Search   Memberlist   Usergroups
 Page 1 of 4 [53 Posts] View previous topic :: View next topic Goto page:  1, 2, 3, 4 Next
Author Message
mariano.suarezalvarez@gma

Joined: 28 Apr 2006
Posts: 58

Posted: Sun Jul 16, 2006 4:52 am    Post subject: Re: Rotations - why are they not vectors

 Quote: I am bothered by the mathematics of rotations. It is I believe mathematically acceptable for any physical reality to be defined on an abstract axiomatic basis. Then anything that fulfills a given defining set of axioms for a type of mathematical object is a mathematically valid example of the defined mathematical object.

A set does not make a vector space. You need to specify
two operations, addition and multiplication by scalars. Moreover,
these need to satisfy certain relations, which you have seen in Halmos'
book.

Now, you want to view the set of rotations as a vector space,
somehow. Well. You need to decide what those two operations will be.
Before you do that, the question "are rotations a vector space?"
is meaningless.

 Quote: [snip] NB I am aware that 2-D rotations do-not-commute, but it seems to me that that has nothing to do with axiomatics or my questions.

Actually, the composition operation on rotations (with a fixed center)
in the plane *is* commutative.

You may want to review Halmos' presentation of what a vector space
is, if you think that commutativity is irrelevant, by the way...

-- m
William Elliot
science forum Guru

Joined: 24 Mar 2005
Posts: 1906

Posted: Sun Jul 16, 2006 5:51 am    Post subject: Re: Rotations - why are they not vectors

On Sun, 16 Jul 2006, Terry Padden wrote:

 Quote: Now consider simple (= 1-D) rotations of a spherical object about any given fixed axis. You mean 3D rotations?

 Quote: Could someone point out to me in what way such 1-D rotations do NOT meet the axiomatic criteria for a Vector Space. In 3D, rotations are represented as a vector in the direction of the axis

of rotation with magnitude of angular displacement.

 Quote: If 1-D rotations are axiomatically vectors, why cannot they be axiomatically compounded into multi-dimensional vector spaces ? Because the cross product doesn't?

 Quote: NB I am aware that 2-D rotations do-not-commute,

Planar 2D rotations around a point are basically scalars.
science forum beginner

Joined: 17 Jun 2005
Posts: 28

Posted: Sun Jul 16, 2006 7:23 am    Post subject: Re: Rotations - why are they not vectors

<mariano.suarezalvarez@gmail.com> wrote in message
 Quote: Terry Padden wrote: I am bothered by the mathematics of rotations. It is I believe mathematically acceptable for any physical reality to be defined on an abstract axiomatic basis. Then anything that fulfills a given defining set of axioms for a type of mathematical object is a mathematically valid example of the defined mathematical object. A set does not make a vector space.

You B***** Fool. Who mentioned sets !!

 Quote: You need to specify two operations, addition and multiplication by scalars.

The obvious ones you moron. You can ADD rotations; and you can SCALE
rotations by a suitable Field. Idiot !!

 Quote: [snip] NB I am aware that 2-D rotations do-not-commute, but it seems to me that that has nothing to do with axiomatics or my questions. Actually, the composition operation on rotations (with a fixed center) in the plane *is* commutative.

Yes you fool - but that is in 1-D ; and I wrote do-not-commute in 2-D.
Can't
you even read a simple sentence ???

 Quote: You may want to review Halmos' presentation of what a vector space is, if you think that commutativity is irrelevant, by the way... NO ! I want you to go AWAY !!!!!!
science forum beginner

Joined: 17 Jun 2005
Posts: 28

Posted: Sun Jul 16, 2006 7:23 am    Post subject: Re: Rotations - why are they not vectors

"William Elliot" <marsh@hevanet.remove.com> wrote in message
news:Pine.BSI.4.58.0607152245480.22224@vista.hevanet.com...
 Quote: On Sun, 16 Jul 2006, Terry Padden wrote: Now consider simple (= 1-D) rotations of a spherical object about any given fixed axis. You mean 3D rotations?

NO, you fool. The axis is fixed. Only 1-D rotations are allowed (so far)

 Quote: Could someone point out to me in what way such 1-D rotations do NOT meet the axiomatic criteria for a Vector Space. In 3D, rotations are represented as a vector in the direction of the axis of rotation with magnitude of angular displacement.

PLEASE GO AWAY and keep this irrelevant 3-D nonsense to yourself

 Quote: If 1-D rotations are axiomatically vectors, why cannot they be axiomatically compounded into multi-dimensional vector spaces ? Because the cross product doesn't?

You are showing gross stupidity by this irrelevance. I am asking about
AXIOMS - not mechanics. Please stop embarrassing yourself in public.

 Quote: NB I am aware that 2-D rotations do-not-commute, Planar 2D rotations around a point are basically scalars.

That's your own little secret. Keep it that way. Now please go away and
think about axioms for a few years.
William Elliot
science forum Guru

Joined: 24 Mar 2005
Posts: 1906

Posted: Sun Jul 16, 2006 9:33 am    Post subject: Re: Rotations - why are they not vectors

On Sun, 16 Jul 2006, Terry Padden wrote:
 Quote: "William Elliot" wrote in message On Sun, 16 Jul 2006, Terry Padden wrote: Now consider simple (= 1-D) rotations of a spherical object about any given fixed axis. You mean 3D rotations? NO, you fool.

Get some manners.
Narcoleptic Insomniac
science forum Guru

Joined: 02 May 2005
Posts: 323

Posted: Sun Jul 16, 2006 9:58 am    Post subject: Re: Rotations - why are they not vectors

On Jul 16, 2006 2:21 AM, Terry Padden wrote:

 Quote: mariano.suarezalvarez@gmail.com> wrote in message news:1153025545.663758.95150@75g2000cwc.googlegroups.com... Terry Padden wrote: I am bothered by the mathematics of rotations. It is I believe mathematically acceptable for any physical reality to be defined on an abstract axiomatic basis. Then anything that fulfills a given defining set of axioms for a type of mathematical object is a mathematically valid example of the defined mathematical object. A set does not make a vector space. You B***** Fool. Who mentioned sets !!

YOU mentioned sets implicitly when you brought up vector
spaces!

 Quote: You need to specify two operations, addition and multiplication by scalars. The obvious ones you moron. You can ADD rotations; and you can SCALE rotations by a suitable Field. Idiot !!

Since rotations are just transformations on R^3, when you
ADD rotations you're just looking at the composition of
two or more transformations.

Moreover, since these transformations can be represented
as matrices the composition of them is definately NOT

 Quote: [snip] NB I am aware that 2-D rotations do-not-commute, but it seems to me that that has nothing to do with axiomatics or my questions. Actually, the composition operation on rotations (with a fixed center) in the plane *is* commutative. Yes you fool - but that is in 1-D ; and I wrote do-not-commute in 2-D. Can't you even read a simple sentence ??? You may want to review Halmos' presentation of what a vector space is, if you think that commutativity is irrelevant, by the way... NO ! I want you to go AWAY !!!!!!

Stop being such a douchebag.
science forum beginner

Joined: 17 Jun 2005
Posts: 28

Posted: Sun Jul 16, 2006 10:54 am    Post subject: Re: Rotations - why are they not vectors

"Narcoleptic Insomniac" <i_have_narcoleptic_insomnia@yahoo.com> wrote in
message
news:7171135.1153043965570.JavaMail.jakarta@nitrogen.mathforum.org...
 Quote: On Jul 16, 2006 2:21 AM, Terry Padden wrote: mariano.suarezalvarez@gmail.com> wrote in message news:1153025545.663758.95150@75g2000cwc.googlegroups.com... Terry Padden wrote: I am bothered by the mathematics of rotations. It is I believe mathematically acceptable for any physical reality to be defined on an abstract axiomatic basis. Then anything that fulfills a given defining set of axioms for a type of mathematical object is a mathematically valid example of the defined mathematical object. Since rotations are just transformations on R^3, when you ADD rotations you're just looking at the composition of two or more transformations. Moreover, since these transformations can be represented as matrices the composition of them is definately NOT VECTOR ADDITION!!!

What has any of that mumbo-jumbo got to do with the AXIOMS -

PLEASE GO AWAY and stop parading your stupidity. Rotations have nothing to
do with R3.
Narcoleptic Insomniac
science forum Guru

Joined: 02 May 2005
Posts: 323

Posted: Sun Jul 16, 2006 11:58 am    Post subject: Re: Rotations - why are they not vectors

On Jul 16, 2006 5:56 AM CT, Terry Padden wrote:

 Quote: "Narcoleptic Insomniac" i_have_narcoleptic_insomnia@yahoo.com> wrote in message news:7171135.1153043965570.JavaMail.jakarta@nitrogen.mathforum.org... On Jul 16, 2006 2:21 AM, Terry Padden wrote: mariano.suarezalvarez@gmail.com> wrote in message news:1153025545.663758.95150@75g2000cwc.googlegroups.com... Terry Padden wrote: I am bothered by the mathematics of rotations. It is I believe mathematically acceptable for any physical reality to be defined on an abstract axiomatic basis. Then anything that fulfills a given defining set of axioms for a type of mathematical object is a mathematically valid example of the defined mathematical object. Since rotations are just transformations on R^3, when you ADD rotations you're just looking at the composition of two or more transformations. Moreover, since these transformations can be represented as matrices the composition of them is definately NOT VECTOR ADDITION!!! What has any of that mumbo-jumbo got to do with the AXIOMS -

It's not "mumbo-jumbo" but fairly basic linear algebra...

...you know, the stuff you learn *after* you see those
axioms.

Hahahaha, seriously, get some new material. For your sake
I hope that you're just trolling and doing this for fun.

 Quote: Rotations have nothing to do with R3.

Actually, you cut out the part in this thread where *you*
began considering simple rotations of a sphereical object.
If you would look past your beloved axioms for a moment
you'd see that any rotation of a sphereical object can be
described as a transformation of R^3 -> R^3.

Going back to your original topic (simple rotations (in
1-D) of a sphereical object and why they're NOT vectors),
it suffices to just consider a simple rotation about the
x-axis since we can transform any arbitrary axis to the
x-axis.

We can the described this rotation by the matrix A(t) =

[1 0 0]
[0 cos(t) sin(t)]
[0 -sin(t) cos(t)].

The set of all rotation matrices of this type, along with
the 3x3 identity matrix, will form a *group* structure,
but I can't see why you would think this could generate
a vector space.

Regards,
Kyle Czarnecki
G.E. Ivey
science forum Guru

Joined: 29 Apr 2005
Posts: 308

 Posted: Sun Jul 16, 2006 12:04 pm    Post subject: Re: Rotations - why are they not vectors Why should any one respond to any question by you in the future? Several people have responded, as best they could, to your somewhat vague questions. (What, exactly do you mean by a "1-D rotation". I can see "flipping", changing (x, 0, 0) to (-x, 0, 0) but how can you "rotate" through an angle in 1 dimension?) You immediately started calling them "fools". That's not a good way to convince people to answer your questions.
science forum beginner

Joined: 17 Jun 2005
Posts: 28

Posted: Sun Jul 16, 2006 12:55 pm    Post subject: Re: Rotations - why are they not vectors

"G.E. Ivey" <george.ivey@gallaudet.edu> wrote in message
news:627837.1153051489453.JavaMail.jakarta@nitrogen.mathforum.org...
 Quote: Why should any one respond to any question by you in the future? Several people have responded, as best they could, to your somewhat vague questions. (What, exactly do you mean by a "1-D rotation". I can see "flipping", changing (x, 0, 0) to (-x, 0, 0) but how can you "rotate" through an angle in 1 dimension?) You immediately started calling them "fools". That's not a good way to convince people to answer your questions.

For 45 years taxes from my hard earned income have been used to fund things
such as the internet and university education. It took me some time to
frame the question. For that it is not unreasonablke for me to expect
people to make a reasonable effort to understand a question before replying
to it . As a starter they should at least read it.

But what rreally makes me see red is the results of all that expenditure on
mathematical education - the results as displayed by prior respondents and
you.

What is unclear about "1-D rotations about a fixed axis" ? It is specified
by a 1-tuple x an anglular displacement; just like a 1-D translation is
specified by a 1-tuple x a linear displacement.

Rotations and Vectors have nothing intrinsically to do with Rn or any
similar pre-supposition. Rotations are just angular displacements - nothing
necessarily to do with translations at all ! Vectors are just things which
satisfy the axioms.

My standards are high but not unreasonably so considering my forced
financial investment. If they seem unreasonable to you and others remember
that as GBS told us all progress depends on unreasonable people.

My question is clear and straightforward. If you don't understand it blame
your maths professors; not me.

By the way the usual physical measurement of 1-D rotations is Time in hours,
minutes, seconds, etc. Perhaps ypu have heard of Babylonian Maths; perhaps
you know that miniutes and seconds also measure angles etc. So far all I
have got back is the maths of Babel.

PLEASE can the next reply be from someone who understands the question.
Narcoleptic Insomniac
science forum Guru

Joined: 02 May 2005
Posts: 323

Posted: Sun Jul 16, 2006 1:37 pm    Post subject: Re: Rotations - why are they not vectors

On Jul 16, 2006 7:57 AM CT, Terry Padden wrote:

 Quote: "G.E. Ivey" wrote in message news:627837.1153051489453.JavaMail.jakarta@nitrogen.mathforum.org... Why should any one respond to any question by you in the future? Several people have responded, as best they could, to your somewhat vague questions. (What, exactly do you mean by a "1-D rotation". I can see "flipping", changing (x, 0, 0) to (-x, 0, 0) but how can you "rotate" through an angle in 1 dimension?) You immediately started calling them "fools". That's not a good way to convince people to answer your questions. For 45 years taxes from my hard earned income have been used to fund things such as the internet and university education. It took me some time to frame the question. For that it is not unreasonablke for me to expect people to make a reasonable effort to understand a question before replying to it . As a starter they should at least read it.

Well that explains the hostility and senility.

 Quote: But what rreally makes me see red is the results of all that expenditure on mathematical education - the results as displayed by prior respondents and you.

Clearly you're mistaken; from the little time I've spent
on these forums I've come to know both William and G. E.
indirectly and they both happen to be very knowledgeble.

 Quote: What is unclear about "1-D rotations about a fixed axis" ? It is specified by a 1-tuple x an anglular displacement; just like a 1-D translation is specified by a 1-tuple x a linear displacement. Rotations and Vectors have nothing intrinsically to do with Rn or any similar pre-supposition. Rotations are just angular displacements - nothing necessarily to do with translations at all ! Vectors are just things which satisfy the axioms.

I definately agree with you on this last paragraph.
Although, when I mentioned earlier that spherical
rotations could be viewed as mappings on vector spaces
you called it "mumbo-jumbo" and called me a fool. I guess
I must be a fool for thinking that rotations are just
transformations that *act* on vector spaces and are *not*
vectors themselves.

 Quote: My standards are high but not unreasonably so considering my forced financial investment. If they seem unreasonable to you and others remember that as GBS told us all progress depends on unreasonable people.

I would like to forget anything that any Bush has told us.

 Quote: My question is clear and straightforward. If you don't understand it blame your maths professors; not me.

The topic of this thread is almost as meaningful as

"Colors - why are they not feelings".

 Quote: By the way the usual physical measurement of 1-D rotations is Time in hours, minutes, seconds, etc. Perhaps ypu have heard of Babylonian Maths; perhaps you know that miniutes and seconds also measure angles etc. So far all I have got back is the maths of Babel. PLEASE can the next reply be from someone who understands the question.
Jürgen R.
science forum beginner

Joined: 06 Feb 2006
Posts: 12

Posted: Sun Jul 16, 2006 2:51 pm    Post subject: Re: Rotations - why are they not vectors

On Sun, 16 Jul 2006 04:42:30 GMT, "Terry Padden"

 Quote: I am bothered by the mathematics of rotations. It is I believe mathematically acceptable for any physical reality to be defined on an abstract axiomatic basis. Then anything that fulfills a given defining set of axioms for a type of mathematical object is a mathematically valid example of the defined mathematical object. Now consider simple (= 1-D) rotations of a spherical object about any given fixed axis. Superficially, to me (not a mathematician), such "angular displacements" meet all of the formal axioms for a Vector Space (as given in e.g. Halmos) as well as 1-D linear displacements do. Could someone point out to me in what way such 1-D rotations do NOT meet the axiomatic criteria for a Vector Space.

They meet the requirements. It's a one-dimensional vector space.
 Quote: If 1-D rotations are axiomatically vectors, why cannot they be axiomatically compounded into multi-dimensional vector spaces ?

I have no idea what you mean by "axiomatically compounded", but the
answer is that you can form the direct product of any number of such
spaces in the usual way to get higher-dimensional vector spaces.

 Quote: NB I am aware that 2-D rotations do-not-commute, but it seems to me that that has nothing to do with axiomatics or my questions. I am not suggesting that rotations ought to be physically vectors. I am just trying to get clarification of the math picture for vectors.

 Quote:
Stephen Montgomery-Smith1
science forum Guru

Joined: 01 May 2005
Posts: 487

Posted: Sun Jul 16, 2006 2:57 pm    Post subject: Re: Rotations - why are they not vectors

 Quote: I am bothered by the mathematics of rotations. It is I believe mathematically acceptable for any physical reality to be defined on an abstract axiomatic basis. Then anything that fulfills a given defining set of axioms for a type of mathematical object is a mathematically valid example of the defined mathematical object. Now consider simple (= 1-D) rotations of a spherical object about any given fixed axis. Superficially, to me (not a mathematician), such "angular displacements" meet all of the formal axioms for a Vector Space (as given in e.g. Halmos) as well as 1-D linear displacements do. Could someone point out to me in what way such 1-D rotations do NOT meet the axiomatic criteria for a Vector Space. If 1-D rotations are axiomatically vectors, why cannot they be axiomatically compounded into multi-dimensional vector spaces ? NB I am aware that 2-D rotations do-not-commute, but it seems to me that that has nothing to do with axiomatics or my questions. I am not suggesting that rotations ought to be physically vectors. I am just trying to get clarification of the math picture for vectors.

I think people might be confused about what you mean by "1-D rotations."
The convention normally used is to describe rotations in R^n as n
dimensional rotations. I don't think you are following this.

Now the sophisticated way to describe your issue, I think, is to say
that there are two answers, depending upon whether you are describing
the Lie Group or the Lie Algebra.

Actual rotations are not described by vectors, but by matrices -
orthogonal matrices. The composition of two rotations is not any kind
of addition, but multiplication of the matrices. The orthogonal
matrices do not form a vector space. This is true even if you restrict
yourself to rotations about a fixed axis (what I think you mean by 1-D
rotations) because rotation by 360 degrees is the same as rotation by 0
degrees, and as such it is impossible to properly define multiplication
by a scalar. And if you don't restrict yourself to rotations about a
fixed axis, matrix multiplication doesn't even commute (as you point out
above).

However the word "rotation" could also mean the rate of rotation, for
example "18 degrees per second clockwise about a certain axis." In that
case rotations do add like a vector space. However you should be
careful, for example in 4 dimensional space, the rotations is a 6
dimensional space (in general n goes to n(n-1)/2).

By the way, the notion of rotation (in the first sense I described)
about "an axis" really only has meaning if the underlying space is two
or three dimensional. In 4 or 5 dimensional space, the generic rotation
will have two axes.

Stephen
Sylvain Croussette
science forum beginner

Joined: 05 May 2005
Posts: 32

Posted: Sun Jul 16, 2006 3:04 pm    Post subject: Re: Rotations - why are they not vectors

G.E. Ivey wrote:
 Quote: Why should any one respond to any question by you in the future? Several people have responded, as best they could, to your somewhat vague questions. (What, exactly do you mean by a "1-D rotation". I can see "flipping", changing (x, 0, 0) to (-x, 0, 0) but how can you "rotate" through an angle in 1 dimension?) You immediately started calling them "fools". That's not a good way to convince people to answer your questions.

I think what he means by 1-D rotation is a rotation in 3 dimensional
space but around one axis only. This is the jargon used in some fields
like robotics where a 1-D rotation joint is a joint that rotates around
only one axis. This seems to be confirmed by his assertion that 2-D
rotations do not commute. To him this means a rotation in 3 dimensions
but around 2 different axes. It is true that they do not commute in
general. The problem is that he is not a mathematician (as he said
himself) and he is using "1-D" and "2-D" in a different context than
that of a mathematician.
Abraham Buckingham

Joined: 10 Mar 2005
Posts: 98

Posted: Sun Jul 16, 2006 3:09 pm    Post subject: Re: Rotations - why are they not vectors

 Quote: I am bothered by the mathematics of rotations. It is I believe mathematically acceptable for any physical reality to be defined on an abstract axiomatic basis. Then anything that fulfills a given defining set of axioms for a type of mathematical object is a mathematically valid example of the defined mathematical object. Now consider simple (= 1-D) rotations of a spherical object about any given fixed axis. Superficially, to me (not a mathematician), such "angular displacements" meet all of the formal axioms for a Vector Space (as given in e.g. Halmos) as well as 1-D linear displacements do. Could someone point out to me in what way such 1-D rotations do NOT meet the axiomatic criteria for a Vector Space. If 1-D rotations are axiomatically vectors, why cannot they be axiomatically compounded into multi-dimensional vector spaces ? NB I am aware that 2-D rotations do-not-commute, but it seems to me that that has nothing to do with axiomatics or my questions. I am not suggesting that rotations ought to be physically vectors. I am just trying to get clarification of the math picture for vectors.

For clarification please explicitly demonstrate your rotations and how
they satisfy the the axioms of a vector space.

 Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First
 Page 1 of 4 [53 Posts] Goto page:  1, 2, 3, 4 Next View previous topic :: View next topic
 The time now is Thu Nov 15, 2018 8:22 am | All times are GMT
 Jump to: Select a forum-------------------Forum index|___Science and Technology    |___Math    |   |___Research    |   |___num-analysis    |   |___Symbolic    |   |___Combinatorics    |   |___Probability    |   |   |___Prediction    |   |       |   |___Undergraduate    |   |___Recreational    |       |___Physics    |   |___Research    |   |___New Theories    |   |___Acoustics    |   |___Electromagnetics    |   |___Strings    |   |___Particle    |   |___Fusion    |   |___Relativity    |       |___Chem    |   |___Analytical    |   |___Electrochem    |   |   |___Battery    |   |       |   |___Coatings    |       |___Engineering        |___Control        |___Mechanics        |___Chemical

 Topic Author Forum Replies Last Post Similar Topics Best fit orthogonal basis for list of vectors chengiz@my-deja.com num-analysis 4 Wed Jul 19, 2006 6:16 pm Null rotations Greg Egan Research 1 Sun Jul 02, 2006 12:08 pm vectors from l_2 and their difference isn't in l_1+uncoun... eugene Math 7 Fri Jun 23, 2006 10:52 pm notation for vectors and points pluton Math 3 Sat Jun 03, 2006 4:15 pm ? e-vectors of sum of rank one matrices Cheng Cosine Math 1 Sat Jun 03, 2006 6:36 am

Other DeniX Solutions sites: Electronics forum |  Medicine forum |  Unix/Linux blog |  Unix/Linux documentation |  Unix/Linux forums  |  send newsletters