https://www.explainxkcd.com/wiki/api.php?action=feedcontributions&feedformat=atom&user=Logicalexplain xkcd - User contributions [en]2026-05-23T23:12:48ZUser contributionsMediaWiki 1.30.0https://www.explainxkcd.com/wiki/index.php?title=2453:_Excel_Lambda&diff=2107412453: Excel Lambda2021-04-22T09:41:36Z<p>Logical: /* Explanation */</p>
<hr />
<div>{{comic<br />
| number = 2453<br />
| date = April 21, 2021<br />
| title = Excel Lambda<br />
| image = excel_lambda.png<br />
| titletext = Extremely rude how Turing's later formulations of the halting problem called me out by name specifically.<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by a SPREADSHEET. Please mention here why this explanation isn't complete. Do NOT delete this tag too soon.}}<br />
<br />
Cueball is computing and Ponytail has opinions.<br />
<br />
A classical {{w|Turing machine}} uses an infinitely long strip of tape as its memory. The large column acts as the "tape".<br />
<br />
The {{w|Church-Turing_thesis|Church-Turing thesis}} is a hypothesis says that a function can be computed by executing a series of instructions if and only if that function is computable by a Turing Machine. All ways of computing are therefor "equally wrong" since, according to this thesis, they can all be translated to a Turing Machine.<br />
<br />
The {{w|Halting problem|halting problem}} is the problem of determining whether a given Turing Machine will halt. The problem has been shown to be undecidable, i.e., there exists no algorithm that computes whether an arbitrary Turing machine will halt or not.<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
:[In a narrow panel, Ponytail is walking in from the left, looking down at her phone]<br />
:Ponytail: Oh cool, Excel is adding a lambda function, so you can recursively define functions.<br />
<br />
:[Ponytail, holding her phone to her side, talks to Cueball, who is working on a laptop. He has turned around to face her.]<br />
:Cueball: Seems unnecessary.<br />
:Cueball: When I need to do arbitrary computation, I just add a giant block of columns to the side of my sheet and have a Turing machine traverse down it.<br />
<br />
:[Ponytail still talking to Cueball, who has resumed working on his laptop.]<br />
:Ponytail: I think you're doing computing wrong.<br />
:Cueball: The Church-Turing thesis says that all ways of computing are ''equally'' wrong.<br />
<br />
:[Ponytail talking to Cueball, who has his finger raised in the air. Cueball's head has a visible sketch layer which has not been erased.]<br />
:Ponytail: I think if Turing saw ''your'' spreadsheets, he'd change his mind.<br />
:Cueball: He can ask me to stop making them, but not prove whether I will!<br />
<br />
{{comic discussion}}<br />
[[Category:Spreadsheets]]<br />
[[Category:Programming]]<br />
[[Category:Comics featuring Cueball]]<br />
[[Category:Comics featuring Ponytail]]<br />
[[Category:Comics featuring real people]]</div>Logicalhttps://www.explainxkcd.com/wiki/index.php?title=2453:_Excel_Lambda&diff=2107402453: Excel Lambda2021-04-22T09:34:35Z<p>Logical: /* Explanation */</p>
<hr />
<div>{{comic<br />
| number = 2453<br />
| date = April 21, 2021<br />
| title = Excel Lambda<br />
| image = excel_lambda.png<br />
| titletext = Extremely rude how Turing's later formulations of the halting problem called me out by name specifically.<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|Created by a SPREADSHEET. Please mention here why this explanation isn't complete. Do NOT delete this tag too soon.}}<br />
<br />
Cueball is computing and Ponytail has opinions.<br />
<br />
A classical {{w|Turing machine}} uses an infinitely long strip of tape as its memory. The large column acts as the "tape".<br />
<br />
The {{w|Church-Turing_thesis|Church-Turing thesis}} is a hypothesis says that a function can be computed by executing a series of instructions if and only if that function is computable by a Turing Machine. All ways of computing are therefor "equally wrong" since, according to this thesis, they can all be translated to a Turing Machine.<br />
<br />
The {{w|Halting problem|halting problem}} is the problem of determining whether a given Turing Machine will halt. The problem has been shown to be uncomputable, i.e., there exists no algorithm that computes whether a Turing machines will halt or not.<br />
<br />
==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
:[In a narrow panel, Ponytail is walking in from the left, looking down at her phone]<br />
:Ponytail: Oh cool, Excel is adding a lambda function, so you can recursively define functions.<br />
<br />
:[Ponytail, holding her phone to her side, talks to Cueball, who is working on a laptop. He has turned around to face her.]<br />
:Cueball: Seems unnecessary.<br />
:Cueball: When I need to do arbitrary computation, I just add a giant block of columns to the side of my sheet and have a Turing machine traverse down it.<br />
<br />
:[Ponytail still talking to Cueball, who has resumed working on his laptop.]<br />
:Ponytail: I think you're doing computing wrong.<br />
:Cueball: The Church-Turing thesis says that all ways of computing are ''equally'' wrong.<br />
<br />
:[Ponytail talking to Cueball, who has his finger raised in the air. Cueball's head has a visible sketch layer which has not been erased.]<br />
:Ponytail: I think if Turing saw ''your'' spreadsheets, he'd change his mind.<br />
:Cueball: He can ask me to stop making them, but not prove whether I will!<br />
<br />
{{comic discussion}}<br />
[[Category:Spreadsheets]]<br />
[[Category:Programming]]<br />
[[Category:Comics featuring Cueball]]<br />
[[Category:Comics featuring Ponytail]]<br />
[[Category:Comics featuring real people]]</div>Logical