Change of basis | Chapter 13, Essence of linear algebra

How do you translate back and forth between coordinate systems that use different basis vectors?
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Thanks to these viewers for their contributions to translations
Vietnamese: @ngvutuan2811

[@kolotoure7902]

I study in Norway, and our professor recommended this series as a supplement resource to the course. I was pleasantly surprised he's humble enough to do so.

[@Dark_OFW]

Hva studerer du, og hvor?

[@mfn1311]

Vet ikke helt hvorfor det gjør han 'humble', videoene har veldig bra kvalitet og er en god måte å få bedre forståelse på, og som du sa er det ikke akkurat som det er faktisk del av pensum. så ville ikke helt sagt det var humble, men var i hvert fall kult gjort.

[@danch_ranch6594]

Norgee🇳🇴. Matte student fra Blindern her

[@snay6869]

Jag studerar i sverige 🇸🇪🇸🇪🇸🇪

[@CStrik3r]

I love how when the "teacher' @5:30 asks "You've all watched chapter 3, right?" the Pi Creature to the left rolls his eyes trying to look normal with that stressed out facial expression, like "nope.." Very meticulous with these videos I love it.

[@TheBrickagon]

Wow, I didn't notice 😂😂😂

[@paprikar]

I was looking for this comment :)

[@habib_khan]

@@paprikar same lol

[@kanhaiyalalrajput3215]

He's a backbencher 😅

[@lemonhead2205]

"Yeah... I totally watched it"

[@JackPunter2012]

Storytime: I watched this video about 6 months ago for the first time when I stumbled across this channel and decided to watch this series (as well as most of the other ones) and I thought. that's cool, doubt I'll ever need to use it but its still cool. Until today, I'm working on a University project where we essentially have to triangulate the GPS coordinates of an object based off of compass bearings from known locations we are doing this over a small enough area that the "grid" of GPS coordinates can be considered rectangular (so the maths is still linear algebra) but sadly stuff doesn't work as nicely as with square coordinates. so after a good few minutes of thinking about how to solve this problem and, getting very frustrated, I took a 5-minute break to rest the brain and BAM!!! I remembered this video and thought "I can just change the base to a rectangular one". So here is a massive thank you for this amazing content that I watch in passing and then next thing I know. I'm thinking back to it using it in a real-world engineering problem, Keep it up dude Love the content. really wish I could support you on Patreon but.....University.

[@TheBrickagon]

👏👏😇

[@AriaHarmony]

I thought "I wonder what application would make Jennifer use that system instead of the "standard" one?" and BAM I found your comment! Haha thanks for sharing!

[@zilytra]

BAM im glad i stumbled upon this comment

[@bestsportsmoments31]

BAM

[@emperor8716]

BAM

[@paradoxicallyexcellent5138]

Grant. Beautiful. Literally tears in my eyes. This isn't just a math education video. It's a valuable contribution to humanity.

[@sakshidwivedi4754]

Hell yes!

[@High_Priest_Jonko]

Could you be any more dramatic?

[@mr.moodle8836]

I am LITERALLY on the floor having a seizure. My essential bodily functions are shutting down rapidly. The beauty of mathematics is just too overwhelming. Please send help.

[@stevey7997]

Ah c'mon, maths can be beautiful but don't exaggerate. Tearing up because of it seems a little too dramatic.

[@spike9314]

its called Stendhal syndrome when when you see something so beautiful you enter a psychosomatic state. its a good thing usually

[@qasidsaleem147]

I was a student who had 91/100 in Linear Algebra but had no intuition about what was actually behind 2-3 pages long answers. After watching this series, my beliefs about linear algebra have completely changed. I owe you a lot!

[@davidk7212]

It's amazing that a free collection of about a dozen short KZbin videos is incomparably more effective than any semester long university course.

[@fagahajakal988]

@Swagger Kekker lol yes

[@MKWiiLuke4TW]

I think people often mistake watching these videos for a full understanding that you would get from an LA course, people just get different things out of it, for example someone who just watches this series might be able to conceptually describe all these concepts, but not be able to actually do the problems associated with them like someone who's taken a linear algebra course, but that second person may have a worse conceptual grasp. they're just different, this isn't a replacement of a uni course, it's more a useful supplement to it.

[@douze-onze]

It surely gives us an easy understanding of the basics, but it is not enough for our own comprehension. Managing to get the point oneself, and then watching this video will give us a much advanced and thorough view of linear algebra: the intrinsic relation between calculation and visualization(intuition). We tend to use our intuition for having the point of mathematical actions, which means that studying this topic isn't enough by only a bunch of videos. It is necessary to make the bridge between the two of ourself.

[@pavelshliaha5841]

God I do a course of LA on Coursera using these videos as a teaching material. I could NEVER be able to do this if I wasn’t watching these, since the teachers do a much worse job of explaining than 3b1b does. I would encourage everyone to do this to get the best of both worlds AND support 3b1b financially (as I do)

[@MrAndreaCaso]

​@@MKWiiLuke4TW​Very well put, I think it's accurate.

[@PrimaSiPensaDopoSiFa]

You are playing an important role in my formation. Thanks.

[@3blue1brown]

Glad I could help! It's always super rewarding to read a comment like this.

[@PrimaSiPensaDopoSiFa]

:)

[@theprimalfuckhead526]

So there's an isomorphism between vector combination problema (cool plural for problem I made up) and linear combination problema. That said with your coordinate grid (basis vectors) being an axiomatic method of viewing space or information in mind, is there an isomorphism between matrices and tensors? Probably a better question would be, what are tensors?

[@glukosio8102]

Incredibile come rimanga la memoria di quel grande artista del quale porti il nome, anche dopo la sua morte!

[@PrimaSiPensaDopoSiFa]

Sempre libero.

[@reezis1619]

Finally a teacher that describes every part distinctly and coherently. My teacher just showed the algebraic part of changing basis but you put everything into reality now I fully understand. You are a genius

[@hovhadovah]

Same here. Our book barely described the intuition behind all this. I had to memorize it all until I found this vid.

[@Juici]

isn't milk expensive protein? beans and rice seem cheaper...

[@felipegonzalezlelong7944]

All of these videos are such an emotional rollercoaster for me. First the confusion, then the illusion of understanding, then frustration when I realize I didn’t, finally the absolute awe when I get it and see the beauty behind it all

[@bhoju_]

indeed

[@dragoncurveenthusiast]

6:44 This is what helped me solve the apparent "backwards" translation: Consider Emily, who uses a (1D) grid which is 5 times larger than ours (her 1D basis vector is 5). So, all of her coordinates are 5 times smaller than "our" coordinates for the same vector. 1 * 5 = 5 vector in her language * her basis in our language = vector in our language 5 * 1/5 = 1 vector in our language * inverse of her basis (in our language) = vector in her language

[@RioStudies]

Thanks

[@fredrik1164]

great

[@Splines]

Wow, that's a great image to remember how the transformation works. Thanks a lot! However, I would recommend to write it the other way around (8:35) since matrix multiplication is in general not commutative; when you write it as follows you can extrapolate from it to 2D-space one to one. her/our language = her/our coordinates 5 * 1 = 5 her basis 1D-vector in our language * 1D-vector in her language = same 1D-vector in our language her basis 2D-vectors in our language * 2D-vector in her language = same 2D-vector in our language (as a matrix rerpresenting transformation) 1/5 * 5 = 1 inverse of her basis 1D-vector in our language * 1D-vector in our language = same 1D-vector in her language inverse of her basis 2D-vectors in our language * 1D-vector in our language = same 2D-vector in her language (as a matrix rerpresenting transformation)

[@im-essi]

Thanks! I *almost* had it down intuitively at the end of the video, but was still slightly confused. This made it sink in properly :) Well worded!

[@kaushikdr]

You can use dimensional analysis to make it even more obvious! 1 Jennifer vector * (3 our vector / 1 Jennifer vector) = 3 our vector. 3 our vector * (1 Jennifer vector / 3 our vector) = 1 Jennifer vector. I like how you simplified it to 1D :)

[@peanutbutterjelly2188]

I have seen this video many times in the past. Now I am in my Ph.D. and whenever I need to refresh my understanding, I always think of Jennifer. Thank you for introducing the ever-complicated Jennifer.

[@kyleo8243]

@3Blue1Brown I’m a long-time watcher of this channel, and I love your content. Normally I don’t comment, but my Linear Algebra teacher told us to watch this video to learn the concept! I’m a student at the University of Washington. That’s a testament to your teaching- well done!!

[@michaelppaull]

This series has been the perfect addition to my current linear algebra course at my university. The lectures are mostly just definitions and lots of jargon and its very difficult to grasp on its own. The visual representations in these videos along with your explanations have really opened my mind up to this beautiful subject and I am very grateful.

[@ash_engineering]

Sir you are undoubtedly the best teacher i ever had...

[@ashutoshpadhi2782]

Bhai hamare studd hai

[@genericnamethingy]

My algebra teacher turned off the lights and read from slides. Course notes saved my ass, wish I'd seen this at the time

[@david21686]

Chapter 9: Change of Basis Chapter 10: Eigenvectors and Eigenvalues ... ... Chapter 100: A full derivation of Einstein's Field Equations, with applicable examples in cosmology Please?

[@thephysicistcuber175]

.... Chapter 200 Renormalization in QED

[@david21686]

The Physicist Cuber But this is a mathematics channel, not a magician channel.

[@thephysicistcuber175]

WTF?!

[@david21686]

The Physicist Cuber We're talking about renormalization in quantum electrodynamics, correct? I.e., the process of making infinities magically go away, correct?

[@thephysicistcuber175]

lol xD

[@KampfKeks04]

You sir, have no idea how much this helps me as a math undergrad. I recommend the Calculus series to anyone who listens to me for more than 2 minutes. Now this one on Linear Algebra is a great help for me. You're doing great work and you should know that!

[@WAA06200]

ありがとうございます！

[@arturtamborski2421]

Those animations are most important part in Your videos. You are doing great job in explaining but animations deserve its own appreciation.

[@docsiasue4615]

I am a student in China,you make me have a much better understanding of linear algebra than what i was taught in the school.Words fail to express my gratitude...Thanks a lot

[@IsmailNashwan]

I've seen this series several times over my academic growth as a biologist and a math enthusiast whenever I've had time to learn more mathematics, and every time I come back for this series (as for honestly all your other videos, they are incredible) I've been fascinated with the newly gained visual intuition from actually seeing what is being done, but I've never really appreciated it until the concept of matricies as linear maps or transformations that are applied in order onto a vector clicked for me, which is such an incredibly abstract concept to understand without your lovely visuals. Thank you very much for what you do, you are beyond inspiring and the way that you bring life into the wonderful machinery of mathematics and how you've gotten so many others to do the same is amazing.

[@YvonneHYJ]

After all readings and stuffs, you're the only teacher who teaches what it truly means!! Thanks a lot! Now I think I could say "I love math!"

[@shunyezheng8332]

确实讲的挺好的

[@melaniebalmick7143]

I literally watched all the advertisements before all of the videos in this series because you deserve all the advertising dollars. It's the least I can do to thank you for deconstructing all these topics in a visually satisfying way that was not accomplished in school.

[@orang1921]

I AM SO PROUD OF MYSELF FOR INTUITING THAT YOU COULD REPRESENT A CHANGE OF BASIS AS A SIMPLE LINEAR TRANSFORMATION OMG

[@adsurbum]

Amazing! Looking forward with anticipation to understanding eigenvectors. It was really the initial push to watch the series.

[@anshgandhi6919]

I love you man. Rigid Body Kinematics, Control theory, Vibrations, Vehicle Dynamics, the majority of my masters boils down to this. Masters professors don't have time to teach the basics or solve fundamental doubts because of time-sensitive courses and frankly because they are basics. That's where you come in, a boon to humanity compensating for all the shitty education prior to this. Utmost respect and admiration for your intellect AND impeccable presentation skills. As soon as I start to earn, I'll make it a point to come back and donate generously. Genius!

[@soumyajitghosh3902]

I was very lucky to have discovered this myself, first with a few disagreements with the teacher and then finally that aha moment of finding out he and I were exactly talking about the inverse operation. As Grant has always talked about.

[@michelleh.5225]

Ok, these videos honestly save my life. I can't believe linear algebra isn't taught this way all the time! 😲

[@MrCmon113]

Mabelcorn N. Most courses don't have the time / resources. Also this is meant as an addendum to students of linear algebra, not as standalone linear algebra course. How do you visualize that R is an infinitely dimensional Q-vectorspace?

[@msergejev]

There are other fields besides mathematics, such as electrical engineering which I studies, that are using linear algebra and who do not need to visualize such things. But yes, this will not teach how to perform calculations, but would certainly help understanding many applications where linear algerbra steps in.

[@weissachpassion]

@@msergejev yeah... I am learning Lin All for mechanical engineering (also in a top 10 university), but the prof only shows the calculations and does not provide us the understanding of what we are really doing. This series is a blessing for me...

[@msergejev]

@@weissachpassion Its a blessing for all of us, tho for me it came about 10 years too late :)

[@yerr234]

@@msergejev hmmm so how would you visualize linear algebra's Analogies in EE? like Eigenfunction for example?

[@Titurel]

You are making what was my least favorite math subject one of my favorites!

[@kaiwalpanchal5872]

yeah

[@JinJinnJinny]

I could never ever ever understand/visualize change of basis until I discovered your videos. You sir are a godsend!!

[@jean-marcrocher1463]

I've been watching the MIT OpenCourseWare lectures on linear algebra with Prof. Strang on KZbin, then coming here and watching your video on the same material. After following the wonderfully detailed explanations from Prof Strang, your visualizations of the concepts add a new level of understanding. Thanks!

[@BlackSwan-sq2iw]

This is absolutely the best explanation I have seen on this topic. The visual is world class. I learned this topic the old way without the visual transformation before and I was totally lost.

[@passionatelaugh7023]

I am grateful that my professor made a terrible job so I could discover this masterpiece.

[@hassaanbaiq3316]

I like your perception basis vector

[@heqingyin6033]

Thanks!

[@omedelbums4609]

Why does Jennifer has to be so complicated tho

[@drdca8263]

she could ask the same of us. i hat and j hat being perpendicular only really makes sense once we have a dot product, so without that, any (linearly independent) choice of basis vectors should work equally well

[@1ucasvb]

From her perspective, we're the ones complicating things.

[@sofia.eris.bauhaus]

for her, we are the complicated ones. it's like different units of measure, except in more than one dimension.

[@zairaner1489]

While the linear transformation used in the video was indeed a lot more complicated from her perspective, there will be other transformations which are far easier from her perspective then from ours! (This will be a part of next video I believe)

[@Neme112]

Ask women.

[@helmutkaczmarek3514]

You just saved my Linear Algebra life. I am finally understanding what two hours of classroom lecture could not teach me. Thank you so much!

[@jinmingtang1545]

This is really helpful for me when I learn image processing now. For example, if I want to flip over an image from right to left, I found it was difficult in the past to transform the coordinates because the origin of an image is at the left upper corner and i hat points down and j hat points right. After this tutorial, now I have two ways to solve this problem. First I directly look for the transforming matrix in the image coordinate system. Second I translate the image coordinate system to x, y system and look for the transforming matrix in x, y system (this is a more natural way) and finally translate back to the image system. And I find that the first transforming matrix is the same as the composite matrix of A(-1)MA in the second way. So I can really find the amazing power of linear algebra once I can understand its implication behind the numbers.

[@abdulmukit4420]

You know you should receive a Nobel Prize for these contributions to humanity. Through just these videos you have accelerated the progress of technology worldwide. I mean it. I am one of those engineers whose work is now better and faster because of you.

[@oconnor8615]

6:47-6:57. Geometricaly, this matrix transforms our grid into Jennnifer's grid. But Numerically, it's translating a vector from her language to ours. It's the key point, Thanks.

[@studentcommenter5858]

Yess very very important point.

[@Robocat754]

Nah. It doesn't matter. Tell me why he's showing that picture of Jennifer's grid after using inverse change of basis matrix for the rotated matrix? No matter which grid you use. The position of that vector doesn't change. Isn't it?

[@hakeemnaa]

@@Robocat754 the position is relative you can not tell the position unless you have a grid so if the gird change, the position must change you think it did not change because the screen did not get distorted and it is fixed to our world

[@swfsql]

I think this part is quite hard to grasp. Specially because the matrix has two meanings in there, and it coincides to be the same matrix. 1. The matrix describes her basis in the standard basis notation (and coincidentally our basis is the same as the standard one) - this is the "her basis" matrix; 2. The matrix also transforms a vector from her basis into our basis, but this is only because our basis is on the standard one - this is the "her basis to our basis" matrix; I think that if our basis wasn't the standard [1,0;0,1] then the matrix for (2), the basis "translation" from her to ours matrix, wouldn't be the same as the matrix for (1), her basis matrix. For example, if our basis were [2,0;0,1], ie. our î axis is stretched by 2 times, the the transformation from her basis into ours would need to take our stretch into account, and thus the matrix representing that transformation would not be the same as her basis matrix.

[@tailund3508]

Wow. Once again, just wow. We live in a time where enlightenment is spoon-fed us by incredibly talented conveyors of the complex, for free on a platform that also shows cats dancing. I am most grateful! Engineer, Copenhagen

[@amrrasslan4329]

what a great world we live in today all you need is just a click to get the information you want . god bless you . hats off to you man .

[@emircanucar6935]

The idea of thinking matrices as linear transformations has magnificently improved my understanding of linear algebra. Thanks for your effort, wish you best.

[@capitanmission]

Im reading Leonard Susskind book on Quantum Mechanics. Its a wonderfully concise book but it assumes that you know linear algebra, so I went to Khan. A couple of months later this serie of videos arrived, thank you!!! Im having a great trip. I understand English, but its really cool that Spanish subtitles are available also, I would recommend it to everyone!

[@namvo9774]

I am currently a CS students, the concept of linear algebra has always been confusing me as i do not know what actually what this will be used for, until now that i know this channel, thank you for all the visualization and the way you show us that math is more than just computation. Thank you teacher!

[@floopthetesseract9557]

Man I just realized something crazy I recently started studying abstract algebra and I just realized that a linear transformation from some vector space A to some vector space B is an isomorphism (assuming it has an inverse if not its a homomorphism) since its commutes with the operations defined on the set, namely vector addition and scalar multiplication.That really helps me when thinking about different bases it’s kind of like when you have two isomorphic sets when you think of an element in one of the you have an associated element in the other set. Thats kind of what this is like each element in one vector space has another associated vector in another vector space with a different basis.Shits crazy

[@justinshin2279]

This is the part I feel like is absolutely awesome... coordinates become vectors and vectors become coordinates , and they span everything.

[@Mawkler]

After watching 6:43 for maybe the fifth time this year you finally made that click for me. THANK YOU! Our lecturer uses notation that says we're going from base B to A when it really feels like we're going from A to B. I now see why! Your videos truly are the best!

[@djebbarabderrahmene1813]

0:34 --> Coordinates of a vector and Scaling Basis Vectors, Coordinate Systems 1:38 --> Different Coordinate System 4:14 ---> Translating Between Coordinate Systems 5:08 ---> Matrices

[@georgeofhamilton]

I love how seamlessly you’ve been sliding new videos into this series.

[@gorgolyt]

5:58 Brilliant, such a clear way of thinking about it -- so helpful!

[@NoOne-tx6oh]

My thirst from highschool finally being quienced in my late twenties. Maths is less scary now, I feel more confident. Thank you!

[@MayankGoel447]

The last topic is a really nice explanation for why similar matrices have same eigenvalues. The eigenvectors are essentially fixed in space for a transformation, the eigenvectors differ because co-ordinate systems are different. But the scaling factor (the eigenvalues) only depends on the transformation, it is independent of the coordinate system. Therefore, similar matrices have same eigenvalues. Essentially similar matrices correspond to writing the same linear transformation in a different coordinate system.

[@the_vine_queen]

Thank you SO MUCH! I am in a Linear Algebra class in engineering college, and my professor only ever talks in abstracts and proofs, never explaining anything in layman's terms. I have been working on change of basis for a few weeks now, never fully understanding it, and this video is what finally made it all make sense. I legit almost cried when it all just clicked in my head. So, again, THANK YOU, 3Blue1Brown!

[@nerd2544]

also engineering student studying Linear Alg and i skipped like 3 weeks worths of lectures since our prof is dogshit but now we got an assignment and it's 10% of the grade so I'm relying on 3b1b to help me not get an F 😔

[@eeerik8]

Your introduction makes me so happy.

[@iam5566]

You cannot believe how thankful I am for the existence in this video. I really hope wherever you are in the world, you have a peaceful life full of wonder and learning and much deserved happiness.

[@adhaarsharma753]

Perfect mix of mathematics and philosophy. I absolutely love it!

[@anantchopra1663]

Even the quotation at the beginning makes a lot of sense when you watch the video a second time! You craft your videos so well, Grant! You're amazing!!

[@quentinjanicot8350]

Oh my god, you made it so clear all this story of the matrix applied to the grid or to the vectors.... Will you do some stuff about topology ? It would be great :D

[@3blue1brown]

The video I'm planning to do after this series will be related to topology. As to a whole "Essence of topology" series, maybe later.

[@DarkEssence26]

@3Blue1Brown, thanks you so much. Even when I've already knew this things about linear algebra from university it is good to construct intuition of visual represented connections of all this concepts. It is even more nice to know of your plans about topology videos.

[@DekuStickGamer]

Oh my god, that's great. Looking forward to it.

[@ProfessorEisenoxid]

+3Blue1Brown I am looking forward to it!! :)

[@zes3813]

nst as storix or not

[@sanskaripatrick7191]

I cannot tell you how grateful I am for these videos. You teach all of us what our professors failed to. God bless and Thank you so much 😄

[@Harlequin314159]

Reminds me of using commutators to come up with Rubik's cube moves. You will often: perform a sequence of moves, then change a small thing, then perform the inverse of that sequence of moves, then end by inverting the small change. Both are non-commutative so it seems similar.

[@zairaner1489]

This sounds indeed similar! Conjugating (thats the name for "multiplying something by something else from the right and the inverse of that fromj the left") appears in more areas than just with matrices

[@gorgolyt]

Random story but a great lecturer of mine put quite a bit of emphasis on the "perspective" perspective of conjugation, but when I talked to my tutor about it, she had never thought of it that way... and she was an algebraist. Surprising!

[@JivanPal]

In Stefan Pochmann's methods (both original Pochmann and M2/R2, both typically used for blindsolving), the "setup moves" are a change of basis, essentially. If S is a setup move, and A is an algorithm that switches the desired pieces once set up, then S^-1•A•S denotes the switch of the desired pieces in situ.

[@BlueGiant69202]

You might find this interesting: kzbin.info/www/bejne/qarcfGmeibyHbbc

[@NomadUrpagi]

@@BlueGiant69202 what is the blue giant your username is namesake to? Is it Ymir?

[@chaotic_clumsyy]

It's been 4 years since you posted this, and I just want to point out that this video, in particular, made me pass my first course in Linear Algebra! Many a thank yous!

[@oscarfriberg7661]

I love how you color the brackets at 10:58. I remember this part as one of the more difficult parts of linear algebra, but the way you describe it makes it really easy to understand :)

[@SuperOnlyP]

- This video should be the first one to watch for this series -> to find who Jennifer is , we will watch all videos ! - The Jennifer's concept: is like explaining a problem/idea( in professoinal field) to a child. You will need have the child's mind/space (kind of the what the knowlege the child could have - not professional's knowlege) to speak the kid language so that you can talk about that problem/idea to them easily.

[@pfever]

A-1 M A That I see in so many places, finally I got what it means =)

[@srujanpanuganti]

This is what which is called as a similarity transform - I guess!

[@side-fish]

We used this to convert local coordinates to global coordinates in matrix analysis of structures.

[@totheknee]

The inverse of Ask Me Anything?

[@tonaxysam]

@@totheknee There are two ways of finding that inverse: The "Don't ask Me Anything" phrase, which could look like the person just doesn't want to answer whatever you want to ask him. The "There exists a topic which I don't want you to ask me about" phrase, which sound unnatural, but is equivalent (logically speaking) to the previous phrase (even tho It doesn't have the same connotation), which seems like the person just doesn't want to talk about "something", but anything else would be fine. So, if A^-1MA = Ask Me Anything, then the inverse of the entire thing (A^-1MA)^-1 = (A^-1)(M^-1)A means one of two things: I don't want to talk about something, or I don't want to talk about anything. I'm sorry, I'm bored :3.

[@thatguy-cf5gs]

Just found this channel. It changed my life, thank you!

[@komolunanole8697]

Its quite confusing to talk about translating vectors as converting them between coordinate systems. When I think "vector translation", I think about adding vectors together, and thus shifting them. Great video though, I wish I could like it multiple times... really man, you deserve more for this awesome work!

[@zairaner1489]

Yeah me too

[@MichaelaGrasko]

i have been working to understand basis vectors for the past 2 days and you've just made me understand it in 12:50 minutes

[@andramaria4426]

I LOVE YOU, YOU JUST GAVE MEANING TO MY LIFE, THANK YOU !!!

[@dvirginz4001]

The empathy analogy is probably the best intuition I had about linear algebra ever. Your course covers for memorizing equations of thousands of students. Thank you.

[@paradoxicallyexcellent5138]

I'm not sure if 3Blue1Brown will be covering this - I don't think it really belongs in this "essence" series - but a really cool question for viewers to ask to play around with this concept is: how does Jennifer compute "dot products" in her coordinate system? The interplay between duality and the concept of change-of-basis is beautiful and important.

[@3blue1brown]

I'm glad you brought this up. It was in the original script, but I cut it out to stay, as you said, in the essence. I remember being truly surprised at the fact that the dot product is, in some sense, a choice that we make, and least in the context of an abstract vector space.

[@fenhirbr]

I think that deserves a footnote video.

[@jngado]

How does she?

[@zairaner1489]

Out of my head I could imagine two obvious options: One practically inherits the dot product: You would take the dot product of two of Jennifers vectors by first transforming them back to "normal" vectors and rhen taking the normal dot product. The other option would be to just take tge dot product of Jennifers vectors like normal. There's an interesting difference because with the second option, jennifers basis vectors will always be orthogonal with length 1, while they normally wont with the first

[@paradoxicallyexcellent5138]

Really well-said! Both interpretations are interesting. Casting aside our "mathematical empathy" suppose we say that our dot product is "right" and hers is "wrong." Then in order for Jennifer to take the "right" dot product, she would have to do what you just said: convert her vectors from her coordinate system to ours before computing. On the other hand, if Jennifer insists that her vectors are, as you say, orthogonal with length 1, then we're at an impasse: she will simply get different answers than we. By the way, you could also ask the question, if we were to "empathize" with Jennifer and agree that her dot product is "right," then you could ask, how would we go about doing that? How could we modify our dot product formula so that we get the same answers she would get? You'll find that there's an interesting difference between the first question and the second: one requires us ultimately to take an inverse matrix. Do you see which one? It's kind of like, if I'm talking to a European (I'm an American) and I want to describe the weather, I'll convert the Fahrenheit to Celsius for them, because neither system is "wrong" per se, but they'll understand it better if I do that.

[@tianchenzheng7464]

I freaking love ur videos. This makes me wonder what the heck was I and my professor doing in my linear algebra class. I can't even express how much I'm impressed by the intuition I gain by watching these videos. It's like a whole new world!

[@robertr6668]

Thank you for helping me actually grasp this concept. Amazing video!

[@commodorekitty]

This throws a whole new light to what I’d been taught - but had barely conceptually understood - in my mathematical methods in physics class. Thank you so much. Bless you. 💖

[@lyuboslavilov]

I love your work here, man. How can we donate?

[@emelradjo7788]

well he has a bitcoin adress so you can send him some coins ?under about in his youtube channel

[@TheCoolcat0]

he also has a patreon: www.patreon.com/3blue1brown

[@rafaeljinzo]

Best way nowadays is donating BATs if you use the Brave browser.

[@krishnaphanindra1841]

I love the detail he adds to the videos. Just look at the color transition in the matrix which represents the change in basis. Kudos to his involvement and patience to work on all these details..!!! :)

[@liams923]

Basis vectors are a social construct. Stop trying to assign them i or j at birth

[@MrCmon113]

Nah, the standard basis is special. 0 and 1 are part of the definition of vector spaces.

[@barfyman-362]

@@MrCmon113 You frickin racist!

[@shirishchinchanikar8199]

Vectorist not racist

[@trumanburbank6899]

Sorry, but I find transvectors creepy.

[@shirishchinchanikar8199]

Look at vectors while the basis vectors i and j are fixed most of the other vectors are fluid And have both i and j charachter They can also transform themselves if they want to So much to learn for humans from these vectors

[@sourabhkhandelwal689]

Man, you are next level stuff. Literally impressed by your genius. Hands down! I wish I had teachers like you. Take a bow. Massive respect.

[@sidaliu8989]

This series is awesome. I am trying to understand deeper, and have a question: At 9:50, you say, "How would Jennifer describe this same 90-degree rotation of space?", I think in Jennifer's space, this rotation is not 90-degree(even not a rotation). Maybe we could say, "How would Jennifer describe a transformation which from our perspective is a 90-degree rotation?" Thank you!

[@swayampal3348]

I totally agree with you. The video part after 9:50 explains how Jennifer would see our 90-degree transformation. But if we want to see Jennifer-90-degree transformation in our perspective, first we should rotate the general (x,y) vector by 90-degree, ie, by multiplying by that [0,1,1,0] matrix and then converting it to our grid by A-inverse

[@deeptochatterjee532]

Sida Liu No, if you look at the angles it's still 90 degrees, unless her measurement of angles is messed up now

[@MuffinsAPlenty]

Deepto Chatterjee - maybe her angles are messed up! If you look into an arbitrary vector space (over the real or complex numbers), sometimes you can develop a notion of an _inner product._ An inner product is a generalization of the notion of the dot product. It is an operation that takes two vectors in your vector space as an input and outputs a real number, subject to certain properties. A vector space together with a specified inner product is called an inner product space. In an inner product space, we _define_ the length of a vector to be the square root of the inner product of that vector with itself; symbolically, ||v|| = √(in(v,v)). And we _define_ the angle between two vectors to be the arccosine of the inner product of those vectors divided by the product of the lengths of those vectors; symbolically, θ = arccos(in(v,w)/(||v||∙||w||)). Knowing this, if Jennifer decides to use the "dot product" with respect to her basis vectors (which would be an inner product on R^2), then her basis vectors would appear to her to be orthogonal and of length 1! And our basis vectors would appear to her _not_ to be orthogonal or of length 1. Of course, Jennifer could also choose a different inner product from the "dot product" with respect to her basis vectors, in which case her basis vectors may not be orthogonal or of length 1 using that inner product.

[@rynin8019]

Nope! Here, everyone sees space the same way. A 90 degree rotation to us is a 90 degree rotation to Jennifer. What's different is how she DESCRIBES space. So, she needs a different matrix to describe a 90 degree rotation.

[@stayingcurious7005]

@@rynin8019 6 months late, but from the video, what looks like a 90 degree angle in our space looks like a greater than 90 degree angle in space from her perspective. So while the rotation is equivalent in both coordinate systems, I am not sure we all "see space the same way."

[@afakcay]

Grant, you know the (A^-1)(M)(A) explanation you added at the end. You are truly something else!!!

[@eurekad2070]

6:57 actually this matrix transforms "the grid Jennifer sees" into "the grid we see", since everyone sees his own basis as the standard unit grid. In this way, the matrix transforms a vector "in her language" to "our language". This would be a more natrual way to describe it. : )

[@dilpreetsingh6592]

thanks man i was confused at this point but your insight cleared my doubt

[@miguelgarciadominguez7190]

You have no idea what this videos means to me and the impact they have had on my life. Thanks

[@DanielOShea29]

You're blowing my mind here, dude.

[@cybersecuritytoday8711]

MemeLord why are crying?

[@ゾカリクゾ]

too many dead memes

[@zachk3396]

The explanation for "How to translate a matrix" with each of the steps and meaning of the intermediate results was incredible! Thanks for making this video.

[@schokoladenjunge1]

5:32 I love how the left pi student is looking to the side to the question like *cough*Of course I've watched chapter 3*cough cough* I have to admit, it's beautiful how you've described similar matrices with empathy. I would have loved if you had gone into covectors here too, they are natural when you get to this point. I always mix up the way the way each transformation matrix works...is there any way to remember that more easily? I learned all of this the hard, computing and strict way.

[@JannikPitt]

Haha didn't notice that, that's very cool haha

[@dhavalsuthar9692]

I have seen twice this video...with pause and play.....and remains in thinking of whole day that your explanation is so wonderful.....

[@Azarothpng]

Fun fact: The inverse matrix is our unit vectors ((1,0), (0,1)) expressed in Jennifer's language as columns.

[@whatever-ko8qx]

It finally clicked for me. This topic got me confused over the entire semester and only now, after rewatching this video multiple times, did I finally understand why the order of translation is the way it is. Thank you Sir!

[@HoaDVu]

If both [1, 2] and [-1, 1] are in Jennifer's space, why is their angle not equal to 90 degrees? Does a 90-degree angle in her space not use the same definition as ours?

[@ellie_deli]

Great question! Almost all of the time, the angle between a pair of vectors that are described with some basis B will change whenever that same pair of vectors is described with a new basis B' His next video in this series, the one on eigenvectors and eigen values, explains this concept well!

[@clos242003]

Every Linear Algebra professor should start their lessons with these videos. Outstanding!

[@atzuras]

"Space itself has no intrinsic grid" Einstein: "Hold my Energy Stress Momentum Tensor"

[@Yohodaify]

Tensors are dependent on the choice of basis though :)

[@baldeepsingh5471]

You my friend are a life saver. Why can't more teachers do these types of visualizations

[@duegia44]

9:15, it's be more useful if you make it specific that the 90 rotation transformation is a transformation in OUR coordinate system but NOT Jennifer's, if it's in Jennifer's there's would be no need for all that formula at all.

[@praveenyadav6813]

I had the same doubt, I thought shouldn't Jennifer multiply the same rotation matrix if she wants the vector in her coordination system to be rotated by 90 degrees.

[@forthrightgambitia1032]

This took me a while to figure out too, I think it's one part that could've been better explained. It finally hit me that the two vectors in some arbitrary basis might not be 90 degrees from each other, so the orthonormal basis transformations will be encoding 'flips' of basis vectors that are NOT 90 degree rotations. To get what a 90 degree flip is you need to find out your basis vectors are in terms of her basis and then flip them according to the result.

[@sillything1031]

I spent 2 hours on this single video but it feels so good that you finally get it. Tbh this change of basis thing has been stuck in my head ever since I watched the earlier video about transformation. Thanks for flushing that question out of my head

[@BlackJar72]

I wouldn't use a computer to compute the inverse. The mechanical, generic computation is complex and computationally expensive, while its often possible to work out a much simpler and more efficient set of computations on paper -- thus, it often makes more sense to find the inverse matrix by hand and then program the computer to use it. At least, this is how I handled inverting the projection matrix used in 3D rendering.

[@TheKurtPrice]

I think the point he makes is more general. It may be easier for you to invert your matrix by hand, but what if you need to invert a 1000x1000 matrix whose values change depending on a previous set of steps? Do you then have the system print out that matrix and wait for your input to provide it the new inverted matrix? In reality, you should work to form an equivalent statement that does not require you to invert a matrix wherever possible (find symmetric matrices maybe) and then bring down the number of computations you'd have to do. However, It is almost never worth inverting these matrices by hand.

[@yedidyadarshan9923]

You literally are one of the best teachers in the world... We need more of your videos, keep up the good work!!

[@EngineeringNS]

I love you.

[@mahmedaa]

Again, another great video. It made things clear. The last part about empathy, especially, is applicable to things in abstract algebra and functional analysis, not only to Linear Algebra. Made me go back to the hours spent trying to understand the motivation behind definitions and finally things are clearer now. Thanks a ton.

[@utsawkumar8199]

why on earth jeneffer needs different basis?

[@eminbaybarstimurstudent3802]

You taught us a word (A M^-1 A) that looks like a terror organization name could actually gives empathy to the others :) Thanks for creating such content sir

[@AgglomeratiProduzioni]

0:04 I usually think the opposite: Mathematics is giving different names to the same thing.

[@MlueBonday]

Köszönjük!

[@yuzezhou2769]

Yep. Me. Loner with no life watching linear algebra on Christmas.