/sci/ - Science & Math

[Anonymous No.5211872]

Internet lingo~!

For commoners:
jk = Just kidding

For Engineers:
jk = 0, because the dot product of any two perpendicular vectors is always 0.

The More You Know

[Anonymous No.5211902]

>implying "jk" means the dot product of j with k

ISHYGDDT

[Anonymous No.5211918]

Good tier

<div class="math">\bar{x}\cdot \bar{y}</div>

Physicist tier

<div class="math">x_{i}y_{i}</div>

Normal tier

<div class="math"><div class="math">\vec{x}\cdot \vec{y}</div></div>

Shoot yourself

<div class="math"><x,y></div>

[Anonymous No.5211920]

>>5211872
I don't see a dot between j and k in your post, neither do I see an arrow above the letters, there is also no way of knowing whether they are perpendicular or not, should they be vectors.

[Anonymous No.5211933]

>>5211872
>Dot product.
>No dot.

[Anonymous No.5211936]

>>5211918

>Not underlining your vectors

[Anonymous No.5211940]

>>5211918

The last one is supposed to be a dot product? When i did multivariable that was how we represented vectors.

[Carl No.5211947]

jk = i

[Anonymous No.5211973]

>>5211947
j x k = i

ftfy

[Carl No.5211984]

>>5211973
>pleb who doesn't know quaternions

[Anonymous No.5211982]

lol us nerdz amirite XD
but no seriously OP go kill yourself

[Anonymous No.5211987]

>>5211918
God tier:
<span class="math">\mathbf{x}\cdot \mathbf{y}[/spoiler]

Vectors are bold lowercase roman letters, period.

[Anonymous No.5211995]

>>5211984
>retard who comes to a thread about vectors and tries to talk about quaternions

[Carl No.5212006]

>>5211995
Instead of being mad you could educate yourself. ;)

[Anonymous No.5212001]

>>5211995
>Filthy brain dead pleb who doesnt want his maths to mix.

[Anonymous No.5212011]

>>5211995
I feel bad defending Carl, but it wasn't a thread about vectors, it was a thread about "jk = ?", so his answer actually works well.

[Anonymous No.5212014]

>>5211918
The only choice is between
<div class="math">(x,y)</div>
and
<div class="math">\langle x,y \rangle</div>
The rest is for fags.

[Anonymous No.5212020]

>>5212011
(continued)
>His answer actually works well
well, except for the fact that quaternions are actually fucking useless and I'd say playing with quaternions is highly correlated with being a math-enthusiast with at most a highschooler or a freshman's understanding of mathematics.

[Anonymous No.5212023]

>>5211987

>writing in bold

[Anonymous No.5212039]

>>5212014
Man, <span class="math">(x,y)[/spoiler] is the worst notation in this thread for dot product. Not only <span class="math">x[/spoiler] and <span class="math">y[/spoiler] don't appear as vectors (not bold, not underlined, not overlined, not overarrowed), but it is actually already the widely used notation for the ordered pair <span class="math">(x,y)[/spoiler] or (equivalently) the vector of length two whose coordinates are <span class="math">x[/spoiler] and <span class="math">y[/spoiler]. Some people even use that for the real interval <span class="math">\{\alpha : x<\alpha<y\}[/spoiler].

I mean seriously, that notation is awful for a dot product.

[Carl No.5212033]

>>5212020

[Anonymous No.5212046]

>Using dots on top to represent time derivatives instead of using d/dt notation

I seriously hope you don't do this

[Anonymous No.5212050]

>>5212014
Uh (x,y) is terrible for dot product

[Anonymous No.5212058]

>>5212046

<div class="math">\frac{\mathrm{d} }{\mathrm{d} t}\frac{\partial L}{\partial \frac{\mathrm{d} q}{\mathrm{d} t}}-\frac{\partial L}{\partial q} = 0</div>

Yeah, no

[Anonymous No.5212059]

>>5212033
After reading this post, I went to wikipedia, to check that the page was indeed a lot of work on the quaternion with nothing that looks like a "Quaternions are a useful framework in [domain 1] and [domain 2]". Not only was I right, but the page has quotes of famous mathematicians and physicists:
>I came later to see that, as far as the vector analysis I required was concerned, the quaternion was not only not required, but was a positive evil of no inconsiderable magnitude; and that by its avoidance the establishment of vector analysis was made quite simple and its working also simplified, and that it could be conveniently harmonised with ordinary Cartesian work.
>… quaternions appear to exude an air of nineteenth century decay, as a rather unsuccessful species in the struggle-for-life of mathematical ideas.
etc.

Quaternions suck.

[Anonymous No.5212068]

>>5212023
No. Typing in bold. I'm answering to a post in LaTeX, so I'm using LaTeX conventions. If I was answering to someone writing on a blackboard, I would have used a different notation for sure.

Properly written mathematical papers use bold for vectors and they have been doing so for decades at the very least.

[Anonymous No.5212073]

>>5212059
>mad because he doesn't understand quaternions.

math major 300k starting any job I want

[Anonymous No.5212075]

>>5212039
>>5212050
This is actually the most used notation for the dot product in math.

[Anonymous No.5212088]

>>5212075
Maybe on a piece of paper because written angled brackets is annoying. Certainly not in any paper I've read.

[Anonymous No.5212096]

>>5212073
Just wondering... how the hell can someone not understand quaternions?

[Anonymous No.5212104]

>>5212075
Does no-one use a fucking dot for a dot product anymore?

Is that just what us dirty Physicists do?

[Anonymous No.5212114]

>>5212075
It might be because I'm still undergrad but I see (x,y) just as a vector

[Anonymous No.5212129]

>>5212104
Because dots are used for multiplications. In a multiplication you take 2 elements of one structure and get an element of the same structure. The dot product is a fundamentally different type of operation.

[Anonymous No.5212151]

>>5211872
>jk means the dot product product between the j and k vectors

Umm, nope. It is would be the scalar multiplication of their magnitudes.

[Anonymous No.5212273]

>not generalizing to inner product

[Anonymous No.5212291]

Let's get this shit started.

>generators

[Anonymous No.5212447]

>>5212151
>writing magnitudes as non-tagged vectors
A tip for when you'll leave highschool and become a freshman: your teachers didn't use meaningful notations, forget about them, nobody uses them after highschool.

[Anonymous No.5212475]

>>5212058
heh, point made.

[Anonymous No.5212486]

I still cry. I'll build her one day.