https://www.explainxkcd.com/wiki/api.php?action=feedcontributions&user=172.70.98.89&feedformat=atomexplain xkcd - User contributions [en]2024-03-28T11:17:04ZUser contributionsMediaWiki 1.30.0https://www.explainxkcd.com/wiki/index.php?title=697:_Tensile_vs._Shear_Strength&diff=220030697: Tensile vs. Shear Strength2021-10-28T23:50:41Z<p>172.70.98.89: /* Transcript */ ce</p>
<hr />
<div>{{comic<br />
| number = 697<br />
| date = February 3, 2010<br />
| title = Tensile vs. Shear Strength<br />
| image = tensile_vs_shear_strength.png<br />
| titletext = Although really, the damage was done when the party planners took the hole punch to the elevator ribbon to hang up the sign.<br />
}}<br />
<br />
==Explanation==<br />
Tensile strength represents how hard you can pull on something without it breaking. Shear strength represents how hard you can try to cut it without it breaking. Many materials have great tensile strength but low shear strength (such as dental floss — try to break it by just pulling on two ends), including whatever this space elevator is made of. The material clearly has extremely high tensile strength because it can hold the elevator in place, with one end on the ground and one in space, but it can be cut with a simple pair of pruning shears. This also highlights the fact that "shear strength" and "shears" are [https://www.etymonline.com/word/shear etymologically related].<br />
<br />
A {{w|space elevator}} is a proposed construction that would make space travel easier. It consists of a long string attached to the Earth (near equator) on one end and a counterweight (beyond the {{w|geostationary orbit}}) on the other end, kept taut and in one place by the gravity and centrifugal forces. This would make it possible to carry spacecraft into the orbit by simple mechanical means, as opposed to requiring the use of rockets as is the case nowadays, saving a lot of energy and resources.<br />
<br />
The phrase "a modern Babel" refers to the biblical story of the {{w|Tower of Babel}} (later referenced in [[2421: Tower of Babel]]), in which humans endeavor to build a tower reaching heaven. Their arrogance angers God and prompts him to sabotage the project. A space elevator can be seen as a modern equivalent of a tower to heaven.{{citation needed}} Additionally, the expression "a modern Babel" may be used figuratively to describe huge projects (especially buildings or human-made structures) that fail because they are too ambitious. <br />
<br />
The title text makes the point that even before [[Black Hat]] cut the space elevator's cable in two, it was ruined by the holes in it for the banner. The holes would reduce the surface area of the cross section of the pole, dwarfing its ability to keep the elevator attached to the ground. The flag and holes would also potentially make it impossible for the elevator to travel up the pole, making the entire elevator useless.<br />
<br />
==Transcript==<br />
:[A space elevator occupies the height of the frame, consisting of a base, a cable extending out into space, and an elevator unit with standard elevator features such as sliding doors and up/down buttons. A banner flutters in the breeze attached to the cable going up above the elevator. There is text on the banner. Text appear in four lines split across the elevator cable itself, the rhyming portions of the text is on the right side of the cable. Five individuals stand at the base of the elevator. To the left are Megan, a Cueball-like guy with his arms raised, and Ponytail, who is holding a bottle of champagne/sparkling wine which is bubbling out down the neck of the bottle. To the right is Black Hat, who cuts the cable with a pruning shear like it was part of the ceremony as a ribbon cutting. Finally further right is Cueball who sees what Black Hat is doing. He is very alarmed holding a hand to his mouth while holding the other out towards Black Hat.]<br />
<br />
:Banner: Space Elevator<br />
:Banner: Grand opening<br />
::{|<br />
|-<br />
|style="text-align:right;"|After countless<br />
|style="text-align:left;"|engineers<br />
|-<br />
|style="text-align:right;"|spend trillions over<br />
|style="text-align:left;"|fifty years,<br />
|-<br />
|style="text-align:right;"|a modern babel<br />
|style="text-align:left;"|disappears<br />
|-<br />
|style="text-align:right;"|because some fuck brought<br />
|style="text-align:left;"|pruning shears.<br />
|}<br />
:Pruning shears: ''Snip''<br />
:Cueball: ''!!''<br />
<br />
{{comic discussion}}<br />
<br />
[[Category:Comics featuring Megan]]<br />
[[Category:Comics featuring Ponytail]]<br />
[[Category:Comics featuring Black Hat]]<br />
[[Category:Comics featuring Cueball]]<br />
[[Category:Multiple Cueballs]]<br />
[[Category:Elevators]]<br />
[[Category:Space]]<br />
[[Category:Science]]<br />
[[Category:Sabotage]]</div>172.70.98.89https://www.explainxkcd.com/wiki/index.php?title=2534:_Retractable_Rocket&diff=2200292534: Retractable Rocket2021-10-28T23:45:47Z<p>172.70.98.89: /* Trivia */ unnecessary</p>
<hr />
<div>{{comic<br />
| number = 2534<br />
| date = October 27, 2021<br />
| title = Retractable Rocket<br />
| image = retractible_rocket.png<br />
| titletext = Hard to believe that for so many years once they were fully extended we just let them tip over.<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by a RETRACTABLE ROCKET SCIENTIST - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
<br />
This comic documents another of [[Beret Guy]]'s [[:Category:Strange powers of Beret Guy|absurdist ventures]]. He explains to [[Megan]] that "we" (possibly [[:Category:Beret Guy's Business|his company]]) are testing their new "retractable" rocket. <br />
<br />
{{w|Reusable launch system|Reusable rockets}} are a growing industry, as they are more economically viable in the long run &ndash; though technically much more difficult to operate &ndash; than rocket boosters that are just discarded after use (which have been standard throughout the majority of space-faring history). Thus, Megan is understandably confused about Beret Guy's assertion that theirs is "retractable", asking if he misspoke. In typical fashion, he assures her that he did not misspeak, with a single "No" without further explanation. <br />
<br />
They proceed to watch the rocket "launch", proving that it is indeed ''retractable''. In fact the rocket does not launch, but merely ''extends'' &ndash; apparently all the way to the {{w|International Space Station}} (ISS), a height of over 250 miles (over 400 km) &ndash; before retracting, as promised, to its original position. The top part, with the astronauts in it, has been left in space. Presumably, it is docked to the ISS, as the crew onboard the ISS say hello to them in panel 4.<br />
<br />
Of course, it would not be possible to extend anything this far.{{Citation needed}} The top would be moving very fast compared to the bottom part, and even with the strongest material a fully extended, very thin, presumably, hollow structure with a payload on top would break very soon after extension began. Also, the ISS moves at 17,100 mph (27,600 km/h) compared to the ground under it, making an orbit in about one and a half hour. So making the tip follow this long enough to dock would be even more impossible. <br />
<br />
A possibility of making a {{w|space elevator}} has been discussed, but it would not extend like this with a payload on top. Randall has for instance referenced space elevators in [[697: Tensile vs. Shear Strength]].<br />
<br />
The title text parodies the 'old' single-use boosters. It appears that the predecessors to the 'retractable rockets' were capable of controlled extension only. Once they had lofted the payload to orbit, they were then allowed to fall over, destroying them in the process so they could not be used again just like booster rockets. However, if a 250 mile/400 km high construction just fell over, it would be much more difficult to avoid other damage, than to the rocket (booster), than for just a few small booster rockets falling out of the sky.{{Citation needed}}<br />
<br />
This comic was released four days before (and possibly refers to) SpaceX's {{w|SpaceX Crew-3|Crew-3 mission}} to send astronauts to ISS with a reusable rocket on 31 October 2021.<br />
<br />
==Transcript==<br />
:[Beret Guy and Megan is talking. Behind them near the horizon is a tall rocket on a launchpad.]<br />
:Beret Guy: We're testing our new retractable rocket.<br />
:Megan: You mean reusable?<br />
:Beret Guy: No.<br />
<br />
:[A zoom in on the launchpad and rocket. It has the appearance of having a long first stage, a second stage with slightly wider fairing and an Apollo-style capsule with escape-tower atop it all. There is a directionless speech-bubble at the top depicting a count down voice.]<br />
:Count down: Three...Two...One...Liftoff!<br />
<br />
:[Same view as before, but while the base of the rocket-stack remains stationary, the first stage is apparently elongated, with a hint of a bend to the right, to raise the total height to which the upper-stage and capsule assembly reaches almost to the top of the panel.]<br />
<br />
:[In a wider panel, with the base to the left, the first stage is now elongated far enough to disappear off the top of the center of the frame, thus clearly bending to the right. Two peoples voices are indicated as coming from the space capsule far above, as it reaches it destination.]<br />
:Voice 1: Hi, welcome to the ISS!<br />
:Voice 2: Hello!<br />
<br />
:[The final panel shows the same view as in the third panel. The first stage is now retracting, and has similar length as in the third panel, but the capsule is no longer atop the 'second stage' fairing. Four movement lines above the top of the retracting rocket indicates that it is returning back to the original position.]<br />
<br />
==Trivia==<br />
*The [https://web.archive.org/web/20211028014542/https://xkcd.com/ original comic] misspelled "retractable" as "retractible". Has been documented on the web archive.<br />
**This was done both in the [https://www.explainxkcd.com/wiki/images/archive/5/57/20211028040721%21retractable_rocket.png comic itself], and [https://www.explainxkcd.com/wiki/index.php?title=2534:_Retractible_Rocket&redirect=no the title]. <br />
<br />
{{comic discussion}}<br />
<br />
[[Category:Comics featuring Beret Guy]]<br />
[[Category:Comics featuring Megan]]<br />
[[Category:Beret Guy's Business]]<br />
[[Category:Strange powers of Beret Guy]]<br />
[[Category:Space]]</div>172.70.98.89https://www.explainxkcd.com/wiki/index.php?title=2532:_Censored_Vaccine_Card&diff=2196742532: Censored Vaccine Card2021-10-23T00:11:28Z<p>172.70.98.89: /* Transcript */ remove</p>
<hr />
<div>{{comic<br />
| number = 2532<br />
| date = October 22, 2021<br />
| title = Censored Vaccine Card<br />
| image = censored_vaccine_card.png<br />
| titletext = CVS's pharmacies are fine, but I much prefer their [censored]s.<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by COVID-13's 5TH DOSE - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
This comic is loosely related to a series of comics related to the 2020 pandemic of the coronavirus SARS-CoV-2, which causes COVID-19. <br />
<br />
The comic hinges on sharing photos on social media of vaccination cards as proof that the user has been {{w|COVID-19 vaccine|vaccinated}} (in this case, gotten a booster shot). Such cards contain {{w|Personal data|personal identification}} that should probably not be made public. The irony is that the user has censored some impersonal lines, such as the instructions that are identical on all vaccination cards, and many easy-to-guess lines, while not censoring any of said personal information.<br />
The fourth line, labelled "other" is probably completely blank (as the third dose was on the current date), but is completely blacked out.<br />
<br />
The caption indicates that his intention is to "seem more mysterious". This is best exemplified by blanking most of the word "clinician" to leave "CIA".<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
:[Profile picture with three unreadable lines on its left:<br />
Check it out, I just got my booster! <br />
<br />
:[Picture of the U.S. COVID-19 Vaccination Record Card attached on a media post. The card includes pre-printed information in black and handwritten information in blue, the latter indicated here by italics. Some of the text has been blacked out, indicated here by "[Censored]".]<br />
<br />
:COVID-:[Censored] Vaccination record card<br />
:[At the upper right of the card appears the logo of the U.S. Department of Health and Human Services, a stylized eagle surrounded by the words "Department of Health & Human Services USA", although those words are not legible in this drawing. Next to that appears the logo of the Centers for Disease Control and Prevention, a shaded box with the letters "CDC" and the words "Centers for Disease Control and [Censored]" below it.]<br />
----<br />
<br />
<br />
:Please keep this record card, which includes [Censored]<br />
:about [Censored]<br />
:Por favor, guarde esta tarjeta de registro, que incluve [Censored]<br />
:[Censored] sobre [Censored]<br />
<br />
:''Munroe'' ''Randall''<br />
----<br />
:Last Name First Name<br />
<br />
:''10-17-[Censored]84'' ''41592653''<br />
----<br />
:Date of birth Patient number<br />
<br />
{{comic discussion}}<br />
[[Category:COVID-19]]<br />
[[Category:COVID-19 vaccine]]</div>172.70.98.89https://www.explainxkcd.com/wiki/index.php?title=2532:_Censored_Vaccine_Card&diff=2196732532: Censored Vaccine Card2021-10-23T00:07:24Z<p>172.70.98.89: /* Explanation */ wlink</p>
<hr />
<div>{{comic<br />
| number = 2532<br />
| date = October 22, 2021<br />
| title = Censored Vaccine Card<br />
| image = censored_vaccine_card.png<br />
| titletext = CVS's pharmacies are fine, but I much prefer their [censored]s.<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by COVID-13's 5TH DOSE - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
This comic is loosely related to a series of comics related to the 2020 pandemic of the coronavirus SARS-CoV-2, which causes COVID-19. <br />
<br />
The comic hinges on sharing photos on social media of vaccination cards as proof that the user has been {{w|COVID-19 vaccine|vaccinated}} (in this case, gotten a booster shot). Such cards contain {{w|Personal data|personal identification}} that should probably not be made public. The irony is that the user has censored some impersonal lines, such as the instructions that are identical on all vaccination cards, and many easy-to-guess lines, while not censoring any of said personal information.<br />
The fourth line, labelled "other" is probably completely blank (as the third dose was on the current date), but is completely blacked out.<br />
<br />
The caption indicates that his intention is to "seem more mysterious". This is best exemplified by blanking most of the word "clinician" to leave "CIA".<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
:[Profile picture with three unreadable lines on its left:<br />
Check it out, I just got my booster! <br />
<br />
:[Picture of the U.S. COVID-19 Vaccination Record Card attached on a media post. The card includes pre-printed information in black and handwritten information in blue, the latter indicated here by italics. Some of the text has been blacked out, indicated here by "[Censored]".]<br />
<br />
:COVID-:[Censored] Vaccination record card<br />
:[At the upper right of the card appears the logo of the U.S. Department of Health and Human Services, a stylized eagle surrounded by the words "Department of Health & Human Services USA", although those words are not legible in this drawing. Next to that appears the logo of the Centers for Disease Control and Prevention, a shaded box with the letters "CDC" and the words "Centers for Disease Control and [Censored]" below it.]<br />
----<br />
<br />
<br />
:Please keep this record card, which includes [Censored]<br />
:about [Censored]<br />
:Por favor, guarde esta tarjeta de registro, que incluve [Censored]<br />
:[Censored] sobre [Censored]<br />
<br />
:''Munroe'' ''Randall''<br />
----<br />
:Last Name First Name<br />
<br />
:''10-17-[Censored]84'' ''41592653''<br />
----<br />
:Date of birth Patient number<br />
<br />
{{comic discussion}}<br />
[[Category:COVID-19]]<br />
[[Category:COVID-19 vaccine]]<br />
[[Category:Identity Theft]]</div>172.70.98.89https://www.explainxkcd.com/wiki/index.php?title=2532:_Censored_Vaccine_Card&diff=2196722532: Censored Vaccine Card2021-10-23T00:06:51Z<p>172.70.98.89: /* Explanation */ wlink</p>
<hr />
<div>{{comic<br />
| number = 2532<br />
| date = October 22, 2021<br />
| title = Censored Vaccine Card<br />
| image = censored_vaccine_card.png<br />
| titletext = CVS's pharmacies are fine, but I much prefer their [censored]s.<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by COVID-13's 5TH DOSE - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
This comic is loosely related to a series of comics related to the 2020 pandemic of the coronavirus SARS-CoV-2, which causes COVID-19. <br />
<br />
The comic hinges on sharing photos on social media of vaccination cards as proof that the user has been vaccinated (in this case, gotten a booster shot). Such cards contain {{w|Personal data|personal identification}} that should probably not be made public. The irony is that the user has censored some impersonal lines, such as the instructions that are identical on all vaccination cards, and many easy-to-guess lines, while not censoring any of said personal information.<br />
The fourth line, labelled "other" is probably completely blank (as the third dose was on the current date), but is completely blacked out.<br />
<br />
The caption indicates that his intention is to "seem more mysterious". This is best exemplified by blanking most of the word "clinician" to leave "CIA".<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
:[Profile picture with three unreadable lines on its left:<br />
Check it out, I just got my booster! <br />
<br />
:[Picture of the U.S. COVID-19 Vaccination Record Card attached on a media post. The card includes pre-printed information in black and handwritten information in blue, the latter indicated here by italics. Some of the text has been blacked out, indicated here by "[Censored]".]<br />
<br />
:COVID-:[Censored] Vaccination record card<br />
:[At the upper right of the card appears the logo of the U.S. Department of Health and Human Services, a stylized eagle surrounded by the words "Department of Health & Human Services USA", although those words are not legible in this drawing. Next to that appears the logo of the Centers for Disease Control and Prevention, a shaded box with the letters "CDC" and the words "Centers for Disease Control and [Censored]" below it.]<br />
----<br />
<br />
<br />
:Please keep this record card, which includes [Censored]<br />
:about [Censored]<br />
:Por favor, guarde esta tarjeta de registro, que incluve [Censored]<br />
:[Censored] sobre [Censored]<br />
<br />
:''Munroe'' ''Randall''<br />
----<br />
:Last Name First Name<br />
<br />
:''10-17-[Censored]84'' ''41592653''<br />
----<br />
:Date of birth Patient number<br />
<br />
{{comic discussion}}<br />
[[Category:COVID-19]]<br />
[[Category:COVID-19 vaccine]]<br />
[[Category:Identity Theft]]</div>172.70.98.89https://www.explainxkcd.com/wiki/index.php?title=2532:_Censored_Vaccine_Card&diff=2196712532: Censored Vaccine Card2021-10-23T00:05:52Z<p>172.70.98.89: /* Transcript */ categories</p>
<hr />
<div>{{comic<br />
| number = 2532<br />
| date = October 22, 2021<br />
| title = Censored Vaccine Card<br />
| image = censored_vaccine_card.png<br />
| titletext = CVS's pharmacies are fine, but I much prefer their [censored]s.<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by COVID-13's 5TH DOSE - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
This comic is loosely related to a series of comics related to the 2020 pandemic of the coronavirus SARS-CoV-2, which causes COVID-19. <br />
<br />
The comic hinges on sharing photos on social media of vaccination cards as proof that the user has been vaccinated (in this case, gotten a booster shot). Such cards contain personal identification that should probably not be made public. The irony is that the user has censored some impersonal lines, such as the instructions that are identical on all vaccination cards, and many easy-to-guess lines, while not censoring any of said personal information.<br />
The fourth line, labelled "other" is probably completely blank (as the third dose was on the current date), but is completely blacked out.<br />
<br />
The caption indicates that his intention is to "seem more mysterious". This is best exemplified by blanking most of the word "clinician" to leave "CIA".<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
:[Profile picture with three unreadable lines on its left:<br />
Check it out, I just got my booster! <br />
<br />
:[Picture of the U.S. COVID-19 Vaccination Record Card attached on a media post. The card includes pre-printed information in black and handwritten information in blue, the latter indicated here by italics. Some of the text has been blacked out, indicated here by "[Censored]".]<br />
<br />
:COVID-:[Censored] Vaccination record card<br />
:[At the upper right of the card appears the logo of the U.S. Department of Health and Human Services, a stylized eagle surrounded by the words "Department of Health & Human Services USA", although those words are not legible in this drawing. Next to that appears the logo of the Centers for Disease Control and Prevention, a shaded box with the letters "CDC" and the words "Centers for Disease Control and [Censored]" below it.]<br />
----<br />
<br />
<br />
:Please keep this record card, which includes [Censored]<br />
:about [Censored]<br />
:Por favor, guarde esta tarjeta de registro, que incluve [Censored]<br />
:[Censored] sobre [Censored]<br />
<br />
:''Munroe'' ''Randall''<br />
----<br />
:Last Name First Name<br />
<br />
:''10-17-[Censored]84'' ''41592653''<br />
----<br />
:Date of birth Patient number<br />
<br />
{{comic discussion}}<br />
[[Category:COVID-19]]<br />
[[Category:COVID-19 vaccine]]<br />
[[Category:Identity Theft]]</div>172.70.98.89https://www.explainxkcd.com/wiki/index.php?title=Talk:2453:_Excel_Lambda&diff=219412Talk:2453: Excel Lambda2021-10-18T04:15:38Z<p>172.70.98.89: </p>
<hr />
<div><!--Please sign your posts with ~~~~ and don't delete this text. New comments should be added at the bottom.--><br />
<!--Use : to indent your replies. --PoolloverNathan ~~~~~ --><br />
Another ghost cueball comic! You can see it in the last panel. [[Special:Contributions/108.162.216.54|108.162.216.54]] 06:03, 22 April 2021 (UTC)<br />
<br />
:Is that something that has happened before? First time noticing it. Is it just a remnant of the sketching? Of doest it mean something? [[Special:Contributions/162.158.93.213|162.158.93.213]] 13:21, 22 April 2021 (UTC)<br />
::It has happened, and is now mentioned in the trivia section. --[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 16:43, 23 April 2021 (UTC)<br />
<br />
:Randall seems to have update the comic to remove the ghost head. Someone should update it here too. (I don't know how). [[User:DrPumpkinz|DrPumpkinz]] ([[User talk:DrPumpkinz|talk]]) 00:07, 23 April 2021 (UTC)<br />
<br />
Someone needs to add an explanation of the Lambda, and possibly how Excel is implementing it. (I suppose it would immediately be useful for cutting down common re-use within a formula line, though =IF(ISERR(FIND(":",A1)),A1,RIGHT(A1,LEN(A1)-FIND(":",A1))) is a trivial repeat of the FIND, once to check, then again to do, I often need to do far more nested things, check for being a value, repeat the FIND to deal with the LEFT, etc.) But it has the smell of being effectively a Macro in this instance. Which already seems to me to be the only way to run a ''proper'' Turing Machine in an Excel column without hitting Circular Reference issues.<br />
<br />
<br />
Would it be a stretch to say that Turing's inability to prove if Cueball will stop is actually equivalent to the halting problem, except it is for Cueball and not an arbitrary Turing machine? I thought that was pretty funny. [[User:XTheBHox|xTheBHox]] ([[User talk:XTheBHox|talk]]) 11:30, 22 April 2021 (UTC)<br />
<br />
<br />
Microsoft themselves claim that the addition of LAMBDA makes Excel turing-comlpete (see here: https://techcommunity.microsoft.com/t5/excel-blog/announcing-lambda-turn-excel-formulas-into-custom-functions/ba-p/1925546). Based on this comic, I would argue that it already was... [[Special:Contributions/162.158.159.36|162.158.159.36]] 12:55, 22 April 2021 (UTC)<br />
<br />
:Someone has already made Conway's game of life in excel (http://dailydoseofexcel.com/archives/2011/04/06/conways-game-of-life-simulation-in-excel) and game of life has been shown to be Turing complete. [[User:Kvarts314|Kvarts314]] ([[User talk:Kvarts314|talk]]) 13:28, 22 April 2021 (UTC)<br />
<br />
:Since Excel has a way to store and do math on numbers, and also a way to 'point' to a certain cell, it is Turing-complete. A lambda function is not necessary for Turing-completeness (e.x. a turing machine does not have one.) [[Special:Contributions/162.158.255.250|162.158.255.250]] 15:14, 22 April 2021 (UTC)<br />
<br />
it should probably be mentioned that the number of excel rows is emphatically *not* infinite, so only simple turing machines could be implemented this way. [[Special:Contributions/162.158.93.15|162.158.93.15]] 17:20, 22 April 2021 (UTC)<br />
<br />
:In fact, it technically isn't Turing complete, as it has only a finite amount of data. It might be a finite-state-machine or the like, though. --[[Special:Contributions/108.162.219.218|108.162.219.218]] 20:22, 22 April 2021 (UTC)<br />
::Turing completeness is a qualilty of a model of computing, not a particular physical implementation. There's no inherent limit to the size of a spreadsheet, so it's as Turing-complete as any programming language. Any actual implementation of a Turing Machine only has a finite tape, not an infinite tape like the theoretical model. [[User:Barmar|Barmar]] ([[User talk:Barmar|talk]]) 15:39, 23 April 2021 (UTC)<br />
<br />
:It may be worth citing this work. https://gotocon.com/amsterdam-2016/presentation/Pure%20Functional%20Programming%20in%20Excel [[User:Noehp|Noehp]] ([[User talk:Noehp|talk]]) 00:02, 23 April 2021 (UTC)<br />
<br />
'''Zerothly''', why is almost everyone here using weird 'indents', or maybe new-contributor-starts-here methods, in this article's Talk comments? Is this some lambdaesque in-joke being carried in here from some script/code dialect I'm not aware of? '''Primarily''', though, I just wanted to say that the (external) explanations of how Lambda works in Python look a lot to me like a nuanced Eval-like process, rather than a typical Anonymous Function that becomes sequestered away as a code-chunk at the end of a loose-pointer, internally. Python's one of the languages I've not yet bothered to learn to write (just sufficiently understand to get the gist and flow), so maybe I'm reading the Lies-To-Children explanations for n00bs. Should we get some other languages represented here, either within the C-family or off into the clans of code that might have an even more interesting implementation? Nothing too esoteric, but a distinct grammar difference would be an interesting comparison.[[Special:Contributions/162.158.159.104|162.158.159.104]] 11:22, 23 April 2021 (UTC)<br />
:Fixed the indents. {{User:PoolloverNathan/Signature}} 14:01, 21 May 2021 (UTC)<br />
<br />
Now if only someone would find examples of creative loop variable abuse (I guess that'd be optimal solutions in lots of Code Golf or Code Olympics problems) that demonstrate the imperative style of code to its full glory. The corresponding solution in λ code is probably rife with applicative functors and monads i.e. ugly and awkward to anyone not familiar with these concepts. The Python example here merely looks like anonymous function sprinkled into an imperative style so not very helpful. [[Special:Contributions/172.70.98.89|172.70.98.89]] 04:15, 18 October 2021 (UTC)</div>172.70.98.89https://www.explainxkcd.com/wiki/index.php?title=2453:_Excel_Lambda&diff=2194112453: Excel Lambda2021-10-18T04:03:20Z<p>172.70.98.89: /* Explanation */ Tried to explain how the λ notation makes the mostly-pure formula language Turing complete. Python example was retained because I haven't figured out a non-trivial yet minimal demo of functionally solving problem and I don't code Python</p>
<hr />
<div>{{comic<br />
| number = 2453<br />
| date = April 21, 2021<br />
| title = Excel Lambda<br />
| image = excel_lambda_new.png<br />
| titletext = Extremely rude how Turing's later formulations of the halting problem called me out by name specifically.<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by TURING HIMSELF. Why is Ponytail pleased, what will she use it for, that she could not before? Another reference to a law/hypothesis about computing? Please mention here why this explanation isn't complete. Do NOT delete this tag too soon.}}<br />
<br />
[[Cueball]] is computing and [[Ponytail]] criticizes him in a way that is reminiscent of the [[:Category:Code Quality|Code Quality series]], although not as harsh. Cueball has lots of strange [[:Category:Cueball Computer Problems|computer problems]], and this will most likely result in another one.<br />
<br />
The comic begins with Ponytail finding out that {{w|Microsoft Excel}} is adding a {{w|Anonymous_function|lambda function}} to their function library. This was [https://techcommunity.microsoft.com/t5/excel-blog/announcing-lambda-turn-excel-formulas-into-custom-functions/ba-p/1925546 announced by Microsoft] for Beta users in December of 2020, but perhaps Ponytail has only discovered this recently. A lambda function is a fundamental mathematical structure that can (alternatively) be used to completely define all possible computations from the ground up, in what is known as {{w|lambda calculus}}, other than using for-loops, pointers and effect-ful functions that bear little resemblance to mathematical functions. They are commonly found in programming languages such as {{w|Lisp}}, {{w|Python}}, and many others. A lambda function is also called an {{w|anonymous function}} because in most languages it can be passed to other functions (including another lambda function) without needing to be given any formal name during coding, or given {{w|Closure_(computer_programming)|'closure'}} under whatever name(s) its calling procedures desire.<br />
<br />
Finding that Excel is adding a lambda function pleases Ponytail. Cueball claims that the lambda function is unnecessary, as when he needs arbitrary computation he just adds a block of columns to the side of his sheet and has a {{w|Turing machine}} process it. This would technically work as lambda calculus is formally equivalent to Turing machines. People have created [https://www.felienne.com/archives/2974 Turing machines in Excel], although not for practical purposes.<br />
<br />
Ponytail finds his solution absurd and is convinced Cueball is "doing computing wrong". But he claims that all computing is equally wrong, citing the {{w|Church-Turing thesis}}, a hypothesis which says that a function can be computed by executing a series of instructions if and only if that function is computable by a Turing machine. A classical Turing machine uses an infinitely long strip of tape as its memory; for Cueball, the large Excel column acts as the "tape". All ways of computing are "equally wrong" since, according to this thesis, they can all be translated to or from a Turing machine. <br />
<br />
Ponytail and Cueball appear to have different ideas of 'computing'. Ponytail, like most programmers, probably includes efficiency and readability as important characteristics of 'doing computing right'. Cueball appears interested only in {{w|computability}}, a more theoretical point of view than Ponytail's.<br />
<br />
Ponytail then says that Turing would change his mind if he saw Cueball's spreadsheet, presumably because of the extreme complexity of Cueball's code in the spreadsheet. Cueball's final statement is that Turing could ask him to stop, but would not be able to prove if he actually will stop. <br />
<br />
Cueball's final statement is a reference to the {{w|halting problem}} mentioned in the title text. It is the problem of determining whether a given Turing machine will halt. The problem has been shown to be undecidable, i.e., it is impossible to build an algorithm that computes whether any arbitrary Turing machine will halt or not. Because of the way Cueball has behaved, he has been specifically mentioned in Turing's later formulations of the halting problem. Cueball finds this very rude. This is of course a joke, since Turing has been dead since 1954, presumably long before Cueball was born. But it would be crazy indeed if a scientist became so mad at a person that he would mention this person by name in his formulation of a serious problem.<br />
<br />
Over-complicated spreadsheets were also mentioned in [[2180: Spreadsheets]].<br />
<br />
While conditional loops with the ability to interact with the loop variable, and functions reading and altering parameters ''not'' passed to it, can be (ab)used creatively to great effect, the fact a same structure may have been vastly different control schemes puts burden on anyone reading preexisting code. Functional programming abstracts computation differently, and uses distinct constructs for plain iterating over a list ('''map''' and co., the inner function is forbidden to interact with the accumulator by semantics) and recursion and iteration with side-effects or implicit input (modeled as various flavors of monads). Constructs like '''map''' take functions as parameter, but giving every tidbit of code a name and hiding it 100+ lines away nullifies the readability. Lambda function is thus a much needed piece for a functional style of expression. <br />
<br />
In the Excel example though, the point is you can finally create custom functions in the original '''formula''' language, not some too-powerful-not-to-be-abused-by-hackers macro language that any security-aware person would strip out before opening an Excel spreadsheet. Excel formulas take only explicit input (cells) and have explicit and controlled output (cells or function return value), fitting the Lambda notion nicely. Combine this with proper recursion support and you have a language that becomes Turing-complete without relying on evaluator abuse ([https://chandoo.org/wp/timestamps-excel-formula-help/ circular reference and F7 for next iteration]) or a [https://www.felienne.com/archives/2974 ''wall'' of Turing machine states]. Now one can '''express''' (pseudo-code follows) CellValue=iterate(recursive-function, num-of-steps) properly, with num-of-steps as an input not *number of F7 presses* or *starting value of a cell which get decremented to zero as recursion proceeds* or *row number from wall of states*. Excel probably still tracks the iteration with a variable in calculating the final value, but that implementation detail is decoupled from the language itself.<br />
<br />
An example of a lambda function in Python that takes a parameter named '''a''' and computes the value '''a'''-squared minus 1:<br />
<br />
lambda a: (a ** 2) - 1<br />
<br />
Lambda values are often used as parameters to other functions, such as '''map''' which applies a function to each item of an "iterable" such as this list of the numbers 1, 2, and 3:<br />
<br />
map(lambda a: (a ** 2) - 1, [1, 2, 3]) ''# will generate the values 0, 3, and 8'' <br />
You can copy/paste this statement into a Python interpreter (such as [https://www.tutorialspoint.com/execute_python_online.php TutorialsPoint]) to see it work (do not copy the leading spaces; that's a wiki thing):<br />
print(list(map(lambda a: (a ** 2) - 1, [1, 2, 3])))<br />
<br />
In the above example, '''map''' takes each element of the list containing the values 1, 2, and 3 in turn, sending each value to the lambda function (as the parameter "a") and so generating the sequence of values: 0, 3, and 8. These are then reconstructed into a '''list''' to '''print''' the complete result: '''[0, 3, 8]'''.<br />
<br />
A recursive lambda might be:<br />
<br />
def pointless_recursion(v):<br />
# If current value (x) is evenly divisible by 4, return the source (v) * current (x)<br />
# Otherwise, print current, and then try the process again with the current value of x + 3<br />
r = lambda x: x * v if x % 4 == 0 else print(x) or r(x + 3)<br />
return r(v)<br />
<br />
pointless_recursion(12) # returns 144 (i.e., 12*12)<br />
pointless_recursion(11) # prints 11, 14, 17 then returns 220 (i.e., 20*11)<br />
<br />
In this instance, the function is given the name 'r', and features a (conditional) call back to this self-same 'r' within it. The 'x' is whatever value is the latest passed to 'r', while 'v' is that which was first passed to the container function.<br />
<br />
Ideally, such techniques should be used to ''reduce'' {{w|Spaghetti code}}, not increase it. But this isn't a foregone conclusion, especially in Cueball's hands.<br />
<br />
==Transcript==<br />
:[In a narrow panel, Ponytail is walking in from the left, looking down at her phone]<br />
:Ponytail: Oh cool, Excel is adding a lambda function, so you can recursively define functions.<br />
<br />
:[Ponytail, holding her phone to her side stands behind Cueball, who is sitting in an office chair with a hand on a laptop standing on his desk. He has turned around to face her, leaning with the other arm on the back of the chair.]<br />
:Cueball: Seems unnecessary.<br />
:Cueball: When I need to do arbitrary computation, I just add a giant block of columns to the side of my sheet and have a Turing machine traverse down it.<br />
<br />
:[In a frame-less panel Ponytail is standing in he same position behind Cueball, who has resumed working on his laptop with both hands on the keyboard.]<br />
:Ponytail: I think you're doing computing wrong.<br />
:Cueball: The Church-Turing thesis says that all ways of computing are '''''equally''''' wrong.<br />
<br />
:[Ponytail is still behind Cueball, who has a finger raised in the air, and the other hand is on the desk. Cueball's head has a visible sketch layer which has not been erased.]<br />
:Ponytail: I think if Turing saw '''''your''''' spreadsheets, he'd change his mind.<br />
:Cueball: He can ask me to stop making them, but not prove whether I will!<br />
<br />
==Trivia==<br />
*In the [https://www.explainxkcd.com/wiki/images/3/3b/excel_lambda.png original version] of the comic, in the final panel, there was a gray pencil outline, slightly different to Cueball's head that had not been removed.<br />
**This was later fixed in a re-upload.<br />
<br />
{{comic discussion}}<br />
<br />
[[Category:Comics featuring Cueball]]<br />
[[Category:Comics featuring Ponytail]]<br />
[[Category:Comics featuring real people]]<br />
[[Category:Computers]]<br />
[[Category:Spreadsheets]]<br />
[[Category:Programming]]</div>172.70.98.89https://www.explainxkcd.com/wiki/index.php?title=2524:_Comet_Visitor&diff=2190722524: Comet Visitor2021-10-09T17:30:32Z<p>172.70.98.89: /* Explanation */ don't think pyramids can?</p>
<hr />
<div>{{comic<br />
| number = 2524<br />
| date = October 4, 2021<br />
| title = Comet Visitor<br />
| image = comet_visitor.png<br />
| titletext = It's a myth that the Great Wall of China is the only human-made structure visible from space--there are LOTS of structures for us to feel self-conscious about!<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by a PACIFIC MOON FOOT-PATCH - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
{{w|C/2014 UN271 (Bernardinelli-Bernstein)|Comet C/2014 UN<sub>271</sub>}} is a large comet that was discovered in 2014 almost as far from the Sun as the orbit of Neptune, and it will reach its closest approach in 2031, near Saturn's orbit. It's an {{w|Oort Cloud}} comet, with a {{w|Orbital period|period}} of more than 4 million years. Since modern humans ({{w|homo sapiens}}) evolved about 300,000 years ago (although tool-making ancestors were around about 2.5 million years ago), the last time it was among the planets was indeed long before humans evolved.<br />
<br />
When a long-period comet comes into the inner Solar System, it's often figuratively called a "visit". But Megan and Cueball treat this more literally (or perhaps more sarcastically). Just as one usually neatens up their home when they're expecting guests, to make a good impression, they realize they need to clean up the Earth and its vicinity in preparation for this "visitor". Cueball starts handing out assignments -- he'll clean up the {{w|Pacific Garbage Patch}}, and suggests that Megan take care of all the {{w|Space debris|debris in orbit}}.<br />
<br />
Cueball and Megan also make notes to sweep up the lunar footprints that NASA astronauts left on the Moon during the Apollo missions and put away the [[:Category:Mars rovers|Mars rovers]]. It's also common for people expecting visitors to put various objects out of view with the intention of returning them to their normal place after the visit, usually because the objects are considered unsightly that under normal circumstances is outweighed by the convenience of being out in the open.<br />
<br />
However, since the comet will not come anywhere close to Earth and Mars, all this hardly seems necessary; it would be like cleaning up your home because the President or some other dignitary will be visiting your town. In addition, while a dignitary would theoretically be able to see one's house, although comets have {{w|comet tails|tails}}, they do not have eyes,{{Citation needed}} so they would not be able to perceive any difference between Earth before and after tidying up (even if the {{w|comet nucleus|nucleus}} had an eye, it would not be able to see because it is in a {{w|Coma (cometary)|coma}}). Furthermore, sweeping footprints in the Moon, that Cueball sees as a way of tidying up, would be seen as [https://www.smithsonianmag.com/science-nature/nasa-looks-to-protect-historic-sites-on-the-moon-47186092/ destroying an invaluable archaeological sites by NASA and other people].<br />
<br />
The title text debunks the claim that the {{w|Great Wall of China}} is the only {{w|Artificial_structures_visible_from_space|human-made structure visible from outer space}}; in fact the Great Wall cannot easily be distinguished from space (as it is very long but not wide), but some other human constructions can (and cities are easily visible at night because they emit light).<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
<br />
:[Megan sits at a desk in front of a computer, looking to the left off-panel and pointing at the screen]<br />
:Megan: Have you seen this big comet, C/2014 UN271? <br />
:Megan: It'll pass near Saturn's orbit in 10 years.<br />
<br />
:[In a frameless panel, Cueball stands behind Megan, who is now looking at the computer and typing]<br />
:Cueball: Wow, look at the orbital period.<br />
:Megan: Yeah, it hasn't been to this part of the solar system since humans evolved. <br />
:Megan: At '''''least.'''''<br />
<br />
:[Cueball starts running off-panel, holding his finger in the air. Megan looks towards him with both arms resting on the back of her chair]<br />
:Cueball: Well, we definitely need to tidy up. I'll start on the Pacific Garbage Patch, you tackle orbital debris.<br />
:Megan: What about the moon footprints?<br />
:Cueball: Sweep them up. Collect the Mars rovers, too! <br />
:Cueball: We can put them back once it's gone.<br />
<br />
{{comic discussion}}<br />
[[Category:Comics featuring Cueball]]<br />
[[Category:Comics featuring Megan]]<br />
[[Category:Astronomy]]<br />
[[Category:Mars rovers]]</div>172.70.98.89https://www.explainxkcd.com/wiki/index.php?title=2524:_Comet_Visitor&diff=2190712524: Comet Visitor2021-10-09T17:30:03Z<p>172.70.98.89: Revert unexplained major changes</p>
<hr />
<div>{{comic<br />
| number = 2524<br />
| date = October 4, 2021<br />
| title = Comet Visitor<br />
| image = comet_visitor.png<br />
| titletext = It's a myth that the Great Wall of China is the only human-made structure visible from space--there are LOTS of structures for us to feel self-conscious about!<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by a PACIFIC MOON FOOT-PATCH - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
{{w|C/2014 UN271 (Bernardinelli-Bernstein)|Comet C/2014 UN<sub>271</sub>}} is a large comet that was discovered in 2014 almost as far from the Sun as the orbit of Neptune, and it will reach its closest approach in 2031, near Saturn's orbit. It's an {{w|Oort Cloud}} comet, with a {{w|Orbital period|period}} of more than 4 million years. Since modern humans ({{w|homo sapiens}}) evolved about 300,000 years ago (although tool-making ancestors were around about 2.5 million years ago), the last time it was among the planets was indeed long before humans evolved.<br />
<br />
When a long-period comet comes into the inner Solar System, it's often figuratively called a "visit". But Megan and Cueball treat this more literally (or perhaps more sarcastically). Just as one usually neatens up their home when they're expecting guests, to make a good impression, they realize they need to clean up the Earth and its vicinity in preparation for this "visitor". Cueball starts handing out assignments -- he'll clean up the {{w|Pacific Garbage Patch}}, and suggests that Megan take care of all the {{w|Space debris|debris in orbit}}.<br />
<br />
Cueball and Megan also make notes to sweep up the lunar footprints that NASA astronauts left on the Moon during the Apollo missions and put away the [[:Category:Mars rovers|Mars rovers]]. It's also common for people expecting visitors to put various objects out of view with the intention of returning them to their normal place after the visit, usually because the objects are considered unsightly that under normal circumstances is outweighed by the convenience of being out in the open.<br />
<br />
However, since the comet will not come anywhere close to Earth and Mars, all this hardly seems necessary; it would be like cleaning up your home because the President or some other dignitary will be visiting your town. In addition, while a dignitary would theoretically be able to see one's house, although comets have {{w|comet tails|tails}}, they do not have eyes,{{Citation needed}} so they would not be able to perceive any difference between Earth before and after tidying up (even if the {{w|comet nucleus|nucleus}} had an eye, it would not be able to see because it is in a {{w|Coma (cometary)|coma}}). Furthermore, sweeping footprints in the Moon, that Cueball sees as a way of tidying up, would be seen as [https://www.smithsonianmag.com/science-nature/nasa-looks-to-protect-historic-sites-on-the-moon-47186092/ destroying an invaluable archaeological sites by NASA and other people].<br />
<br />
The title text debunks the claim that the {{w|Great Wall of China}} is the only {{w|Artificial_structures_visible_from_space|human-made structure visible from outer space}}; in fact the Great Wall cannot easily be distinguished from space (as it is very long but not wide), but some other human constructions such as the Pyramids can (and cities are easily visible at night because they emit light).<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
<br />
:[Megan sits at a desk in front of a computer, looking to the left off-panel and pointing at the screen]<br />
:Megan: Have you seen this big comet, C/2014 UN271? <br />
:Megan: It'll pass near Saturn's orbit in 10 years.<br />
<br />
:[In a frameless panel, Cueball stands behind Megan, who is now looking at the computer and typing]<br />
:Cueball: Wow, look at the orbital period.<br />
:Megan: Yeah, it hasn't been to this part of the solar system since humans evolved. <br />
:Megan: At '''''least.'''''<br />
<br />
:[Cueball starts running off-panel, holding his finger in the air. Megan looks towards him with both arms resting on the back of her chair]<br />
:Cueball: Well, we definitely need to tidy up. I'll start on the Pacific Garbage Patch, you tackle orbital debris.<br />
:Megan: What about the moon footprints?<br />
:Cueball: Sweep them up. Collect the Mars rovers, too! <br />
:Cueball: We can put them back once it's gone.<br />
<br />
{{comic discussion}}<br />
[[Category:Comics featuring Cueball]]<br />
[[Category:Comics featuring Megan]]<br />
[[Category:Astronomy]]<br />
[[Category:Mars rovers]]</div>172.70.98.89