explain xkcd - User contributions [en]

Category:Footer comics

2016-01-08T23:51:20Z

199.27.130.234: find the earliest instance of the current version

:These five comics ([[150]], [[730]], [[162]], [[688]], & [[556]]) are all found on the current footer of the [[xkcd|xkcd site]].
:[[File:footer.png|alt text]]

The earliest footer available seems to be from [https://web.archive.org/web/20060207154349/http://www.xkcd.com/ Feb 7, 2006]. It features [[40]], [[49]], [[37]], [[44]] & [[10]], in that order.

On [https://web.archive.org/web/20060408214700/http://www.xkcd.com/ April 8, 2006] the first one changed to [[77]].

On [https://web.archive.org/web/20061013224954/http://www.xkcd.com/ Oct 13, 2006] it changed to its current style, but with [[150]], [[123]], [[162]], [[55]] & [[77]], rather than the current set.

On [https://web.archive.org/web/20100817210844/http://xkcd.com/ Aug 17, 2010] it changed to the current version.

[[Category:Distinctive comics]]

123: Centrifugal Force

2016-01-08T23:43:01Z

199.27.130.234:

{{comic
| number = 123
| date = July 3, 2006
| title = Centrifugal Force
| image = centrifugal force.png
| titletext = You spin me right round baby, right round, in a manner depriving me of an inertial reference frame. Baby.
}}

==Explanation==
[[Black Hat]] has strapped {{w|James Bond}} to a centrifuge and claims the {{w|Centrifugal force|centrifugal}} force will be lethal. Bond objects that there is no such thing, but just {{w|Centripetal force|centripetal}} force. The notion of centrifugal force is a common one, as we experience it whenever we turn. Teachers will initially teach Newtonian mechanics in an inertial frame, and in inertial frames the centrifugal force is zero. Instead, a body that moves in a circle does so because of a centripetal force (acting towards the centre of the rotation). This is a reasonable, and correct view, but is a subtle point that many students find hard to grasp as it seems to contradict their personal experience of centrifugal forces. For the sake of exposition, teachers may claim that "There is no such thing as centrifugal force". This however is also a misconception which is addressed in the explanation below:
;Observers' point of view (Black Hat, us, etc.)
:James Bond is moving in a circle, and is therefore accelerating. The force keeping him there is an inward force of contact against the centrifuge, a centripetal force. Via Newton's {{w|Newton's laws of motion#Newton's third law|third law}}, since the centrifuge is pushing Bond inward, Bond is pushing the centrifuge outward. The centrifuge's material is strong enough not to break under this force, however.
;James Bond's point of view
:In James Bond's frame of reference, Bond is at rest. He is kept there by two forces: the above-mentioned inward force of contact against the centrifuge, and an ''outward centrifugal force''. He feels both forces.

As mentioned in the explanation, as the centrifuge rotates faster, the forces needed to keep him in motion get larger, so the force he feels gets larger. This will eventually kill him. The conclusion will be the same regardless of which frame of reference is chosen.

Teachers of mechanics are well aware of this, however in introductory expositions these ideas are often not taught. In theoretical mechanics, one describes the positions and velocities of the particles in a model relative to a frame of reference. This means that a time is chosen to be time 0, and positions are chosen to be (0,0,0), (1,0,0), (0,1,0) and (0,0,1). With these chosen, the position and time of any particle in the system can be described. It is an axiom of Newtonian Mechanics that there exist "Inertial Frames". In an inertial frame a particle will remain at rest or at a constant speed unless acted on by an external force, and Newton's second law takes a simple form: F=ma. The surface of the Earth approximates an inertial frame. In a non-inertial frame, such as one rotating with a giant centrifuge, or moving with an accelerating vehicle, a particle will accelerate, relative to the frame. Newton's second law, when formed in such a frame is much more complicated, as it has terms for the linear acceleration of the frame, the angular acceleration of the frame, the centrifugal force and the {{w|Coriolis force}}. These extra terms are sometimes called "fictitious forces" as they result from the choice of the frame of reference. The mathematics required to describe problems in a non-inertial frame is more sophisticated, and all problems may be solved using an inertial frame. Thus is reasonable that teachers at school level "lie to children" and teach the mechanics in inertial frames.

The final statement by Black Hat is that said by {{w|Auric Goldfinger}} in {{w|Goldfinger (film)|Goldfinger}} in response to James Bond's question "Do you expect me to talk?"

The title text is inspired by {{w|Dead or Alive (band)|Dead or Alive's}} famous song from 1985, "{{w|You Spin Me Round (Like a Record)|You Spin Me Round}}".

Randall feels very strongly that the centrifugal force is a real thing. He links to this comic in the first footnote of his [[what if?|What if?]] article [https://what-if.xkcd.com/92/ One-Second Day], stating that it is a real thing.

As can also be seen in the [https://twitter.com/bohacekp/status/531500491180875776/photo/1 footnote on page 132] in his [[what if?#The book|What if? book]] he will even fight you about it. From the book: 
"Furthermore, if you're on the equator, you're being flung outward by a centrifugal force1."
 "1Yes, centrifugal. I will fight you."
 (The article itself is about what happens if you lose all you DNA, so it has not much to do with this "real" force... The sentence is just stating that the actual weight loss from losing all your DNA is similar to the weight loss you would experience by moving from the poles to the equator due to this force.)

==Transcript==
:[James Bond is strapped to a giant wheel suspended from the ceiling. Black Hat is standing next to two levers.]
:Black hat: How do you like my centrifuge, mister Bond? When I throw this lever, you will feel centrifugal force crush every bone in your body.
:[Same scene, but a closer shot.]
:Bond: You mean centripetal force. There's no such thing as centrifugal force.
:Black hat: A laughable claim, mister Bond, perpetuated by overzealous teachers of science. Simply construct Newton's laws in a rotating system and you will see a centrifugal force term appear as plain as day.
:[Closer shot, only Bond's head is visible.]
:Bond: Come now, do you really expect me to do coordinate substitution in my head while strapped to a centrifuge?
:Black hat: No, Mister Bond. I expect you to die.
{{comic discussion}}

[[Category:Comics featuring Black Hat]]
[[Category:Physics]]
[[Category:Comics featuring Cueball]]
[[Category:Footer comics]]

55: Useless

2016-01-08T23:42:39Z

199.27.130.234:

{{comic
| number = 55
| date = January 27, 2006
| title = Useless
| image = useless.jpg
| titletext = Even the identity matrix doesn't work normally
}}

==Explanation==
[[Randall]] is attempting to apply mathematics to the concept of love to no avail. Specifically, he is attempting his "normal approach" which is a term used in mathematics for the method one typically uses to solve a certain type of problem. However, as love is not a well-defined mathematical, his normal approach is useless. Simply put: he's saying he has found no way of describing love using only the tools of mathematics.

From the top, moving left to right, he tries the {{w|square root}} of love, the {{w|cosine}} of love, and the {{w|derivative}} of love with respect to x. He then attempts to left-multiply love by a 2x2 {{w|identity matrix}}, and finally he defines a {{w|Function (mathematics)|function}} of love as a {{w|Fourier transform}}. These are all "normal approaches" to solving certain math problems.

The message of the comic is that for someone who uses math to solve all their problems, defining love is impossible. It also indicates that love is not always a rational phenomenon.

This comic has been made into a [http://store.xkcd.com/products/useless t-shirt] in the xkcd store, with a {{w|Laplace transform}} in place of the bottom integral.

===Basic explanations of the functions===
:''Note: The Wikipedia links will provide far more detailed explanations of the mathematics.''
*The {{w|square root}} of x is the number which, when multiplied by itself, equals x.
*{{w|Cosine}} is a {{w|trigonometric function}} which, when given the measure of an angle in a {{w|right triangle}} as an input, outputs the ratio of the lengths of two sides of that triangle (for cosine it is the non-{{w|hypotenuse}} side adjacent to the angle and the hypotenuse).
*A {{w|derivative}} of a function is the rate of change of that function at a given value of x. It is a primary focus of {{w|calculus}}. A basic example is where "velocity" is the rate of change of displacement at a given time, the derivative of velocity is "acceleration" which is the rate of change of velocity at a given time.
*{{w|identity matrix|Identity matrices}} are {{w|matrix (mathematics)|matrices}} which consist of only zeros and ones, with zeros everywhere except along the {{w|main diagonal}}. Multiplying a matrix by the equal-sized identity matrix will result in the same output in the same way that multiplying a non-matrix by 1 does not change the original term. The title text suggests that multiplying love by the identity matrix does not return the same "love" value.
*A {{w|Fourier transform}} converts a function from one (sophisticated) function into an endless continuous series of (more simple) functions, where each next part is bringing the equation closer to the real result. This means that you can stop your calculations after a few iterations and you are very close to the real result, and it also can be used to deconstruct signals.

==Transcript==
:[Different mathematic equations, all with heart on left side, and all equal question mark. Below is a caption.]
:√♥ = ?
:cos ♥ = ?
:d/dx ♥ = ?
:[10]♥ =?
:[01]
:F{♥} = 1/√2π ∫∞-∞f(t)eit♥dt = ?
:My normal approach is useless here

==Trivia==
*This was the 52nd and last comic originally posted to [[LiveJournal]].
**The previous was [[53: Hobby]].
*This comic kept its original title: "Useless"
**It is part of the last six comics on LiveJournal which all had a title without the word "Drawing" in it.
**Five of these had exactly the same title on both sites.
**Only 11 comics have the same title on both sites.
**Apart from the [[:Category:First day on LiveJournal|thirteen first comics]] posted to LiveJournal, there were only three other comics without the word "Drawing" in the title before these last six.
*There was no original [[Randall]] quote for this comic.
*This comic was the last of the last 11 comics posted on LiveJournal.
**These 11 comics were [[:Category:Posted on LiveJournal after xkcd|posted both on LiveJournal and xkcd]] after the [[xkcd]] site opened on the 1st of January 2006.
**The first six comics were posted on both sites on the same day.
**And then this first happened again with this last comic.
*The version used on the [http://store.xkcd.com/products/useless t-shirt] and in ''[http://store.xkcd.com/products/xkcd-volume-0 xkcd: volume 0]'' is slightly different. The derivative is with respect to time (''t'') instead of ''x'', and the function at the bottom is a {{w|Laplace transform}}.
*This comic was adapted to a wedding cake featured on [http://www.cakewrecks.com/home/2011/6/26/sunday-sweets-geek-wedding-cakes.html an installment of "Sunday Sweets"], a regular feature on popular blog [http://cakewrecks.com Cake Wrecks].

{{comic discussion}}

[[Category:Comics posted on livejournal| 52]]
[[Category:Posted on LiveJournal after xkcd]]
[[Category:Romance]]
[[Category:Math]]
[[Category:Footer comics]]

77: Bored with the Internet

2016-01-08T23:40:50Z

199.27.130.234:

{{comic
| number = 77
| date = March 17, 2006
| title = Bored with the Internet
| image = bored_with_the_internet.jpg
| titletext = I used to do this all the time.
}}
==Explanation==
A character that has hair (not to be confused with [[Hairy]]) suggests to [[Black Hat]] that he is wasting his life on the internet and they should go explore the world. They appear to walk a great distance, through what appears to be a swamp or perhaps a forest in winter, across a plain, and down to a river valley. Despite travelling so far and through such varied landscapes, in the last panel one of the characters admits that all he can think about is what a great Livejournal post their trip would make. It appears that the plan to get the Internet off their mind has failed.

{{w|Livejournal}} is a website on which users can make accounts and, effectively, blog; although the site is designed around the premise that the blogs ought to be used as personal journals, with the ability to privatize the journal or only let certain friends see certain entries. Livejournal was an early social network and an early blog platform, and was a good way for people to let others know what was going on in their lives. As of 2013, Livejournal still exists; although sites like Facebook have become far more powerful and popular sites for sharing one's daily life.

Unlike in most of his appearances (especially later ones), Black Hat does not exhibit any of his signature [[Classhole]] tendencies.

The title text suggests that [[Randall Munroe|Randall]] has overcome a tendency to think about how he will document what he has been doing, rather than concentrate on the thing itself.

==Transcript==
:[Black Hat and Hair are talking in a room with a computer on.]
:Hairy: I feel like I'm wasting my life on the internet. Let's walk around the world.
:Black Hat: Sounds good.
:[The two men are shown walking through trees.]
:[The two men are shown walking on flat stretch, with mountains in the distance.]
:[The two men are shown in a magnificent canyon. They stand, silently looking at the scene.]
:Hairy: And yet all I can think is, "This will make for a great LiveJournal entry."

==Trivia==
*Livejournal was the site where Randall presented his comics before starting xkcd.

{{comic discussion}}
[[Category:Comics featuring Black Hat]]
[[Category:Comics featuring Hairy]]
[[Category:Comics with color]]
[[Category:Internet]]
[[Category:Footer comics]]

10: Pi Equals

2016-01-08T23:39:58Z

199.27.130.234:

{{comic
| number = 10
| date = September 30, 2005
| title = Pi Equals
| image = pi.jpg
| titletext = My most famous drawing, and one of the first I did for the site
}}

==Explanation==
There are two possible references here. One is from the book ''{{w|Contact (novel)|Contact}}'' by Carl Sagan, where the existence of God was shown in the last chapter to be encoded in the digits of {{w|pi}}. The other is an old joke of a {{w|Fortune cookie|fortune cookie}} with a fortune that reads "Help! I'm trapped in a fortune cookie factory!" Similar jokes are often repeated for any mass-manufactured personalized item, often implying that the worker who made the item is working in a sweatshop somewhere or is literally trapped inside a factory and calling for help via the items he produces. This joke is also referenced in [[327: Exploits of a Mom]]'s title text, where [[Mrs. Roberts]] [[Elaine Roberts|daughter]]'s name is "Help I'm trapped in a driver's license factory."

The most literal interpretation of the joke would be that some being who helped to create the universe in a "universe factory" snuck a message into the digits of pi (a number that has an endlessly long decimal that never repeats) asking for help to get out. Mathematical concepts being manufactured in a factory is the main mental image here. One can't help but wonder if the [http://static.tvtropes.org/pmwiki/pub/images/TimeBandits.jpg primordial beings who labored on the universe] to produce things like the gravitational constant and pi have a labor union. Judging by the fact that they're calling for help, it seems they don't.

Since pi never ends and does not follow any sort of known pattern, if each number pair were assigned a letter from the alphabet, or if it was converted to base-26 (or preferably ASCII or some other form of text encoding, if you desire capitalization and punctuation), the entire works of Shakespeare, as well as any other expressible piece of information, including the message in this comic, could presumably be found (it is not really ''known'' that pi really has {{w|normal number|this property}}, but the absence of this property would in itself be a weird coincidence); although the probability of finding any given string of numbers within a calculable range of digits of pi [http://www.angio.net/pi/whynotpi.html diminishes rapidly as the string length increases].

In the novel {{w|Contact (novel)|Contact}} by {{w|Carl Sagan}}, he includes a "[http://goddoesnt.blogspot.dk/2013/10/pi-and-signature-of-god-from-carl.html Signature of God]". In brief the signature consists of a very long string of 1s and 0s far out (after some 10^20 seemingly random numbers) in the base-11 expansion of pi that when arranged in a square of a specific size yields a clear drawing of a circle with a diameter of several hundred digits. The existence of this pattern was hinted to the protagonist by a member of an advanced alien civilization as being encoded in physics by an even more advanced civilization with the ability to create universes.

Interestingly enough, this could also work for pictures: if you assign a set of nine numbers to equal an RGB hexadecimal color value, eventually you will find the Mona Lisa.

In the title text [[Randall]] notes that this became one of his most famous comics (at the time it was re-released on the new [[xkcd]] site on the 1st of January 2006.) He also notes that it was one of his first drawings for the site (it was the 11th posted originally). See [[#Trivia|trivia]] below.

==Transcript==
:[A huge π to the left, then a large equal-to sign, and then five rows of text.]
:'''π ='''
:::3.14159265
:::3589793help
:::imtrappedin
:::auniversefac
:::tory7108914...

==Trivia==
*This was the 11th comic originally posted to [[LiveJournal]].
**The previous is [[9: Serenity is coming out tomorrow]].
**The next is [[14: Copyright]].
*Comic #36 was originally posted as a duplicate of comic 10: Pi Equals. This was corrected some time between April 23, 2006 and July 5, 2006 when the current version showed up in the web archive (see the links).
*This comic kept its original title: "Pi Equals"
*There were no original [[Randall]] quotes for this comic.
*This was one of the [[:Category:First day on LiveJournal|thirteen first comics]] posted to LiveJournal within 12 minutes on Friday September 30, 2005.
*This comic was posted on [[xkcd]] when the web site opened on Sunday the 1st of January 2006.
**It was posted along [[:Category:First day on xkcd|with all 41 comics]] posted before that on LiveJournal as well as a few others.
**The latter explaining why the numbers of these 41 LiveJournal comics ranges from 1-44.
*One of the original drawings drawn on [[:Category:Checkered paper|checkered paper]].
*The book version of this comic (in ''[http://store.xkcd.com/products/xkcd-volume-0 xkcd: volume 0]'') has different title text:
**''"I've put rescue instructions in e. You'll need the cheat codes for your universe, which I hid in the square root of two."''

{{comic discussion}}

[[Category:Comics posted on livejournal| 11]]
[[Category:First day on LiveJournal| 11]]
[[Category:First day on xkcd]]
[[Category:Checkered paper]]
[[Category:Math]]
[[Category:Footer comics]]

44: Love

2016-01-08T23:38:09Z

199.27.130.234:

{{comic
| number = 44
| date = October 19, 2005
| title = Love
| image = love.jpg
| titletext = This one makes me wince every time I think about it
}}

==Explanation==
This comic expresses how the nature of love can be painful when closely examined, as in every relationship one party must love the other party the most.

Instead of continuing [[Cueball]]'s escalation by saying the expected response "I love ''you'' more!" [[Megan]] stops and agrees with him: he does love her more than she loves him. The final frame shows the couple standing in silence.

Often couples escalate the claims of how much they love each other. Typically, however, the couple never openly admit this not wanting to cause pain to their partner, but love by its very nature must be unbalanced as no two things can ever truly be equal. This is one of love's painful truths.

In the title text, [[Randall]] expresses how this comic is shockingly stark in its portrayal of the nature of love.

==Transcript==
:[Cueball and Megan stand facing one another.]

:Cueball: I love you!
:Megan: I love you!

:[Cueball and Megan stand facing one another.]
:Cueball: I love you more!
:Megan: Yeah.

:[Cueball and Megan stand facing one another - saying nothing.]

==Trivia==
*This was the 21st comic originally posted to [[LiveJournal]].
**The previous was [[21: Kepler]].
**The next was [[40: Light]].
*Original title: "Wednesday's Drawing"
*There were no original [[Randall]] quote for this comic.
*This comic was posted on [[xkcd]] when the web site opened on Sunday the 1st of January 2006.
**It was posted along [[:Category:First day on xkcd|with all 41 comics]] posted before that on LiveJournal as well as a few others.
**The latter explaining why the numbers of these 41 LiveJournal comics ranges from 1-44.
*One of the original drawings drawn on [[:Category:Checkered paper|checkered paper]].
**Of those comics drawn on such paper this is the one with the highest number released on xkcd.
**But it was an early comic which got a different number after the transfer to xkcd.
**The last comic on such paper was, by release-date, [[39: Bowl]] although it is likely that [[36: Scientists]] was released in 2006, which would make it the last.

{{comic discussion}}

[[Category:Comics posted on livejournal| 21]]
[[Category:First day on xkcd]]
[[Category:Checkered paper]]
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Romance]]
[[Category:Footer comics]]

37: Hyphen

2016-01-08T23:37:07Z

199.27.130.234:

{{comic
| number = 37
| date = October 28, 2005
| title = Hyphen
| image = hyphen.jpg
| titletext = I do this constantly
}}

==Explanation==
This is the first "[[My Hobby]]" comic in ''[[xkcd]]''. In these comics, [[Randall]] suggests an obscure activity or pastime he enjoys which he declares as his "hobby". In the premiere "My Hobby" comic, Randall's hobby is mentally re-interpreting what people mean when they say "[adjective]-ass [noun]" by moving the hyphen to after the word "ass" instead of before.

The semi-{{Wiktionary|scatological}} suffix "-ass" is used as an intensifier in informal US English speech, usually attached to an adjective directly modifying a noun, as in "big-ass car" or "funny-ass comedian". In this comic, [[Cueball]] is exploring the increased humor aspect of changing "-ass" from a suffix modifying the adjective, to "ass-", a prefix modifying the noun, yielding a "big ass-car" or a "funny ass-comedian", the former presumably being a large car for carrying buttocks, the latter being a humorous comedian specializing in jokes about lower backs. The prefix "ass-" may also have a negative connotation, indicating that something is disliked. An "ass-car" may be a very terrible car, for example.

Another explanation would be that, since this suffix/prefix refers to an element of human anatomy, the car would be in the shape of said anatomical piece.

Outside of North America, most English speakers use "arse" to mean the buttocks, so to them it may sound as if Randall's talking about Donkeys.

On an interesting note; there '''really is''' such a thing as an [[Wikipedia:ASS (car)|Ass-Car]]!

==Transcript==
:[Cueball is talking to his Cueball-like friend about a car that resembles a Volkswagen Beetle. Above the drawing is a statment:]
:My hobby: whenever anyone calls something an [adjective]-ass [noun], I mentally move the hyphen one word to the right.

:Cueball: Man, that's a sweet ass-car.

==Trivia==
*This was the 25th comic originally posted to [[LiveJournal]].
**The previous was [[23: T-shirts]].
**The next was [[25: Barrel - Part 4]].
*Original title: "Friday's Drawing - Hyphen"
**After a series of comics with no real title, only the week day as a heading, he began again, with this one, to add a titles, but only after stating the week day.
**He kept this practice with including the title after the weekday, until he began using the xkcd site - see [[45: Schrodinger#Trivia|this trivia]].
***Except the next Barrel comic, without no added title.
***And the last Barrel comic [[31: Barrel - Part 5| Barrel - Part 5]] with the original title but not the week day.
*Original [[Randall]] quote: "Tune in Monday for the conclusion to the story of the boy and his barrel."
**The next comic on Monday really wasn't the conclusion of the [[:Category:Barrel|barrel story]] as mentioned above.
**This is the first, and probably last time, that Randall has used a quote/[[Title text|title text]] to advertise the next comic.
*This comic was posted on [[xkcd]] when the web site opened on Sunday the 1st of January 2006.
**It was posted along [[:Category:First day on xkcd|with all 41 comics]] posted before that on LiveJournal as well as a few others.
**The latter explaining why the numbers of these 41 LiveJournal comics ranges from 1-44.
*One of the original drawings drawn on [[:Category:Checkered paper|checkered paper]].
*This is one of the two comics featured in ''[[Blue Eyes]]: The Hardest Logic Puzzle in the World'', the other being [[82: Frame]].

{{comic discussion}}

[[Category:Comics posted on livejournal| 25]]
[[Category:First day on xkcd]]
[[Category:Checkered paper]]
[[Category:Comics featuring Cueball]]
[[Category:Multiple Cueballs]]
[[Category:My Hobby]]
[[Category:Language]]
[[Category:Footer comics]]

49: Want

2016-01-08T23:36:16Z

199.27.130.234:

{{comic
| number = 49
| date = January 14, 2006
| title = Want
| image = want.jpg
| titletext = Well, she's pretty hot.
}}

==Explanation==

In the first three panels of this comic, [[Cueball]] is expressing what he wants, voicing poetic romantic notions towards someone. In the last panel, Cueball contradicts his previous poetic statements, as he crassly states that he also really wants to have sex with his paramour's sister.

In the title text he attempts to excuse his crass statement.

==Transcript==
:[Cueball is standing talking in the same position in all four panels. Seems like he has hair in panel 2.]
:Cueball: I want to be brave enough to tell you how I feel.

:Cueball: I want to say "I love you" before I hang up the phone for once.

:Cueball: I want to drive all night with you, listening to mix tapes, not caring where we end up.

:Cueball: Oh, and I also really want to get with your sister.
:Cueball: I mean, DAMN.

==Trivia==
*This was the 46th comic originally posted to [[LiveJournal]].
**The previous was [[48: Found]].
**The next was [[50: Penny Arcade]].
*Original title: "Drawing - Want"
*There were no original [[Randall]] quote for this comic.
*This comic was one of the last 11 comics posted on LiveJournal.
**These 11 comics were [[:Category:Posted on LiveJournal after xkcd|posted both on LiveJournal and xkcd]] after the [[xkcd]] site opened on the 1st of January 2006.
**This comic was posted on the same day on both sites.
**They were not all posted on the same day though.
*During the start-up of xkcd four of the last 11 comics were released on days that deviated from the normal Monday, Wednesday, Friday scheme.
**This one was thus '''released on a Saturday'''.
**It was the middle part of a series of three were the release day was shifted to one day later.
**This one was posted so late, 11:41 pm, that it almost became a Sunday comic.
**The next "Friday" comic [[52: Secret Worlds]] was also released on a Saturday.

{{comic discussion}}

[[Category:Comics posted on livejournal| 46]]
[[Category:Posted on LiveJournal after xkcd]]
[[Category:Comics featuring Cueball]]
[[Category:Romance]]
[[Category:Footer comics]]

40: Light

2016-01-08T23:35:16Z

199.27.130.234: this was in the footer

{{comic
| number = 40
| date = October 21, 2005
| title = Light
| image = light.jpg
| titletext = Like a beacon
}}

==Explanation==
Lighthouses were built on coasts to give ships a point of reference where land was, so that they could find where they were going, and to know where they should avoid during a storm. [[Megan]] fills this role for [[Cueball]]. She is his lighthouse to know where he can be safe.

==Transcript==
:[A crowd of figures stand around in the dark. One figure is illuminated by a beam of light.]
:In a dark and confusing world, you burn brightly. I never feel lost.

==Trivia==
*This was the 22nd comic originally posted to [[LiveJournal]].
**The previous was [[44: Love]].
**The next was [[22: Barrel - Part 3]].
*Original title: "Friday's Drawing"
*There were no original [[Randall]] quote for this comic.
*This comic was posted on [[xkcd]] when the web site opened on Sunday the 1st of January 2006.
**It was posted along [[:Category:First day on xkcd|with all 41 comics]] posted before that on LiveJournal as well as a few others.
**The latter explaining why the numbers of these 41 LiveJournal comics ranges from 1-44.
*One of the original drawings drawn on [[:Category:Checkered paper|checkered paper]].

{{comic discussion}}
[[Category:Comics posted on livejournal| 22]]
[[Category:First day on xkcd]]
[[Category:Checkered paper]]
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Cueball]]
[[Category:Multiple Cueballs]]
[[Category:Romance]]
[[Category:Footer comics]]

Category:Footer comics

2016-01-08T23:26:07Z

199.27.130.234: add more versions

Category:Footer comics

2016-01-08T01:04:09Z

199.27.130.234: add change

:These five comics are all found on the current footer of the [[xkcd|xkcd site]].
:[[File:footer.png|alt text]]

The earliest footer available seems to be from [https://web.archive.org/web/20060207154349/http://www.xkcd.com/ Feb 7, 2006]. It features [[40]], [[49]], [[37]], [[44]] & [[10]], in that order.

On [https://web.archive.org/web/20060408214700/http://www.xkcd.com/ April 8, 2006] the first one changed to [[77]].

[[Category:Distinctive comics]]

Category:Footer comics

2016-01-08T00:58:51Z

199.27.130.234: add link and description of oldest footer, from Wayback Machine

Talk:1608: Hoverboard

2015-11-25T00:02:25Z

199.27.130.234:

Well, this will be the next incomplete explanation for a while. -[[Special:Contributions/162.158.90.165|162.158.90.165]] 21:58, 24 November 2015 (UTC)

Yes, one thing to note is how to get the hell out of the cave near the volcano [[Special:Contributions/108.162.249.159|108.162.249.159]] 22:38, 24 November 2015 (UTC)

The image is made up of small images with addresses of the form http://xkcd.com/1608/XXXX:-YYYY+s.png (although not every coordinate inside the bounds has an image associated). A script could probably dump out all the images and paste them together. --[[Special:Contributions/108.162.216.6|108.162.216.6]] 22:46, 24 November 2015 (UTC)

West -- Under Lava Pools -- Elon Musk's Secret Volcano Base (not as enjoyable as you might expect).

The Starship out east contains, among other things, Darth Vader, apparently explaining Steven Universe to a subordinate. (Steven and the Crystal Gems can be found a the west end of the ship, near an ice cream cooler.) The same ship contains an elaborate homage to the original Prince of Persia.

There, have at thee an image! [[User:Arch-TK|Arch-TK]] ([[User talk:Arch-TK|talk]]) 22:58, 24 November 2015 (UTC)

There are 168 coins spread throughout the map according to the source code [[Special:Contributions/173.245.54.53|173.245.54.53]] 23:03, 24 November 2015 (UTC)

When using a device, instead of saying "use arrow keys to move", it says "tilt to move, tap to jump". It's also a lot harder to control.

It's actually 169 coins (t.length). --[[Special:Contributions/188.114.111.129|188.114.111.129]] 23:22, 24 November 2015 (UTC)

I got 153 coins!! :D There's two starships, one's a star destroyer with an expansive maze dropping regular torpedoes on the other. May be noteworthy that there are various references to Star Wars and Steven Universe throughout. [[Special:Contributions/108.162.221.13|108.162.221.13]] 23:27, 24 November 2015 (UTC)

The second starship is the TantiveIV, Leia's ship at the beginning of episode 4. Note directly below the Tantive, the terrain seems to be sand dunes. Also there are two more space ships by the volcano; an X-wing at a gas station and an Apollo Command Module.

https://xkcd.com/1608/tigl.js - Looks like there's an easier to read version of the code there. Maybe that'll help someone with extracting all the images.

I've got all the images downloaded. Zipping/uploading now. Should I post a link here when complete or what's the best way to share these? I'm also working on setting up a zoomable map. [[Special:Contributions/173.245.54.53|173.245.54.53]] 23:57, 24 November 2015 (UTC)

The collision detection is glitchy. I keep landing/bumping against platforms I'm far away from. Is getting stuck against walls normal? --[[Special:Contributions/199.27.130.234|199.27.130.234]] 00:01, 25 November 2015 (UTC)

Talk:1608: Hoverboard

2015-11-25T00:01:57Z

199.27.130.234:

Well, this will be the next incomplete explanation for a while. -[[Special:Contributions/162.158.90.165|162.158.90.165]] 21:58, 24 November 2015 (UTC)

Yes, one thing to note is how to get the hell out of the cave near the volcano [[Special:Contributions/108.162.249.159|108.162.249.159]] 22:38, 24 November 2015 (UTC)

The image is made up of small images with addresses of the form http://xkcd.com/1608/XXXX:-YYYY+s.png (although not every coordinate inside the bounds has an image associated). A script could probably dump out all the images and paste them together. --[[Special:Contributions/108.162.216.6|108.162.216.6]] 22:46, 24 November 2015 (UTC)

West -- Under Lava Pools -- Elon Musk's Secret Volcano Base (not as enjoyable as you might expect).

The Starship out east contains, among other things, Darth Vader, apparently explaining Steven Universe to a subordinate. (Steven and the Crystal Gems can be found a the west end of the ship, near an ice cream cooler.) The same ship contains an elaborate homage to the original Prince of Persia.

There, have at thee an image! [[User:Arch-TK|Arch-TK]] ([[User talk:Arch-TK|talk]]) 22:58, 24 November 2015 (UTC)

There are 168 coins spread throughout the map according to the source code [[Special:Contributions/173.245.54.53|173.245.54.53]] 23:03, 24 November 2015 (UTC)

When using a device, instead of saying "use arrow keys to move", it says "tilt to move, tap to jump". It's also a lot harder to control.

It's actually 169 coins (t.length). --[[Special:Contributions/188.114.111.129|188.114.111.129]] 23:22, 24 November 2015 (UTC)

I got 153 coins!! :D There's two starships, one's a star destroyer with an expansive maze dropping regular torpedoes on the other. May be noteworthy that there are various references to Star Wars and Steven Universe throughout. [[Special:Contributions/108.162.221.13|108.162.221.13]] 23:27, 24 November 2015 (UTC)

The second starship is the TantiveIV, Leia's ship at the beginning of episode 4. Note directly below the Tantive, the terrain seems to be sand dunes. Also there are two more space ships by the volcano; an X-wing at a gas station and an Apollo Command Module.

https://xkcd.com/1608/tigl.js - Looks like there's an easier to read version of the code there. Maybe that'll help someone with extracting all the images.

I've got all the images downloaded. Zipping/uploading now. Should I post a link here when complete or what's the best way to share these? I'm also working on setting up a zoomable map. [[Special:Contributions/173.245.54.53|173.245.54.53]] 23:57, 24 November 2015 (UTC)

The collision detection is glitchy. I keep landing/bumping against platforms I'm far away from. --[[Special:Contributions/199.27.130.234|199.27.130.234]] 00:01, 25 November 2015 (UTC)

Talk:1606: Five-Day Forecast

2015-11-21T03:48:14Z

199.27.130.234:

As far as I can figure out, -452 F is something like 4 K, which seems a bit too warm (above OTL microwave background). It probably should be -456 in the next-to-last row and -458 in the last row (-459 for the last column). --[[Special:Contributions/141.101.81.76|141.101.81.76]] 12:58, 20 November 2015 (UTC)

Thanks for the conversions to degrees C as being a 58 year old Brit I have never understood degrees F (I know what they are just I have no idea whether 60F is cold, cool or comfortable). I have always used 5, 10 and 21, Winter, Spring and Summer sun - well works for Middle Brittan) [[User:RIIW - Ponder it|RIIW - Ponder it]] ([[User talk:RIIW - Ponder it|talk]]) 19:09, 20 November 2015 (UTC)

There will be ambient starlight in addition to the 2.7K background which should raise the temperature slightly. However, the 2.7K background will also redshift to a lower temperature as time goes on: T propto 1/a where a is the scale factor of the Universe. Would be a good assignment for a cosmology class. [[Special:Contributions/173.245.54.48|173.245.54.48]] 13:07, 20 November 2015 (UTC)

Aha, what will last longer than stars etc is the silly Fahrenheits.
[[Special:Contributions/162.158.91.165|162.158.91.165]] 17:49, 20 November 2015 (UTC)

There are five columns. Either the first column is "today" and one should not speak of predictions after five (m/b/trillion) years (as is currently the case a couple of times), or the first column is "tomorrow (etc.)" and then the prediction of "A bright yellow sun; 38°F" for one trillion years would be very strange. [[User:Jkrstrt|Jkrstrt]] ([[User talk:Jkrstrt|talk]]) 18:39, 20 November 2015 (UTC)

Randall lives in a cold climate! [[Special:Contributions/188.114.97.127|188.114.97.127]] 21:37, 20 November 2015 (UTC)

If the "red giant" temperature measures the sun's core, how do you explain the last panels showing decidedly non-white-dwarf temperatures? --[[Special:Contributions/199.27.130.234|199.27.130.234]] 03:48, 21 November 2015 (UTC)

Talk:1605: DNA

2015-11-18T21:47:30Z

199.27.130.234:

The source for Google.com can be found at `<nowiki>view-source:https://www.google.com/</nowiki>` for Firefox and Chrome. Also [http://pastebin.com/raw.php?i=u8SMf7G6 here]. —[[User:Artyer|Artyer]] <big>([[User Talk:Artyer|talk]]<big>'''|'''</big>[[Special:Contributions/Artyer|ctb]])</big> 16:06, 18 November 2015 (UTC)
:Should there be a link to the code in the explain. I do not understand these links or the source code, and would not like to place these links in the explanation. --[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 18:43, 18 November 2015 (UTC)

I really like this comic. IMHO, just another good example of intelligent design. Google's dev had to design, plan and carefully code. If that is seemingly simple compared to DNA and biology then how much more intelligence and thought was needed for the coding of all living things?--[[User:R0hrshach|R0hrshach]] ([[User talk:R0hrshach|talk]]) 17:18, 18 November 2015 (UTC)
:With all the stupid things going on in our bodies (rendered useless by natural selection but staying put anyway like the {{w|Appendix (anatomy)|Appendix}} or our {{w|tailbone}}) then it is to me just a clear example that there has been no intelligence behind our genome, but just trial and error, and then 4 billion years to get it right enough that it works but not smart. And don't get me started on how our air and food/drink has to go in the same way with the risk of being (nearly) killed by a pretzel...([http://www.dailymail.co.uk/news/article-94567/I-feel-great-President-Bush-declares-pretzel-incident.html even if you are the president of the US] ;-) That is just plain stupid design. But few enough dies from this, that it was necessary for nature to change it once it was working. Humans and the genes survived long enough to reproduce. --[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 18:43, 18 November 2015 (UTC)

Apologies, when I saved my comments it blitzed someone else's that must have been being written at the same time :'-( [[User:RIIW - Ponder it|RIIW - Ponder it]] ([[User talk:RIIW - Ponder it|talk]]) 19:13, 18 November 2015 (UTC)
:Yeah it was my two comments above? I have now moved the one right her above back in place from the bottom where Davidy22 had placed it when he tried to fix it. No harms done but as he says: ''Read error messages, I know mediawiki gives them to you''. You can always see in the history what you have changed. --[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 21:08, 18 November 2015 (UTC)
::I, for my part read the edit conflict (with Kynde, 18:43) like a good little boy, re-edited in light of that, resubmitted and... forgot to answer the security question. For completeness I wrote the following. If it's still helpful...
Had the same thought. Although I just use "View | Source" from the menu or right-click and "View Page Source", or whatever that browser tends to want to give me. And, having had that same thought: For reference, in case anybody wants it, the source of the google.co.uk main page (assumed not far off google.com in its nature) is 51 lines. But that's 51 ''long'' lines of mostly javascript, with much of the unnecessary whitespace (including line-feeds) taken out of it, overwhelmingly single-character variable names, over 150 'if' statements (including 'else if' ones, in continuation to a prior one) and perhaps 56 'for' loops, at first glance. Whether 'optimised' or obfuscated, it certainly could be a challenge to fully understand.
:: HTH, HAND [[Special:Contributions/141.101.106.161|141.101.106.161]] 21:43, 18 November 2015 (UTC)

IMHO DNA with its redundant sections for things not currently used and the bodges in biological design are a good example of unintelligent design. For example the blood supply to the retina is between the iris and the retina, so it is in the way. An intelligent designer would do an eye mark II. But this has nothing to do with the comic. [[User:RIIW - Ponder it|RIIW - Ponder it]] ([[User talk:RIIW - Ponder it|talk]]) 19:07, 18 November 2015 (UTC)

White Hat is showing the hubris often seen by people who think their (often limited) knowledge in one field can be used as an anology for something very different. Megan only manages to showchim his error by showing that a "simple" web page, which has only been evolving for a few years is more complex than he thinks, and the role of any one line/command in the page is probably far from clear without deep analysis [[User:RIIW - Ponder it|RIIW - Ponder it]] ([[User talk:RIIW - Ponder it|talk]]) 19:07, 18 November 2015 (UTC)

The evolution of life is composed exclusively of copy-paste programming on top of legacy code, global variables, and hacks on hacks on hacks at every level, from telomeres and DNA looping, to the structure of the human hip (childbirth), to our breathing tract, optic nerve, and brain structure and cognition. --[[Special:Contributions/199.27.130.234|199.27.130.234]] 21:47, 18 November 2015 (UTC)

1603: Flashlights

2015-11-13T23:32:09Z

199.27.130.234: "xeon" -> "xenon" - Hmmm... maybe we shouldn't overclock our Intel i7 to 10GHz!

{{comic
| number = 1603
| date = November 13, 2015
| title = Flashlights
| image = flashlights.png
| titletext = Due to a typo, I initially found a forum for serious Fleshlight enthusiasts, and it turns out their highest-end models are ALSO capable of setting trees on fire. They're impossible to use without severe burns, but some of them swear it's worth it.
}}

==Explanation==
In this comic, [[Cueball]] has acquired or built a new high powered flashlight, which he wants to demonstrate to [[Megan]]. When Cueball refers to classic {{w|flashlights}} (battery torches) as dim and finnicky, this gives reason to assume that the flashlight he is holding is going to be ridiculously overengineered.

Indeed, when he switches it on outside the house, the intense light beam completely drowns out the scene. Only the reflected light from the forest lights up the part of Cueball and Megan's faces that are turned towards it.

Cueball comments that the flashlight lights up the entire forest, but Megan observes that it is the trees that are on fire, indicating that Cueball's flashlight is so overpowered that the energy of its beam is sufficient to cause the organic matter of trees to combust.

Of course, a flashlight that cannot safely be pointed at things is fairly useless for the traditional purpose of a flashlight, which would be to find things in the dark by directing light over them. This mundane and practical reasoning does not seem to matter to Cueball of course, who appears only interested in the intensity and brightness the device is capable of achieving.

Cueball might allude to a number of technical improvements, notably xenon-based incandescent bulbs, multiple-LED assemblies, Lithium batteries (usually used for photography flashes) or rechargeable batteries. A number of companies market "tactical" flashlights that are supposedly powerful enough to incapacitate an opponant, using terms such as "scorching" to advertise their products.

The title text refers to {{w|Fleshlight}} a brand of male masturbation toys modeled after various female or male orifices. Cueball (or [[Randall]]) claims that he only arrived on a forum for Fleshlight enthusiasts due to a typo. Apart from the "e" vs. "a" in Fleshlight, they are also fashioned to look like oversized flashlights. On that forum here he found out that the highest-end models of their product lines was also capable of setting trees on fire. This would probably happen due to violent vibrations inside the orifice, or excessively powerful internal heating. If you use one of these you should expect to obtain severe burns in a very unpleasant area. But some of the enthusiasts swear that it is still worth it, in the same manner that Cueball only cares about the intensity of the flashlight, regardless of the consequences. Maybe they are just trying to trick you into doing something stupid!

==Transcript==
:[Four panels are laid out horizontally.]

:[Panel 1: Cueball carries a flashlight walking towards Megan who is sitting on a couch]
:Cueball: Remember how flashlights sucked when we were kids? Always dim and finnicky?
:Megan: I guess?

:[Panel 2: Cueball and Megan walking to the left]
:Cueball: Well, I discovered there are now internet flashlight enthusiasts.
:Cueball: And the technology has... improved.
:Megan: OK, Let's see.

:[Panel 3: It is dark outside where Cueball turns on the flashlight. The beam is very bright and very visible even seen from the side. Backscattered light reflects off Cueball and Megan's faces, turning them into bright white beings in the dark. The facade of the house and the stairs are also visible in the same manner, with deep dark shadows where anything is in the shadow. Megan averts her face from the light holds up a hand to cover her eyes. When the flashlight turns on it even makes a sound, written in white above the beam:]
:Flashlight: '''''FWOOSH'''''

:[Panel 4: Cueball and Megan look at what the beam falls on (outside the frame). Megan has taken her hand down. Both their faces are only lit up like a crescent moon. Cueball is holding the flashlight with both hands as if it is pushing back on him. The text is written in white on the dark sky above them.]
:Cueball: See how it lights up the whole forest?
:Megan: ... The trees are on fire.
:Cueball: Real bright, though.

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Comics with inverted brightness]]
[[Category:Sex]]

1563: Synonym Movies

2015-08-12T19:38:33Z

199.27.130.234: /* Made ''The Power Gets Up'' into ''Power Gets Up'' */

{{comic
| number = 1563
| date = August 12, 2015
| title = Synonym Movies
| image = synonym_movies.png
| titletext = Fans eagerly await 2015's 'Space Fights: Power Gets Up', although most think 1999's 'Space Fights: The Scary Ghost' didn't live up to the hype.
}}

[[File:synonym movies rotated.png|right]]
==Explanation==
This comic shows several "Synonym Movies". It takes several well known movies, but change the titles using words that are different, but mean essentially the same thing. So ''{{w|Star Wars}}'' has turned into ''Space Fights'', ''{{w|The Lord of the Rings (film series)|The Lord of the Rings}}'' into ''The Jewelry God'' and ''{{w|Star Trek}}'' into ''Space Trip''. All these movies series have the same heading, and then a subtitle. There are ten of them in the comic, and two more in the title text.

The use of synonyms makes all these movies look ridiculous, for example, "The Sword Wizard Is Back" is a laughable sounding movie{{Citation needed}}, whereas "{{w|The Return of the Jedi}}" sound perfectly reasonable to us. [[Randall]] may be poking fun at movies that have ridiculous titles already, for instance some people think this applies to a title like "{{w|Terminator: Genisys}}".

The title text refers to the new Star Wars movie coming up later this year (2015-12-18), after {{w|The Walt Disney Company|Disney}} acquired the movie rights. The movie is called {{w|Star Wars: The Force Awakens}} and has now turned into ''Power Gets Up''. As usual, with any Star Wars related material, there is a huge fan base that eagerly awaits the new movie. But then again many people fear that it will not live up to their expectations, as was the case with the fourth movie, first of the three movies in the second installment of Star Wars, {{w|Star Wars: The Phantom Menace}}. As mentioned in the title text, that movie did not live up the hype. Of course in this comic it has been dubbed ''The Scary Ghost''.

==Table of the titles==
*All cases of Star has turned into Space
*Wars has turned into Fight
*Lord to God
*Rings has been turned into {{w|Jewelry}} — which also include, amongst others, rings.
*Trek has been turned into Trip.

{| class="wikitable"
|-
!width=12em| Synonym
!width=12em| Real Title
! Comment
|-
| ''Space Fights: Sudden Optimism''
| ''{{w|Star Wars: A New Hope}}''
| If you suddenly feel optimistic, you could say that you have gained a new hope.
|-
| ''Space Fights: The Government Wins This One''
| ''{{w|Star Wars: The Empire Strikes Back|Star Wars: The Empire Strikes Back}}''
| In the second Star Wars movie the Empire comes out on top — as opposed to the first and third where a Death Star is destroyed at the end of each of the movies. So the government = the Empire, wins that movie.
|-
| ''Space Fights: The Sword Wizard Is Back''
| ''{{w|Star Wars: Return of the Jedi|Star Wars: Return of the Jedi}}''
| A {{w|jedi}} is a kind of wizard, wielding {{w|The Force (Star Wars)|the Force}} (like magic) and the {{w|lightsaber}} (a kind of sword).
|-
|colspan=3|
|-
| ''The Jewelry God: The Jewelry Team''
| ''{{w|The Lord of the Rings: The Fellowship of the Ring|The Lord of the Rings: The Fellowship of the Ring}}''
| The fellowship has become a team in the synonym version.
|-
| ''The Jewelry God: Double Houses''
| ''{{w|The Lord of the Rings: The Two Towers|The Lord of the Rings: The Two Towers}}''
| Two towers may not be so close to double houses... But at least there are two in either case.
|-
| ''The Jewelry God: We Have a Czar Again''
| ''{{w|The Lord of the Rings: Return of the King}}''
| Czar is a title for Slavic monarchs, but generally regarded as equivalent to king.
|-
|colspan=3|
|-
| ''Space Trip: The Movie''
| ''{{w|Star Trek: The Motion Picture|Star Trek: The Motion Picture}}''
| Today we would say ""The Movie" rather than "The Motion Picture".
|-
| ''Space Trip: That Guy is Angry''
| ''{{w|Star Trek: The Wrath of Khan|Star Trek: The Wrath of Khan}}''
| {{w|Khan Noonien Singh|Khan}} (a fictional villain in the series) is now just ''That Guy'', and wrath has been turned down to merely angry.
|-
| ''Space Trip: Where is the Vulcan''
| ''{{w|Star Trek: The Search for Spock|Star Trek: The Search for Spock}}''
| {{w|Spock}} is of the alien race {{w|Vulcan (Star Trek)|Vulcan}}, and the search has turned into the question ''where is he?''
|-
| ''Space Trip: Let's Go Back''
| ''{{w|Star Trek: The Voyage Home|Star Trek: The Voyage Home}}''
| When you decide to travel home you could also say let's go back.
|-
|colspan=3|
|-
| ''Space Fights: Power Gets Up''
| ''{{w|Star Wars: The Force Awakens|Star Wars: The Force Awakens}}''
| From the title text. When you awake, you typically get up (from the bed). Force and power are similar in common vocabulary, but in Star Wars terminology, the Force is never referred to as just "power".
|-
| ''Space Fights: The Scary Ghost''
| ''{{w|Star Wars: The Phantom Menace|Star Wars: The Phantom Menace}}''
| From the title text. Ghost = Phantom. A menacing phantom would be quite scary.
|}

==Transcript==
:[Ten DVDs on a shelf. The first three stand together to the left, the two to the right leaning on the first. The next three are standing straight in the middle and then the next four are standing straight to the right. The movie titles are written on the back of the DVD cases, in white on the gray DVD cases. The text is written, so it is supposed to be read when the DVD is lying down.]
:Space Fights: Sudden Optimism
:Space Fights: The Government Wins This One
:Space Fights: The Sword Wizard Is Back

:The Jewelry God: The Jewelry Team
:The Jewelry God: Double Houses
:The Jewelry God: We Have a Czar Again

:Space Trip: The Movie
:Space Trip: That Guy is Angry
:Space Trip: Where is the Vulcan
:Space Trip: Let's Go Back

:[Caption below the frame:]
:'''Synonym Movies'''

{{comic discussion}}

[[Category:Star Wars]]
[[Category:LOTR]]

Talk:1270: Functional

2014-10-26T06:41:02Z

199.27.130.234:

Am i the only one considering this can be presented also in opposition to Object Oriented Programming, where tail recursion is very difficult to achieve at execution time, and impossible to achieve at compilation time, due to the possibility of method overloading?[[Special:Contributions/193.190.231.132|193.190.231.132]] 15:17, 30 September 2013 (UTC)
:Since tail recusion is special case of tail call you don't need to know where the last function called goes - you just replace call by jump - if you don't know where by indirect jump. AFAIK both clang and gcc are doing it and in FP this gives the 'continuation passing style' of programming. The problem with it is that you loose the stacktrace so usually it is done only for optimized builds. [[Special:Contributions/199.27.130.234|199.27.130.234]] 06:41, 26 October 2014 (UTC)

I'm getting the adblock message at the top.. on mobile. On an unrelated note, I laughed and I don't even get it. Edit: I'm also seeing an ad while seeing the message.[[Special:Contributions/50.159.5.112|50.159.5.112]] 06:03, 27 September 2013 (UTC)
:This shouldn't be in comic discussion. I have written an updated version of our ad plugin that should only display a message to people using adblock, but we're using a sitenotice for now to test the waters. We'll take it down in about a day, promise!
:Also, would you be complicit if I were to move this to the relevant forum? '''[[User:Davidy22|{{Color|#707|David}}y²²]]'''[[User talk:Davidy22|<tt>[talk]</tt>]] 06:13, 27 September 2013 (UTC)
I removed that misguided explanation about lists that was not tail recursive. I'm also wondering if we should also mention that tail call optimization is also applicable to mutually recursive functions. In fact proper functional languages will always apply it whether the functions are recursive or not. Maybe emphasize the fact that "The efficiency and elegance are the literal rewards of tail recursion."?

I feel like the examples should be in Haskall[sic], because that is the major functional language... [[Special:Contributions/67.160.98.42|67.160.98.42]] 09:48, 27 September 2013 (UTC) GBGamer117
:I think {{w|Haskell (programming language)|Hask'''e'''ll}} is more common, but I agree. And to emphasize the clarity, usually if/else blocks are avoided using pattern matching. I.e. tail-recursive factorial can be written as follows:
fac2::Integer->Integer-> Integer -- optional function header
fac2 acc 0 = acc
fac2 acc n = fac2 (acc*n) (n-1)

fac::Integer-> Integer
fac = fac2 1
:--[[User:Chtz|Chtz]] ([[User talk:Chtz|talk]]) 10:34, 27 September 2013 (UTC)
::Addendum: I did not dare to edit that yet, as I am unsure if this actually helps anyone not familiar with functional programming (and I don't think this page should include a Haskell crash course just to explain this comic). --[[User:Chtz|Chtz]] ([[User talk:Chtz|talk]]) 10:43, 27 September 2013 (UTC)
:::I think the pseudo-code examples currently in the explanation are easy enough to understand regardless of which programming languages one works in, but the [I'm assuming] Haskell example here in the comments makes no sense to me. Saibot84 12:51, 27 September 2013 (UTC)
::::Even though they are as clear and intuitive as abstract mathematics ... We could write it in a pseudo-functional language like this:
fac2(acc,0):=acc;
fac2(acc,n):=fac2(acc*n,n-1)
fac(n):= fac2(1,n)
::::The main point of the functional programming paradigm is not that all functions return values (as currently stated in the explanation) but that functions don't have side-effects and don't have an internal state (i.e. they can have parameters, but they don't have variables). This makes recursion the only way to implement things which are usually implemented using loops in procedural languages. Tail-recursion has the benefit that it can be optimized very easily. --[[User:Chtz|Chtz]] ([[User talk:Chtz|talk]]) 21:18, 28 September 2013 (UTC)

I thought about the text a little and don't the the interpretation "tail recursion is an end unto itself" is correct. I think what's going on is a pun of the word "reward". "Tail recursion is it's own reword" makes more sense since you are calling the same function but are "rewording" the arguements. To reword means to re-express something with different words. --[[Special:Contributions/24.187.72.209|24.187.72.209]] 11:31, 27 September 2013 (UTC)

Why would you start a wall of text with TL;DR? Doesn't that belong at the end, followed by a very short synopsis? [[User:Smperron|Smperron]] ([[User talk:Smperron|talk]]) 13:17, 27 September 2013 (UTC)

Oy, this explanation doesn't actually explain anything. To start with, it needs a definition of "functional programming". Also, a single example of recursion should be plenty: this isn't a programmer's textbook. I really, really don't understand the reward/reword "pun" (if it is such a thing); is the "reword" version really in current use in functional programming circles? If it is, you need to highlight the o vs. a difference (bold and underline) to make it pop out - it took me four readings to notice it. Unfortunately, I don't understand these topics enough to even begin to edit the explanation. (Smperron is right: TL;DR belongs at the end, not the beginning, and it really can't be followed by a wall of text like this.) [[Special:Contributions/108.36.128.166|108.36.128.166]] 14:52, 27 September 2013 (UTC)

"tail recursion is its own reword" - The only instance of this on Google is this page. Searching for tail recursion reword on Google also yields no results on the first page that agree with the proposed usage in functional programming circles. I think the pun explanation should be taken out, as it's clearly wrong. -- [[Special:Contributions/67.170.217.103|67.170.217.103]] 15:55, 27 September 2013 (UTC)

I wasn't happy with the pun line this morning, and worked out what was niggling me earlier this evening, so I changed it to point out that the 'tail call' of a 'tail recursive' function is the end for *all* the invocations. That seems punnier to me. [[User:SleekWeasel|SleekWeasel]] ([[User talk:SleekWeasel|talk]]) 22:17, 27 September 2013 (UTC)

So.... can someone explain why the recursion code examples are written in Python? [[User:Schiffy|Schiffy]] ([[User_talk:Schiffy|Speak to me]]|[[Special:Contributions/Schiffy|What I've done]]) 13:30, 28 September 2013 (UTC)
:Why not? While python [http://neopythonic.blogspot.ch/2009/04/tail-recursion-elimination.html doesn't eliminate tail recursions] (i.e., it lacks the optimization mentioned in the explanation) it is well suited to illustrate the idiom/pattern. Even though there's little reason to use the pattern in python, one can show how it'd look like.
:In my experience, simple python code can easily be read (often correctly!) by programmers not knowing that language, which cannot be said about many functional languages. Therefore I tend to say that "python is executable pseudo-code", which makes it perfect for explanatory examples. (Unlike actual pseudo-code, it has well-defined semantics, but like pseudo-code, it's mostly readable for programmers not knowing its exact syntax.) --[[User:Das-g|Das-g]] ([[User talk:Das-g|talk]]) 15:01, 28 September 2013 (UTC)
::I changed the functional examples to functional pseudo code. In imperative programming languages it rarely makes sense to write tail recursive functions using recursion instead of a loop. (Sure, there are cases, but factorial is not one of them) --[[User:Chtz|Chtz]] ([[User talk:Chtz|talk]]) 23:42, 28 September 2013 (UTC)

;Title text

The title-text explanation is not quite right in my opinion. The joke is that abstract mathematics is not intuitive or clear to *anyone*, including mathematicians. Functional programming borrows many concepts from higher-level mathematics, so understanding the concepts behind functional programming often requires an abstract mathematical mind.

In other words, the title-text explanation is wrong because it claims that a contrast is being drawn between mathematicians and non-mathematicians. This is not the case (at least by my interpretation).

[[Special:Contributions/27.32.32.199|27.32.32.199]] 12:01, 29 September 2013 (UTC)

:Being a mathematician, I can't agree. Even though I would consider myself more an applied mathematician, I find the basic concepts of abstract mathematics quite clear and intuitive (at least to a level which is required to understand functional programming). I do agree that there are many areas of abstract mathematics neither intuitive nor clear ''to me'', but I am quite sure for people working in these areas this is not the case. --[[User:Chtz|Chtz]] ([[User talk:Chtz|talk]]) 21:06, 29 September 2013 (UTC)

;sinus(X)?

In English math, it's sin(x) as an abbreviation for sine of x -- is sinus something specific to programming, or is it just a typo? {{unsigned ip|50.23.115.122}}
:I'm not native English, but sine or just sin in programming is correct. Thanks for your help.--[[User:Dgbrt|Dgbrt]] ([[User talk:Dgbrt|talk]]) 17:56, 29 September 2013 (UTC)
: I'm not sure if sine(x) is any good example at all. It is a function, but as I tried to explain below, that does not make it relate to functional programming. And I would say that sine(pi/2)=1 and sine(90) is approximately 0.894. --[[User:Chtz|Chtz]] ([[User talk:Chtz|talk]]) 20:23, 29 September 2013 (UTC)
::A standard calculator works in degrees and so sine(90°) is exactly 1, while when using {{w|Radian|radians}} sine(pi/2)=1 is correct. But this doesn't matter, it always describes how to invoke a function and get the result.--[[User:Dgbrt|Dgbrt]] ([[User talk:Dgbrt|talk]]) 10:38, 30 September 2013 (UTC)
:::However, I don't know any programming languages that use degree instead of radians by default. But that was indeed not my point: The point is that sine is an example of a ''function'' (independent of the programming paradigm used) and not a good example of '''{{w|functional programming}}'''. --[[User:Chtz|Chtz]] ([[User talk:Chtz|talk]]) 11:14, 30 September 2013 (UTC)

;There is a difference between functional programming and using functions in imperative programming

@Dgbrt: I'm not reverting your last rewriting, since I'm fearing it will lead to an edit war. I don't doubt that you are a real programmer, but I somehow doubt that you have experience with functional programming (like e.g. Haskell, Lisp, ...).
As I tried to explain, functions in functional programming don't have a state and therefore they don't have statements (especially no return statement). They simply describe functions in a mathematical sense, i.e. they have input parameters and result in a value. (They don't ''return'' that value, they just have that value).
The if-else construct I was using was supposed to describe a case distinction, similar as a mathematician would describe the abs function: <math> |x| = \begin{cases} x & x>0 \\ -x & \text{else}\end{cases}</math>.

Actually, a functional programmer would avoid such if-else constructs and write (for the non-tail-recursive variant)
factorial 0 = 1
factorial n = n * factorial (n-1)
And the interpreter/compiler will automatically find the most specialized case of the definition which can be matched to the input arguments: [http://ideone.com/1ZWZ9T]

Here is a demonstration how a valid Haskell program with tail-recursion and the if-else construct would look like: [http://ideone.com/VvqYSI] and this is how it (usually) would be written with pattern matching: [http://ideone.com/hj4VfO]
--[[User:Chtz|Chtz]] ([[User talk:Chtz|talk]]) 20:15, 29 September 2013 (UTC)
:You're right, I am a real programmer. And so I try to explain the "recursive" issue to NON specialists. We should EXPLAIN but not ENHANCE the comic. My two cents...--[[User:Dgbrt|Dgbrt]] ([[User talk:Dgbrt|talk]]) 20:34, 29 September 2013 (UTC)
::Ok, then the question remains if it is not more important to explain functional programming first? Currently, the second paragraph explains the difference between a function and a procedure in imperative programming and then mostly explains recursion for imperative programming (which I doubt will help understanding the comic -- how is it relevant if and where memory is allocated?). In the next paragraph I originally tried to describe how functional programming is different from imperative programming (after some editing there is not much left of it at the moment, it currently again describes more what imperative programming is). I assume there are more people who know recursion but have no idea of functional programming than the other way around. --[[User:Chtz|Chtz]] ([[User talk:Chtz|talk]]) 20:58, 29 September 2013 (UTC)

I'm not sure "which should not work because the return statement is missing" is relevent. In a given language, functions may only return values when a "return" is given (and ''immediately'' that one is given, ending all processing), otherwise giving "undefined", or "void" or the equivalent default state for an explicitly stated return-type. But in others they (in the absence of anything else, like an explicitly terminating "return" well within its own code) will use the bare evaluation of the very last statement within it as the return-value of that function/sub/procedure, if in tested at all by the calling-block (although it's prefereble to "return variable" at the end rather than just put "variable" as the last statement, for readability purposes, especially when it isn't "variable" but something that looks like (or is!) an evaulation/function call in its own right). The above being pseudocode (or "composite relatively common dialect code" not far off various common languages), surely the ''readability'' is the big concern, not the fact that (in certain languages, but not others) should not work. (Basically, have I just spent a paragaph saying "don't add that above statement, just put a 'return' into the pseudocode and everyone should be happy"? Yes. Yes, I believe I might have. Still.) [[Special:Contributions/178.98.253.80|178.98.253.80]] 15:35, 30 September 2013 (UTC)
:This [http://ideone.com/VvqYSI] is a valid functional definition of the factorial function. There are no ''statements'' in pure functional programming, especially no return statements. (There are ways to simulate them, but that's beyond this conversation). If everyone thinks that we shall just explain recursion and tail-recursion and avoid talking about functional programming, go ahead and revert it back to before my first attempt to describe functional programming. I agree that functional programming can be hard to get at first, especially to programmers used to imperative programming, but I do think it is worth to know about it. If it is just the brace-less syntax that is confusing, we can use this [http://ideone.com/NYKQeb] alternative (very uncommon in Haskell, but I agree that it's more important to make the code easy to understand). --[[User:Chtz|Chtz]] ([[User talk:Chtz|talk]]) 15:52, 30 September 2013 (UTC)
::Lest I have made myself unclear (and you're replying to me), I'm happy with the code as is. The 'statement' I mentioned, above, was regarding the added explanatory text (not yours) not any code-statement. The other pseudocodes had "return"s in them, however, so for an argument of readability it might be useful to make that "prod" "return prod", although I (especially as a bit of a Perl fanatic) don't mind either way. I can deal with braces substituted by idents, in pseudocode, much as I can read either XML or YAML encoded data, fairly easily. ;) However, we've got quite a technical discussion going which (unlike code, even deliberately obfuscated Perl!) is not so easily untangled into who is replying to which bit and what they are trying to say (and why). Maybe we should switch to Lojban! [[Special:Contributions/178.98.253.80|178.98.253.80]] 20:48, 30 September 2013 (UTC)
:::There is no agreement yet, if and when we should introduce/''explain'' the concept of functional programming. At the moment the transition is very abrupt, partly because someone changed my first functional example to imperative code. The tail recursive example is at this very moment exactly the same as [http://ideone.com/OrCUMp this valid functional code (written in Haskell)]. --[[User:Chtz|Chtz]] ([[User talk:Chtz|talk]]) 21:07, 30 September 2013 (UTC)
::::I agree, this is still chaos! Please explain "An imperative, recursive (but not tail-recursive) implementation can look like this:", I disagree and there is still no prove helping me or other people to understand. And beside: My first recursive program was to solve a one player game, written in {{w|Turbo Pascal}} in the middle of the eighties of the last century. And it was ''fast'' even at that time. --[[User:Dgbrt|Dgbrt]] ([[User talk:Dgbrt|talk]]) 21:47, 30 September 2013 (UTC)
:::::I guess you mostly disagree on the non tail-recursiveness? Basically, this can be seen as the recursion can't be replaced by a simple replacement of the return statement with another function call, because after the call another operation (the multiplication by n) needs to be performed before the value can be returned. My original attempt on this article was to switch to functional programming at this point, since it does not make much sense to implement such a simple function recursively in an imperative language (admittedly, the transition to functional programming was way to abrupt). When implementing a function which searches inside a tree it often/usually makes sense to implement it recursively even in imperative languages and with some tricks you can also make this comparatively fast (I assume that was the point of your last two sentences?). To come back to 178.98... My intention was to structure the explanation approximately as follows:
:::::1) Describe the difference between functional and imperative programming (assuming that most readers know what imperative programming is -- if we can't assume that, where shall we start?)
:::::2) Give an example of a simple imperative function (e.g. the factorial function) written with typical imperative constructs (loops, assignments)
:::::3) As this is not possible in functional programming introduce the concept of recursion and define the function recursively (this step was clearly to fast)
:::::4) Explain the benefit of tail-recursion and give an tail-recursive example of factorial (also in functional programming)
:::::5) '''Explain the actual joke!'''
:::::6) Explain remaining parts (title text, ...) --[[User:Chtz|Chtz]] ([[User talk:Chtz|talk]]) 22:41, 30 September 2013 (UTC)
::::::On your fourth point, the functional programming example is confusing, and strange. Why are you defining two seperate functions, when a single function would do? For example, an easy way to show this is:
factorial[0] = 1
factorial[n] = n * factorial(n - 1)
::::::which, though not valid computer code, is valid mathematical syntax, and shows perfectly what a factorial function, in functional programming, does. The explanation would then be:
factorial[6] = 6 * factorial[6-1] = 6 * 120 = 720
factorial[5] = 5 * factorial[5-1] = 5 * 24 = 120
factorial[4] = 4 * factorial[4-1] = 4 * 6 = 24
factorial[3] = 3 * factorial[3-1] = 3 * 2 = 6
factorial[2] = 2 * factorial[2-1] = 2 * 1 = 2
factorial[1] = 1 * factorial[1-1] = 1 * 1 = 1
factorial[0] = 1
::::::or something similar to that. [[User:GBGamer117|GBGamer117]] ([[User talk:GBGamer117|talk]]) 05:07, 2 October 2013 (UTC)
:::::::I would be totally fine (and originally intended) to have this definition at step 3). If you replace your [ ] brackets by ( ) parentheses, or leave them, [http://ideone.com/1ZWZ9T it is actually valid Haskell code] (and as you point out, [clear and intuitive as] ''valid mathematical syntax''). The evaluation, however would rather go like:
factorial(4) = 4 * factorial(3)
= 4 * ( 3 * factorial (2) )
= 4 * ( 3 * ( 2 * factorial (1) ) )
= 4 * ( 3 * ( 2 * ( 1 * factorial (0) ) ) )
= 4 * ( 3 * ( 2 * ( 1 * 1 ) ) )
= 4 * ( 3 * ( 2 * 1 ) ) = 4 * ( 3 * 2 ) = 4 * 6 = 24
:::::::That would actually give a nice example, why this recursion is less efficient than actual tail recursion: During evaluation, you need to build up an entire expression tree which you don't have to do for the tail-recursive way (it does not really matter for this simple function, though).
factorial(4) = factorial_helper(4, 1) = factorial_helper(3, 4) = factorial_helper(2, 12) = factorial_helper(1, 24) = factorial_helper(0, 24) = 24
:::::::The number of numerical operations is actually the same (I omitted the steps of evaluating the products and differences), but you don't have to build up a large expression, before you can actually start multiplying. --[[User:Chtz|Chtz]] ([[User talk:Chtz|talk]]) 07:51, 2 October 2013 (UTC)

;Tail Recursion?

Are we really certain "tail recursion" isn't also an innuendo for ongoing sexual relations? Tail is sometimes used as slang, and if it were received regularly, it would be tail recursion.{{unsigned ip|69.67.112.5}}

;Explain the concept, not the history?

I think that this page would benefit from simplifying the beginning to explain the concept without providing all of the background. Background can be applied later. I would suggest this:

:Recursion is a common programming practice where a function calls itself. This can result in many layers of the function, all of which need to be kept track of until the program can get to the bottom layer. The last step of this process is to return the final value through all of the layers of function calls.

:If there is nothing left for a function to do when the lower level returns, then there is no longer a need to keep track of the state of that layer. Instead of creating a new layer, a compiler that is smart enough can overwrite the existing layer with the new layer. This means that the new layer will pass its results directly to whatever initially called the function and not have to waste time passing the results up the stack of function calls. Making use of this optimization is called ''tail recursion'', and it saves both time and memory requirements.

:Functional programming is a programming language style that appeals to people who spend a lot of time staring at the notation used to describe higher math. This notation commonly uses recursion and formulas that include entire other formulas as variables in a higher level formula. Tail recursion was first introduced as a more efficient manner of handling recursion within functional programming languages, and they are currently the only programming languages that support this optimization.

[[User:Mythobeast|Mythobeast]] ([[User talk:Mythobeast|talk]]) 21:07, 3 March 2014 (UTC)

:Frankly, I don't think the point here is about what concept it is. Tail recursion is just one of the many peculiar aspects of functional programming that, frankly, does not make that much different in the long run. (Frankly, a loop is about 20 times easier than tail recursion in about 90% of the cases; same for passing functions around). However, those things are rewarding to play with in and of themselves (and who care about the long run anyway? In the long term, we are all dead). At least that how I think of this slide. [[User:magice|magice]] ([[User talk:magice|talk]])

Maybe the long explanation should be a trivia item?[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 21:59, 21 June 2014 (UTC)