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Jeff Kaufman's Writing from post 1181 back

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  • 11/06/14--05:00: Flux Timing
  • Apps that make your screen dimmer and redder at night are pretty useful. Blue light wakes you up, so you want to minimize it when you're going to sleep. Unfortunately, these apps default to following the sun while the people using them generally wake up after sunrise and go to bed long after sunset. At work I look around at 4:30pm and I see screens going red, but I doubt my coworkers want to start getting sleepy already. Our schedules are offset from the sun, and our technology should be too: things should shift red a couple hours before bed, and blue when it's time to wake up.

    With Twilight (Android) I can just set the hours to dim, but with Flux (Mac, Windows, Linux, iOS) it just asks where you are. I can tell it I'm in a city that's west of where I am, but I don't want seasonal variation. Which is funny: matching sunrise and sunset for a location was probably a fun technical problem for the developers and I suspect they're proud they got it right, but it's not actually helpful if your life isn't tied to the sun.

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    Talking about effective altruism with coworkers can be really awkward. There's potential to come off as "I'm more moral than you," potential for "I think the charities you do support are useless," for "I'm so rich I can afford to give away lots of money,""I'm trying to convert you,""I think you're a bad person because you don't do this," and for just seeming weird. Most of the year I just don't bring it up, but as we get into giving season I feel like I ought to try.

    I think most of the social difficulty around effective altruism comes from the demandingness aspect, the idea that to be a good person you should be devoting a substantial effort to making the world better. One way around this is to mostly focus on the effectiveness angle, saying "here's an awesome charity that can do huge amounts of good with your donation". The best charities are so muchbetter than the rest that pushing effectiveness seems well worth it, and any sort of discussion of giving helps normalize it and lead people to give more. So here are three ideas for promoting effective giving among your coworkers:

    1. Matching Donations. Offer to match donations to one of GiveWell's picks. This provides openings to talk about effective altruism, why evaluation matters, and the good this charity can do. Lots of people are more willing to give if they see the people around them are giving too.

    2. Donation Drives. Many workplaces traditionally have donation drives around the holidays. If your work has one, consider getting involved and helping out. This can then let you push some for effectiveness as a consideration in choosing what charity to raise money for. If you don't have one yet, or the one you have is tightly coupled to an existing charity, like collecting cans for a foodbank, then consider starting a new one.

    3. Updated Recommendations Discussion. GiveWell will be putting out their updated recommendations by December 1st, and judging from their recent blog posts there are likely to be several new top charities, each presenting different benefits and tradeoffs. Hosting a discussion to talk about these new options when they come out is a great opportunity to get into ideas about how to choose a charity and what matters.

    I hosted a recommendations discussion last year and this year I'm doing that again plus getting together with some other EAs here to match donations. I haven't tried organizing a donation drive but it seems promising.

    Comment via: google plus, facebook, the EA Forum, r/smartgiving


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    If you want emacs keybindings in desktop apps on Linux people will tell you to run:

    $ gsettings set \
      org.gnome.desktop.interface \
      gtk-key-theme "Emacs"
    If you're running a full desktop environment that's enough, but if you're running something lighter weight like Fluxbox or Awesome you'll also need to run:
    $ gnome-settings-daemon
    
    Unlike the gsettings change, this needs to run every time you log in, so put it in your .xsession or your window-manager-specific startup file.

    (I just upgraded my linux desktop to Ubuntu 14 LTS (Trusty) and this broke Unity, the window manager I'd been using. I could probably have fixed this by blowing away the configuration and replacing it, but I never really liked it anyway so I decided to go with fluxbox instead.)

    For reference, here's my .xsession contents:

    # Replace the 'caps-lock' key with a second 'control' key.
    /usr/bin/setxkbmap -option 'ctrl:nocaps'
    
    # We want emacs keybindings, especially in Chrome.  Things like Ctrl+d
    # to mean "forward delete" instead of "create a bookmark".  Fixing
    # this has two parts: we need to set a configuration option, and we
    # need to run a settings daemon to make it available.
    #
    # This only needs to be run once, but no harm in running it every
    # login:
    gsettings set org.gnome.desktop.interface gtk-key-theme "Emacs"
    # This needs to run every time:
    gnome-settings-daemon &
    
    # Make the background black.
    fbsetroot -solid black
    
    # Start and place terminals.  81 columns because code here is limited
    # to 80 columns and emacs reserves a column for the wrapping
    # indicator.  73 columns because that's what fits in the remaining
    # space.
    uxterm -geometry 81x90+1428+0 &
    uxterm -geometry 81x90+1920+0 &
    uxterm -geometry 81x90+2412+0 &
    uxterm -geometry 81x90+2904+0 &
    uxterm -geometry 73x22+3396+0 &
    uxterm -geometry 73x22+3396+310 &
    uxterm -geometry 73x22+3396+620 &
    uxterm -geometry 73x19+3396+930 &
    
    # Chrome.
    google-chrome &
    
    # Start the window manager last, and don't run it in the background.
    fluxbox
    

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  • 11/05/14--05:00: Index Fund Endgame
  • Index funds are becoming more and more popular. As a share of overall investment, index funds went from nearly nothing in the mid 80s to 18% in 2013. Over the same period stock advice for individual investors has shifted from "try to identify stocks that will go up" to "put your money in an index fund". As people who grew up with the earlier advice age out of the market and index funds continue to become more acceptable, we should expect the fraction of money in these funds to keep increasing. What happens if index funds keep growing to become most of the market?


    2014 Investment Company Fact Book

    When A sells a stock to B the two are playing a zero-sum game. B believes the stock will go up, A believes it will go down, and they can't both be right. [1][2] There is a positive externality, however, in that the price they agree on becomes public and gives us all information about the stock. As people who notice their tendency to find themselves on the losing end of trades realize this and switch to index funds, the size of the actively traded market falls and the potential gains from better analysis fall. With less gains comes less effort, comes less useful prices. But does this matter to index investors?

    Index investors want to buy a slice of everything. As the world becomes more prosperous the value of everything rises, so this makes money. The value of some individual things will fall, however, while others will rise, so you need some way to decide how much of each thing to buy. We could just buy a constant percent of everything, so 1% of Company Q, 1% of Company R, 1% of Company S, etc. But then if R and S merge, what do we do? Or what if someone founds a new company that does nothing profitable solely for the purpose of creating a stock that we'll want to buy 1% of? To fix this, we weight on price: if the total value of company Q is twice the total value of company R then we would like to own twice as much Q as R. If R and S merge this doesn't change our allocation, and if someone starts a new company its price will be very low so we won't buy much of it. So we're trying to buy a slice of everything in proportion to its value.

    Which gives us a problem: index investors are dependent on the prices generated by active trading in order to decide how much of everything to buy and sell, but as index investing becomes more popular this price signal will get worse.

    So what happens? Do enough people keep money under active management that the prices indexes use to decide how much of things to buy still work? Do index funds start to decrease in profitability as they take over more of the market because they're open to exploitation by active traders? Do companies start failing because stock price stops being useful to them?


    [1] This isn't entirely right. Perhaps A works for Google and wants to sell the company stock as it vests. Even though A is selling the stock they may still expect it to rise in value over time, but because they're a Google employee they stand to lose enough if Google starts doing poorly that they would like to reduce their exposure to the company. Ideally they invest the money from selling the stock into an "everyone but Google" index fund, and now should expect similar returns with less overall Google-correlated risk.

    [2] Another possibility is that both of them agree the stock will go down if A holds it but go up if B holds it. For example, B could intend to purchase a large portion of the company, put in new management, and turn the company around.

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  • 10/27/14--06:00: Baby Sleep II
  • Two months ago I wrote about how we had recently switched to a new method of putting our then five-month-old to sleep. Instead of comforting her until she fell asleep we would comfort her only until she stopped crying, after which she would start crying again and we would resume comforting, repeating this cycle until she fell asleep. This was an improvement—she slept in longer blocks at night than she had been—but she still would sometimes wake up on her own and need to be settled.

    Two weeks ago we decided she was old enough to be falling asleep on her own, and we stopped comforting her to sleep. We would put her down in her crib, and let her cry until she fell asleep. If she cried for more than ~15 minutes we would double check her diaper, see if she was hungry, calm her down, and then put her back down. Hearing her cry was painful. Really painful. But she does need to learn how to fall asleep.

    We did this for both night-time sleep and naps, and for the naps I tracked what time I put her down, when she fell asleep, and when she woke up. Some naps are missing if I forgot to write them down, and these are only her crib naps; if she napped on me in the sling or riding in the car I didn't include those. Here are all these naps, arranged from shortest time falling asleep to longest:

    Her median time was 6 minutes, average was 8.6. The longest few times, however, don't represent continuous crying. Instead those are times when I put her down and she did a bunch of babbling and humming before falling asleep. She was probably not tired enough to go down these times, and over time I think I would get better at telling whether it's good to put her down yet.

    One big change we noticed was that she started taking longer naps. When I had been comforting her to sleep she tended to nap for just 30-50 minutes but once we started letting her fall asleep on her own she would often sleep much longer. Here's her naps lined up from shortest to longest, blue for comforting and red for not:

    You can see almost all her short naps were from before, and most of her long naps were from after. [1] Qualitatively she also seemed less cranky during the day.

    Still, we're not sure whether we'll keep with this. She's still crying for 5-10 minutes each time we put her down, and while the research is a mess this does seem like something that might not be good for her. (While she would still cry when we would comfort her to sleep, it wasn't as intense as when she's crying alone.) On the other hand, the longer naps do seem like something that would be good for her. And then there's the hard-to-consider factor that comforting her can be tiring and frustrating, especially in the middle of the night, so it's physically really nice not to need to do that. But how to weigh these I'm really not sure.

    (It also doesn't seep to work well when the situation changes: this weekend we were spending time with relatives and she just wouldn't fall asleep in the crib there, even with comforting. And she's starting daycare soon when I go off paternity leave, where I'm not sure how they'll do naps.)

    Update 2016-10-16: I wanted to pull this graph out from the comments, that I think is especially helpful. It compares the length of sleep at naps before and after the changes:


    [1] Running a two-tailed t-test I got a p-value of 0.00025 which seems extreme enough that I'm really not sure I did the test right. The raw data is here.

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  • 10/28/14--06:00: Pricing Benefiting Everyone
  • Parking, traffic, CO2: there's not enough street parking in our cities, not enough room on our roads, and too much carbon in our air. Economists have a simple solution: charge for it! Instead of free street parking, or $40 permits issued to any resident, count the spaces and auction them off. Instead of allowing so many people onto the highway that it clogs up and stops moving, put in tolls and keep raising the price until traffic flows freely. Instead of letting anyone burn as much as they want, charge a tax high enough to cover the full cost the polluters impose on everyone else.

    No more traffic jams, no more circling the block to find parking, even no more global warming if we can get the rest of the world to sign on; sounds great! So why don't we do this? A big concern is often that these charges hurt poor people more. For example, if I'm a rich gentrifier I could afford the permit to park my car at home and the tolls to drive it to work, while if I'm a poorer long-time resident this change might make my current driving commute expensive enough that I can't keep my job. What happens to our society when we put things up for sale to the highest bidder?

    The thing is, all of these raise money. If they get up to unaffordable levels, they raise a lot of money. What do we do with this money? What if we distribute the money back to residents? We can give it preferentially to poor people [1] or just distribute it equally: just as taking $10 from everyone hurts poor people more, giving $10 to everyone helps them more. The important thing is to include the money distribution in the same law as the money collection, to make sure you do have both halves of this.

    Does this get these market-based changes to where most people would support them?


    [1] The downside of adding another means tested program is high effective marginal tax rates, which can form a "poverty trap" which keeps poor people poor.

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  • 10/30/14--06:00: State Name Popularity
  • After Brandon posted a map of places in one state named after other states, I was curious which states are the most popular. I had some guesses: lots of Washington because of the president, older and bigger states more heavily represented, but I wasn't very confident in any of it. So I downloaded the list of domestic names from the USGS to find out. [1]

    179 Washington
    42 Virginia
    41 Texas
    28 California
    22 Delaware
    21 Wyoming
    20 Oregon
    19 Kansas
    16 Georgia
    15 Oklahoma
    15 Michigan
    14 Montana
    14 Maryland
    13 Nebraska
    12 Nevada
    11 Minnesota
    11 Florida
    11 Colorado
    11 Alabama
    10 Ohio
    10 New York
    9 Maine
    9 Iowa
    7 Vermont
    7 Connecticut
    6 Missouri
    6 Kentucky
    6 Illinois
    6 Idaho
    6 Arkansas
    6 Alaska
    5 Tennessee
    4 Utah
    3 Rhode Island
    3 New Hampshire
    3 Arizona
    2 West Virginia
    2 Pennsylvania
    2 Indiana
    1 Wisconsin
    1 New Mexico
    1 Louisiana

    No matches for: Hawaii, Massachusetts, Mississippi, New Jersey, North Carolina, North Dakota, South Carolina, South Dakota. The Dakotas and Carolinas make sense: if you consider them without "North" or "South" you get 9 for "Dakota" and 16 for "Carolina". You could think "New Jersey" is just suffering because it has "New," but "New York" did fine. Still, I can see why people don't want to name their town "New Jersey," and "Massachusetts" and "Mississippi" are kind of awkwardly long, but why not "Hawaii"? That's a nice place, and "Alaska," equally recent, has six towns including two in PA.

    If people aren't naming their towns "Massachusetts" are they at least honoring our excellent state in naming their children? The Social Security Administration provides names for people born since 1880, where at least five people were given that name and gender that year. Doing the same calculation we get:

    Virginia 648,005
    Georgia 146,132
    Montana 9,879
    Florida 3,532
    Nevada 3,431
    Washington 2,518
    Arizona 2,273
    Indiana 1,553
    Missouri 1,541
    Maryland 1,288
    Kansas 1,017
    Tennessee 806
    Texas 544
    Alaska 400
    Utah 341
    Louisiana 278
    Alabama 194
    California 150
    Iowa 79
    Nebraska 75
    Colorado 59
    Vermont 28
    Illinois 16
    Wyoming 11
    Maine 9
    Oklahoma 5
    Michigan 5
    Hawaii 5
    Because first names can't have spaces, the ten states with two-word names aren't included. But again if we break out "Dakota" and "Carolina" we get 108,013 and 39,348 respectively, so they would be up there.

    How well do these two measures of popularity correlate?

    Not very well. Except everyone agrees not to name things "Massachusetts".


    [1] Following Brandon, I filtered out anything containing "trailer,""historical," or "mobile home". Unlike Brandon I required whole-word matches, so Bidahochi AZ would not be counted towards Idaho.

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  • 10/26/14--06:00: Two Kinds of Vegan
  • "Go vegan!", you hear, "it's cheaper, more environmentally sustainable, and just as healthy and delicious!" The problem is, these aren't all true at the same time. You cut animal products out of your diet, and what do you replace them with?

    • Beans, peanut butter, lentils.
    • Tofu, nutritional yeast, hummus, tempeh, seitan, soy cheese, soy milk, almond milk, almonds, "fake-meat" products.
    There are a small number of vegan protein [1] options that are cheaper than the animal-based equivalent, and then there are a wide variety of ones that are more expensive. If you build your diet from the first category it's cheap and environmentally sustainable, but the limited choices mean most people won't find it as enjoyable as what they were eating. On the other hand, the second category offers enough options to suit most palates but it costs more.

    And really, we should expect this. When deciding what to eat people balance taste, health, time, variety, and money. Remove some options, and something has to give. If you're willing to accept less taste and variety, you can go with beans. If you're willing to accept more cost you can go with seitan and soy milk. If you're willing to accept less time you can cook more meals at home and become an excellent cook who does more with less.

    (This is a motte-and-bailey argument, where the defensible "motte" is "the cheapest diets are vegan" and the expansive "bailey" is "eating vegan is cheaper".)


    [1] I'm mostly just talking about lysine here. Fruits and vegetables don't have much of it, and while Grains tend to have enough of the other essential amino acids that it's easy to get enough of those, in order to meet your lysine needs with them you'd need to eat very large amounts. For example, 12.75 cups of corn or 15.5 cups of cooked brown rice will meet all your amino acid needs, but they will also give you 7,300 and 3,350 calories respectively. Instead you need to eat some foods that have more lysine per calorie, and while beans really shine here other options are generally more expensive than animal products.

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  • 10/25/14--06:00: Paying Cash on T Buses
  • The MBTA should add a $0.50 surcharge for loading your CharlieCard on a bus. When people pay cash on buses it slows everyone down. The MBTA understands this and set up fares to discourage paying cash:

    • CharlieCard: $1.60
    • Cash-on-board: $2.10
    This makes sense: people can pay cash if they need to, but you save money for yourself and time for everyone else if you put money on a CharlieCard (RFID) at a fare machine instead.

    The problem is, there's a loophole: the bus also lets you put cash on a CharlieCard. This is an even longer process than paying with cash: press a button, tap your card, put in cash, and tap your card again. And then you can immediately use the money on the card to pay your bus fare. Someone doing this saves themself $0.50, getting the discounted $1.60 CharlieCard fare instead of the normal $2.10 cash fare, while making everyone else wait.

    A $0.50 surcharge would fix this. If you needed to you could still use the machine on the bus to load your card, but there would be savings for putting more money on at once: you'd only pay the $0.50 once per transaction whether you were putting on $2 or $20. And you could save even more money by using a fare machine, off the bus, where you wouldn't be holding up a bus full of people.

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  • 10/24/14--06:00: Trumpets Belong in C#
  • People typically write for trumpets in Bb [1] or nearby keys because that's where their fingerings are simplest. But if you're willing to tune your trumpet for the key you're going to play in, C# is actually the one where the notes will need the least lipping to play in tune.

    The valve system of a trumpet is superficially simple: you have three valves, one that lowers pitch by a whole step, one by a half step, and one by a step and a half. For example, the easiest note to play on a trumpet is the 'Bb' you get with all the valves open. From this position the first valve will lower you from Bb to Ab, the second from Bb to A, and the third from Bb to G. To get other notes, however, you're going to need to start combining valves, and that's where the fudging comes in.

    The note you get out of a trumpet depends on the length of tubing the air travels through. To make a valve that lowers pitch by a half step, you send the air through 5.95% more tubing. [2] The problem is, after the first valve lowers us a whole step by adding 12.2% more tubing, adding the second valve on top of that only lowers us by 5.30%. But it really gets bad once we add the third valve. If the valves are set at exactly a whole step, half step, and step and a half, then when we put all three in we'll be adding 37% instead of 41%. So as you play the note you adjust with your lips, or you use a third-valve slide to add a bit more tubing.

    But what if you don't want to have to make adjustments? What if you want each note to come out as close to where it should be as possible? Then play in C# major and set the tuning slides to make that as in-tune as it will go. I wrote a simulator that figures out the optimal settings for the tuning slides for a given set of notes and computes the remaining error, and here are the twelve major keys in descending order of intonation:

    Key Error
    C# 0.20%
    Eb 0.26%
    Bb 0.31%
    F 0.36%
    Ab 0.37%
    C 0.39%
    F# 0.47%
    E 0.49%
    D 0.51%
    A 0.51%
    G 0.53%
    B 0.58%
    This is assuming that you use the standard fingerings, but what if we allow the optimization to also choose the best fingering for each note, even if that gives us something pretty weird? Then it can do even better:
    Key Error
    C# 0.05%
    Eb 0.05%
    E 0.05%
    Bb 0.12%
    Ab 0.25%
    F 0.26%
    A 0.29%
    C 0.35%
    F# 0.45%
    G 0.49%
    D 0.50%
    B 0.58%
    What crazy fingerings did it come up with for C#?
    Note Normal Fingering Optimal Fingering
    F3 2-13 (sharp 0.07%) 2-13 (flat 0.04%)
    F#3 2-23 (flat 0.09%) 2-23 (flat 0.04%)
    Ab3 2-1 (sharp 0.06%) 2-1 (flat 0.05%)
    Bb3 2-0 (flat 0.04%) 2-0 (sharp 0.01%)
    C4 3-13 (sharp 0.19%) 3-13 (sharp 0.07%)
    C#4 3-23 (sharp 0.02%) 3-23 (sharp 0.07%)
    Eb4 3-1 (sharp 0.17%) 3-1 (sharp 0.06%)
    F4 3-0 (sharp 0.07%) 4-13 (flat 0.04%)
    F#4 4-23 (flat 0.09%) 4-23 (flat 0.04%)
    Ab4 4-1 (sharp 0.06%) 4-1 (flat 0.05%)
    Bb4 4-0 (flat 0.04%) 4-0 (sharp 0.01%)
    C5 5-1 (flat 0.73%) 6-13 (sharp 0.07%)
    C#5 5-2 (sharp 0.20%) 6-23 (sharp 0.07%)
    Eb5 6-1 (sharp 0.17%) 6-1 (sharp 0.06%)
    F5 6-0 (sharp 0.07%) 8-13 (flat 0.04%)
    F#5 8-23 (flat 0.09%) 8-23 (flat 0.04%)
    Ab5 8-1 (sharp 0.06%) 8-1 (flat 0.05%)
    Bb5 8-0 (flat 0.04%) 8-0 (sharp 0.01%)

    The fingerings are actually almost the same. It made four substitutions:

    • 13 on the fourth partial instead of the raw third partial for F#4
    • 13 on the sixth partial instead of 1 on the fifth partial for C5
    • 23 on the sixth partial instead of 2 on the fifth partial for C#5
    • 13 on the eigth partial instead of the raw sixth partial for F5

    These let it tune the fundamental (Bb and harmonics) sharp by just a little bit more and lengthen the first valve to compensate, and then choose more notes using the first valve.

    Overall, the main thing I'm taking away from this is that the intonation issues I'm having playing trumpet and baritone in contra dance sharp keys like D and A is to be expected and requires active compensation by the player. In other words, I should learn to use the third valve slide.

    (All this holds for other three valve instruments like the ones I was talking about yesterday.)


    [1] Which trumpet players call "C" for historical reasons. In this post (and in life in general) I'm going to be ignoring this and using concert pitch.

    [2] Why? Well, if you lower a note by a half step twelve times you need to get the same note an octave down, which means we need to end up with twice as much tubing. Solve for this amount and you get 5.95%. It's the twelfth root of two (1.0595), less one to make it a percentage increase instead of something to multiply by.

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  • 10/22/14--06:00: Low Trumpets
  • I picked up the trumpet a few years ago and while I've been making slow and steady progress expanding my range and stamina, it's still a very hard instrument for me physically. About a year later I tried my cousin's old 3/4-size baritone horn, and was blown away by how much easier it was to play. That, combined with really liking how various people used the trombone in contra dance, got me wanting something in this range. A standard baritone has the bell pointed up, however, which didn't seem like a good fit for unamplified outdoor playing, or unamplified playing in general. When I saw a picture of a marching baritone, a bell-forward design, however, I thought "let's get that!". So, one King 1124 later:

    Very little research went into this. I was excitied about the idea, I'd played a little on something somewhat similar, and I found one one ebay. It arrived in mid April and a month later it was on the new Free Raisins CD. I'm pretty happy with how it's been working out, but I hear people talking about euphoniums, bass trumpets, flugabones, and I wonder: what are all these?


    bass trumpet


    valve trombone


    marching baritone


    marching euphonium

    (Not pictured: flugabone, bass cornet, marching trombone, marching french horn, mellophone, trombonium. To some people some of those are synonyms.)

    These are all variations on the same idea. You have a bell-forward Bb horn with a bit over 8 feet of tubing, plus valves that can extend this by a whole step, half step, and a step in a half. Basically a trumpet an octave down. So why have all so many? Tone. By changing the width of the bore and the degree to which the bore is conical you can get very different timbres. For the most part, in the order pictured, they range from narrow mostly-cylindrical bore through wider mostly-conical bore ones. The narrowest bore models of the bass trumpet are about 0.460" while the widest bore models of the marching euphonium are about 0.590". Wider conical bore instruments are generally richer and darker while narrower cylindrical ones are brighter and more brassy.

    One thing you can't see from pictures alone is the range of sizes, so here's one together with them scaled to a common size. From top to bottom the bell sizes are 7", 7.5", 10", and 12":

    This is big downside to the marching euphonium: it's enormous, making it kind of hard to hold out in front of you like that. The baritone is better, but I'm kind of curious whether I'd like the sound of a bass trumpet: it's the most compact of the bunch, and my baritone in its case is awkwardly large. [1]


    [1] Large enough that with careful packing I can also fit my trumpet and my foot percussion equipment in the same case. Plus valve oil, slide grease, and microphone.

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  • 10/20/14--06:00: Glasses Angles
  • I see people wearing glasses in a variety of positions:

    The closer you wear your glasses to your eye, however, the more of your field of view they cover:

    80° 60° 50°

    With my glasses all the way in my field of view is only slightly restricted, while with them further down my nose many more things require angling my head. Lots of people seem to be happy wearing their glasses farther down; what am I missing? Discomfort? Fashion? Not taking the time to adjust them to where they'll stay farther up?

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  • 10/21/14--06:00: Better Apartment Price Map
  • The initial model for my apartment price map was good enough for getting a sense of what different areas cost, but it was not an ideal fit for the underlying distribution. Specifically it assumed a linear relationship between number of bedrooms and cost (pretty reasonable) going through the origin (not reasonable). The problem is, a 2br doesn't cost twice as much as a 1br:

    Yes, it's approximately linear, but the line doesn't go anywhere near the origin. Another way of saying this is that there's a price-preimum for having your own unit. This is the cost of a kitchen, bathroom, etc. I originally tried to handle this by eyeballing it and saying that we could count apartments as having a number of "rooms" equal to one more than the number of bedrooms, but this isn't right either. If we do a simple linear regression we see an intercept of $1,526 and a slope of $481/bedroom. The intercept is the cost of a studio or "0br" and the slope is how much each additional bedroom costs $481, on average, over the whole Boston area.

    To fix this, I've updated the map generation to work in two steps. First it considers all the data, runs a linear regression, and determines the slope and the y-intercept. As before, the slope is the marginal cost of a bedroom and the y-intercept is the cost of a studio. Then it finds the x-intercept, which is the number of "phantom bedrooms" it needs to add to each listing in order to get a model that will run through the origin. This is assuming that regardless of the cost of the apartment the price premium for having your own unit is a similar percentage, which sounds reasonable but I haven't verified. Once it has the number of phantom bedrooms it can run the modeling from before and get the colored map overlay.

    I also changed the way colors are assigned. Before I spaced colors at even intervals ($1000/bedroom, $1100/bedroom, $1200/bedroom, ...) but this also reflects a bad assumption about the distribution. Even spacing would make sense if we had an approximately uniform distribution of prices over a range, but instead it's much more like a bell curve:

    To get sufficient gradations to handle the bulk of the data in the middle while still covering the whole range we can assign colors so each color has equal area [1] on the final map. This gives gradations like:

    There's also a selector now where you can choose how many bedrooms you're interested in, and it will recalculate the key to take that into account. The math is relatively simple: apartment bedrooms plus phantom bedrooms, times the marginal cost indicated on the map, but it's annoying enough that you wouldn't want to do it in your head. Note that we can still use the same map image because that's colored by marginal bedroom cost; we only have to adjust the key for different apartment sizes.

    So: better modeling of the data, better color buckets, and you no longer have to do math in your head. Here it is!


    [1] Well, almost. There's a bug where the most expensive bucket will sometimes go entirely unused. So some maps have no full-red. I'm not sure why yet.

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  • 10/19/14--06:00: Why Reduce Swelling?
  • Recently I jammed my fingers, and aside from resting them the standard healing advice is to reduce the swelling with ice, compression, elevation, and ibuprofen (advil/motrin). This is surprising, especially the medication. Why would we evolve swelling, a response to a common injury, if it's harmful? I could believe that in some cases you could have excessive swelling and it would be good to reduce that, but in the typical case you would expect swelling to be useful.

    A similar argument applies to fevers: the body raised its temperature, so why does it make sense to come in with acetaminophen (tylenol) and bring it back down? Again, if a fever gets high enough we do need to control it, but we should expect letting the fever run its course to be the healthiest option in most cases.

    What is it that these systemic medications do that our bodies weren't able to evolve on their own? Or is the modern environment different enough from the one in which we evolved that a response like fever or swelling once was useful but no longer is? Or maybe it's not useful after all; has anyone done an RCT looking at the impact of swelling reduction actions or medication on healing? Can I get some volunteers willing to self-administer hammer blows? [1]

    (This is basically an algernon argument, a use of the evolutionary optimality challenge.)


    [1] People would first need to administer the hammer, then check to see which treatment to apply. The trauma must be applied blind.

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