• More Adventures with Machines

    The knitting machine had thought that this was going to be its weekend to shine. I had all sorts of plans queued up to follow-up on my two-color brioche knitting as well as a sweater pattern that is mostly rectangles. But then Line-us arrived.

    Line-us is a little robot that holds a pen and draws with it.

    Of course, you need to tell Line-us what to draw. Line-us uses a language that is also used by a lot of CNC machines. You can send the pen to a particular (x, y, z) point within its reach, and then you send it to the next point and so on and so forth.

    robots

    While this is a delightfully simple file format, it’s not something that you are going to write by hand. Fortunately, there is an Inkscape extension that lets you convert Inkscape paths to robot instructions. Unfortunately, it does not work with the current version of Inkscape. Now I have two versions of Inkscape installed on my computer so that I can use various features that are only in one or the other but not both and sling svg files between them. Also I spent far too much of Saturday trying to rewrite the extension that works with Inkscape 0.92 to see if I could get it to work with Inkscape 1.0. Despite not actually knowing Python, I was able to get it to minimally communicate with the robot but not to actually do anything useful.

    I will take this opportnity to mention that the knitting machine hacking software is also written in Python. You would think that this would motivate me to learn Python so that I could talk to all my machines in their prefered language. But, no, I can not motivate myself to learn Python.

    But as I do have a short attention span and flit about from project to project, I will take a moment to say WHY DIDN’T ANYONE TELL ME ABOUT BOBBIN LACE? Also, once it is safe to go to conferences again, what do I need to do in order to meet Veronika Irvine? In my exploration of Inkscape extensions, I discovered one that makes the most amazing patterns for bobbin lace. And it describes the math well enough that I might be able to steal some of its ideas for cool circular knitting.

    circular symmetry


  • Two Color Brioche Knitting with my Knitting Machine

    Instead of spending the time working on my COVID-19 tracking website (which shows that the number of new cases of COVID-19 in San Diego County have been decreasing for zero days in a row), I devoted the weekend to playing with my knitting machine.

    I have been spending a lot of time sitting on the couch and reading about knitting. One of the things that I’ve been reading a lot about is brioche knitting. Some people use the name “English rib” or “Fisherman’s rib” to refer to this stitch; others insist that those names apply to something similar but different. In any event, brioche knitting is a squishy fabric with prominent ribs. The defining feature of creating it with hand-knitting is that you slip a stitch while simultaneously doing a yarn-over. Morally this is equivalent to doing a regular knit stitch but giving up halfway through and moving on to the next stitch on the needle. In machine knitting, this is called “tuck,” and there is a button on the carriage to tell it that you want to do tuck stitches rather than knit stitches. Do not be confused by the name tuck; it doesn’t seem to have any connection to the other meanings of that word in English.

    Due to the tuck button, it is pretty easy to make one-color brioche knits on a double-bed knitting machine. You cast on for 1x1 rib (or full needle rib if your machine is happy with that – mine is not). Then you set one carriage to knit in one direction and tuck in the other and the other carriage to do the reverse. Easy peasy, brioche knitting. (Fun fact, if you watch machine knitting YouTube videos with the Google auto-captions, when the speaker refers to the knitting machine’s “ribber bed,” the captions will say “river bed.”)

    With hand knitting, once you know how to do brioche knitting, then you can do two-color brioche knitting, in which the ribs on one side are one color and the ribs on the other side are the other color. When knitting in the round, you need to go around once with each color to knit the full round: You do the knits with one color and then the purls with the other color. In flat knitting you do one color then you slide the work back so that you can do the row again with the other color. Neither of these strategies work particularly well with home knitting machines. These machines don’t do any sort of ribbing in the round. The operation of “slide the work back” is super annoying because you need to take the yarn out of the carriage, switch how the buttons are set, put the yarn back in, and then reset the buttons correctly.

    This weekend I found an alternative. And I mean “found” in the sense of “Columbus discovered America.” Lots of people must know about it already, but I was previously unaware of it. I was able to use a stitch pattern that was relatively easy to knit on my knitting machine and that looks a lot like two-color brioche.

    brioche-knitting

    Note that this swatch no longer exists. I have ripped it out and rewound the yarn. This yarn is Noro, and the knitting machine was not happy about the thick-thin texture and all of the leaves and twigs and whatnot.

    In order to make this work, I did two rows with each color. Work the main color across and back, then switch to the contrasting color. Work the contrasting color across and back and then switch back to the main color. In machine knitting lingo, I set one carriage to knit both directions and the other to tuck both directions (KK/TT) and knit back and forth with the main color. Then I set the first carriage to tuck and the second to knit (TT/KK) and used the contrasting color. I repeated this pattern until the machine started crying about how Noro yarn is impossible to work with.

    In term of hand knitting what this would mean for flat knitting of brioche is that you would use one color to go across and back, then you would use the next color to go across and back, like normal knitting (no sliding the work to the other end of the needle). The strategy would be to start with the main color and knit a row of brioche like normal. And then on the way back, work the normal stitches normally and for the doubled-stitches (stitch + yo), do that again: slip again and add another yarn over. Switch to the contrasting color. This is sort of like normal brioche stitch again, only instead of working a stitch together with its yo, you work the stitch together with both of its yarn overs and do the slip+yo to the other stitches like in regular brioche. And on the way back, work the normal stitches normally and add another yo to the slip+yo stitches.

    It’s hard to explain for hand knitting without pictures or a video or something, and I don’t have time now for either of them right now. Much easier to describe for the machine. Too bad the machine hates Noro so much.


  • Someone on the Internet is Wrong

    There was an article in the local paper about the spread of COVID-19 in the county. They have a paywall, so you might or might not be able to read the article. It was posted several days ago, and Letters To The Editor are no longer A Thing (being replaced by comment sections where everyone argues), so my thoughts about this article are going to have to go in my blog.

    The gist of the story is that they claim that the number of cases of COVID-19 is growing the fastest in ZIP code 92154, an upside-down U shaped ZIP code right on the Mexican border. This is true, in one sense, because this is the ZIP code in San Diego County that has the most COVID-19 cases overall. You need to have, on average, the highest rate of cases per day in order to end up with the highest number of cases.

    The paper notes:

    To determine average growth rates, The San Diego Union-Tribune first calculated a change in cases between each day from March 31 through May 31, and then averaged these totals for an overall daily growth rate.

    Assuming that I am understanding what they mean here, this is equivalent to taking the number of cases on May 31, subtracting the number of cases on March 31 and then dividing by 61. They are not taking into account any changes in the rate of growth over the course of the pandemic. Also, they are assuming that the growth rate is linear, which is fine because since the middle of April it has been fairly linear. I would have been happier if they had calculated growth rates over shorter time intervals. I haven’t yet built out the analysis to look at growth rates over time, but the data that I’ve seen suggests that a naive model of “92154 is growing the fastest” does not tell the whole story. Once I run all the data, I’ll have a better story to tell, but mine would probably be “Things were pretty bad near the border, especially in San Ysidro, but all the other places that you think of as ‘poor’ or ‘Mexican’ or ‘immigrants’ are starting to catch up pretty quickly.” Not as catchy of a hot take, I know. I’m planning on changing my “new cases GIF” to show a moving average rather than the daily data, so we’ll see what that shows.

    One thing that the newspaper’s analysis entirely ignores is population. The population of 92154 is 81,645. On the day that the paper did its reporting (June 3), there were 707 reported cases in that ZIP code. This meant that 86.6 per 10,000 people in the ZIP code had contracted the disease. However, this ZIP code surrounds San Ysidro (92173), which had 339 cases out of a population of 27,741, or a rate of 122.20 cases per 10,000 population. You can see this by going to my COVID-19 tracking site and setting the map to June 3.

    By neglecting how the rate of growth changed over time (what we in the math biz would call the second derivative) as well as the relative populations, the newspaper article misses the fact that both San Ysidro and its surrounding ZIP code both had roughly the same number of cases per capita in early May (in fact, San Ysidro had a slightly lower rate) but that San Ysidro now has significantly more cases per capita. Based on this information, I would say that COVID-19 is spreading faster in San Ysidro than it is in nearby areas.

    I know that the local newspaper can’t get too sophisticated in terms of the math that it uses in articles for the general public, but I would have liked for them to acknowledge that the growth rate changes over time and that the impact on a ZIP code depends both on the number of cases as well as the population.


  • Robots Stealing Our Blogs

    Since I don’t do much, I don’t have much to write about. You might have heard that AI will advance to such a point that robots will steal our jobs. So I asked an AI system to write a blog post for me. This is what it came up with.

    1. I finished the knitting project that I’d been working on. And it’s ready for blocking! It’s taken me a really long time to knit this, mostly because I’m usually too busy with deadlines to work on non-profitable knitting projects. It was fun to do something a little different, though. :)

    2. I’ve set up one of my cameras exclusively for taking cat photos. Before, I couldn’t get any decent pictures of him. Today I have at least eight great ones. He’s not the brightest bulb in the cage, you see, so I need the flash to freeze him. When the camera comes near him, he freezes and opens his mouth. His expression says he’s saying something along the lines of “Hey, don’t you know you’ve been caught?” I’m a little sad. We had great hopes for at least one of our cats,

    3. I started sewing another mask. I own a lot of homemade masks for someone who never goes outside. Most of them are the foam and latex kind of masks. Some of them have eye and nose holes but they have little in the way of ventilation. I added some ventilation holes to my latest version but it is still too heavy to wear in public. After all of the previous attempts I came to the conclusion that the only option left to me is the simple surgical mask. With its big eye and nose holes and small chin strap it provides me with a full face mask that is light enough

    4. I’m taking a break from working on web page with the COVID data. I want to post another video that you all may find very funny. #thesearchcontinues #johnlennon #thebeatles #peace The Beatle Bible: The Fab Four’s Guide to the Good Life A good read if you want to learn about the Beatles. Many different viewpoints are given in this book. The Beatle Bible is written as a biographical yet informative look at their history, sound and content. The


  • Tales from the Bugmaster

    1. Our students do online homework and then they spend a lot of time kvetching about points in the bug reports. They seem to believe that they already own all the points and then the problems steal the points from the students; students will get a problem wrong due to what the student considers a minor oversight and then write in “GIVE ME BACK MY POINTS.” In a work-related conversation yesterday, I had to explain to a colleague that there is a good reason why I am not the Jay Powell of points. I think that in the students’ minds the problems are some sort of wealth tax on points and solving the homework problems is the equivalent of finding the correct tax loopholes.
    2. Every time a student in one of our programming classes submits a bad bug report (“The thing is not working.”), I hope that karma is keeping score. I imagine this student’s future self having to deal with bug reports just as bad.
    3. Bug report with TMI. Starts fine; goes dark. I’m fuzzing the details quite a bit, but the bug report went something like:

      I don’t remember me doing that many problems . oooooooooohhhhhhhhh I remember me doing those problems !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! I love math ! it is so fun !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! I mean ssssssssoooooooooooooo muchhhhhhhhhhhhhhhhhhhhhhhh ffffffffuuuuunnnnnnnnnnnnnnnnnn !!!!!!!!!!!!!!!!!!!!!! my house burned down in August 2019 so my family is living with my grandma . she is really sick !!!!!!!!!!!!!!!!!! please write back very soon!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! math is so fun !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! I love writing bug reports !!!!!!!!!!!!!!!!!!!!!!! it is so fun writing bug reports !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! I just love writing … …and reading!!!!!!!!!!!!!!!!!!!!!! it is fun writing bug


  • Making GIFs in My Free Time

    We’ll see if this GIF stays animated once I put it on the web. It might depend on your browser and the whims of ImageMagick. It’s animated on Facebook, which is something.

    animated-map

    This GIF should be showing you the spread of COVID-19 through San Diego County, based on the total denisity of people infected (number of total cases per 10,000 population) by ZIP code. Orange-based colors are for ZIP codes with more than 10,000 people and more than 5 cases. Other ZIP codes are in gray-scale. Darker colors means a greater density of cases. Yes, this is total cases (not new cases). Yes, I might work on the GIF for new cases at some point, but this GIF was already kind of annoying to make.

    Instead of devoting my recreational screen time to writing blog posts or watching TV or browsing knitting patterns that I might never make, I have been putting the infrastructure in place to make GIFs like the one I linked above. (But if it is not animating itself, I hope that the next version of it will stay animated.)

    You might think: “Take some images, toss them in a directory, and then run ImageMagick over them all to get a GIF.” If you don’t know ImageMagick, it is the best ever command line tool for making images do things without having to open up some GUI-based software and click on things. You can script all sorts of amazing things with images.

    Let me tell you about what it has taken me to create the images. I guess we’ll work backwards.

    Each image comes from an SVG (scalable vector graphics file) that is created by the d3 data visualization library. For those outside of this field, this is a JavaScript library meant for displaying data on the web. My data is a tangled JSON object, and the array of ZIP code data holds an array of total number of cases in the ZIP code, by date. I can tell d3 to alter the fill color for each ZIP code based on the number of cases. Easy? Well, that is fine if you are showing the map on a web page (which d3 was designed for) and having the map update itself when you click a button on something, but I want to have this all work on in the background in the middle of the night and have a new GIF waiting for me each morning. We’re not there yet. I still need to meddle with the process in order to produce the GIF automatically.

    Enter nodejs, which will let me run JavaScript on the server instead of in the browser. Also I needed a virtual DOM because there is no web page displaying the map when it is all running in the mind of the server, so I need to tell JavaScript that it should pretend that there is a web page so it would know where to put things. Also, JavaScript has some sort of weird stuff going on about things running synchronously vs. asynchronously, so I couldn’t just put my mapping function in a for loop and loop over all of the possible dates. I guess I could, but I didn’t really want to use Promises, which is how JavaScript deals with such things.

    Can’t loop over all the dates inside JavaScript? Rewrote the JavaScript script to take a command line argument and then wrote a bash script to call the JavaScript via node at the command line. Each call to the JavaScript script writes out a frame. OK, now we have a way to make all the images. And then I can have the bash script call ImageMagick over the directory full of images and then move the finished GIF to the right place so that it can be served by the webserver.

    Where does my JavaScript mapping script get the data from? It reads in a JSON file from disk. Where does this JSON file come from? The bash script tells a PHP script to make it. How does the PHP script make the JSON data? Well, it has a connection to a MySQL database that contains the information that it needs in order to build the JSON file. Eventually all the data came from the County’s data service.

    The PHP script is a bit more than I’ve mentioned above. What it does is it checks the MySQL database to find the timestamp of the most recent update that it has from the County. If that timestamp is long enough ago that the County should have published more data by now, it makes an API call (this is a very annoying API, btw) to get the new data and processes it to save in the database. The PHP script can use all of the data (both new and old) in order to create the JSON object. Note that the County’s API limits the amount of information that it will send you in a single call so you can’t get all of the data over all time by sending one query to the API. You either need to do a bunch of calls (SLOW!) and string them all together, or else you need to cache the older data so that you only need to get a little bit from the County. I went with caching because this data is only updated once a day, so it seems silly to keep looking for it in The Cloud if you know that there won’t be any new data for many hours.

    (Since I’m doing all this on a server that a friend lent me, not some sort of professional hosting, I had to install the webserver, the database server, etc. and configure them all to play nice together.)

    I should clarify here, the County API provides the case count per day per ZIP code. It doesn’t tell me anything about the ZIP code boundaries. These I got from a shapefile from a different part of the County’s data stores. Did you know that professional geographers have all sorts of ways to encode locations on the surface of the planet? Those of us outside of the geography biz probably use latitude and logitude for this purpose. I know that the d3 mapping functions use latitude and longitude. There are several geographic coordinate systems that use latitude and longitude. The County’s ZIP code shapefile does not use one of them. Not only did I need to convert the shapefile to a data format that could be read in by d3 in JavaScript, but I also needed to convert the coordinate system to WGS84. I tossed this geographic information into a different table in my database, and whenever I get new data about COVID-19 case counts in the various ZIP codes in the County, I can join the data up on the ZIP code and then write out a JSON object that contains everything that my script needs to make the map: Boundaries of the ZIP code, population of the ZIP code (found in a different data source published by the County), and an array of the total number of COVID-19 cases in that ZIP code (since the County started publishing this).

    Now I just need to put the finishing touches on the bash script and set it to run on a cron so that I can have a fresh GIF each morning. And this is why I have not been blogging. Once the code is nice enough that I’m not embarrassed by it, I might make the GitHub repo public so that other people can make their own GIFs in a similar way.


  • The Worst Documentary Ever

    Just to be clear, this is not a film that already exists. This is my terrible pitch for something that would be a terrible idea. Also that no one would allow to happen for so very many reasons.

    There are a lot of people who do research on Kids On The Internet, so the fact that this idea would never happen is not going to keep you from hearing about kids on the internet. Someone I know just got a grant to study something along these lines. Tweens on the internet during social distancing? Something like that.

    Roughly half a million accounts have been created on our site, and a lot of them belong to people who are currently kids on the internet. I don’t know how many of these accounts are still active or how many of them are still kids, but, oh my goodness, there are a lot of kids spending a lot of time on our site. Now, don’t get me wrong, there are also a lot of adults who spend too much time on our site as well. The thing about our site is that you kind of assume that everyone is a 13-year-old boy, but you can’t really know that.

    So here is the pitch: pick some number of sub-groups of our users and watch their interactions on our site and then also meet them in real life. I think that this sort of story-telling works best with an odd number of subjects, so to make this imaginary pitch be feature-length, I’m going to say that we should look at five groups.

    We’d start with a group that is somewhat unsurprising. A bunch of kids who post about their math contest goals and aspirations. Kids at the high school level. The sort of kids who aspire to be the sort of kids who would be featured in a film like Hard Problems. Send a crew to the kids’ houses, look at their wide array of math books. See the kids put together their schedules of how much time that they’ll spend studying each day. Talk to the parents about what they think of the kids’ math contest goals. Have the kids read some of their posts out loud. There are certain types of posts that they make all the time: “This Is My Math Contest Journey” or “Tell Me How Many Hours I Should Study Which Topics In Order To Win” or “How Many Points Do I Need To Score To Be Guaranteed Admission To Harvard.” As counter-point to this part of the narrative, we’d also talk to some of the long-term moderators who tell each new crop of students that there is not a fixed recipe to become a math contest champion. You should sit back and enjoy the problems. This is what everyone expects when it comes to the journey of math olympians.

    As is true of the genre, we should probably skip around back and forth among the groups that we are documenting. We shouldn’t just have the Math Contest Strivers taking up the entire first fifth of my imaginary film.

    I guess from here we would move on to a particular social group. I’m not going to mention their group by name because they try to stay under the radar – not in a troublemaking way, just in a minding their own business kind of way. A lot of the students from The Group are into math contests and take classes on our site. But they also put a lot of time and effort into maintaining their group. The Group is run via a system of private forums (students can only join if invited + approved by someone who runs the private forum, kind of like a secret Facebook group). They have a system of elections in order to select moderators and approve new members. Just about everything that I’ve seen on The Group has been pretty wholesome. There are a lot of homeschool students in The Group. Members of The Group has arranged – with their parents’ permission – to meet up outside of our site. There will be overlap between The Group and the math contest strivers. A lot of the math contest strivers won’t know that The Group exists, though. This group has been around for several years, and it is kind of amazing that they have been able to keep things up and pass it down to the next group of kids.

    Not sure which group to move our focus to next. If we have a lot of money for our imaginary documentary, we could look at a forum that is devoted to a particular country’s students. There are a lot of students from this country who participate on our site. The way that education is run in this country is that there are national exams in order to decide who is admitted to higher education, and the competition is cut-throat. So we have all these students who are discussing math together but who are also competing against each other. They are posting rumors about the exam process. Additionally, the culture of these students differs from my culture in many ways, so the sorts of things that they say and do seem quite unusual to me because I am not familiar at all with their way of looking at the world. It would be pretty interesting to see these students in their regular lives. I might learn something about WHY DO THEY DO THAT. How does math contest preparation in their country differ from math contest preparation in mine? What do their homelives look like compared to the math contest strivers and the homeschoolers from The Group? If we have enough money to travel to their country, we could find out.

    Here is where it turns dark. Everything that I’ve mentioned so far has been on our message board system. Most of the forums that I’ve talked about (with the obvious exception of The Group) has been done on the public parts of our site. And it’s a persistent public part of our site. If you went to our site, you could search through the forums and find the sorts of things that I am talking about. If you made enough wholesome posts about Harry Potter or whatever, you might even get invited to join The Group.

    There is a part of our site that has a rated game and a chat for spectators. This is a game where students compete against each other solving math problems as quickly as possible. The winner gains rating and the loser loses rating. The is a lot of commentary and trash-talking in the chat. There are a lot of accusations of cheating. This is reasonable because some of the most committed players of this game want to be at the top of the leaderboard, and they will go to extensive lengths to gain rating and to keep it. Bugs in the system have been carefully documented, and they know how to exploit them in order to disrupt the game. This is the math website equivalent of the high school kids who smoke behind the gym. Some of these kids are 12. But some of them are the math website equivalent of the people who graduated several years ago but who still smoke behind the high school gym with the high school kids. Maybe they’re the ones who buy the metaphorical cigarettes? Probably not a lot of crossover with the wholesome kids from The Group. Also not a lot of crossover with the International Students. This is kind of a thing unto itself. You might see some of the math contest strivers trying to practice their fast-draw problem-solving skills here, but a lot of them will get eaten alive by the lifers who have memorized (“memmed”) the answers to hundreds (perhaps thousands) of problems in the database.

    But what are these kids like outside our site? Does their ruthless streak extend outside of this game that they obsess over? I can’t imagine them running kitten rescues. I know from the timestamps on the games that a lot of them stay up all night playing against each other. Maybe instead of comparing them to the smokers behind the gym I should have compared them to the old men who hussle chess in the park.

    Where do we go from here? I know that I’m pretending that we will cut back and forth between the groups and that we won’t be treating them in an isolated way. But that is hard because the International Students do keep to themselves to some extent – and are pushed away by the math contest strivers. The strivers might see the international students post about some non-US contest, and the strivers will insist that this should not be discussed in the main forums but rather in the forum specific to the country that runs the contest. But we should also end with something that ties everything together and on a somewhat positive note. We don’t want to delve into the niche petty arguments that a group of adults who should know better are making about each others’ approach to posing and solving problems about inequalities.

    Maybe we go back to the beginning and look at the youngest kids who are just getting started with Middle School math contests. They don’t have the focus and dedication of the older and more competitive students. Some of them play the games on the site. Some of them are focused on math. Some of them spend a lot of time chatting. After we meet the next generation of students, we could speculate about where they will end up.


subscribe via RSS