# Talk:Euclidean vector

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## Coordination among articles

The article linear algebra has been demoted to "start class". Several people are trying to fix it. But this article and the articles linear map, vector space, linear algebra, and matrix seem to have been written without reference to one another. A good goal would be to have all of these articles agree in terminology and style, and this article seems to be the place to start. There are probably other articles that should also be included in this project.

The first thing to consider is whether the title "Euclidean vector" is the best title for this article, leaving no article on the more general subject "Vector".

Rick Norwood (talk) 16:57, 9 February 2010 (UTC)

Considering the length of the disambiguation pages at Vector and Vector (mathematics and physics), I think the scope and title of this article -- for physical vectors in 2 and 3 real-world dimensions -- are not badly chosen.
There was extensive discussion on the title in /Archive 5. IMO the present title is better than any alternatives that were being canvassed at that time. Jheald (talk) 17:49, 9 February 2010 (UTC)

I don't have any problem with an article titled "Euclidean vector". My problem is with the lack of an article titled "vector (mathematics)". I haven't checked, but I suspect every mathematical encyclopedia has such an article. For example, this article at MathWorld http://mathworld.wolfram.com/Vector.html. At one point, Wikipedia explicitly wanted an article on every subject on MathWorld. Rick Norwood (talk) 14:20, 10 February 2010 (UTC)

Right now, vector (mathematics) redirects to vector space. I think that's a good solution: After all, a vector (strictly speaking) is just an element of a vector space, so you can't really discuss one without the other. Ozob (talk) 14:32, 10 February 2010 (UTC)

Consider the intelligent layperson who hears the word "vector" and wants to know what it means. To say that a vector is an element in a vector space is not helpful. I've been trying to find a good definition that will include vectors over an arbitrary field of scalars, and still be something a layperson can understand. Something like "a vector is a mathematical object that has both magnitude and direction, though in abstract mathematics the concepts of magnitude and direction may also be abstract." Rick Norwood (talk) 14:55, 10 February 2010 (UTC)

If you can think of a good article to put at vector (mathematics), then go for it. Myself, I don't know what could be put there; but I'll be interested to see what you come up with. Ozob (talk) 15:25, 10 February 2010 (UTC)

Sometimes its easier to define what something is by defining what it isn't.

It's hard to find an equationally defined class used in practice that wasn't originally motivated by its concrete instances. A Boolean algebra can be defined concretely as, any structure (with the appropriate operations) isomorphic to a subalgebra of a power set, or more abstractly as, any model of the equational theory of the two-element Boolean algebra. (That this theory has a finite basis, or finite axiomatization, is convenient but not the main point in the concrete-abstract distinction.)
The article Introduction to Boolean algebra begins with the finite axiomatization, but from the point of view of elementary algebra rather than abstract algebra. Section 5 on Boolean algebras (necessarily plural to avoid confusion) initially ignores the axioms and begins with concrete Boolean algebras (a) because they arise naturally and (b) to make the point that one can speak about at least the concrete kind without reference to any axiomatic definition of the concept.
The same should apply to vector spaces, with the parallels being strikingly clear when one considers that a vector space over GF(2), when equipped with a second constant 1 as the complement of the origin 0, is equivalent to a Boolean algebra via the evident translations in each direction between their respective languages. In particular, just as there is one finite concrete Boolean algebra 2n for each natural number n, so (given any field k) is there one finite-dimensional concrete vector space k n for each n. In both cases these are, up to isomorphism, the only finite/finite-dimensional such. (That the only non-free algebras here are some of the Boolean ones is an interesting but not central point.)
The benefit of the abstract definition, that it does not commit to a basis, can be had almost as well in the concrete case by defining an isomorphism of a concrete n-dimensional vector space to be a non-singular n×n matrix and pointing out that the resulting automorphism group elegantly links all bases in a way that makes the concrete concept basis-independent. One can then ask whether there might be an even neater approach to basis independence, which then leads naturally to the notion of an abstract vector space.
The problem with starting with the abstract definition is that it comes with no intuition. The point that is often lost is that concrete vector spaces are still vector spaces, despite not being defined equationally. It is enough for an object merely to satisfy the equations for a vector space, however the object was defined. --Vaughan Pratt (talk) 20:20, 13 July 2010 (UTC)
I think there ought to be an article about vector spaces in general, and one about vectors as used in classical mechanics and engineering with a short mention about other kinds of vectors used in physics. The first is what is currently at vector space, and either the current title or vector (mathematics) would be fine for it. For the latter, the current Euclidean vector is a good start but vector (physics) would be a better title. (Note also that physical vectors are not mathematical vectors, rather they are described by mathematical vectors: in modern mathematics all elements of all sets -- hence all vectors -- must be sets themselves, but the gravitational force acting on me right now in my frame of reference is not a set... A. di M. (formerly Army1987) (talk) 12:45, 14 July 2010 (UTC))

## History of vectors reduced to just one line?

The history, as we can see from the article, is only ONE LINE. Would someone help expand the histories? Thank you. KaliumPropane (talk) 09:05, 4 November 2010 (UTC)KaliumPropane

## Formal definition

I have removed the "formal definition" from the first paragraph of the article:

More formally, a Euclidean vector is any element of a Euclidean vector space, i.e. a vector space that has a Euclidean norm. A Euclidean vector space is automatically a type of normed linear space and a type of inner product space.

For one thing, this is rather at odds with the way the article introduces vectors as directed line segments in the usual Euclidean space (which is more properly speaking an affine space, not a vector space). This is typical of how most mathematical treatments deal with geometric vectors (see, for instance, the EOM entry). It's also important to observe WP:NPOV. When most people consider geometric vectors, e.g., in mechanics, they are usually not thinking of the "element of a Euclidean space" viewpoint, but rather are thinking of a vector in the sense described in this article: a directed line segment in a (naive) Euclidean space. It might be worth having more discussion somewhere to disambiguate the naive vectors described here and the elements of a Euclidean vector space, i.e., an inner product space. A perusal of the archive shows that there is substantial confusion over what the scope of this article is, with formalists often trying to impose the "rigorous" definition (which is not even mathematically the same notion that the rest of the article is talking about). Sławomir Biały (talk) 13:52, 15 January 2011 (UTC)

Indeed: once upon a time this page was titled (IIRC) vector (physics) and it was the counterpart to scalar (physics); look for example at the 500th-oldest revision. Then the mathematicians took over and completely messed up with both the scope and the title of the article. :-) Now it's about any three-dimensional vector space over the real numbers with a positive-definite inner product, regardless of its relationships to physical space.
I once even proposed to keep this article with its "new" scope and "new" title and to start another article which would then be the new counterpart to scalar (physics) (and wrote a draft of it), but there were too few physicists (or engineer) around :-) so no-one saw the need for such an article. --A. di M. (talk) (formerly Army1987) 14:45, 15 January 2011 (UTC)

## I'm getting sick of it

I know Wikipedia is written for different readers, but this is just ridiculous. The sum of the null vector with any vector a is a (that is, 0+a=a) is way too obvious and useless to be here. I don't mind if we remind readers that 1 + 1 = 2, but 0 + 1 = 1 is a little extreme. I mean I can't understand 90% of the mathematics on Wikipedia, and even I think this is too basic. 173.183.79.81 (talk) 03:10, 30 March 2011 (UTC)

I disagree. The existence and behavior of the null vector is central to the notion of a vector space. Without it and it's admittedly trivial-seeming behavior that 0+a=a, you don't have a linear space, you have an affine space. Plenty of times in advanced mathematics, seemingly trivial things are very important and need to be mentioned. —Ben FrantzDale (talk) 12:18, 31 March 2011 (UTC)

## History

The history of vectors focuses entirely on quaternions. A brief mention of quaternions is fine, but the section simply describes the history and properties of quaternions and leaves out the history of vectors entirely. The section obviously does not satisfy quality standards and if an experienced knowledgable editor doesn't revise it the section should be removed. — Preceding unsigned comment added by 174.109.94.64 (talk) 02:19, 11 September 2011 (UTC)

This is absolutely correct. I've removed the section. Someone who wants to add a relevant history section is welcome to do so. The removed text is copied below. --JBL (talk) 21:44, 17 April 2013 (UTC)
I disagree. We are an encyclopaedia not a text book so we need to cover a history of the subject. To properly discuss how the concept of vectors came about we need to discuss what came before, complex numbers and quaternions were important precursors. Also note this section shows where the word "vector" first appears, part of a quaternion. Yes it could use some editing Grassmann’s Calculus of Extension needs a mention. Crowe's A History of Vector Analysis [1] seems a good basis for extending the section.--Salix (talk): 07:00, 18 April 2013 (UTC)
(copied from my talk page)--Salix (talk): 22:07, 18 April 2013 (UTC)
Yes, of course the history of a topic is important in an encyclopedia, and it's always nice to see historical information in math articles. But we have here a history section that is the history of a different topic than the subject of the article: there were 4 out of 5 or 6 paragraphs written to emphasize quaternions, with vectors an afterthought at best. (I've now re-removed one of these paragraphs, a comparison of quaternion and complex multiplication.) Three such paragraphs remain. If you'd like to keep them, please rewrite them so that they are about vectors, not quaternions. (Or move content over to the quaternion article as appropriate.) Right now the section is extremely misfocused and misleading. --JBL (talk) 14:13, 18 April 2013 (UTC)
The history of vectors is quite convoluted. Many of the important features of vectors, like the dot and cross products and the del operator were arrived at through studying quaternions. There was also a parallel development following Grassmann which is closer to what we would recognise as vector, however at the time this was very marginal. It was not until the 1880's when Gibbs and Heaviside both publish works which we would recognise as vector analysis.--Salix (talk): 23:07, 18 April 2013 (UTC)

### Removed section

The concept of vector, as we know it today, evolved gradually over a period of more than 200 years. About a dozen people made significant contributions.[1] The immediate predecessor of vectors were quaternions, devised by William Rowan Hamilton in 1843 as a generalization of complex numbers. Initially, his search was for a formalism to enable the analysis of three-dimensional space in the same way that complex numbers had enabled analysis of two-dimensional space, but he arrived at a four-dimensional system. In 1846 Hamilton divided his quaternions into the sum of real and imaginary parts that he respectively called "scalar" and "vector":

The algebraically imaginary part, being geometrically constructed by a straight line, or radius vector, which has, in general, for each determined quaternion, a determined length and determined direction in space, may be called the vector part, or simply the vector of the quaternion.[2]

Whereas complex numbers have one number $(i)$ whose square is negative one, quaternions have three independent imaginary units $(i, j, k)$. Multiplication of these imaginary units by each other is anti-commutative, that is, $ij \ = \ -ji\ =\ k$. Multiplication of two quaternions yields a third quaternion whose scalar part is the negative of the dot product and whose vector part is the cross product.

Peter Guthrie Tait carried the quaternion standard after Hamilton. His 1867 Elementary Treatise of Quaternions included extensive treatment of the nabla or del operator.

In 1878 Elements of Dynamic was published by William Kingdon Clifford. Clifford simplified the quaternion study by isolating the dot product and cross product of two vectors from the complete quaternion product. This approach made vector calculations available to engineers and others working in three dimensions and skeptical of the fourth.

Josiah Willard Gibbs, who was exposed to quaternions through James Clerk Maxwell's Treatise on Electricity and Magnetism, separated off their vector part for independent treatment. The first half of Gibbs's Elements of Vector Analysis, published in 1881, presents what is essentially the modern system of vector analysis.[1] In 1901 Edwin Bidwell Wilson published Vector Analysis, adapted from Gibb's lectures, and banishing any mention of quaternions in the development of vector calculus.

## Why is there an overview section?

Right now, this article has an excellent introduction, followed by an overview section that mostly repeats the same content, but with less clarity and a variety of issues (like the idea that "an arrow" is the definition). I suggest simply removing the "overview" part of the first section (I.e., before the subsection "examples in 1 dimension"). --JBL (talk) 15:55, 28 August 2012 (UTC)

## Vectors, pseudovectors, and transformations

Does this section have contravariant and covariant backwards? Not only does the word contravariant seem to imply it should vary in the opposite way, but the description seems to say so to.

In other words, if the reference axes were rotated in one direction, the component representation of the vector would rotate in exactly the opposite way. Similarly, if the reference axes were stretched in one direction, the components of the vector, like the co-ordinates, would reduce in an exactly compensating way.

Why then does it say, just above that, that they "transform like the coordinates" and the give math transformation both the coordinates $x'=Mx$ and the vector $v'=Mv$ the same. Also why, if they are both transformed by the forward transformation, is the need for an inverse to exist mentioned. Combined with the fact that covariance and contravariance of vectors page give the contravariant transformation in terms of the inverse, $v[fA] = A^{-1}v[f]$, I think this section got the transformations crossed over for part of it somehow. 207.112.55.16 (talk) 04:50, 5 February 2013 (UTC)

## vector subtraction

The article states: "to subtract b from a, place the end points of a and b at the same point, and then draw an arrow from the tip of b to the tip of a. That arrow represents the vector a − b, as illustrated below:". However the section on representations tells us that the tip and the endpoint are synonymous. I presume that it should read "place the tails of a and b at the same point" or similar (this is what is illustrated). This subject is pretty fresh to me so I will leave it to somebody else to make the change. Kelly F Thomas (talk) 16:59, 1 April 2013 (UTC)

Quite right. I've made everything "head"s and "tail"s in that section. (In general this article is something of a mishmash and needs someone to go through and sort it out. Not volunteering, though.) --JBL (talk) 21:59, 1 April 2013 (UTC)

## WT: WikiProject Mathematics #“Vector” redirects and next subsection

Please, contribute to these discussions. See also talk: Vector (mathematics and physics) #A CONCEPTDAB article is needed. Incnis Mrsi (talk) 07:58, 25 April 2013 (UTC)
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