Apple are evil?

by John on February 8, 2010

Mike Croucher wrote a post the other day explaining why he’s going to buy an iPad. He said that one of the objections to the iPad he’d heard was

Apple are evil because they take away control of how we use their devices.

I teased Mike that I would never say “Apple are evil.” On this side of the Atlantic we’d say “Apple is evil.” But in the UK it is accepted usage to say “Apple are evil.”

“Apple” is a collective noun when used to refer to Apple Inc. British English treats collective nouns as plural, but American English treats them as singular. Although the British usage sounds odd to my American ears, it makes sense just as much sense as the American convention. You could argue for plural verbs because corporations are made of individual people, or you could argue for singular verbs because the corporations act as a single entity. See Grammar Girl’s tip on collective nouns for more background.

By the way, I don’t believe Apple is evil. They’re just a company, no more or less virtuous than most other companies.

Apple posts:

I am not an operating system
Inside Steve Job’s brain
Protestant PCs, Catholic Macs

Grammar posts:

Important because it’s unimportant
English grammar
Finding grammatical errors in software

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Twitter daily tip news

by John on February 8, 2010

I have five Twitter accounts that send out one tip per day, including a new one I just added last week.

Regular expressions

@RegexTip started over today. It’s a cycle of tips for learning regular expressions. It sticks to the regular expression features common to Python, Perl, C#, and many other programming languages. This account posts Monday through Friday.

Keyboard shortcuts

@SansMouse gives one tip a day on using Windows without a mouse. By practicing one keyboard shortcut a day, you can get into the habit of using your mouse less and your keyboard more. This cycle of tips started over January 29 with the most common and most widely useful shortcuts. I’m also sprinkling in a few extra tips that are less well known. This account also posts Monday through Friday.

Math

I have three mathematical accounts. These post seven days a week.

@AlgebraFact, just started February 2. It will be a mixture of linear algebra, number theory, group theory, etc.

@ProbFact gives one fact per day from probability. Usually these facts are theorems, but sometimes they include a note on history or applications.

@AnalysisFact gives facts from real and complex analysis. The topics range from elementary to advanced.

What if I don’t use Twitter?

You can visit the page for a Twitter account just like any other web page. And every Twitter account has an RSS feed link allowing you to subscribe just as you would subscribe to a blog.

How do you write these?

I write up content for these accounts in bulk. I may sit down on a Saturday and come up with several weeks worth of tips. Then I use HootSuite to schedule the tips weeks in advance. Sometimes I’ll post something spontaneously, such as link to something relevant, but most of the work is done in advance. I use my personal Twitter account for live interaction.

Related links:

Using Windows without a mouse

Regular expressions in

Chart of probability distribution relationships

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You can’t force people to provide metadata

by John on February 7, 2010

I ran across a long rant from Steve Yegge this evening about junior programmers. In a nutshell, Yegge says they like to play around with metadata rather than getting real work done.

Here’s an insightful observation Yegge makes along the way.

And Haskell, OCaml and their ilk … try to force people to model everything. Programmers hate that. These languages will never, ever enjoy any substantial commercial success, for the exact same reason the Semantic Web is a failure. You can’t force people to provide metadata for everything they do. They’ll hate you.

Related post:

Probability of semantic markup being correct

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Weekend miscellany

by John on February 6, 2010

Computing

Online diff tool
HTTP flowchart
Astroinformatics
Python propaganda
How to safely store a password
Google Docs dropping IE6 support
Why it’s hard to move Facebook off PHP
Keyboard shortcuts for Windows, Mac, and Linux

Math

Fundamental examples in math
Daily fact from algebra and number theory
62nd Carnival of Mathematics

Miscellaneous

Always wear your seatbelt
Space shuttle repaired with duct tape (lunar rover too)

How to peel a pummelo. YouTube video with nice soundtrack.

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Carnival of Mathematics #62

by John on February 5, 2010

What is the Carnival of Mathematics? Math bloggers submit articles they have written recently and each month a host writes a post linking to the submitted posts. The sister carnival, Math Teachers at Play, focuses on math education and on math up through high school level. For a more thorough description of the two carnivals and some FAQs, please see Mike Croucher’s article What is a Maths Carnival?

I’m taking a turn hosting this month. Tradition dictates that the host begin with some trivia about the number of the post. As this is the 62nd Carnival of Mathematics, here are a few facts about 62.

  • 62 is the only number whose cube (238328) consists of 3 digits each occurring 2 times.
  • The great rhombicosidodecahedron has 62 sides.
  • Louis Pasteur developed the first rabies vaccination at age 62.

And now onto the posts.

Math and science teacher Cory Poole sends in a video that he created along with his partners and students. The video features a 64-foot Sierpenski triangle about of 12,000 tortilla chips. Read more about the story of the video. Also, here are the bloopers from making the video.

St. Swithun’s day is a sort of British analog of America’s Groundhog Day. If it rains on St. Swithun’s day, it is supposed to rain for the next 40 days. Is there some truth to the legend? See Jon McLoone’s article Mathematica Tests the St. Swithun’s Day Proverb posted at Wolfram Blog.

Edmund Harriss from Maxwell’s Demon presents Spirographs and the third dimension. Interesting visually and mathematically.

toral spirograph

Rachel Thomas presents Beautiful symmetry provides glimpse into quantum world on News from the world of maths. This article reports on a low-termperature experiment that implies that the exceptional Lie group E8 is at work.

Did you know that sine and cosine are equal for all x? Heather (Xi) submitted a pseudo-proof in A=B implies that 1=1, therefore? by her colleague TwoPi at 360. (If there is ever a 360th Carnival of Mathematics, Heather should host it.)

Update: The 360 blog has agreed to host the 360th Carnival of Mathematics, tentatively scheduled for December 1, 2034. (Mike, I hope it’s OK that I scheduled this date without consulting you. ;) )

Marc West presents The curse of the duck, a post about mathematics and cricket. His blog is Mr Science Show: Where Science Meets Pop Culture.

Dan M presents Appolonian Gaskets and Ford Circles on his blog mathrecreation. This post relates number theory and geometry as Ford circles are related to the Farey sequence.

Ford circles

Rick Regan presents Counting Binary and Hexadecimal Palindromes posted at Exploring Binary. Rick counts base 10 palindromes as a warm-up before diving into new territory with binary and hexidecimal numbers.

Gregory Astley wrote a guest post Maxima Tutorial – plotting direction fields for 1st order ODEs for Mike Croucher’s blog Walking Randomly. (Maxima is part of the SAGE mathematics system. Mike has written several posts about SAGE lately.)

Annarita Ruberto from Matem@ticaMente presents the article “How heavy the fish?” The original post was written in Italian, and here is Google’s translation of the page into English.

Matt McDonnell presents Mathematical Recreations: Tweetable Game Of Life, a guest blog for Loren Shure’s blog Loren on the Art of MATLAB.

For some mental arithmetic shortcuts and an explanation of why they work, see Sol Lederman’s post Trachtenberg speed multiplication: exploring why it works on his blog Wild About Math.

Politics impacts sphere of human activity, including math education. See Jason Dyer’s post Anatomy of a Political Math-Ed Reaction on The Number Warrior.

Peter Rowlett from Travels in a Mathematical World presents Substitution ciphers: Ancient – Renaissance, video included below.

You can keep up with Carnival of Mathematics news on Twitter by following @CarnivalOfMath. You may also be interested in daily math facts on Twitter from @ProbFact (probability), @AnalysisFact (real and complex analysis), and @AlgebraFact (algebra and number theory).

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A few days ago I wrote a post on finding parameters so that a probability distribution satisfies two percentile conditions. Since then I’ve written Python code to carry out the calculations described in that article and the accompanying technical report.

The article is Finding probability distribution parameters from percentiles posted on CodeProject. The article comes with Python source code and some commentary. The article shows how SciPy and the functools module make it possible for the code to be very succinct.

Related posts:

Probability distribution parameters in SciPy
Numerical computing in IronPython with Ironclad
Getting started with SciPy

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Parameterizations are the bane of statistical software. One of the most common errors is to assume that one software package uses the same parameterization as another package. For example, some packages specify the exponential distribution in terms of the mean but others use the rate. [click to continue...]

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Little programs versus big programs

by John on February 3, 2010

From You Are Not a Gadget:

Little programs are delightful to write in isolation, but the process of maintaining large-scale software is always miserable. … Technologists wish every program behaved like a brand-new, playful little program, and will use any available psychological strategy to avoid thinking about computers realistically.

Related posts:

Writes large, correct programs
Why there will always be programmers

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Sleep debt and industrial accidents

by John on February 2, 2010

From The Power of Full Engagement:

… every one of the great industrial disasters of the past twenty years — Chernobyl, the Exxon Valdez, Bhopal, Three Mile Island — occurred in the middle of the night. For the most part, those in charge had worked very long hours and built up considerable sleep debt.

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New Python podcast: A little bit of Python

by John on February 1, 2010

There’s a new Python podcast: A little bit of Python with Michael Foord, Brett Cannon, Jesse Noller, Steve Holden, and Andrew Kuchling.

So far I’ve found the first episode most interesting. It discusses the “moratorium”, the plan to give Python library authors time catch up with Python 3 before extending the core language further. This sounds like a very smart move.

Related posts:

Good enough for Google and NASA
Plain Python

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Last year I wrote a little 10-page booklet called PowerShell Day 1. It covers many of the things I wish I had known when I started using PowerShell.

  • How do I configure PowerShell?
  • How do I make PowerShell launch faster?
  • How do I get documentation?
  • Why did PowerShell make some of the design decisions they did?
  • Once I’ve written some useful functions and scripts, where do I put them?
  • Where can I find more PowerShell resources?

Now I’ve started updating the booklet to reflect changes in PowerShell version 2.0. I haven’t had a lot of experience with version 2.0 and would appreciate your help updating the booklet. I have put a link to an alpha version of the update for version 2.0 on the download page.

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Parameters and percentiles

by John on January 31, 2010

The doctor says 10% of patients respond within 30 days of treatment and 80% respond within 90 days of treatment. Now go turn that into a probability distribution. That’s a common task in Bayesian statistics, capturing expert opinion in a mathematical form to create a prior distribution.

Graph of gamma density with 10th percentile at 30 and 80th percentile at 90

Things would be easier if you could ask subject matter experts to express their opinions in statistical terms. You could ask “If you were to represent your belief as a gamma distribution, what would the shape and scale parameters be?” But that’s ridiculous. Even if they understood the question, it’s unlikely they’d give an accurate answer. It’s easier to think in terms of percentiles.

Asking for mean and variance are not much better than asking for shape and scale, especially for a non-symmetric distribution such as a survival curve. Anyone who knows what variance is probably thinks about it in terms of a normal distribution. Asking for mean and variance encourages someone to think about a symmetric distribution.

So once you have specified a couple percentiles, such as the example this post started with, can you find parameters that meet these requirements? If you can’t meet both requirements, how close can you come to satisfying them? Does it depend on how far apart the percentiles are? The answers to these questions depend on the distribution family. Obviously you can’t satisfy two requirements with a one-parameter distribution in general. If you have two requirements and two parameters, at least it’s feasible that both can be satisfied.

If you have a random variable X whose distribution depends on two parameters, when can you find parameter values so that Prob(X ≤ x1) = p1 and Prob(X ≤ x2) = p2? For starters, if x1 is less than x2 then p1 must be less than p2. For example, the probability of a variable being less than 5 cannot be bigger than the probability of being less than 6. For some common distributions, the only requirement is this requirement that the x’s and p’s be in a consistent order.

For a location-scale family, such as the normal or Cauchy distributions, you can always find a location and scale parameter to satisfy two percentile conditions. In fact, there’s a simple expression for the parameters. The location parameter is given by

\frac{x_1 F^{-1}(p_2) - x_2 F^{-1}(p_1)}{F^{-1}(p_2) - F^{-1}(p_1)}

and the scale parameter is given by

\frac{x_2 - x_1}{F^{-1}(p_2) - F^{-1}(p_1)}

where F(x) is the CDF of the distribution representative with location 0 and scale 1.

The shape and scale parameters of a Weibull distribution can also be found in closed form. For a gamma distribution, parameters to satisfy the percentile requirements always exist. The parameters are easy to determine numerically but there is no simple expression for them.

For more details, see Determining distribution parameters from quantiles. See also the ParameterSolver software.

Update: I posted an article on CodeProject with Python code for computing the parameters described here.

Related posts:

Biostatistics software
Diagram of distribution relationships
How to calculate percentiles in memory-bound applications

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Economics rap

by John on January 30, 2010

The debate between economists John Maynard Keynes and F. A. Hayek set to rap.

Related post:

The one thing to remember in economics

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Weekend miscellany

by John on January 29, 2010

Science

Diamond oceans
Plants put the bend in rivers
State of biology data integration

Programming

Developer town (little individual houses as offices)
.NET framework install base
Evolution of a Python programmer
How to recognize a good programmer

Miscellaneous

Crayola history
Visa restriction index
LaTeX search
The perverse economics of college construction
Odds that best potential chess player has never played chess
Paying more for information than for food

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Universal time

by John on January 28, 2010

Universal time (UTC) is the same as Greenwich Mean Time (GMT), give or take a second. It’s essentially the time in Greenwich, England except it ignores Daylight Savings Time.

The abbreviation UTC is an odd compromise. The French wanted to use the abbreviation TUC (temps universel coordonné) and the English wanted to use CUT (coordinated universal time). The compromise was UTC, which doesn’t actually abbreviate anything.

Sometimes a ‘Z’ is appended to a time to indicate it is expressed in UTC. The NATO phonetic alphabet code for ‘Z’ is ZULU, and so UTC is sometimes called “Zulu Time.”

It’s useful to know how your time zone relates to UTC. (You can look it up here.) For example, I live in the US Central time zone. Central Standard Time (CST) is UTC-6, i.e. we’re 6 hours behind Greenwich. Knowing your time relative to UTC makes international communication easier. It also helps you read computer time stamps since these almost always use UTC.

One of the advantages of UTC is that it avoids Daylight Savings Time. DST is surprisingly complicated when you look at it in detail.  Some countries observe DST and some do not. Countries that do observe DST may begin and end DST on different dates, and those dates can change from year to year. And inside countries that observe DST some regions are exceptions. For example, the United States generally observes DST, but Arizona does not. Actually, it’s even more complicated: The Navajo Nation inside Arizona does observe DST.

Related posts:

Mercator projection
Find distances using longitude and latitude
Visual Source Safe and time zones

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