explain xkcd - User contributions [en]

2642: Meta-Alternating Current

2024-02-02T16:49:47Z

Wibeasley: apostrophe for possession

{{comic
| number = 2642
| date = July 6, 2022
| title = Meta-Alternating Current
| image = meta_alternating_current.png
| titletext = It's always bothered me that you can't cancel out an inverter by putting a second inverter after it.
}}

==Explanation==
This is the sixth installment in the series of [[:Category:Cursed Connectors|Cursed Connectors]] and presents Cursed Connectors #120: Meta-alternating current extension cord.

{{w|Direct current}} is a unidirectional flow of electrons from a power source to something being powered, through one or more conductors, before returning to the power source via one or more other conductors, thus completing the circuit. Batteries produce direct current. It is commonly used in electronics applications, including computers. {{w|Alternating current}}, on the other hand, frequently reverses the direction of electron flow, and is commonly used for longer-distance transmission (such as from the power plant to an outlet).

This comic proposes a humorous ''Meta-Alternating Current'', which uses a series of adapters to "alternate" between DC and AC current along the length of a connector. This is absurd in part because typical {{w|power inverter}} efficiency is 90%, and maximum {{w|bridge rectifier}} efficiency is about 99% for 120 V,{{actual citation needed}} so an {{w|extension cord}} made in this manner would lose about 11% power (compounded) per such pair.

The title text bemoans that an inverter, which converts direct current to alternating current, does not work in the other direction, as a layman's interpretation of the word "inverter" might assume. Rather, a separate device, a {{w|rectifier}}, also pictured in the comic, must be used for this second conversion. (However, a similar circuit to an inverter may be used to rectify in a process called {{w|active rectification}}.)

==Transcript==
:[Above the drawing there is a header. Below the header is a chain of rectifiers and inverters. There are seven pairs of rectifiers (the smaller ones) and inverters (the big chunky ones). The first five inverters have arrows pointing to them from a label above the chain, whereas the last five rectifiers are labeled below the chain, but also with arrows pointing to them from that label. The chain starts on the left with a mains plug (type B), followed by the first rectifier. It ends with the last inverter, and a female mains plug (type B socket) to the right. Beneath the chain there is label for the connector and an explanation in brackets below that.]
:Cursed Connectors #120
:Inverters
:Rectifiers
:Meta-alternating current extension cord
:(alternates between AC and DC)

==Trivia==
*This comic replaced [[No One Was Hurt]] as comic 2642 after it was taken down from [[xkcd]]'s website.
**See why on that comic's explanation.
*This comic initially did not have a high-resolution (2x) image for high-DPI displays, making it look more blurry than usual on such devices (such as smartphones). This was probably because it was uploaded hastily to replace No One Was Hurt quickly. It has since been updated to include a high-resolution version.

{{comic discussion}}

[[Category:Cursed Connectors]]

2118: Normal Distribution

2019-03-02T19:05:01Z

Wibeasley: soften "form" to "resemble"

{{comic
| number = 2118
| date = March 1, 2019
| title = Normal Distribution
| image = normal_distribution.png
| titletext = It's the NORMAL distribution, not the TANGENT distribution.
}}

==Explanation==
{{incomplete|Created by PEOPLE NEW ENOUGH TO STATISTICS TO NOT LEAVE IN ANNOYANCE. Please mention here why this explanation isn't complete. Do NOT delete this tag too soon.}}
[[File:Empirical_Rule.PNG|thumb|{{w|Normal distribution}}s and the intervals of the standard deviation are a topic commonly seen in introductory statistics. Randall's chart is similar, but his lines are perpendicular.]]
In statistics, a {{w|Probability distribution|distribution}} is a representation that can be understood in terms of how much of a sample is expected to fall into either discrete bins or between particular ranges of values. For example, if you wanted to represent an age distribution using bins of ten years (0-9, 10-19, etc.), you could produce a bar chart, one bar for each bin, where the height of each bar represents a count of the portion of the sample matching that bin. To turn that bar chart into a distribution, you'd get an infinite number of people, put them into age bins that are infinitely narrow, and then divide each bin count by the total count so that the whole thing added up to 1. It is common to ask how much of the distribution lies between two vertical lines; that would correspond to asking what percent of people are expected to fall between two ages.

Many statistical samplings resemble a pattern called a "{{w|normal distribution}}". A theoretically perfect normal distribution would have an infinite sample size and infinitely small bins. That would produce a bar chart matching the shape of the curve in the comic.

The area between two vertical lines of the distribution represents the probability that the value is between the x-values of the lines, and the total area is 1. Randall finds the area between two ''horizontal'' lines instead, which is mathematically completely meaningless, because the y-axis of a probability distribution represents {{w|absolute magnitude|magnitude}} as a fraction of unity. The items represented by the magnitude at any given horizontal position are indistinguishable, unordered, and interchangeable; the idea that one could be above another is meaningless, and the fact that two items happen to fall at the same position on the y-axis doesn't mean they have anything in common. So, the comic explores the humor of annoying people by deliberately misunderstanding their work.

The title text refers to the {{w|Normal (geometry)|normal line}}, which is perpendicular to the {{w|tangent}} line at a given point. Given a shape of interest, a normal line points perpendicularly away from it at a point, making a 90-degree angle with it in all directions, while a tangent line crosses a point on it and is exactly parallel to it at that point. The normal line is not at all related to the normal distribution, as the former is a geometry concept and the latter is probability/statistics one. Saying this to a statistician would only annoy the statistician further. This refers to the fact that the diagram attempts to divide the graph with horizontal lines when such a division would usually be done with perpendicular vertical lines.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}

:[A bell curve of a normal distribution, with the area between two horizontal lines shaded.]

:[The center of the chart is marked between the two lines:]
:Midpoint

:[The distance between the lines is marked to the right of the midpoint, with the label:]
:52.7%

:[A label on the outside of the graph, describing the distance between the two lines:]
:"Remember, 50% of the distribution falls between these two lines!"

:[Caption below the panel:]
:How to annoy a statistician

{{comic discussion}}
[[Category:Charts]]
[[Category:Statistics]]

1987: Python Environment

2018-05-23T22:16:30Z

Wibeasley: A little more descriptive of problems caused by a poorly managed build environment.

{{comic
| number = 1987
| date = April 30, 2018
| title = Python Environment
| image = python_environment.png
| titletext = The Python environmental protection agency wants to seal it in a cement chamber, with pictoral messages to future civilizations warning them about the danger of using sudo to install random Python packages.
}}

==Explanation==

A development environment is the collection of tools used to create a computer program. It generally includes an {{w|Interpreter_(programming)|interpreter}}, a {{w|package manager}}, and various {{w|Library_(computing)|libraries}} that the project needs. Computer programs often depend on a specific version of these tools, such as a program that only runs on Python 2.7. A badly configured build environment can lead to mysterious errors as the program looks for libraries or features that aren't there, making it hard to develop stable and portable software.

{{w|Python_(programming_language)|Python}} is a {{w|computer}} {{w|programming language}} which has been around for quite a while, especially on {{w|Linux}} platforms. [[Randall]] has likely used it on his computer for quite a few years, from the early years where it wasn't so easy to install, through newer versions where there is a more defined way to install it. Because standards change over time (in particular, although the newest version of Python is Python 3.x, many people prefer Python 2.x and it's still widely used for backwards-compatibility), and he didn't completely uninstall old versions before installing new versions (likely to not break what was already working), he's ended up with a mess where different pieces and versions of Python and its related components litter his {{w|hard drive}}'s {{w|directory structure}}.

{{w|Superfund}} is a US federal government program created for cleaning up contaminated land. The comic is saying that his computer's Python environment is so messed up that it's comparable to a real-world environmental disaster.

The title text may refer to the philosophical debate surrounding the construction of warning features around the [[wikipedia:Waste_Isolation_Pilot_Plant#Warning_messages_for_future_humans|WIPP]] site in New Mexico, and other nuclear waste disposal sites. In particular, it may refer to [https://web.archive.org/web/20090320054657/http://www.wipp.energy.gov/picsprog/articles/wipp%20exhibit%20message%20to%2012,000%20a_d.htm this article]. These would have to last and be understandable for tens of thousands of years, longer than any known human-made structure or language to date.

{| class="wikitable"
! Text
! Explanation
|-
| $PATH
| $PATH refers to the {{w|PATH (variable)|PATH}} environment variable, which determines where to search for executable files. In this case, it indicates that the pip, Homebrew Python (2.7), and OSX's pre-installed Python are accessible on path, with ~/newenv/ and a mysterious ???? as part of PATH.
|-
| pip
| {{w|pip (package manager)|pip}} is the Python {{w|package management system}}, and is used to install and manage python packages. As it is written in Python, it requires Python to run. It leads to easy_install, Homebrew Python (2.7), "(misc folders owned by root)", and ????.
|-
| Homebrew Python (2.7)
| {{w|Homebrew (package management software)|Homebrew}} is the de facto standard third-party OSX package manager. Homebrew Python (2.7) is the Python 2 version installed through Homebrew. This leads to Python.org binary (2.6) and /usr/local/Cellar.
|-
| OS Python
| Apple bundles an (out of date) version of Python with OSX. This only leads to ????.
|-
| ????
|
|-
| easy_install
| easy_install, much like pip, is a cpan-like tool to download and install Python packages. As of the creation of the comic, many people discourage its use. (e.g., [https://stackoverflow.com/questions/3220404/why-use-pip-over-easy-install this question on stack exchange.]
|-
| Anaconda Python
| {{w|Anaconda (Python distribution)|Anaconda}} is a Python distribution for data science and machine learning related applications.
|-
| Homebrew Python (3.6)
| As of the creation of the comic, Python 3.6 is the current stable version of Python.
|-
| Python.org binary (2.6)
|
|-
| (Misc folders owned by root)
|
|-
| /usr/local/Cellar
|
|-
| <code>/usr/local/opt</code>
| Both <code>/usr/local</code> and <code>/opt</code> are directories that store files that do not belong to a Unix-like operating system. Usually, files in <code>/usr/local</code> were created with a {{w|make (software)|make command}}, and files in <code>/opt</code> are unbundled packages. The joke is that <code>/usr/local/opt</code> should really, really not exist.
|-
| /(A bunch of items with "Frameworks" in them somewhere)/
|
|-
| $PYTHONPATH
|
|-
| Another pip??
| There should only be one PIP (package management system) in place. More that one would lead to them contradicting each other. Randall is confused as to how the second one got there.
|-
| ~/python/
|
|-
| ~/newenv/
| Probably a virtualenv. Virtualenvs are mechanisms for having Python environments that don't conflict with the system Python. They include the Python interpreter, independent library paths, and usually a copy of pip. The user typically installs packages using the virtualenv's pip such that they can only be accessed by the virtualenv's Python instances, while more common packages are still referenced via the system Python paths.
|-
| /usr/local/lib/python3.6
|
|-
| /usr/local/lib/python2.7
|
|}

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:[A single frame depicting a flowchart is shown. Many chaotic arrows are arranged between the items which are:]
:$PYTHONPATH
:EASY_INSTALL
:ANACONDA PYTHON
:HOMEBREW PYTHON (3.6)
:ANOTHER PIP??
:HOMEBREW PYTHON (2.7)
:PYTHON.ORG BINARY (2.6)
:PIP
:EASY_INSTALL
:$PATH
:(MISC FOLDERS OWNED BY ROOT)
:????

:[The endpoints are:]
:/usr/local/Cellar
:/usr/local/opt
:/(A BUNCH OF PATHS WITH "FRAMEWORKS" IN THEM SOMEWHERE)/
:~/python/
:~/newenv/
:/usr/local/lib/python3.6
:/usr/local/lib/python2.7

:[Caption below the panel:]
:My Python environment has become so degraded that my laptop has been declared a superfund site.

{{comic discussion}}

[[Category:Computers]]
[[Category:Programming]]
[[Category:Flowcharts]]

1673: Timeline of Bicycle Design

2016-04-27T12:20:59Z

Wibeasley: Fix external Velocipedia link

{{comic
| number = 1673
| date = 27 April, 2016
| title = Timeline of Bicycle Design
| image = timeline of bicycle design.png
| titletext = I'll be honest--the 1950s were a rough time for cycling.
}}

==Explanation==
Randall created a 200 year history for bicycles as created by Gianluca Gimini in his project [https://www.behance.net/gallery/35437979/Velocipedia Velocipedia]. Gimini asked people to draw free hand sketches of bicycles and rendered the results as real bikes.

The 1925 model is reminiscent of a {{w|fractal}}; {{w|Benoit Mandelbrot}} was born just before this date, in late 1924.

This comic is possibly also a reference to "The Science of Cycology", a cognitive psychology project run by Rebecca Lawson at the University of Liverpool that asked study participants to draw a bicycle from memory. The error rate was high, supporting a hypothesis that humans over-estimate their ability to explain how things work. https://www.liverpool.ac.uk/~rlawson/cycleweb.html

Alternatively, the comic could be an analogue to the process of meiosis and pregnancy. If each wheel of the bicycle represents a cell, than the bikes going from 1 wheel to two wheels to four would represent the zygote dividing twice into four haploid gametes. Once the gametes have been formed, they must interact with another human, here represented by the wheels chasing after a man. Then, the bicycle is ridden by a female for an amount of time, representing the process of pregnancy. Finally, after the process of pregnancy is complete, the bike/child grows up into a unique individual unlike any other bicycle in existence today. Another thing to note about this explanation is that the bicycles ridden by men are much easier to get moving, as spermatozoa are much more mobile than the female ovum.

==Transcript==
{{incomplete transcript}}

{{comic discussion}}

1661: Podium

2016-03-29T23:31:58Z

Wibeasley: Possessive

{{comic
| number = 1661
| date = March 28, 2016
| title = Podium
| image = podium.png
| titletext = BREAKING: Senator's bold pro-podium stand leads to primary challenge from prescriptivist base.
}}

==Explanation==
{{incomplete|More on the info in the title text and links to dictionaries should be real links.}}

A "{{w|podium}}" in most of the world is a small platform like the one on which [[Cueball]] stand in the comic. This word originates from Greek ''podion'' meaning ''foot''.

A "{{w|lectern}}" in all English speaking countries is a stand for holding notes, like the one Cueball stand behind in the comic. In American English this stand may be also called a ''podium'', which is not backed up by etymology. (See [http://www.oxfordlearnersdictionaries.com/definition/english/podium podium] and [http://www.oxfordlearnersdictionaries.com/definition/english/lectern lectern] in Oxford Learners Dictionaries).

The comic is playing on a stereotypical politician, without any real beliefs, here represented by Cueball, but they want to appear to stand for something. Alternatively, this is what might happen if someone like Cueball (or the strip's author [[Randall]]), who tend to think literally and who get interested in and distracted by tangents, were running.

Thus, Cueball picks up what is, in some American circles, an argument: whether the standing desk used by public speakers should be called a "podium" or a "lectern." This argument is actually [http://www.messagemasters.squarespace.com/articles/what-is-a-lectern-or-podium.html common] among [http://mannerofspeaking.org/2012/03/10/podium-vs-lectern/ members] of {{w|Toastmasters International}} (see more [http://joyfulpublicspeaking.blogspot.com/2012/03/what-should-we-call-stage-furniture-on.html here]), though it would usually not rise to the level of needing to be part of a national discourse. And it is not only the Toastmasters that [http://www.platformgiant.com/podium-vs-lectern care about this].

The fact is, though the etymological definition is clear - the lectern is the desk that stands on the podium - and the difference might be important if you were setting up an auditorium, in common American usage it really doesn't matter.

The title text is presented as a breaking news that implies that a senator has taken a bold stand on the subject of podium vs. lectern (This senator could be Cueball, but it could also be another who has been rallied by Cueball's speech). The senator is pro- podium, meaning that he thinks the lectern should be called a podium. This leads to the people who follow a prescriptivist position to organize and put forward a political candidate to challenge this senator in the {{w|primaries}}.

The {{w|Linguistic prescription|prescriptivist}} position relies on rules rather than on usage. In this case a prescriptivist relies on etymology and would thus be pro-lectern. In the U.S., the primaries are used to select a single candidate from a particular party to represent that party at final election (whether national or on a state level). At the time of this comics release (2016-03-28) the {{w|United States presidential primary}} elections to determine the candidates for the {{w|United States presidential election, 2016}} was in full progress and not at all determined yet.

The title text is also a pun, as 'stand' is another word for an object like a lectern (e.g. as used by musicians to hold sheet music), and 'base' a word for something a stand or lectern might be placed on, as is a podium.

It is unclear from this comic which position Randall favors. He likes that rules are followed, but he also like that it is easy to talk with people, especially friends. This was recently displayed in [[1643: Degrees]], see especially the last "benefits" in the third panel.

==Transcript==
:[Cueball is speaking at a lectern standing on a podium.]
:Cueball: The American people are tired of politics as usual.
:Cueball: They're tired of-
:Cueball: Okay, brief tangent: is this thing a podium or a lectern? People say "podium" is wrong, but I also see it used that way in pretty formal contexts. Is usage just changing?
:Cueball: If elected, I will get to the bottom of this for once and for all.

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Public speaking]]
[[Category:Politics]]
[[Category:Language]]

1597: Git

2015-10-30T14:43:11Z

Wibeasley: changed "users' version" to "users' versions"

{{comic
| number = 1597
| date = October 30, 2015
| title = Git
| image = git.png
| titletext = If that doesn't fix it, git.txt contains the phone number of a friend of mine who understands git. Just wait through a few minutes of 'It's really pretty simple, just think of branches as...' and eventually you'll learn the commands that will fix everything.
}}

==Explanation==
{{incomplete|Title text - with he name of the friend not explained yet.}}

{{w|Git (software)|Git}} is a {{w|Version control|version control}} system often used to track changes to (usually) plain text files, such as computer code. Within a folder and its subfolders, the user can tell Git which files to keep track of changes for. All the files that are being tracked in this manner make up a repository. Internally, Git works by saving the differences between various versions of the files, rather than creating a new copy each time the user "commits" the current version of the code. This approach allows the user to switch between various versions of the code fairly quickly. However, this can be confusing for new users because when changing between versions, Git effectively rewrites the files under its control to match that version - one file may have several different versions depending on which state Git has set it to, but only one of these versions is visible at any given moment. The others are not hidden or moved, they do not exist until Git modifies the file to match that version.

In addition to allowing the user to track changes to the files over time using "commits" (versions of the files stored by the user), Git also allows the user to develop several versions of the files in parallel using "branches" (mentioned in the title text). This allows a programmer to, for example, keep a stable, functioning version of their code in one branch, while developing a new feature in a separate branch. When the new feature is ready, Git provides tools to efficiently "merge" the changes from the development branch back into the main branch. While powerful, there are also several pitfalls which can confuse users. For example, a file may have only been committed in one branch (so it is only visible in that branch), causing a user who has switched to a different branch to think that file was lost somehow.

Sharing a Git repository with other users is done through a remote repository, such as [https://github.com/ GitHub], [https://about.gitlab.com/ GitLab], or one set up by the user themselves. This remote repositories act as a central location through which collaborates share their work. Changes do not automatically propagate between users; instead, once someone has changes they are ready to share, they must upload ("push" in Git terminology) their changes to the remote repository. Other users can then download ("pull") those changes. This allows each user complete control over when changes are applied to their version of the files. Once one user has pushed his or her changes, all other users will need to merge those changes into their code before they can push. Depending on how much the changes conflict, Git may be able to automatically combine both users' versions, or the user may need to do so manually.

In programming, Git is a very popular way to share source code of programs between computers and users and thus work on projects collaboratively.

However, problems often arise when, for example, one attempts to upload code to a file someone else has already edited.
Git has quite a few tricks to handle "merging" itself.

One way of simplifying collaboration is to work in a "branch", the same files that everyone has, but your changes do not become visible to other users yet. Only when you merge (there we go again) your branch with the master branch, other users will see your "commits".

But, due to the complex nature of Git (and its notoriously counter-intuitively named commands), a large portion of users are unable to use it beyond basic commands. They consider it usually much more efficient just to save the code to a different file, download a newer copy, and then re-apply their original changes to the new copy than to try and understand and use Git's own convoluted built-in commands to attempt to fix it properly.

Git was originally created by {{w|Linus Torvalds}}, the same person who originally created {{w|Linux}}.

==Transcript==
:[Cueball points to a computer on a desk while Ponytail and Hairy are standing further away behind an office chair.]
:Cueball: This is Git. It tracks collaborative work on projects through a beautiful distributed graph theory tree model.
:Ponytail: Cool. How do we use it?
:Cueball: No idea. Just memorize these shell commands and type them to sync up. If you get errors, save your work elsewhere, delete the project, and download a fresh copy.

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring Hairy]]
[[Category:Programming]]
[[Category:Computers]]
[[Category:Internet]]