explain xkcd - User contributions [en]

Talk:998: 2012

2025-01-03T14:01:28Z

172.70.162.70:

2012 is almost over, and no end of the world yet. Makin' progress. [[User:Davidy22|<span title="I want you."><u><font color="purple" size="2px">David</font><font color="green" size="3px">y</font></u><sup><font color="indigo" size="1px">22</font></sup></span>]][[User talk:Davidy22|<tt>(talk)</tt>]] 02:08, 13 November 2012 (UTC)
: We have until Winter Solstice, it seems, whereupon we face a calamity the likes of which haven't been seen since Y2K. -- [[User:IronyChef|IronyChef]] ([[User talk:IronyChef|talk]]) 06:33, 20 November 2012 (UTC)

I haven't been this disappointed by the apocalypse since Y2K. Not even worth a rental. [[Special:Contributions/69.127.136.211|69.127.136.211]] 03:51, 24 January 2013 (UTC)

Upgraded to past tense. [[User:Alpha|Alpha]] ([[User talk:Alpha|talk]]) 20:32, 23 February 2013 (UTC)

The Mayan did not predict the end of the world, they just would have to use a new calendar.--[[User:Dgbrt|Dgbrt]] ([[User talk:Dgbrt|talk]]) 19:56, 31 July 2013 (UTC)
:That's what the explanation says... why the incomplete/incorrect tag? [[Special:Contributions/173.245.53.117|173.245.53.117]] 10:11, 5 December 2013 (UTC)
::I think it's the "numerous ''other'' faulty predictions" line in the third paragraph. That said, it's not the Mayans who predicted the end of the world, but those who failed to learn from history. Anonymous 01:46, 8 January 2014 (UTC)

I take 4 AP courses this year. AP courses have a bonus point to GPA; for example, an A in an AP course translates to a GPA of 5. I also take a non-AP English course. I am certain that I will get straight-A's in the AP courses, so I can fail the English class and still get a 4.0 GPA, which means straight-A's across the board. --[[User:Troy0|Troy0]] ([[User talk:Troy0|talk]]) 13:16, 27 August 2014 (UTC)

It would certainly have been the end of the world for those who died or committed suicide on that day. {{unsigned ip|108.162.250.223}}

Except for those who did so on Ilkley Moor (unless it was involuntarily. (Or related in some way to the comic.))

Plans to advertise Mayan culture after the year indicate that journalism is a major cause of Fail. Discuss. [[User:Weatherlawyer| I used Google News BEFORE it was clickbait]] ([[User talk:Weatherlawyer|talk]]) 06:36, 22 January 2015 (UTC)

Just had a 'Duh' moment, and I don't know why no-one else has noticed this, but not only does 354 days only get you to December 20, that's in non-leap years. 2012 was a leap year. Hence, the number of days should be 356. {{unsigned ip|173.245.48.237}}
:Please do not forget to sign your comments. And your 'Duh' moment is wrong. The comic was released on January 2. Just check the new trivia section. --[[User:Dgbrt|Dgbrt]] ([[User talk:Dgbrt|talk]]) 19:25, 2 January 2018 (UTC)

Can we start talking about Mayans again? As mentioned, they're still around in the millions, and languages like Yucatec Maya have ~800,000 speakers, and plenty of resources. The Mayan languages are super cool grammatically. Yucatec Mayan has no tense whatsoever, nor does it have any words like next, after, before, etc. It handles telling the listener about the order and time of events in a completely unique way. [[Special:Contributions/172.70.111.76|172.70.111.76]] 15:38, 15 October 2022 (UTC)

2021 brought them back for a bit {{unsigned ip|172.69.0.165|10:54, 3 January 2025}}

Talk:3026: Linear Sort

2024-12-19T17:31:59Z

172.70.162.70:

First in linear time![[User:Mr. I|Mr. I]] ([[User talk:Mr. I|talk]]) 13:28, 18 December 2024 (UTC)

Due to the fact that O(nlog(n)) outgrows O(n), the Linear Sort is not actually linear. [[Special:Contributions/162.158.174.227|162.158.174.227]] 14:21, 18 December 2024 (UTC)
:If your sleep() function can handle negative arguments "correctly", then I guess it could work. [[Special:Contributions/162.158.91.91|162.158.91.91]] 16:27, 18 December 2024 (UTC)

That was fast... [[User:CalibansCreations|'''<span style="color:#ff0000;">Caliban</span>''']] ([[User talk:CalibansCreations|talk]]) 15:35, 18 December 2024 (UTC)

Do I even want to know what Randall's thinking nowadays? [[User:Definitely Bill Cipher|⯅A dream demon⯅]] ([[User talk:Definitely Bill Cipher|talk]]) 16:02, 18 December 2024 (UTC)

The title text would be more correct if Randall used e.g. Timsort instead of Mergesort. They both have the same worst-case complexity O(n*log(n)), but the former is linear if the list was already in order, so best-case complexity is O(n). Mergesort COULD also be implemented this way, but its standard version is never linear. [[User:Bebidek|Bebidek]] ([[User talk:Bebidek|talk]]) 16:35, 18 December 2024 (UTC)

According to my estimates extrapolated from timing the sorting of 10 million random numbers on my computer, the break-even point where the algorithm becomes worse than linear is beyond the expected heat death of the universe. I did neglect the question of where to store the input array. --[[Special:Contributions/162.158.154.35|162.158.154.35]] 16:37, 18 December 2024 (UTC)
:If the numbers being sorted are unique, each would need a fair number of bits to store. (Fair meaning that the time to do the comparison would be non-negligible.) If they aren't, you can just bucket-sort them in linear time. Since we're assuming absurdly large memory capacity. [[Special:Contributions/162.158.186.253|162.158.186.253]] 17:14, 18 December 2024 (UTC)

What system was the person writing the description using where Sleep(n) takes a parameter in whole seconds rather than the usual milliseconds? [[Special:Contributions/172.70.216.162|172.70.216.162]] 17:20, 18 December 2024 (UTC)
: First, I don't recognize the language, but sleep() takes seconds for python, C (et. al.), and no doubt many others. Second, the units don't have to be seconds, they just have to be whatever `TIME()` returns, and multiplicable by 1e6 to yield a "big enough" delay. Of course, no coefficient is big enough for this to actually be linear in theory for any size list, so who cares? To be truly accurate, sleep for `e^LENGTH(LIST)`, and it really won't much matter what the units are, as long as they're big enough for `SLEEP(e)` to exceed the difference in the time it takes to sort two items versus one item. Use a language-dependent coefficient as needed. [[User:Jlearman|Jlearman]] ([[User talk:Jlearman|talk]]) 18:02, 18 December 2024 (UTC)
: Usual where, is that the Windows API? The sleep function in the POSIX standard takes seconds. See https://man7.org/linux/man-pages/man3/sleep.3.html . [[Special:Contributions/162.158.62.194|162.158.62.194]] 18:57, 18 December 2024 (UTC)

If I had a nickel for every time I saw an O(n) sorting algorithm using "sleep"… But this one is actually different. The one I usually see feeds the to-be-sorted value into the sleep function, so it schedules "10" to be printed in 10 seconds, then schedules "3" to be printed in 3 seconds, etc., which would theoretically be linear time, if the sleep function was magic. [[User:Fabian42|Fabian42]] ([[User talk:Fabian42|talk]]) 17:25, 18 December 2024 (UTC)

This comic also critiques/points out the pitfalls of measuring time complexity using Big-O notation, such as an algorithm or solution that runs in linear time still being too slow for its intended use case. [[User:Sophon|Sophon]] ([[User talk:Sophon|talk]]) 17:46, 18 December 2024 (UTC)

Current text is incorrect, but I'm not sure how best to express the correction -- there <b>do</b> exist O(n) sorting algorithms, they're just not general-purpose, since they don't work with an arbitrary comparison function. See [https://en.wikipedia.org/wiki/Counting_sort counting sort]. [[Special:Contributions/172.69.134.151|172.69.134.151]] 18:25, 18 December 2024 (UTC)

Hi! I'm just gonna say this before everyone leaves and goes on their merry way. Significant comic numbers coming soon:
Comics 3100, 3200, 3300, etc, Comic 3094 (The total number of frames in 'time'), Comic 4000, Comic Whatever the next April fools day comic will be, and Comic 4096. Wait for it...[[User:DollarStoreBa'al|DollarStoreBa'al]] ([[User talk:DollarStoreBa'al|talk]]) 20:42, 18 December 2024 (UTC)
:Comic 3141.592654[[Special:Contributions/172.70.163.144|172.70.163.144]] 09:16, 19 December 2024 (UTC)

As everyone observed, the stated algorithm is not theoretically linear, but only practically linear (in that the time and space to detect O(n log n) exceeds reasonable (time, space) bounds for this universe). Munroe's solution is much deeper than that though - it trivially generalises to a _constant_ O(1) bound. [run a sort algorithm, wait 20 years, give the answer]. That's the preferred way of repaying loans, too. {{unsigned ip|172.69.195.27|21:46, 18 December 2024 (UTC)}}

Continues comic 3017's theme of worst-case optimization. [[Special:Contributions/172.70.207.115|172.70.207.115]] 00:32, 19 December 2024 (UTC)

It looks as though this function does not actually do the sort in Linear Time, it only returns in Linear Time.
The MERGESORT Function itself looks to only take one parameter and does not have an obvious return value indicating that it performs an in-place sort on the input mutable LIST.
This means that the LIST is sorted at the speed of the MERGESORT function, but flow control is only returned after Linear Time.
For a single threaded program calling this function there is not practical difference, but it would make a difference if some other thread was concurrently querying the LIST.
A clearer linear time sort might look like this:

function LinearSort(list):
StartTime=Time()
SortedList=MergeSort(list)
Sleep(1e6*length(list)-(Time()-StartTime))
return SortedList

Leon

3019: Advent Calendar Advent Calendar

2024-12-04T13:27:54Z

172.70.162.70: /* Explanation */ add link to topic, and remove 2x needless "Note that"

{{comic
| number = 3019
| date = December 2, 2024
| title = Advent Calendar Advent Calendar
| image = advent_calendar_advent_calendar_2x.png
| imagesize = 482x324px
| noexpand = true
| titletext = The growth rate of items per day may may seem absurd, but it's actually much less than the acceleration in the 12 Days of Christmas song.
}}

==Explanation==
{{incomplete|Created by 5 [CITATIONS NEEDED], 4 ENVELOPE BACKS, 3 NERDS [https://fancyclopedia.org/Neeping A-NEEPING], 2 TURTLE BOTS, AND A FUNNY NEW XKCD - Please change this comment when editing this page. Do NOT delete this tag too soon.}}
{{w|Advent calendar}}s are a form of countdown to Christmas consisting of a card or structure with one closed "window"/opening for each day. Every day, another "window" is opened (e.g. a cardboard flap is opened along perforations), revealing a small present (traditionally, just a thematic picture or chocolate). While the religious season of {{w|Advent}} traditionally begins four Sundays before Christmas, most Advent calendars begin on December 1st for simplicity. In 2024, when this comic was published, the Advent season coincidentally starts on December 1st. Advent calendars usually have either 24 or 25 doors (ending on either Christmas Eve or Christmas Day), depending on manufacturer's choice and/or local tradition.

In this comic, Randall has devised an Advent calendar that contains multiple smaller Advent calendars, each of which contains the same number of items as there are days left until (and ''including'') Christmas Day. By the time he reaches Christmas, he will have 325 different items, or 350 if counting the sub-calendars. The calendar is shown as it might be on December 2<sup>nd</sup>, the date of publication of this strip. The "window" in the upper left, presumed to be for the 1<sup>st</sup> of December, has 25 sub-windows, of which two are open. (One would have been opened on December 1<sup>st</sup> and the next for the day after.) The "window" 5<sup>th</sup> from the left in the bottom row, probably for December 2<sup>nd</sup>, has 24 sub-windows, of which one (that for the initial 2<sup>nd</sup>) is open.

The title text refers to {{w|The Twelve Days of Christmas (song)|The Twelve Days of Christmas}}, a traditional Christmas carol in which the singer receives many gifts from their paramour for each day of the Twelve Days of Christmas. On day one, they receive one gift, and on day ''n'', they receive again all the gifts they received on day ''n-1'', plus ''n'' copies of a new gift. The exact gifts given each day vary by version of the song, receiving 78 gifts on day 12, for a total of 364 gifts. For the Advent calendar Advent calendar, each day a number of items equal to the number of days left until Christmas are added. There are 364 items total in the 12 Days of Christmas, the final day itself having exceeded the gifts of the nested calendars (the sub-gift count being 325, and regardless of the 25 calendars also being included). However the advent calendar uses 25 days rather than just 12, hence the song's acceleration in number of gifts each day is much higher. The title text says “may” twice, either mistakenly, or maybe on purpose since the comic's name has word duplication.

The advent calendar's advent calendar gift total follows the {{w|triangular number}} sequence of all new gifts on a given day being one more than those the day before: on the first day, this is 1 (the first sub-gift of the first sub-calendar); on the second, we now have 3 (add two sub-gifts from two sub-calendars); on the third, we have 6 (three sub-gifts added), etc. The formula for the total on day ''n'' is <table style="display: inline-table; line-height: 0.6em; vertical-align: middle; font-size:9pt; text-size-adjust: none;"><tr><td style="text-decoration: underline">''n''(''n''+1)</td></tr><tr><td style="text-align: center">2</td></tr></table>. For the Twelve Days song (which goes from the 25th of December to 5th of January), ''each day'' adds to the total the next ''triangular number'' in the sequence: +1=1, +3=4, +6=10, etc... The formula for this {{w|tetrahedral number}} (a 'pyramid of triangular numbers') is <table style="display: inline-table; line-height: 0.6em; vertical-align: middle; font-size:9pt; text-size-adjust: none;"><tr><td style="text-decoration: underline">''n''(''n''+1)(''n''+2)</td></tr><tr><td style="text-align: center">6</td></tr></table>, and matches a triple-nested meta-Advent Calendar's non-calendar gift count. This already starts in a more rapid escalation of gift-giving, immediately after the first day where both counts are at one item. However, due to the later start of the Twelve Days, one would have to extend the gift-giving patterns to the 17th Day Of Christmas (and thus the 41st day of Advent) for the number of ''true love'' gifts (969) to properly overtake the continuing meta-calendar's ones, with (902) or without (861) counting the sub-calendars as gifts. (The number of ultimate gifts in any quadruple-nested Advent Calendar would be <table style="display: inline-table; line-height: 0.6em; vertical-align: middle; font-size:9pt; text-size-adjust: none;"><tr><td style="text-decoration: underline">''n''(''n''+1)(''n''+2)(''n''+3)</td></tr><tr><td style="text-align: center">24</td></tr></table>, excluding all the calendars themselves.)

It is not clear what is inside each sub-calendar. The typical filling would be chocolate, however it could also be possible that the advent calendar advent calendars had even more advent calendars within. That this is not the case is revealed in the title text as, if they were (and were run concurrently), the number of (sub-sub-)gifts would always equal those in the song.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:[On a grey board, there are 23 Advent calendars behind large "windows", numbered from 3 to 25, plus two open calendars with their covers torn off.]
:[From top-left to bottom-right, the boxes are numbered as such: (opened), 14, 23, 16, 11, 3; 5, 24, 18, 7, 21; 10, 17, 4, 9, 22, 15, 12; 8, 20, 13, 25, (opened), 19, 6]
:[Each calendar numbered ''n'' has 26−''n'' squares in it.]
:[The open calendar on the top left has 25 squares, two of which are black. The other open calendar has 24 squares, one of which is black.]

:[Caption below the panel:]
:I like Advent calendars, so I got an Advent calendar that gives me a new one every day until Christmas.

{{comic discussion}}

[[Category:Christmas]]
[[Category:Calendar]]
[[Category:Songs]]

752: Phobia

2024-12-03T15:30:14Z

172.70.162.70: /* Explanation */ Rearranged a bit. Really tried to find a way to re-include the Twisters (2024) film reference, but it was so long after the comic that it would have been a Trivia footnote (with Night Of The Twisters, etc, more relevent to the comic).

{{comic
| number = 752
| date = June 11, 2010
| title = Phobia
| image = phobia.png
| titletext = Oh God, the tornado picked up snakes!
}}

==Explanation==
This comic seems to be about {{w|Phobia|phobias}}, i.e. being afraid of specific and non-specific things like [[Blondie]]'s {{w|Ophidiophobia|fear of snakes}}.

Prompted by Blondie's admission, [[Megan]] becomes philosophical ([[220: Philosophy|as she often does]]) and reveals an unusual phobia of her own: outrightly rejecting something until next year by making the excuse that ''everything is complicated right now'' up to the point where there is no next year left anymore because the opportunity has passed or she died. This may be applied to a romantic relationship (possibly with Blondie) but is equally applicable to any (big) decision, like migrating to another country, changing the job or, as in this case, fulfilling one's dreams.

After Megan has said this, Blondie thinks for some time (in the beat panel). When she finally decides to ask Megan something (perhaps to go out on a date), Megan cuts her off to say that she wants to be a storm chaser.

In the last panel we see that both, Megan and Blondie, have become {{w|Storm chasing|storm chasers}} — individuals who pursue severe weather conditions, for either scientific investigation or providing media coverage, or simply for adventure. Ironically, chasing adverse weather, especially tornadoes, is more dangerous than the source of either character's original phobia. Indeed, one's ability to control the risk while being near a tornado is far less than one's ability to control the risk of being bitten by a snake; the tornado is violent and unpredictable, while snakes only attack humans when they feel threatened. Additionally, one needs to deliberately expose oneself to the snake in order to have any risk of being attacked.

This comic may be related to the movies {{w|Snakes on a Plane}} (if not the similar fears of {{w|Indiana Jones (character)|Indiana Jones}}, instead), {{w|Twister (1996 film)|Twister}} and {{w|Thelma & Louise}}. The first two cover the issues of snakes and tornados. The last of these movies has two women friends on a road trip, and in the end they kiss, and there have been [http://www.etonline.com/news/186576_susan_sarandon_thinks_her_thelma_louise_character_may_have_become_a_lesbian_if_she_had_lived/ several] [http://s1.zetaboards.com/L_Anon/topic/5185938/1/ discussions] on whether one or both of them are lesbian or not. ''Snakes on a plane'' was previously mentioned in [[107: Snakes on a Plane! 2]], with tornados and weather chasing with [[640: Tornado Hunter]].

In the title text, Megan and Blondie notice that the snakes have been {{w|Rain of animals|picked up by the tornado}} they are chasing; so now, in addition to the violent weather, they are also exposed to the danger of snakes falling from the sky. (This is similar to the plot of {{w|Sharknado (film series)|Sharknado}}, although that movie was released several years after this comic.)

This is the third comic about tornadoes and storm chasers, a [[:Category:Tornadoes|recurring subject]] on xkcd. These were first mentioned in [[402: 1,000 Miles North]], and first shown in [[640: Tornado Hunter]].

==Transcript==
:[Blondie, with extra long hair and Megan in the background of the image observes a long snake on the ground in the foreground.]
:Blondie: Whoa, a snake!
:Megan: Cool!
:Blondie: I'm afraid of snakes.

:[Zoom in only on Megan's upper half.]
:Megan: I'm afraid of saying "everything's complicated right now, but maybe next year" until there are no more years left.

:[Slim panel with a zoom to a full picture of only Blondie as she considers this. Beat panel.]

:[Same type of image of Megan, who cuts Blondie's reply (from off-panel) off in mid-sentence.]
:Blondie (off-panel): Do you-
:Megan: I want to be a storm chaser.

:[A black tornado reaches from the black storm clouds to the earth, kicking up a sizable cloud of debris at its base. Blondie is at the wheel of a car, with Megan hanging out the window and holding a camera.]

{{comic discussion}}

[[Category:Comics featuring Blondie]]
[[Category:Comics featuring Megan]]
[[Category:Animals]]
[[Category:Tornadoes]]

3016: Cold Air

2024-11-26T00:13:41Z

172.70.162.70: /* Transcript */

{{comic
| number = 3016
| date = November 25, 2024
| title = Cold Air
| image = cold_air_2x.png
| imagesize = 713x283px
| noexpand = true
| titletext = We also should really have checked that the old water tower was disconnected from the water system before we started filling it with compressed air.
}}

==Explanation==
{{incomplete|Created by a 204 atm COMPRESSED BOT - Please change this comment when editing this page. Do NOT delete this tag too soon.}}
Tornadoes generally create winds of about 40-400 mph [https://www.weather.gov/ffc/fujita] (about 50-500 kph) which causes damage to buildings. Cueball proposes a method to essentially blow tornadoes away from cities by keeping enough "tornado repelling" air in a tank. Whether this would work is questionable since it's precisely the mixing of warm and cold air that produces the swirling motion that creates tornadoes.

In a compressed air system, peak pressure is considered about 40 bar [https://www.directindustry.com/prod/kaeser-kompressoren/product-4742-24559.html] (about 500 psi). Cueball proposes keeping the tank at 6 times that pressure to properly counteract the tornado. The title text confirms the tower's resemblance to a water tower is intentional which, if using 16 inch pipes as is common [https://www.waterworld.com/home/article/14071043/the-perfect-pipe] would produce much stronger winds than those of the tornado, because flow speed is inversely proportional to the diameter of the pipes and even a "wide" 16 inch pipe is very narrow for this purpose indeed.

(equation needed)

Further, highly compressed tanks are prone to bursting{{citation needed}}, which is why they are only used for small volumes of air in highly controlled settings. Cueball's proposal would put it in the center of a dense city, creating the possibility for further damage.

Finally, Tornadoes tend to form in ''sparsely'' populated areas, where structures are few and wind can flow uninterrupted, making his invention's necessity questionable at best. Even if Cueball's air tanks produce winds no faster than a normal tornado, they are now being produced in the center of a heavily constructed area, heavily increasing the potential buildings that can get damaged.

The result is a quadrupling in damage caused by wind, since now, not only are the tornadoes causing heavy winds, the tanks when functioning properly, and the tanks when malfunctioning, are causing heavy winds too

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:[Cueball is seen in front of a diagram of a tornado with a pointer in his hand. The diagram has arrows flowing from the bottom toward the tornado at the top and from the tornado toward the rain below it]
:Cueball: Tornado supercells are powered by the inflow of warm, moist surface air.

:[Cueball is now seen in front of a representation of his compressed air tank with a PSI of 3000 next to smaller buildings, appearing to be high-rise buildings or even skyscrapers in their own right, on either side of the tank]
:Cueball: Compressed air tanks could produce artificial pools of cold, dry air on demand, disrupting tornado inflow to protect cities.

:[Cueball, again with a pointer, is seen in front of a line graph labeled "Wind Damage over Time" (wind damage has increased after a point on the graph labeled "Giant experimental compressed air tanks installed in the middle of every major city"). In a frame in the top left corner, there is a label:]
:Several years later:
:Cueball: In retrospect, I can see how my plan went wrong.

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Tornadoes]]
[[Category:Line graphs]]