I like to shuffle poker chips while I work. It gives me something to do while pages are loading or while I'm thinking that doesn't involve checking Twitter or Hacker News.

I got curious how long it took for chip stacks of various heights to return to their shuffled state. However right now I can only shuffle stacks of 18 chips (9 red, 9 blue) before they come tumbling back to the floor, out of my hand. So I wrote a short program to simulate chip shuffles and determine how long it would take to get the stacks back to their shuffled state.

Here are the results:

Number of Red Chips    Total Shuffles
1                      2
2                      4
3                      3
4                      6
5                      10                     
6                      12
7                      4
8                      8
9                      18
10                     6
11                     11
12                     20
13                     18
14                     28
15                     5
16                     10
17                     12
18                     36
19                     12
20                     20

That's a pretty interesting pattern. I'm sure there's a bunch of cool math behind it; I'll look it up soon and then update this post if I find any. Note that if the number of shuffles is divisible by two, the chips reverse order in the stack (ex. go from all red on the bottom to all red on the top) before returning to their original state.

Update: I found the pattern behind the poker chip shuffle sequence, on a site that lets you plug in any integer sequence and try to find the pattern that matches. You can find the pattern here. Glad I found that page, because I'm not sure I would have guessed the pattern. Here is more detail:

In other words, least m such that 2n+1 divides 2^m-1. Number of riffle shuffles of 2n+2 cards required to return a deck to initial state. A riffle shuffle replaces a list s(1), s(2), ..., s(m) by s(1), s((i/2)+1), s(2), s((i/2)+2), ... a(1) = 2 because a riffle shuffle of [1, 2, 3, 4] requires 2 iterations [1, 2, 3, 4] -> [1, 3, 2, 4] -> [1, 2, 3, 4] to restore the original order.

Here's the example code, in Haskell:

To output numbers, save that code as a file called

chips.hs

and run:

$ ghci
GHCi, version 6.10.4: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer ... linking ... done.
Loading package base ... linking ... done.
Prelude> :l chips.hs
[1 of 1] Compiling Main             ( chips.hs, interpreted )
Ok, modules loaded: Main.
*Main> zip [1..20] (map getNumberOfShuffles [1..20])

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I had a lot of trouble with this recently, so hope this helps. Google is pretty strict with the CSV files it imports.

First off open Excel. In the first row of your file, add the following headers:

Subject, Start Date, Start Time, End Date, End Time, All Day Event, Reminder On/Off, Reminder Date, Reminder Time, Meeting Organizer, Description, Location, Private

Every event (every row in Excel) needs to have a Subject, Start Date, and Start Time. The other headers are optional and you can mix and match them as much as you please. Here is a complete sample I uploaded today.

Subject, Start Date, Start Time, End Date, End Time, Private, All Day Event, Location
Ramsay Shield, 7/26/2008, 7:00 PM, , 9:00 PM, FALSE, , TBC
Training, 7/27/2008, 12:00 PM, , TRUE, FALSE,

Make sure you format your cells properly

Highlight every time under Start Time, End Time, and Reminder Time, click “Format Cells,” then “Time,” then “1:30 PM.”

Also, highlight every date under Start Date, End Date, and Reminder Date, then click “Format Cells,” then “Date,” then “3/14/2001.”

You need to do both of those things for Google to recognize your file.

For Private, All Day Event, and Reminder On/Off, type True or False in the relevant cell. If you leave them blank, Google Calendar will use the default settings for these events (for privacy, it will make the event private or public depending on whether the calendar is private or public). If there isn’t any info after Start Date & Start Time, Google assumes the event is one hour long. Also, make sure that the only data on the spreadsheet is events – otherwise Google will return an error.

Once you’re done click File –> Save As, then click down at the bottom where it says “Microsoft Office Excel Notebook” for file type, and change it to CSV (Comma Separated Value) format. Then you’re ready to upload to Google!

Note: if you upload the same CSV file twice, Google will create duplicates of your events rather than replace the first set. There’s no “Remove duplicates” button either – you have to do it manually, or erase the whole calendar and start again.

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How do you know if your website is up, right now? Maybe you are browsing it and got an error, or a friend texted to tell you it was down. Otherwise your website might be down and you'd have no idea. Here is a simple script that will help you learn faster whether your website is up or down. I wrote it in Ruby to start learning Ruby syntax.

require 'uri'
require 'net/http'
require 'net/smtp'

def send_email(to, opts={})
    # Send an email. In Ruby, the ||= operator means 'only assign the
    # new value if the value has not been set yet'
    opts[:server]      ||= 'localhost'
    opts[:port]        ||= 25
    opts[:ehlo_domain] ||= 'localhost'
    opts[:username]    ||= 'username'
    opts[:password]    ||= 'password'
    opts[:from]        ||= 'youremail@domain.com'
    opts[:from_alias]  ||= 'First Last'
    opts[:subject]     ||= 'Test email'
    opts[:body]        ||= 'This is a test!'

    # the following says 'create a new string called msg containing everything
    # from here to the END_OF_MESSAGE marker'
    # then, we fill in the email with all of the values we filled in above. Note
    # that there has to be a newline between the subject and the body of the
    # message.
    # This is a plaintext message - to send HTML emails, we would need a more
    # complex template.
    msg = <<END_OF_MESSAGE
From: #{opts[:from_alias]} <#{opts[:from]}>
To: <#{to}>
Subject: #{opts[:subject]}

#{opts[:body]}
END_OF_MESSAGE
    Net::SMTP.start(opts[:server], opts[:port], opts[:ehlo_domain],
                    opts[:username], opts[:password], :plain) do |smtp|
        smtp.send_message msg, opts[:from], to
    end
end

# test for main method
if __FILE__ == $0
    # the domain we want to check
    url = 'http://testdomain.com'
    my_email = "myemail@gmail.com"
    r = Net::HTTP.get_response(URI.parse(url))
    if r.code != "200"
        # we have a big problem, server is down or other
        opts = {
            :server     => 'smtp.yoursmtpserver.com',
            :port       => 587,   # should be 25 or 587
            :ehlo_domain => 'localhost',      #this doesn't matter too much
            :username   => 'yoursmtpusername',
            :password   => 'yoursmtppassword',
            :from_alias => 'testdomain.com Admin',
            :subject    => 'The website is down',
            :body       => "Hey,\nan attempt to reach the homepage returned " + 
            "the status code " + r.code.to_s() + ". \n\nYou should check it out."
        }
        send_email my_email, opts
    end
end

That will send an HTTP request to your website. If the request was successful, you'll get an HTTP Header Response that says 'Status Code: 200 OK'. If we don't get a 200, this means the site is definitely wrong. We may get a 200 and still have problems with the database or other, but this is meant to be a simple test. Other well known codes are 404 (File Not Found), 500 (Internal Server Error), and 418 (I'm a teapot). Once you've got the script in place, save it as "is_server_up.rb" somewhere on a computer which has lots of uptime (your school's CS server, a remote SSH server, or otherwise). Your laptop is a bad choice because when you close your laptop, or are not connected to the Internet, the test will not be able to run. The computer hosting your website is also a bad choice because if that computer goes down, your website will be down but the script will not run. On a Linux or Mac machine, type

$ crontab -e

which should open up a Terminal text editor. Then type:

0-59/2 * * * * /usr/local/bin/ruby /path/to/your/file/is_server_up.rb

where

/usr/local/bin/ruby

is the path to the Ruby executable on your laptop. If you don't know where it is, try typing "which ruby" in the Terminal. If nothing comes up, you probably need to download Ruby. The

0-59/2

bit says to run the script every 2 minutes. You might be worried that fetching your homepage every 2 minutes will generate an extra 720 hits to your site every day and affect your Analytics stats. However, Analytics will only measure visits from browsers that can execute Javascript, and this Ruby script will not execute any Javascript, so you are safe. Note that if you have an important site, or one which generates revenue, you probably should not use this tool - there are better tools like Pingdom that will let you know right away whether your site is down.

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Posting's been kind of light, so I'll link to two presentations I've done for class recently. I'm currently taking a course on compilers, which is the best course I've taken in college. Very quickly, your computer can only understand a very limited set of instructions: add 01110011 to 11001011, load eight zeroes and ones from memory (the cache, or random-access memory (RAM)), overwrite a set of zeroes and ones, etc. However, if you had to write entire programs using only this instruction set, it would be hard for programmers to keep track of variable state, to write error-free code and to find bugs when they are made (Notable exception: Roller Coaster Tycoon was written entirely in x86 assembly language, which explains (a) why there has never been a Mac version released, and (b) why RCT3 was so much worse - it was written in a higher-level language by a different company). So what programmers did was invent abstractions - control flow tools like if-then-else branching, while and for loops, as well as data structures like arrays and dictionaries. These allow programmers to write in a more natural language, but programs must be translated - "compiled" - down to machine language. Because this is done automatically, and many people use the same compiler (so everyone benefits from errors caught by one person), generated machine code is usually free of errors. I gave a talk in class on a special type of compiler, called just-in-time (JIT). Normally you write your program, compile it, and then run the machine language. But a JIT compiler is writing and compiling new machine language as the program is running. Here are the slides: There are a few reasons this can be quicker than compiling beforehand ("static" compilation). First, you have more information about the values of variables at runtime that you can use to eliminate redundancy in your code. Second, in the case of loops, where you are following the same code paths hundreds or thousands of times in a row, you can see which paths are being used the most often, and rewrite your code so that the most common code path is executed in a straight line. This is important because modern processors will try to pre-fetch and execute several instructions at a time, and if you keep jumping from place to place in your code, the processor can't execute instructions in advance. I also wrote a paper (and gave a talk) on some of the threats facing the Cavendish banana, which will probably go extinct soon. I've been fortunate to write papers this year on some fun topics; last semester I was able to cite Robin Hanson, Tyler Cowen, Eliezer Yudkowsky and Alan Turing in one philosophy paper, which was pretty fun. That paper's here. The Unfortunate Sex Life of the Banana

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I wrote a Google Chrome extension that stops videos and ads from playing automatically on ESPN.com. This is another example of scratching my own itch; most people can enable this feature by clicking Autostart Off on any ESPN video, but I clear out my cookies every time I close Chrome, so that tool doesn't work for me. Also, this is more important for me than other people because I'll click to open three stories at once, and if the videos all begin playing at the same time, it gets extremely annoying. Anyway, here's the extension, all six lines of it in Javascript:

jQuery("#videoPlayer").ready(function(){
    var script = document.createElement("script");
    script.type = "text/javascript";
    script.text = "function check_if_ready(){if (espn.video.player.adPlaying){espn.video.pause();} else{setTimeout(check_if_ready, 100);}}check_if_ready();"
    document.body.appendChild(script);
});

Unfortunately getting to that point took a while; I tried a few other things before I hit on that solution. It's not perfect but it gets the job done. In the future it would be nice to skip the ads entirely, or auto-play only the video in the tab I'm currently watching. You can download the extension here or improve the source code here.

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Yesterday I was part of CMC's first ever entry into the ACM ICPC, an international programming competition. Last year solving three problems would have been good enough for 5th place, but this year solving three problems was only good enough for 29th out of 75 or so. The easiest three problems were easy to pick out and we started work on them. The first problem was, given an expected distribution of T-shirt sizes and a number of participants, write some code to determine how many T-shirts to order. The code for this problem was more or less written in the problem description and I was able to solve it in the first twenty minutes or so. While I was doing that my teammates were working on a cipher problem - given a codeword, create a simple code alphabet and use it to decrypt a message. While they were doing that going on I started working on the third problem, which was a map labeling algorithm. It was like a Rand McNally map where if you go off the top of the map you have to go to another page on the map. You were given a 'map' divided up into a series of blocks, and had to number each block, and then for each block label the block's neighbors. I solved this one pretty quickly too, however I forgot to remove a print statement from my code, so it was printing an empty line before the output, which cost two incorrect submissions and 40 penalty minutes. The cipher problem turned out to be fairly difficult. There was a problem with the program that took about an hour to solve, partly because we kept printing out code that we thought was showing one thing when in fact it was showing something else. Also, we had an array of characters that was supposed to hold all of the letters of the alphabet from A to Z, but in fact was missing W. Once we solved those we submitted the code and got the correct answer on the first submission, but by this point we had an hour and a half left. I started working on the fifth problem, which I thought was the next easiest. The problem was, given a triangle and a thousand points inside that triangle, split the points into three even groups by finding another point inside the triangle. I found the algorithm right away, which was to do a binary search and always move toward the region that contained the most points. However, this turned out to be tricky to implement in practice. Ultimately this problem was really difficult and only a few groups solved it correctly (the winning Harvey Mudd team solved seven of eight problems and this was the one problem they didn't solve). Trying it was a tactical mistake on my part, and we might have been able to solve a fourth if we'd attempted a different problem. Ultimately it was a long day and as my teammate Jacob noted, "the nerdiest thing I've ever done." It was good I guess, considering I was the only person on our team who'd practiced before the contest and we were the first team ever from CMC to go to the competition. I'd wanted to join the competition because I show my resume to people and they say "Great you're an economics major, so, marketing?" and I wanted to show that I could code a little bit. It would have been great to do better in the competition but them's the breaks. Among other things this shows how wide the differences between programmers can be; it's estimated that the best programmers are 10 times as efficient as average programmers, and looking at the times to completion it's easy to see how this is true. By the time I solved Problem 1 the Harvey Mudd team had already solved three problems, and there were some teams there that didn't even solve a single problem. These are hard to measure, which is why it's so important to actually look at someone's code to see how they do things, or ask them to write sample code. All of my practice code can be found here; unfortunately you can't keep the code you wrote during the competition.

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