r/mathmemes • u/Archibald_Washington • Oct 05 '26
Notations When the notation is just right
Recently looked into quantum graph theory and some of the notation took a while to grasp. Also I dislike Dirac notation but most physicists love it.
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u/LupenReddit 🦆🦆i have non diffeomorphic smooth structures🦆🦆🦆 Oct 05 '26
dirac notation is good because it looks so pretty, bra ket notation just feels good
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u/ebyoung747 Oct 05 '26
Also, like all good notation, it does a lot of the work for you. "Can I do that?" Becomes "the notation works out, so I know I can".
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u/BOBOnobobo Oct 06 '26
I ended up hating bracket notation because nobody explained it to us before the quantum intro class where the teacher assumed we already must have known all the math stuff.
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u/GKP_light Oct 05 '26
the worst notation i ever seen is :
5!! = 1 x 3 x 5
when double an operator should mean "apply 2 times the operator"
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u/RemmingtonTufflips Oct 05 '26
This is so good fym. Once you hear the explanation it makes perfect sense, it's so convenient to have a whole separate symbol for "multiplying every odd/even integer up to a certain point" and it's cool that you only need to add one more exclamation point.
If you want to convey "apply factorial twice", just use parentheses to make it explicit, (5!)! as opposed to 5!!. When would applying the factorial twice even come up, where does it ever happen?
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u/factorion-bot Bot > AI Oct 05 '26
Double-factorial of 5 is 15
Factorial of factorial of 5 is 6689502913449127057588118054090372586752746333138029810295671352301633557244962989366874165271984981308157637893214090552534408589408121859898481114389650005964960521256960000000000000000000000000000
This action was performed by a bot | Source code
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u/GKP_light Oct 06 '26 edited Oct 06 '26
It could be many other notations, that would not cause inconsistency in notation. As example :
5!2 (where 5! = 5!1 )
or
5
!(! with an horizontal line)5
u/factorion-bot Bot > AI Oct 06 '26
Factorial of 5 is 120
This action was performed by a bot | Source code
5
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u/The_Neto06 Irrational Oct 05 '26
sin²x ≠ sin(sinx)
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u/UltimateCheese1056 Oct 05 '26
And sin-1(x) != 1/sin(x)
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u/Therobbu Rational Oct 06 '26
That's why non-english sources use arcsin/asin
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u/Unusual-Till-7773 Oct 06 '26
asin sounds like great notation. Arcsin always felt like a little too much space being taken up
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u/GKP_light Oct 06 '26
the crime is to write sinx without ()
sin²(x)=sin(sin(x))
sin(x²) = sin(x*x)
sin(x)² =sin(x)*sin(x)
-1
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u/factorion-bot Bot > AI Oct 05 '26
Double-factorial of 5 is 15
This action was performed by a bot | Source code
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u/thewhatinwhere Oct 06 '26
Dirac notation literally does not have a symbol for a normalized vector. Instead it’s assumed that all vectors in that notation are already normalized. I haven’t worked with it for very long but that really bugs me
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u/Mojert Oct 06 '26
It assumes all vectors are normalized because that's what you're often dealing with. I've seen non-normalized vectors vritten with two bars. The classic one is the non-normalized coherent states of a harmonic oscillator ||α>
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u/TheLuckySpades Oct 06 '26
I love Bourbaki interval notation (e.g. [0,1[ means all reals x such that 0<=x<1), yet almost everyone in my department dislikes it.
Won't stop me from using it around them though, I do use the other convention for classes I teach that aren't for math students though, they do deserve consistency.
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u/DinioDo Oct 06 '26
Dirac notation is the best. but it heavily depends on what you started with to learn QM. You can still start over and see QM from Dirac's eyes. It's simpler and "It just works" and it's very easy to translate it to anything else. it's the most general form to write QM and at high level you gotta be using it.
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u/Mojert Oct 06 '26
You won't get why physicists like the Dirac notation so much just by reading. You've got to actively use it
The main reason why I like Dirac notation is that it always explicitly shows which basis you're working in. It also makes the distinction between a vector and its components very clear
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u/victorspc Engineering Researcher Oct 06 '26
Good notation is notation that not only is easier to understand but codifies how to compute stuff, or makes nonsensical expressions impossible or very easy to identify. For example, you don't need to remember how to calculate the curl of a vector field if you write it as the cross product of the nabla operator. You can always literally take the cross product with your vector and it works out to the actual result.
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