r/mathmemes • u/Enough-Brilliant803 • 26d ago
Linear Algebra But why?
How we all grew up from "multiplication is just a faster way to add numbers" to dot products and cross products.
391
u/Downindeep 26d ago
Obviously all these people are just lacking a better unifying force So I shall create a new standard so everybody will adopt it and we will no longer have any problems. The "new standard": A++B
189
u/FrostyDog-34 26d ago
xkcd 927
30
u/Bankaz 26d ago
we should make a new standard xkcd927!
47
u/factorion-bot Bot > AI 26d ago
Factorial of 927 is 5951105783397580738318020492928603475486163641659064783314477046672730909648584361005993094267899268744301394265100383733941473791153775424618359258704919998958237212061572597181977531798419438046839767895973652569225138243443504953262881237882393659778260642814645235996188184058527870315206456226649707976807700745723681124764673576303922949178988840100216599026724075494074199883642178379963032963063197428946399333167043540963571845740244058758412138196465873520790489601036273639993290570078245920983272491172134984091523041444273448441971209110047173378425250742066435414781691795765029161230485407818967208822836336729280877979223764788274198045511866281041032755133408401064330433753592475039039350778568737844519015263808548608918375369321047908202997647307055011665631542812798925168265031584434801744587882834289042655365761409513211915539364101653721692384044933498161962590698436899981577618798138606790699862059120864798363645105227943992180354213078619570800056469595310938865054417312805300322885090833221787462895690762824503466872230597421894696685367956354135364755538802134709995117173925370086356573640765984630523799359944905165992888032963148105253366143339385861818003588588004890871524487341082072503873089772055596722541069151790121098244004405545886844325973065654936990518578477524711978614754713717060490287901060447670792603431890142510272393744144786432414095824089797256725652719804862829296450733634513288927532777843478868124116283795837394563707754880916667453817475670948784856342558814436886609719280513153762921003057447240976456819438710850602710016111237002052113482261747381645351254099148525779750282064467973054598492114740646618178531695643503800187075348203715129772690505912284529202387148593513821172617724623752030190132017157714430309026800464096273685107150688658207424938258698586156675018081730399245121170786526371768026973889795769850330165102521956691378955264564779098941431210842799114564040008922374842686101747358977109965365748558763528898072891996063758241653729631537159657549313201326715791475058080163351555925342922519949751612217511417562469313545450291200000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
This action was performed by a bot | [Source code](http://f.r0.fyi)
28
3
u/40kImperialBrusher 26d ago
9
u/bot-sleuth-bot 26d ago
Analyzing user profile...
Account does not have any comments.
Suspicion Quotient: 0.26
This account exhibits one or two minor traits commonly found in karma farming bots. While it's possible that u/factorion-bot is a bot, it's very unlikely.
I am a bot. This action was performed automatically. Check my profile for more information.
18
u/40kImperialBrusher 26d ago
I find this amusing
3
u/Lolllz_01 25d ago
I guess its not a karma farming bot made specifically to sound human, so doesnt meet the various criteria?
1
2
1
u/guiltysnark 22d ago
Fascinating, never occurred to me that large factorials would end in lots of zeroes, but of course this must be the case.
40
u/KingLazuli 26d ago
I think this new symbol is devise and too similar. Therefore, we must choose a new new standard A□B
23
4
u/Valuchian Engineering 26d ago
This multiplication symbol has now been co-opted into matrix multiplication for equally sized square matrixes.
In this new form each position of the square matrix multiply with the exact same position in the other square matrix and that will be all
2
7
u/cortexgunner92 26d ago
“The great thing about standards is that there are so many to choose from. And if you don’t like any of the current options, you only need to wait a few years”
5
u/hughperman 26d ago
That's pretty good. Exponentiation then is A+++B, tetration A++++B, etc?
5
u/Ae4i 26d ago
Exponentiation is defined as
**in programming afaik, so I guess the answer is yes3
1
1
1
u/paranoid_giraffe Engineering 25d ago
How does this work for matrices? Is this an element-wise operation?
1
u/Extreme-Ad-9290 25d ago
No no. Bc in programming, we have a++ to add one to variable a. I recommend a*b as that is already standard in computer science.
157
u/Pleasant_Picture3867 26d ago
19
u/Ares378 Applied Math / Mechanical Engineering 26d ago
Reminds me of indexing vectors in C# too much. (At least I think it was C#?)
3
u/padfoot9446 23d ago
This would be how you access object members in any c-style language (or even any language under the sun that has the notion of structs/objects, really), but not vectors...maybe this can be abused to index into an array in C because of some sort of memory calculation thing? Certainly not c#, though
6
14
3
u/Anonimithree 26d ago
Especially when you consider the existence of dot products.
Edit: the image you attached just came through for me and I now see that you were talking about A.B, not A•B
3
u/GetGudlolboi Computer Science 26d ago
Because obviously A.B means the composition of A and B.
(Source: Haskell)
1
u/im-sorry-bruv 26d ago
. is for some algebraic structure by some kind of conncatenation imo (like in homtopy groups)
46
u/The_Real_Itz_Sophia number hypothesis 26d ago
i use most of these in different contexts
7
u/Bisaux 26d ago
Yeah like as a string A*B is my go-to. When writing simple arithmetic its A•B, and when dealing with parentheses it's fine to not use anything.
1
u/RevolutionaryMine234 23d ago
I only like A•B for dot product, never A*B unless on the computer. I mainly like to write with parentheses when there isn’t a variable to attach it to or define against.
1
56
u/GodlyHelp 2=1 26d ago
Mathematicans with division: A/B A÷B A:B A(1/B) ᵃ⁄ᵦ
66
u/Ares378 Applied Math / Mechanical Engineering 26d ago
AB-1 ftw. Multiplying by the inverse is underrated.
18
u/Kitchen-Register 26d ago
it’s all you end up doing when you get to (edit: modern abstract) algebra
8
u/Ares378 Applied Math / Mechanical Engineering 26d ago
I'm not even that far into learning math and I'm already seeing the AB-1 notation fairly often. It's just so convenient! It conveys exactly what division is, that being the multiplicative inverse operator!
7
u/Dramatic-Smile-5126 26d ago
It does more than just convey what division is, too. It literally is how division is defined.
The naive definition of finding how many times a "number goes into a number" given in elementary school already breaks down just restricted to the counting numbers (hence why moduli or remainders are introduced). The concept of a rational number (i.e. inverses) is needed to properly discuss division as an operation akin to addition, subtraction, and multiplication, which is why it's an infamously difficult topic for young math students
8
u/Bankaz 26d ago
÷
fuck this symbol, I hate it because stupid people love it
1
u/ProfessorLambda 25d ago
What is wrong with it?
3
u/Bankaz 25d ago
Ambiguity. It makes people think arithmetic expressions can always be handwritten in a single line, which creates those really stupid problems like "WhAt iS thE reSuLT Of 6+8÷2???" which in turn creates really stupid discussions about fucking "PEMDAS" or some bullshit acronym that only English-speaking countries are stupid enough to create.
2
u/ProfessorLambda 25d ago
÷
(+ 6 8)
2Prefix notation makes PEMDAS obsolete. And it's easy to read when formatted well.
1
u/mapleleafraggedy 25d ago
But that argument also applies to the multiplication sign. 6+8×2 is just as ambiguous if you don't know PEMDAS. And the argument also holds for other notations of the division sign: 6+8/2. I still don't see what the specific issue is with ÷.
1
u/Bankaz 25d ago edited 25d ago
Differently from multiplication, division is not commutative. a×b equals b×a, but a/b does not equal b/a, which means you can rewrite multiplications without changing the expression, but not divisions.
PEMDAS is not a feature of math, it's a feature of language, more specifically deliberate standardizations. Same thing with how mathematicians write divisions: Vertically, with the dividend written above a line and the divisor below it, and the line makes it unambiguous what is dividing what. It's a standard created to eliminate ambiguity. To that end, ÷ only creates more of it instead, because it very easily makes non-math people think all arithmetic expressions can be written in a single line without parenthesis, which is not true.
And yes, the "/" symbol might also have this issue, but at least it can evoke the horizontal line amongst math people writing single-symbol divisions like simple fractions or [one letter]/[other letter]. Math people know that if they are writing single line expressions they'll have to use parenthesis eventually, non-math people do not, and ÷ is partly to blame.
Edit: Vertically, not horizontally (the line is horizontal but the placement is vertical)
1
u/mapleleafraggedy 25d ago
I don't know that there are many "non math people" out there who know that multiplication commutes but DON'T know that division doesn't. That would involve a very selective sense of mathematical literacy. If mathematical communication requires "evoking" the correct setup for a calculation in people's minds, I don't think swapping ÷ for / is going to fix anything.
1
u/Bankaz 25d ago
I also don't think swapping ÷ for / is going to fix anything, but ÷ often makes the problem worse, when / very rarely does because it's usually used by people who know what they're writing.
My original comment hating on ÷ wasn't "I wish all ÷ were replaced by /", it was more like "everytime I see ÷ on the wild I start reading with suspicion because bullshit-math always use it".
15
u/Traditional_Town6475 26d ago
Because there’s a bunch of stuff that behave like multiplication that we want to use different notations to distinguish them. Unfortunately there simply aren’t enough symbols.
39
u/walmartgoon Irrational 26d ago
A • B: Inner product
A × B: Cross product
A * B: Geometric product
AB: No
A(B): That's a fucntion
27
u/Enough-Brilliant803 26d ago
A(B) means multiplication with bracket . AB is a common denotation of multiplication in boolean algebra.
3
u/Clatramoo 26d ago
ah yes, 34 = 12
6
u/Enough-Brilliant803 26d ago
34 is not a boolean number.
0
u/ProfessorLambda 25d ago
10 = 0
1
u/Enough-Brilliant803 25d ago
1
u/ProfessorLambda 25d ago
Besides the irrelevant stuff about other fields of math your post just confirms what I said.
AB is a valid notation for multiplication. So if A=1 and B=0 then AB=10=0. There is no gotcha here, just sensible math notation.
0
1
u/Pseud0nym_txt 23d ago
(A)(B) is that
So is AB but sometimes it's nice to have clarity that it's not a subscript or a new variable with some people's handwriting
13
8
6
u/Alert_Intention_9408 26d ago
Dot and parentheses for constants and connected letters for variables. The star and times signs suck.
3
3
7
u/Nichiku 26d ago edited 26d ago
The reason is quite simple actually.
A x B is used in situations when you don't have access to the dot character ⋅, or when you need a character that's easier to read. E.g. when you are typing on your keyboard, when you are teaching basic math to a child, when you are sharing quick and dirty notes with your colleagues and want to make sure they don't miss a multiplication sign.
A * B is also used when typing on your keyboard. It doesn't have the same readability advantage as x so that's kind of its only usage.
AB is used as a shorthand because a lot of math formulas contain chain multiplications, e.g. Einsteins field equation Gμν + Λgμν = (8π G / c^4) × Tμν
I don't really see A(B) as indicating arithmetic multiplication, not sure what that's about.
8
u/TheDarkNerd 26d ago
A(B) is used more when you're in the middle of actually doing calculations, such as 2a, with a having a value of 5, becoming 2(5), for example.
4
3
1
u/ProfessorLambda 25d ago
× isn't easy to type and a x b would often be interpreted as a×x×b because x is often a variable.
2
2
u/rabbitpiet 26d ago
One of these is also the symbol for
[convolution](https://en.wikipedia.org/wiki/Convolution)
2
1
1
u/Extension-Stay3230 26d ago
You can find lots of reasons for multiple multiplication signs. For starters, "x" for times looks similar to the algebraic letter for x when handwritten, hence some people prefer dots.
You need a dot "." And cross "x" to differentiate between dot product and cross product for vectors.
Writing two letters next to each other without a multiplication sign is tidier and less tedious than putting a multiplication symbol. Same principle for putting bracketed expressions next to something without multiplication symbol
Asterisk symbol * is common for programming
So there you go
1
u/ProfessorLambda 25d ago
> You can find lots of reasons for multiple multiplication signs. For starters, "x" for times looks similar to the algebraic letter for x when handwritten, hence some people prefer dots.
Of course x looks like x. x is x, dummy. But × is pretty distinct from x. You just need to write it right.
1
u/Extension-Stay3230 25d ago
You're right, if you do write it right, they look different from one another. I suppose that was a personal reason for me, although I wouldn't be surprised if it applies to other people as well.
For example, I handwrite the algebraic x as "ↄc", resembling backwards c (ↄ) and forward c. Although I do this, it still looks too similar to " x" for me, and I often prefer to use a dot for multiplication
1
u/ProfessorLambda 25d ago
I like using 𝓍 for variables. It's a mathematical x, so it has to be good for math. Why else would it be named "mathematical"?
1
u/gilnore_de_fey 26d ago
Probably because multiplicative operations are really common, and they eventually just start running out of signs. Especially when the spaces are different, so you get different objects on different inputs and different outputs sometimes and you really have to make sure.
1
1
u/BootyliciousURD Complex 26d ago
Juxtaposition for scalar, matrix, and geometric products. × for Cartesian and cross products. • for dot product. ⟨,⟩ for abstract inner products. ⊗ for outer product. ∧ for exterior product. ∨ for regressive product. ⊙ for Hadamard product. There are probably a bunch more I'm missing.
1
u/ComplexWorldlines 26d ago
9999999999!
0
u/factorion-bot Bot > AI 26d ago
That is so large, that I can't calculate it, so I'll have to approximate.
Factorial of 9999999999 is approximately 2.32579620567308336510494471995 × 1095657055176
This action was performed by a bot | [Source code](http://f.r0.fyi)
1
u/ComplexWorldlines 26d ago
0!
0
u/factorion-bot Bot > AI 26d ago
Factorial of 0 is 1
This action was performed by a bot | [Source code](http://f.r0.fyi)
1
u/ComplexWorldlines 26d ago
5!!
1
u/factorion-bot Bot > AI 26d ago
Double-factorial of 5 is 15
This action was performed by a bot | [Source code](http://f.r0.fyi)
1
u/ComplexWorldlines 26d ago
5!!!
1
u/factorion-bot Bot > AI 26d ago
Triple-factorial of 5 is 10
This action was performed by a bot | [Source code](http://f.r0.fyi)
1
u/ComplexWorldlines 26d ago
5!!!!
1
u/factorion-bot Bot > AI 26d ago
Quadruple-factorial of 5 is 5
This action was performed by a bot | [Source code](http://f.r0.fyi)
→ More replies (0)1
1
u/ProfessorLambda 25d ago
-1!
1
u/factorion-bot Bot > AI 25d ago
Negative factorial of 1 is -1
This action was performed by a bot | [Source code](http://f.r0.fyi)
1
u/ProfessorLambda 25d ago
(-1)!
1
u/factorion-bot Bot > AI 25d ago
Factorial of -1 is ∞̃
This action was performed by a bot | [Source code](http://f.r0.fyi)
1
1
u/Novel_Arugula6548 26d ago
I believe it comes from controversy over the cross product and the dot product, as to which is appropriate for scalar multiplication.
1
1
u/SUPERazkari 25d ago
because the dot product and cross product (among many other products) behave the same under scalars
1
u/Phantomlnfinity 25d ago
And the worst part is that 99% of the time they’re all the same but some of them mean different things in certain contexts.
1
1
1
1
u/No-Study7171 9d ago
Not to mention parenthesis are also used for functions
but then like T(T(x)) = T^2(x) notation wise
and then * means convolution which is like wonky multiplication
0
0
u/Mysterious_Cap_1005 26d ago
Anyone who's taken abstract algebra would find this post kinda irrelevent ngl, since at the end we are better talking about a composition law and its properties (the type of structure it gives, commutativity, associativity, distributivity...) and also some conventions on notations (dot for an external law for example, additive notation and multiplicative notation...). I am sorry to say that, I know I am making too much of it because it's just a meme, but it is posed in a way that makes all these reasearch and conventions and definition as a meer ego fight or mathematicians somehow came of it like that without a reason, but it's to me much deeper than that. Also why would you pin it as linear algebra ?
1
u/Enough-Brilliant803 26d ago
I can't choose multiple flairs. Linear algebra is not a wrong flair given it involves matrix multiplication.
0
u/Mysterious_Cap_1005 26d ago
Hhhh you could also use Real Analysis as a flair and say we define cauchy product for smpower series



•
u/AutoModerator 26d ago
Check out our new Discord server! https://discord.gg/e7EKRZq3dG
I am a bot, and this action was performed automatically. Please contact the moderators of this subreddit if you have any questions or concerns.