explain xkcd - User contributions [en]

Talk:1887: Two Down, One to Go

2017-09-08T22:55:04Z

108.162.221.58: ALternate interpretation for supernova

Worth noting that the Orionids are the last major shower of the year: https://www.timeanddate.com/astronomy/meteor-shower/orionid.html {{unsigned ip|108.162.246.215}}

Venus is sometimes visible during the day. A daylight supernova need not be the second brightest object in the night sky.[[Special:Contributions/162.158.62.159|162.158.62.159]] 13:30, 8 September 2017 (UTC)
:The Moon is also sometimes visible during the day. SN 1006 and SN 1054 were brighter than Venus at maximum brightness but still dimmer than the Moon. --[[User:Dgbrt|Dgbrt]] ([[User talk:Dgbrt|talk]]) 14:02, 8 September 2017 (UTC)

Randall is likely talking about the expected replenishment of the Leonids http://www.imo.net/50-years-ago-the-1966-leonid-meteor-storm/ [[Special:Contributions/172.68.65.18|172.68.65.18]] 14:55, 8 September 2017 (UTC)

Aurora viewing in "perhaps parts of Maine"? Maine's northern limit is ~47.5 degrees. Most of the US/Canada border is at 49 degrees, which is still too far south for good aurora views, but being in Seattle gets you closer to the pole than Maine. [[Special:Contributions/108.162.216.160|108.162.216.160]] 18:59, 8 September 2017 (UTC)

Could Randal's mention of a supernova be interpreted to mean that our sun goes supernova and since that's the last thing he sees, he jsut closes off his bucket list? [[Special:Contributions/108.162.221.58|108.162.221.58]] 22:55, 8 September 2017 (UTC)

1823: Hottest Editors

2017-04-12T15:49:28Z

108.162.221.58:

{{comic
| number = 1823
| date = April 12, 2017
| title = Hottest Editors
| image = hottest_editors.png
| titletext = Elon Musk finally blocked me from the internal Tesla repository because I wouldn't stop sending pull requests for my code supporting steering via vim keybindings.
}}

==Explanation==
{{incomplete|Created by a BOT - Please change this comment when editing this page. Do NOT delete this tag too soon.}}

The comic has a play on the word 'Editor'. The editors from 1995 to 2000 are plain-text editors, popular among many programmers and other computer scientists to edit machine-readable text.
Two of the earlier editors, VIM and EMACS, allow the user to perform common actions (like scrolling, marking text, saving or searching) using keyboard shortcuts.
As VIM and EMACS use different shortcuts, someone who is proficient in one editor may have difficulty using the other editor, since the shortcuts are different.
The 'Editor wars' refer to VIM and EMACS users debating heavily on which of the two editors is the best (for which keyboard shortcuts, or bindings, are just one of the arguments employed).
Modern editors (including Notepad++ and Sublime Text) mainly use the shortcuts determined the operating system, again different from VIM and EMACS.

{{w|Notepad++}} is a popular text and source code editor, initially released in 2003.

The 2020 editor 'CRISPR' is not a text editor, but a technique used to edit DNA. The comic may suggests that we will not be editing digital plain-text files, but DNA in 2020, possibly due to advances in [https://en.wikipedia.org/wiki/DNA_digital_data_storage DNA digital data storage].

To make the transition between editors easier, some editors offer VIM or EMACS key-bindings: the shortcuts will be (roughly) the same as in VIM or in EMACS, so that someone who used to be proficient in one of those editors can proceed to use the keyboard shortcuts in the way he or she was used to.
The comic suggests that in 2025, the VIM key-bindings will be the most popular for editing genes using CRISPR.
This creates a comical effect: CRISPR is a technique that operates on genes, and not on digital hardware, so it does not use a keyboard per sé. Consequently, it is surprising that CRISPR would have key bindings. The comic also suggests that in 2025, VIM will make a comeback in DNA editing, thus having 'won' the battle with EMACS.

==Transcript==
HOTTEST EDITORS

(horizontal line)

1995-2000 - EMACS-VIM EDITOR WAR

2005 - VIM

2010 - NOTEPAD++

2015 - SUBLIME TEXT

2020 - CRISPR

2025 - CRISPR (VIM keybindings)

{{comic discussion}}

1292: Pi vs. Tau

2016-01-03T21:25:08Z

108.162.221.58: The bug no longer exists. Expanding now gives the decimal digits.

{{comic
| number = 1292
| date = November 18, 2013
| title = Pi vs. Tau
| image = pi vs tau.png
| titletext = Conveniently approximated as e+2, Pau is commonly known as the Devil's Ratio (because in the octal expansion, '666' appears four times in the first 200 digits while no other run of 3+ digits appears more than once.)
}}

==Explanation==
This is yet another of [[Randall]]'s [[:Category:Compromise|compromise comics]]. A few mathematicians argue as to whether to use pi, which is the ratio between a circle's circumference and its diameter, or tau, which is the ratio between a circle's circumference and its radius.

Some consider pi to be the wrong convention and are in favor of using tau as ''the'' circle constant; see the [http://tauday.com/tau-manifesto Tau Manifesto], which was inspired by the article "[http://www.math.utah.edu/~palais/pi.html Pi is wrong!]" by mathematician Robert Palais. Others consider proponents of tau to be foolish and remain loyal to pi (see the [http://www.thepimanifesto.com Pi Manifesto]). Of course, regardless of which convention is used, the change is merely in notation — the underlying mathematics remains unaltered. Still, the choice of pi vs. tau can affect the clarity of equations, analogies between different equations, and how easy various subjects are to teach.

Most people know π (pi) by the approximation 3.14, but do not know τ (tau) which, by definition, is twice as large as pi. Randall is suggesting using "pau", which is a portmanteau of "pi" and "tau", as a number situated, appropriately enough, halfway between pi and tau, i.e. 1.5 pi or 0.75 tau. But of course his number would be inconvenient, as this value does not naturally turn up when working with circles or other mathematical constructs, so there are no commonly used formulas that would use pau.

The title text claims that pau can be approximated by e+2, as both values are roughly 4.71 — a similarity that holds little since it requires another irrational constant, {{w|E (mathematical constant)|e}}. It also attributes the nickname "Devil's Ratio" to pau, due to the sequence {{w|Number of the Beast|666}} supposedly appearing four times in the first 200 digits of pau when expressed in the {{w|octal}} base. However, this is not the case, and was likely due to an error in the computer system used by WolframAlpha; for more details see below.

==Transcript==
:[On the left is a "forbidden"-style slashed circle with the π symbol, captioned "Pi". On the right is a "forbidden"-style slashed circle with 2π, captioned "Tau". In the middle it reads 1.5π, captioned "Pau".]
:A compromise solution to the Pi Tau dispute

==Math details==
Possibly, [[Randall]] used [http://www.wolframalpha.com/ Wolfram|Alpha] to calculate the result (he uses it a lot, for example [http://what-if.xkcd.com/70/ What-if 70: The Constant Groundskeeper] or [http://what-if.xkcd.com/62/ What-if 62: Falling With Helium]).
However, when the comic was published, there was a bug in Wolfram|Alpha so that, when getting 200 octal digits from "pau", it just calculates the decimal value rounded to 15 significant digits (this is 4.71238898038469) and expands that as octal digits as far as needed.

This gives a periodically repeating number. In the first 200 digits of the octal expansion, the sequences 666 and 6666 do occur, twice and once, respectively. There are 4 occurrences, however, in the first 300 digits:
<pre>
4.554574376314416445676661714336617116240444076666510533533077631151350452060436452476274022621206136310000177621674175071262255702044274154476005744176002676623042402346036604733130522524127534777714554305412763636566643022106616734723661726160312772574551366370203115523402704104015532221722772357666</pre>
Expansion that long indeed does contain 666 (the {{w|Number of the beast|number of the beast}}) four times (with one instance as 6666). It also contains 0000, 222, 444, and 7777, but they only appear once in a run.

{{w|Mathematical coincidence|Coincidentally}}, e+2 is also very similar to 1.5 pi, although only to a few digits.
<pre>
1.5π = 4.71238898038...
e+2 = 4.71828182845...
</pre>

==Trivia==
*For Pi the sequence '666' occurs for the first time at position 2440. Many more occurrences can be found here: [http://www.angio.net/pi/ The Pi-Search Page].
*Note that pau is Catalan for peace, which is a good solution for the pi/tau dispute.
*In the discussion it has been theorized that Randall used [[356: Nerd Sniping|Nerd Sniping]]. In which case he was aware of the mistake in Wolfram!
*For an entertaining introduction to the concept of tau, see this [https://www.khanacademy.org/math/recreational-math/vi-hart/pi-tau/v/pi-is--still--wrong Vi Hart video].

{{comic discussion}}
[[Category:Comics with color]]
[[Category:Math]]
[[Category:Compromise]]

Talk:835: Tree

2015-06-23T17:25:15Z

108.162.221.58: Can't be a red-black tree

I didn't really look too closely, but it seems to be based on Red-Black trees (Red Green in the case of Christmas): http://en.wikipedia.org/wiki/Red_black_tree

: Nope. For a Red-Black tree, all the leaves have to be the same color as the root, and no red nodes can have a red parent. The root here is a yellow star, the leaves are mixed colors, and both colors have instances of a node with a color that matches it's parent, so nether red nor green can be the "Red" for the algorithm.

Then again it could just be a color scheme. [[Special:Contributions/132.3.25.79|132.3.25.79]] 12:35, 23 April 2013 (UTC)Tyler

The title text doesn't really make sense - removing the root of a heap is a very common practice for a variety of applications. In fact, you almost always want to process heaps by removing the root. [[User:Ciotog|Ciotog]] ([[User talk:Ciotog|talk]]) 14:05, 2 March 2014 (UTC)
: It is common, ok. And, in fact, Billy WILL process the heap by removing the root. It makes however sense, since all heaps must be "refreshed" after you remove the root. While it takes small time for a computer, it can be lengthy for a human. And it would be probably better an unsorted array of presents, so Billy can open any present without effecting any effect (see Comic 326) --[[Special:Contributions/108.162.229.42|108.162.229.42]] 14:10, 17 June 2014 (UTC)

Hmmm... The heap seems sketchy. Note the second and third levels. Not a heap by C++ standards.
[[Special:Contributions/108.162.245.218|108.162.245.218]] 22:08, 18 June 2014 (UTC)