explain xkcd - User contributions [en]

Talk:3097: Bridge Types

2025-06-03T12:34:07Z

172.71.164.73: /* Suspended arch - tied-arch vs. through arch */ new section

For budget overrun, see olympic stadium of Montreal, Quebec, Canada.

[[Special:Contributions/162.158.126.202|162.158.126.202]] 01:23, 3 June 2025 (UTC)

Very disappointed there's no bridge card game reference, but I guess that's not one of Randall's types of nerdiness :( [[Special:Contributions/172.71.254.203|172.71.254.203]] 01:45, 3 June 2025 (UTC)

I would like to note that cable stayed bridges, budget overrun here, are much cheaper than equivalent suspension bridges. It because they use less materials and can be built faster meaning less labor. [[Special:Contributions/172.69.58.51|172.69.58.51]] 01:50, 3 June 2025‎
:Tru dat in general, but I think that this is a reference to the {{w|Leonard_P._Zakim_Bunker_Hill_Memorial_Bridge|Zakim Bridge}} in downtown Boston, part of the {{w|Big_Dig|"Big Dig"}} project that became notorious for its budget overruns and related shenanigans. Given that Randall M. lives in Boston, that makes this panel something of an inside joke. [[Special:Contributions/172.71.147.224|172.71.147.224]] 03:15, 3 June 2025 (UTC)

The [[wikipedia:St. Louis Arch|St. Louis Arch]] is a repurposed-elevator-suspended-arch-but-without-the-base-and-wires bridge if you squint hard enough. The elevator is also fun. [[Special:Contributions/172.69.67.214|172.69.67.214]] 01:57, 3 June 2025 (UTC)

Nothing about a a [[wikipedia:Bridge circuit|bridge circuit]] or these [[Wikipedia:Bridges (disambiguation)|many]] [[wikipedia:other|other]] bridges either. Sigh. [[Special:Contributions/172.69.67.214|172.69.67.214]] 01:57, 3 June 2025 (UTC)
:And where, oh where, are Lloyd, Beau, Jeff, and Jordan? [[Special:Contributions/162.158.41.84|162.158.41.84]] 03:19, 3 June 2025 (UTC)

The L'Engle is a take off on a Wrinkle in time? But this one is in space? -- [[User:162.158.91.124|162.158.91.124]] ([[User talk:162.158.91.124|talk]]) 02:26, 3 June 2025‎ ''(please sign your comments with <nowiki>~~</nowiki>~~)''
:There's some space-warping in L'Engle's books. [[Special:Contributions/162.158.174.63|162.158.174.63]] 02:44, 3 June 2025 (UTC)

The "budget overrun" bridge doesn't really look like the Zakim bridge to me. It looks a lot like the Samuel Beckett Bridge in Dublin. I don't know what the budget of that bridge was, but according to wiki it cost 60 million euros, which sounds like a lot given that the bridge isn't all that long or wide. [[Special:Contributions/172.70.126.87|172.70.126.87]] 03:24, 3 June 2025 (UTC)
: Perhaps if Randall M. drew too close a likeness to the Zakim Bridge, he feared a visit from officials with lawyers and/or cement shoes. ("Only the paranoid survive ...") It seems, from a quick tour of the Internet, that words like "grandiose and overblown" are easily applied to cable-stayed bridge designs/aesthetics. I wasn't easily able to find information on budget overruns for these bridges, and see the commentator above who pointed out the lower costs overall of cable-stayed ''vs'' suspension bridges. But as a former resident of Greater Boston, I can report the pervasiveness of the Big Dig and its challenges, budgetary and otherwise, in local life and lore. [[Special:Contributions/172.68.22.108|172.68.22.108]] 04:32, 3 June 2025 (UTC)
::The cable-stayed bridge is the current darling of artists that accidentally went to engineering school, who are notorious for running over budget and behind schedule. [[User:RegularSizedGuy|RegularSizedGuy]] ([[User talk:RegularSizedGuy|talk]]) 04:40, 3 June 2025 (UTC)
: I can see the suggestion of the Beckett bridge, but in my eyes the obvious template would be [https://en.wikipedia.org/wiki/Erasmusbrug Rotterdam's Erasmus Bridge] [[User:Nachtvogel|Nachtvogel]] ([[User talk:Nachtvogel|talk]]) 06:00, 3 June 2025 (UTC)

I think the repurposed elevator should be considered a dig at Elon Musks The Boring Company, even though they tunnel rather then bridge
[[Special:Contributions/162.158.182.138|162.158.182.138]] 04:37, 3 June 2025 (UTC)

Added a bunch of explanations [[Special:Contributions/162.158.8.132|162.158.8.132]] 07:31, 3 June 2025 (UTC)

The Repurposed Elevator is actually a real thing! https://en.wikipedia.org/wiki/Schmid_Peoplemover It's not as strange as you think. It's a space effective, but too expensive solution to the problem of not making cramped railway crossroads more cramped. [[Special:Contributions/162.158.172.112|162.158.172.112]] 07:39, 3 June 2025 (UTC)
: I've added it to the list. Feel free to do such changes yourself if you know something that can contribute. --[[Special:Contributions/172.71.183.12|172.71.183.12]] 08:07, 3 June 2025 (UTC)

For the "Google Earth Bridge" remark, [https://www.fastcompany.com/90186315/the-strange-art-of-the-melting-bridges-of-google-earth this article] might work as a citation. [[User:Conster|Conster]] ([[User talk:Conster|talk]]) 07:57, 3 June 2025 (UTC)

There seem to be stick figures on each bridge, except for the Arch. Is that on phone? Maybe he's saying nobody uses arch (Linux)? Or does anyone has any other idea as to why? [[Special:Contributions/172.69.128.184|172.69.128.184]] 08:21, 3 June 2025 (UTC)

Is there a reason for the trestle bridge to have a raised deck? They were iconically used for railways, where that would not work. --[[Special:Contributions/162.158.110.59|162.158.110.59]] 09:56, 3 June 2025 (UTC)

The jump in particular feels a lot like polybridge and I love it [[Special:Contributions/172.71.167.160|172.71.167.160]] 11:27, 3 June 2025 (UTC)

== Suspended arch - tied-arch vs. through arch ==

The "suspended arch" bridge may or may not be a tied-arch bridge. Something has to stop the ends of the arch sliding outwards when there's a large load in the middle, but you can't tell what that something is from the image.

If that something is the bridge deck, being connected to the ends of the arch and under tension, than it's a tied-arch bridge (the deck ties the ends of the arch together). If that something is the arch foundations, and the deck is not under tension, then it's not a tied-arch bridge; it's just a simple through-arch bridge.

3015: D&D Combinatorics

2024-11-24T21:48:45Z

172.71.164.73:

{{comic
| number = 3015
| date = November 22, 2024
| title = D&D Combinatorics
| image = dnd_combinatorics_2x.png
| imagesize = 328x446px
| noexpand = true
| titletext = Look, you can't complain about this after giving us so many scenarios involving N locked chests and M unlabeled keys.
}}

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

Dungeons and Dragons (D&D) is a role-playing game that usually has a "Dungeon Master" (narrator) that takes a team of players through scenarios where they attack monsters and go on quests.

Often, there will be semi-random events: e.g., when attacking a monster, often a player will roll a die and deal damage based on the result. D&D uses a variety of dice, from regular d6 (6-sided, cubic dice) to other polyhedral dice, with the number of faces denoted by dX (e.g., d10 is a 10-sided die, with numbers from 1 to 10 on it). Common sets include: d4, d6, d8, d10, d12, d20, and occasionally d100 (typically not, however, the [[2626:_d65536|d65536]]).{{cn}}

With these, you can simulate events with a wide variety of denominators. In this case, Cueball gives a {{w|combinatorics|combinatorial}} problem:

* There are 10 arrows.
* 5 arrows are cursed.
* You randomly take two.
* What are the odds that neither of them are cursed?

Calculating using {{w|binomial coefficients}}, there are “10 choose 2” (45) ways to choose two arrows, of which there are “5 choose 2” (10) ways to choose 2 arrows that are non-cursed. As a result, the odds of taking all non-cursed arrows is 10/45, which simplifies to 2/9.

To see this in a different way, the probability of choosing one non-cursed arrow is 5/10, which then must be multiplied by the probability of choosing the second non-cursed arrow, which is now 4/9, giving 20/90 or 2/9, the same result as before.

The Dungeon Master (DM) in this case [[356: Nerd Sniping|has to]] map that probability into rolling multiple dice, whose sums are also not evenly distributed: i.e. if rolling 3d6 (3 six-sided dice) and a d4 (1 four-sided die), the sums can range from 4 to 22. It's pretty hard to do this in one's head, but it does happen that the odds of rolling 16 or more with this combination is 2/9, matching the probability that we want to simulate. Here's a table of all the 6*6*6*4=864 possible outcomes -

{| class="wikitable"
|+ All possible combinations of rolls for 3d6 + 1d4
|-
!Total!!4!!5!!6!!7!!8!!9!!10!!11!!12!!13!!14!!15!!16!!17!!18!!19!!20!!21!!22
|-
|Ways to roll it||1||4||10||20||34||52||71||88||100||104||100||88
| style="background:#ffffcc;" | 71
| style="background:#ffffcc;" | 52
| style="background:#ffffcc;" | 34
| style="background:#ffffcc;" | 20
| style="background:#ffffcc;" | 10
| style="background:#ffffcc;" | 4
| style="background:#ffffcc;" | 1
|}

71+52+34+20+10+4+1 = 192

192/864 = 2/9, which matches the desired probability from earlier. The table of outcomes can either be bruteforced with a program, or can be derived using generating functions.

The caption elaborates that the DM has a degree in the relevant field, and is unable to resist applying this to the D&D game when the opportunity arises - opportunities that Cueball eagerly provides for this very reason.

There are several much easier ways of implementing this operation, without coming up with a more complex solution:
#Do not even attempt to abstract the chances with dice-rolls. Literally present 10 similar-looking arrows, or other objects that are taken to represent arrows (face-down playing cards, for example), where the assigned information of whether each one is cursed initially hidden away from Cueball, and then just let Cueball pick any two.
#Even just with D&D dice, the DM could ask Cueball to roll a 1d10 for the first arrow, and then again for the second, re-rolling the second so long as Cueball gets the same number as before (which emulates the same sort of process, but with a non-zero chance of having to make and reject an arbitrary number of extra dice-rolls). One could specify that 1-5 represents the cursed arrows and 6-10 represents the non-cursed arrows, following the convention that lower rolls are bad in D&D.
#If understanding the actual odds, but wishing to keep the dice in use simple, a 2/9 probability can also be found by saying Cueball would succeed when 2D6 produces a 9, 10, or 12 (4/36, 3/36, and 1/36 probability, respectively, giving 8/36, i.e. 2/9).
#Alternatively, approximate the odds by using a d100 (or equivalent roll of two D10s) and seeking an 79 or higher (79-99), assuming double-zero is not taken as 100, which gives a 22% percent chance (substantially similar to 2/9 = 22.222...%), which may be sufficiently acceptable.
The first two options also instantly reveal cases of whether ''two'' cursed arrows are nominally chosen (at identical odds to the possibility of neither being so), should this be useful information on top of merely failing to avoid them. The third option could also be used to suggest this if (for example) the complementary results of 1, 3 or 4 are rolled, and the fourth in the event that the 'percentage' given is 0-21.

One could argue that the above solutions do not have the "polished" D&D feel of rolling a certain number of dice, adding them up, and seeing if the result is greater than or equal to an entirely correct required total. This is a commonly used mechanic for difficulty checks, hit calculations, and other such chance-based events in D&D. The DM may feel that this dice format is a requirement, but this approach is far too clunky for most DMs to be practical. It may be inferred that as the DM's mind tends towards more combinatorial solutions, she is either unable or unwilling to consider more straightforward and less time-consuming solutions to this cursed arrow problem.

The title text claims that Randall only started doing this to the DM after she herself insisted on forcing another combinatorial puzzle on the players several times, involving a bunch of locked treasure chests and a multitude of keys to unlock them with. This might be a reference to an M-of-N encryption system, where a system has ''n'' valid passwords (instead of just one) but requires ''m'' of those passwords to be given before it will open; it is assumed m is greater than 1 but less than n. While this is easy enough to implement in a computer system, it would be extremely cumbersome to build for a physical lock with keys, and spreading the mechanism across multiple separate treasure chests would be impossible without literal magic (luckily, magic is in plentiful supply in a typical Dungeons and Dragons game).{{cn}}

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:[Cueball, Megan, Ponytail, White Hat, and Knit Cap are sitting at a table. Everyone is looking at Cueball. Ponytail is facepalming. The table is covered in sheets of paper and assorted dice.] 
:Cueball: I grab 2 of the 10 arrows without looking and fire them, hoping I didn't grab one of the 5 cursed ones. Did I?
:Ponytail: Sigh. Umm. Okay.
:Ponytail: Roll... Uh... Hang on...
:Ponytail: Roll 3d6 and a d4. You need... 16 or better to avoid the cursed arrows.

:[Caption below the panel:]
:I got '''''way''''' more annoying to play D&D with once I learned that our DM has a combinatorics degree and can't resist puzzles.

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring White Hat]]
[[Category:Comics featuring Knit Cap]]
[[Category:Games]]
[[Category:Math]]

Talk:3012: The Future of Orion

2024-11-19T08:35:31Z

172.71.164.73:

this is my second first comment. -[[User:Psychoticpotato|P?sych??otic?pot??at???o ]] ([[User talk:Psychoticpotato|talk]]) 17:47, 15 November 2024 (UTC)
:This is my first second comment. [[Special:Contributions/162.158.63.8|162.158.63.8]] 17:56, 15 November 2024 (UTC)
::I plead the third. [[Special:Contributions/172.69.136.188|172.69.136.188]] 19:57, 15 November 2024 (UTC)
:::you mean the fifth????? [[User:CalibansCreations|'''Caliban''']] ([[User talk:CalibansCreations|talk]]) 20:18, 16 November 2024 (UTC)
::::Probably not. I believe it's a perfectly legitimate request. If not because of the muddy boots, then because of the MRE wrappers they leave around (or don't put in the right recycling bin). [[Special:Contributions/172.68.205.92|172.68.205.92]] 21:51, 16 November 2024 (UTC)
:::::This is my French: comment?[[Special:Contributions/172.69.194.226|172.69.194.226]] 13:26, 18 November 2024 (UTC)

okay we need to destroy the stars, any suggestions? [[User:CalibansCreations|'''Caliban''']] ([[User talk:CalibansCreations|talk]]) 19:02, 15 November 2024 (UTC)
:Don't worry, the [https://www.qwantz.com/index.php?comic=4264 insects] should take care of it. (If the rocks don't do it first) [[User:Trogdor147|Trogdor147]] ([[User_talk:Trogdor147|talk]]) 20:23, 15 November 2024 (UTC)

Maybe add a reference to #1020? [[Special:Contributions/172.71.147.100|172.71.147.100]] 19:43, 15 November 2024 (UTC)

now instead of a hunter [[1020: Orion Nebula|with a dong]], its a dinosaur with diarrhea! [[User:Firestar233|guess who]] ([[User talk:Firestar233|if you want to]] | [[Special:Contributions/Firestar233|what i have done]]) 19:47, 15 November 2024 (UTC)

"There are no dinosaur constellations, because dinosaur fossils had not yet been discovered when constellations were first being named in around 3000 BCE." Faulty logic, compare: "There are no microscope constellations, because microscopes had not yet been discovered when constellations were first being named in around 3000 BCE." [[Special:Contributions/162.158.154.221|162.158.154.221]] 20:03, 15 November 2024 (UTC)
: {{w|Microscopium|link}}. Besides, weren't legends about dragons blamed on people finding dinosaur bones? -- [[User:Hkmaly|Hkmaly]] ([[User talk:Hkmaly|talk]]) 21:48, 15 November 2024 (UTC)

::Besides, Microscopium isn't even 300 years old, much less 5000 [[Special:Contributions/108.162.245.113|108.162.245.113]]

Has anyone figured out how far in the future Randall has projected the new star positions? [[Special:Contributions/172.69.135.5|172.69.135.5]] 21:04, 15 November 2024 (UTC)

There ARE dinosaur constellations, [[1211: Birds and Dinosaurs|nine of them in fact]]p [[Special:Contributions/108.162.245.113|108.162.245.113]]

Meh, dinosaurs. Where are the zombie constellations? [[Special:Contributions/172.69.109.77|172.69.109.77]] 08:54, 16 November 2024 (UTC)

My favorite part is that the dinosaur sill has a dong [[User:Apollo11|Apollo11]] ([[User talk:Apollo11|talk]]) 20:04, 16 November 2024 (UTC)
:If dinosaurs had penises, they would have usually been retracted within their cloaca (Alnilam) so North's ''T. rex'' is either excited to get with a female, or Orion's sword could instead be excrement being expelled. [[Special:Contributions/172.70.207.184|172.70.207.184]] 08:14, 17 November 2024 (UTC)

:: It's funny because one of the first attempts to depict dinosaurs in their natural environment - the painting "[https://en.wikipedia.org/wiki/Duria_Antiquior/ Duria Antquior]" - had dinosaurs pooping everywhere. It was apparently both a reference to coproliths as well as simple scatological humour. --[[Special:Contributions/172.71.164.73|172.71.164.73]] 08:35, 19 November 2024 (UTC)

Dinosaur Comics nearly always uses the same art in every strip, with the T-Rex in the same six poses. But the pose used in this XKCD strip isn't one of them. --[[Special:Contributions/172.71.254.101|172.71.254.101]] 18:05, 17 November 2024 (UTC)
:Yes-and-no. It seems to be a pretty much perfect (or even exact, I haven't dug down into it at the pixel level to check it's ''not'' just a very good Randall-redrawn version) mirror image of the [https://qwantz.com/ 'panel 6' pose]. [[Special:Contributions/172.70.58.5|172.70.58.5]] 19:33, 17 November 2024 (UTC)

When I was a kindergartner my parents had a mini wet bar inside a 1.5+ foot diameter star globe. I remember thinking how much higher quality my own drawings for class were than the really terrible stick figures formed by the lines of the constellations, and how poorly they matched their intended subjects. I still think about that when I see stick figure comics like XKCD. But as an adult I realize that their purpose wasn't art, it was mnemonic help for navigators, just like everyone in the northern hemisphere growing up away from city lights learns the big dipper instead of the Ursa bears, because it's easier to remember for finding the north star.

So, what I'm getting at is, maybe it would be a good idea to replace a bad constellation with the winner of a competition (including with the status quo) for something better every century or so. I'm not sure we really need to take proper motion into account for that though. [[Special:Contributions/108.162.245.132|108.162.245.132]] 02:56, 18 November 2024 (UTC)
: that competition gives the risk of a constellation named 'Starry McStarface.' {{unsigned ip|172.71.195.49|00:22, 19 November 2024}}