and three AP25s (etc.) so these numbers undercount a little.


Aside from the secret projects and winter hibernation, I played a slightly-old puzzle game called Closure which was pretty good. Definitely an interesting mechanic that they get plenty out of, if perhaps with slightly sluggish controls. I also just started Luigi's Mansion 3 for the cozy-factor, but you probably don't need me to tell you about AAA franchise Nintendo titles. I rarely recommend TV on here, but the second season of Castle Rock was unexpectedly good, if you like that sort of thing (first season is fine but there's no reason to watch them in any particular order). OK byeeee
  [ comment ]
Entries from December 2019
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HNY 2020! (31 Dec 2019 at 22:14)
Hello and happy new year! I’m currently at a party and basically forgot to post, which is fine because I didn’t finish anything this month! I did make progress on my project, but then also expanded the scope (as is my way) and then also ruined a part of it, both activities pretty much consuming all the free time of the holiday break with such excursions. I've still been running the prime-finding space heater as described in post 1175 but my luck has regressed to the mean and I have no new primes despite running for 30x longer than last time. The winter slows me down for sure. In the melancholy I played a few video games, which were unremarkable except for Fidel Dungeon Rescue, which I really like. It’s described as a roguelike, but it’s really a puzzle game. It won my heart when I convinced myself that one level was impossible, then implemented a solver for it, which made me realize I was missing something, but then convinced myself that it was still impossible, but then the solver solved it and proved my brain is soft.
  [ comment ]
Entries from November 2019
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2609 * 2^1549069 + 1 (30 Nov 2019 at 21:42)
Happy Thanksgiving!

One interesting thing that happened this month: A few weekends ago it was feeling cold in my office, so I thought about turning on a space heater, but why do that when I've got a 850W power supply hooked up under my desk that can provide a "useful" resistive load? My current projects don't have any long-running computations, so I fired up PrimeGrid, which is a distributed computing project that lets you hunt for prime numbers (etc.) using your stupidly overpowered home computer. Amazingly, the next day, I had discovered this prime:

2609×21549069 + 1


It's a Proth prime, one of the several special forms of numbers that have efficient primality tests. This particular one is 466,320 decimal digits long, in fact big enough that when I discovered it, it was the 3461st largest prime number known to mankind (see its entry in the list of Top 5000 Primes). As you know, computers are pretty fast these days, and there exist many nerds, so this number has already slipped 62 places to #3523.

Finding this on my second day was pretty lucky, although not really beginner's luck since in college I ran Prime95 ("Great Internet Mersenne Prime Search") on any computer I could get my hands on. You can see my historic page exhorting internet strangers to join the Tom7 prime team for example. Apparently we were once in the top 100 teams in the world, so I think I deserve a prime 20 years later, right?


I finally assembled my current project and it is kind of working! There are several things I can do to improve it, which I am trying, but at this point it at least does something interesting/funny enough to make into a video. Next the trick will be finding the right stopping point. I was hoping to get a lot done over Thanksgiving break (mercifully, not traveling this year), but (not mercifully) I immediately got sick and have spent most of my time playing Pokémon in bed or warming my toes on the prime-powered heat sink. So sad to finally have some free time but not have the energy. Oh, well!
Category:  momentous (5 comments — 5 months ago)   [ comment ]
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