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Latitude doesn’t exactly mean what I thought
There are two kinds of latitude: geocentric and astronomical. On a perfect sphere, they're the same, but on an oblate spheroid like Earth they're different.
John D. Cook
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Visit johndcook.com → RSS feedOn Hacker News Jan 2010 – Sep 2026
Math & Algorithms 44Software Engineering 24Life, Learning & Writing 11Career & Management 11Science & Space 9Programming Languages 6
62
The R language, for programmers
Some things about the R programming language that programmers coming from other languages are likely to trip over.
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R programming for those coming from other languages
Things a programmer coming from another language needs to know about R, especially those things that might be most surprising
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Visually symmetric words
The word "kayak" is a palindrome, but it isn't visually symmetric. The word "bud" is visually symmetric, but not a palindrome.
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Monads and Macros
Monads and macros have an almost gnostic mystique about them. Why is that? Why does hardly anyone use both?
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Where to wait for an elevator (2010)
Where do you stand in order to minimize the expected distance to walk to catch the first elevator that arrives? Maybe not where you think.
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Why a Slide Rule Works
Why does lining up two scales of a slide rule let you multiply numbers?
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The "Soft Maximum" function
The soft maximum approximates the maximum function, and approaches it in the limit, but is easier to work with.
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Weighting an average to minimize variance
How would you allocate money to a set of independent assets with to minimize volatility if some assets are more volatile than others?
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Regular expressions that work “everywhere”
What regular expression features work everywhere. Very few unless you relax your definition of "everywhere."
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Selection bias and bombers (2008)
During WWII, statistician Abraham Wald told the RAF to add armor where it didn't seem planes needed it. But he was right.
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Life lessons from differential equations (2015)
Some problems simply have no solution. Some problems have no simple solution. Some problems have many solutions. ...
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What use is mental math in 2022?
The ability to quick estimates is still valuable, maybe more valuable than it used to be.
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Why do C++ folks make things so complicated?
This morning Miroslav Bajtoš asked "Why do C++ folks make things so complicated?" in response to my article on regular expressions in C++. Other people asked similar questions yesterday. My response has two parts: Why I believe C++ libraries are often complicated. Why I don't think it has to be that way. Why would…
76
Floor, Ceiling, Bracket
The notation [x] reigned for nearly two centuries before being replaced by ⌊x⌋. Why the latter is much better and what else we might learn from its inventor.
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Mathematically correct but psychologically wrong
The snowball strategy says to pay off your smallest debt first, then the next smallest, and so on until you're out of debt. When I first heard of this I thought it was silly. Clearly the optimal strategy is to pay off the debt with the highest interest rate first. That assessment is mathematically correct,
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Divisibility by 7
How can you tell whether a number is divisible by 7? Almost everyone knows how to easily tell whether a number is divisible by 2, 3, 5, or 9. A few less know tricks for testing divisibility by 4, 6, 8, or 11. But not many people have ever seen a trick for testing divisibility
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Gell-Mann Amnesia
Michael Crichton coined the term Gell-Mann Amnesia effect to describe forgetting how unreliable a source is in one area when you trust it in another area.