# Why is linear Algebra so hard to understand?

whereismyname

Why is linear Algebra so hard to understand?

Supergrass

because it isn't

Booteefool

@whereismyname
If linear algebra is hard conceptually, just give up.

Harmless_Venom

@whereismyname
because of determinants.
Grab Linear Algebra Done Right. If that doesn't work for you then you are a certified brainlet.

farquit

@whereismyname
$\mathbf{\vec{i}\times\vec{j}=\vec{k}}$
It's either $\mathrm{\vec{i}\times\vec{j}=\vec{k}}$ or $\mathbf{i\times j=k}$ you fucking mouthbreating drooling inbred m*tt.

5mileys

maybe you just need to git gud

takes2long

It's not. If you're really having trouble understanding it, check out this guy's videos about it. He does a good job explaining the essence of linear algebra with great visuals and clear explanation. Also it's only 2 hours long, divided into 15 short clearly defined segments, so you don't have to binge it all at once.

https://www.youtube.com/watch?v=kjBOesZCoqc&list=PLZHQObOWTQDPD3MizzM2xVFitgF8hE_ab

askme

It's just lines lol how is that hard?

askme

@whereismyname
Tbh it's the epitome of understandable math. It's the only math we really can do

likme

@whereismyname
if you struggle for algebra don't even dare to touch an analysis book

Spazyfool

@farquit
second

also, $\vec{\imath}>>>\vec{i}$

Soft_member

@whereismyname
Because you spend your time shitposting instead of reading

Methnerd

@Spazyfool
yeah but I didn't remember the command to put it that way. I always use bold anyway, looks classier to me.
Arrows are useful when handwritting since bolding is hard (altough I am switching to blackboard bold)

ZeroReborn

because you're taught to use it before you understand why you use it. after second year of physics degree it was piss easy.

@Spazyfool
i always struggled to convince myself to drop the dot, but it always felt a little weird without it

MPmaster

think of a 2d/3d example and everything is intuitive

FastChef

@Harmless_Venom
determinants are bad
self studying from "Linear Algebra Done Right"
Not sure what's most disgusting, a brainlet finding linear algebra hard, or a brainlet posturing as a non-brainlet and regurgitating a meme-book pretending he's read even a single page from it.

haveahappyday

omg i cant believe you all took the bait

perhaps you all have to reconsiderer who's the retard here

Poker_Star

@farquit
never took linear algebra but how does 2 vectors equal a vector? shouldn't it be a scalar?

BlogWobbles

@Poker_Star
Depends on how you operate on the vectors.

If you add or subtract two vectors, you get a vector. If you take the dot product of two vectors, you get a scalar. If you take the cross product, you get a vector.

Spazyfool

@Spazyfool
@farquit
hats denote unit vectors, boys
$\hat{\imath}, \hat{\jmath}, \hat{k}$

TalkBomber

I agree it can be tedious when you're first learning it, but it sure as shit isn't hard. Just stick with it and learn all the annoying definitions and try to remember how matrix multiplication works.

It is actually a subset of a much cooler area called group theory. It's only really important because it is the only intuitive algebraic system we have. Most of group theory is trying to represent abstract things as matrices so we can do linear algebra with them and prove shit about abstract algebra.

Pretty neato, but you need to learn linear algebra first so yeah... stick in there. Also, if you're not trolling, Veeky Forums is full people who like to act like they are high functioning autistic geniuses when in reality they only check the first part. Things are almost always difficult the first time you learn them.

Unless you actually are a brainlet. In which case, you should find out soon and should give up because linear algebra isn't actually that difficult.

Stupidasole

@BlogWobbles
dot product
cross product
Just call them scalar and vector product, brainlet

King_Martha

@Spazyfool
Physishit detected

LuckyDusty

@TalkBomber
Yeh, doing it is easy. I just dont understand how stuff like matrix multiplication works in the order it does for example.

AwesomeTucker

@LuckyDusty
Row one times column one for row one, column one
Row two times column one for row two, column one

etc.

Ignoramus

@FastChef
That book is great

I can tell you haven't read it because you don't think so

Stupidasole

@AwesomeTucker
Nice, now tell me why it's like that?

Illusionz

@Booteefool
Can't, got to learn it because the only "trade school" in my city is the community college and they want me to take a math test before letting me weld shit together.

Need_TLC

@Stupidasole
Otherwise the result isn't meaningful.
Matrices are linear transformations in disguise, and vice-versa. Linear transformations are functions. When you multiply two matrices, you're composing two linear transformations.

Here's a very hot stack exchange post that goes into detail:
https://math.stackexchange.com/questions/31725/intuition-behind-matrix-multiplication

Lord_Tryzalot

@whereismyname
because you're a brainlet

Sir_Gallonhead

@LuckyDusty
Thats why you should learn proper linear algebra with a general theory of linear functions and it's representation instead of meme matrix algebra that should be thought at hs.

haveahappyday

I've had two separate classes where linear algebra is taught and I still have no fucking idea how to find a basis for a vector space, or the usefulness of eigenvectors, or any of that other crazy shit.

eGremlin

@Need_TLC
Thanks for that

whereismyname

@eGremlin
Of course! Keep reading! Linear Algebra is lovely.

Sir_Gallonhead

@Spazyfool
This tb h

farquit

why is linear algebra so hard to understand

likme

@FastChef
Not the above poster, but I have read it and recommend it. Also recommend "Linear algebra done wrong" for another perspective. The Schaums book is good too.

Linear algebra is new stuff, you need to climb up one layer of abstractions at a time. Just like with all math.

LA is key to many fields - statistics, machine learning, quantum mechanics. Deal with it.

GoogleCat

I got a C in high school so it wasn’t hard for me

Lord_Tryzalot

I'm right there with you OP... I'm right there with you....

Lord_Tryzalot

@FastChef
putnam larper right there lads

King_Martha

@Stupidasole
inner product
outer product

5mileys

Does this make intuitive sense?

StonedTime

@5mileys
Also:
[eqn]\begin{align}\left[\begin{array}{c}3 \\ 2 \\ 0\end{array}\right] &= 3\left[\begin{array}{c}1 \\ 0 \\ 0\end{array}\right] + 2\left[\begin{array}{c}0 \\ 1 \\ 0\end{array}\right] + 0\left[\begin{array}{c}0 \\ 0 \\ 0\end{array}\right] \\
\left[\begin{array}{c}2 & 1 & 2 \\ -1 & 3 & 2 \end{array}\right] \left[\begin{array}{ccc}3 \\ 2 \\ 0\end{array}\right] &= 3\left[\begin{array}{c}2 \\ -1 \end{array}\right] + 2\left[\begin{array}{c}1 \\ 3 \end{array}\right] + 0\left[\begin{array}{c}2 \\ 2 \end{array}\right]
\end{align}
[/eqn]

Methnerd

Matrices are just linear operators expressed in a different fancy way, which gives them some interesting properties. A 2x2 matrix with columns (a,b) (c,d) could be written as a function T:R^2 -> R^2, T(x,y) = (ax + cy,bx + dy), which you can also write as x(a,b) + y(c,d), which is a sum of two linear operators T_1:R^2 -> R^2, T(x,y) = x(a,b) and T_2:R^2 -> R^2, T(x,y) = y(c,d).

So as you can see, a matrix is just a collection of linear operators, where the n:th column representing a linear operator maps the n:th component of a vector on some line.

As for multiplying two or more matrices, it's actually just a function composition. Stick another linear function in T and see what happens.

iluvmen

@whereismyname
lol wait until group theory

Poker_Star

@5mileys
Dude. I do this in one step (in my head).

FastChef

@Methnerd
Matrices are just linear operators
under a fixed basis

brainlet

BunnyJinx

@farquit
it is just notation
it is a non-issue unless you go full retard and do things like <insert example here>

Lunatick

@FastChef
Fuck off. Completely pointless comment.

happy_sad

I found it way easier than calculus.

They should teach it before calculus desu.

Bidwell

@happy_sad
they teach it at the same time as calculus where I'm from

FastChef

@happy_sad
Vectors is sometimes part of precalculus

Sir_Gallonhead

@whereismyname
It's hard if you are taught it the wrong way; same goes for any other subject.
Linear Algebra is taught wrongly way too often though, because they teach it by focusing on matrices rather than linear maps.
Rule of thumb for Linear Algebra is "Think with maps, compute with matrices".

cum2soon

@5mileys
Yes. Let f represent the left matrix and g represent the right matrix (given the usual base $\{e_i\}$ .
Then $g(e_i)$ is the i-th column of the right matrix.
The i-th column of $f \circ g$ is $f \circ g (e_i) = f(g(e_i)) = f( \text{ i-th column of the right matrix } )$ .

TreeEater

@LuckyDusty
Matrix multiplication is defined this way so that it if you have:
the matrix A of a linear map g under the bases u and v
and
the matrix B of a linear map f under the bases v and w,
then the matrix of f ο g under the bases u and w can be acquired by BA.

That's the only reason it is defined this way.

w8t4u

@TalkBomber
It's misguided to call linear algebra a subset of group theory. They really serve totally different purposes. The fact that a vector space forms an abelian group under addition doesn't mean you're doing group theory. In fact, abelian groups are really closer to being linear algebra than vice versa.

Evilember

Welders don't need linear algebra you cuck

Need_TLC

everything becomes easier when you understand that matrices are really just functions if they are on the left, and a group of column vectors that serve as arguments a function (matrix) if they are on the right

takes2long

@Need_TLC
this guy got it

Sharpcharm

@whereismyname
you cant be serious right?

Dreamworx

@FastChef
Linear Algebra Done right is one of the best textbooks out there in general.

Crazy_Nice

@Dreamworx
its ok but not one of the best textbooks in any way
hoffman&kunze is better for linear algebra for example

RavySnake

it's not hard, it's just your first encounter with real math, calculus, it's little bit simpler because you learn it in HS in almost all countries, and you can give it a physical meaning easily...

likme

am I a brainlet for not understanding all the stupid vocab that goes along with linear algebra? I understand all the concepts, I just don't give a fuck about all the stupid 20+ things that all mean the exact same thing. I know linear algebra is just setting up a basis for a whole range of mathematics, but I really don't want to learn all of the terms. Also I'm taking the class online and I'm a piece of shit, so I do the bare minimum to pass the class.

ZeroReborn

@King_Martha
gay product
straight product

Nude_Bikergirl

@farquit
Third.

Also preferable ${ \boldsymbol{i} \times \boldsymbol{j} = \boldsymbol{k} }$

Sir_Gallonhead

@likme
if you think there are "20+ things that mean the exact same thing", you don't understand as well as you think, my friend.