Talk:Eigenvector slew

Criticisms

"Dangero" has worded serious critics to this article which I have removed. That this a grave misjudgement on the side of "Dangero" can be proven as follows:

Technical quality and adequacy

- It has been written by a world leading expert in flight dynamics as applied to spacecraft

- It is essentially a copy of an article for the internal WIKI of European Space Agency

- The space observatories XMM and Integral make slews computed with this algorithm since many years

Interest

- It is one of the few application of "non-trivial mathematics" to attitude control of spacecraft

- Not only laymen but also many aerospace engineers specialising in attitude control of spacecraft are unfamiliar with this "mathematical algorithm". It can be found in some classical handbooks about attitude control, though!

Is "Dangero" an official reviewer? Can it be that the selection of reviewers has to be made more carefully! —Preceding unsigned comment added by 79.216.244.139 (talk) 2008-07-25T18:48:36Z

Reply

First of all, please assume good faith and remain civil. Anyone may edit or 'review' an article on Wikipedia. Here are the steps in the process so far. You created the article and User:Dengero placed a tag template on it indicating it should be speedily deleted on the grounds that it was patent nonsense. As an administrator I then looked at the page. I decided that although at first glance it seemed to fit the criteria in that it was so "irredeemably confused that no reasonable person can be expected to make any sense of it" on investigation of both the mathematics and your edit history that it did not fit the WP:CSD but that it was in serious need of cleanup. I therefore added those templates, which you have now removed.

The article urgently needs a simple explanation of what "Eigenvector slew" is, and why it is a subject of note. This needs to be in a written form that an interested and intelligent non-mathematician can follow. It also needs a couple of references. I am not a mathematician and I am concerned that it may be original research. I will replace a 'clean-up' tag as the need for this is not in doubt in my mind. If the above information is not provided soon I will follow up with further tags, including, if necessary, a suggestion the article be deleted. In its current form it is unacceptable. Ben MacDui 19:32, 25 July 2008 (UTC)

Reply to Ben MacDui

It is absolutely clear that to understand this article a University degree (a good one!!) in mathematics is needed! If you do not have this background it is definitely not understandable . But Wikipedia (in cathegories Physics/Mathematics) is full of articles that addresses this rather limited fraction of the general public! Professionals also use Wikipedia!

Stamcose (talk) 20:03, 25 July 2008 (UTC)

Dubious

The article currently has a statement which indicates that every unitary matrix (possibly only unitary 3 × 3 matrices), has an eigenvalue of 1. The eigenvalues of unitary matrices have absolute value 1, but need not be equal to 1. If the entries are real, then the eigenvalues are either all real, or include one complex number z, its conjugate 1/z, and a real eigenvalue, either 1 or -1. The determinant of the matrix is either 1 or -1. If the determinant is 1, then in this case, it must have an eigenvalue of 1, but if the determinant is -1, then it must not. Similarly in the three real case, if the matrix has eigenvalues -1, -1, -1, then it cannot have an eigenvalue of 1. In case the matrix has complex entries (which is implicitly encouraged by using the term unitary matrix instead of orthogonal matrix), then of course it can have arbitrary triples of eigenvalues chosen from the set of complex numbers of absolute value 1. For instance the diagonal matrix with entries i,-i,-1 is unitary has determinant 1 and has no eigenvalue equal to 1. JackSchmidt (talk) 20:06, 25 July 2008 (UTC)

It seems most likely that unitary matrix should simply be replaced by orthogonal matrix: thre is no hidden complex structure on three-dimensional real euclidean space, right? Plclark (talk) 20:33, 25 July 2008 (UTC)Plclark

(per comment in WT:MATH, edit conflict) I'm afraid it's not nonsense, but it's not precisely interesting. It's true that every transformation in SO₃(R) (not the implied U₃(R)) is a rotation, and properties of the transformation, including the axis and rotation angle, can be recovered from properties of the eigenvalues and eigenvectors (over C) of the matrix, but that information might be better placed in the vector (spatial) article. — Arthur Rubin (talk) 20:29, 25 July 2008 (UTC)

I can deliver a mathematical proof that all unitary 3 × 3 matrices has an eigenvalue of 1. Actually just write down the characteristic equation and use that the determinant is =1 and that ${\hat {x}}\times {\hat {y}}={\hat {z}}$ etc. $\lambda =1$ makes the characteristic equation zero!

There should be a subcategory to "spacecraft" called "attitude control". There the concept "slew" should be explained as a mini-article of its own

Stamcose (talk) 01:19, 26 July 2008 (UTC)

Nonsense. Unitary matrices are over $\mathbb {C}$, and so even the determinant need not be 1. Now, if the determinant is 1, and the matrix is real orthogonal, so that the eigenvalues come in conjugate pairs, then one can show that an eigenvalue is 1. I've fixed that now, although I really don't see this article as notable. It's a combination of basic linear algebra, rotation group, and rotation matrix.

However, reorienting a spacecraft by a simple rotation may minimize fuel use with respect to all other possible reorientations in a given time. Or, maybe not. If that's the case, it may provide a specific reason why this is of interest in spacecraft orientation. — Arthur Rubin (talk) 01:50, 26 July 2008 (UTC)

You write:

Nonsense

and then:

the determinant need not be 1

From the Wikipedia article Properties of unitary matrices:

• $U$ is invertible
• $U^{-1}=U^{*}$
• |det($U$)| = 1
• $U^{*}$ is unitary
• Unitary matrices preserve length $\|Ux\|_{2}=\|x\|_{2}$

|det($U$)| = 1 and in 3X3 case there is one and only one eigenvalue and this is 1

Kind regards!

Stamcose (talk) 12:16, 26 July 2008 (UTC)

Read the third line of the quoted section closely. Let me make it larger for you

• |det($U$)| = 1

That's why I changed it to "orthogonal" in the article. It's still unsourced, and the article should be deleted unless you can provide a reliable source that this term is actually used, but what you wrote is still nonsense. — Arthur Rubin (talk) 15:29, 26 July 2008 (UTC)

Merge proposal

Recommend merge to rotation matrix and/or RENAME to (something sensible), removing redirect, and then merging to rotation matrix. — Arthur Rubin (talk) 20:38, 25 July 2008 (UTC)

I'd agree with the merge if this was a math article, but I think it is supposed to be a space flight article. Certainly the current *contents* are not notable, but I would think steering spacecraft is pretty notable (failing to steer them definitely has gotten thousands of substantial mentions in reliable sources for sure!). I've marked the article as mostly related to spaceflight, and I hope somebody in wikiproject (whatever) takes over. I'd be happy assuming this article is none of our "business". I'll go link rotation matrix too (if it is not already). I linked SO(3,R), Rotation group, and rotation, already. JackSchmidt (talk) 20:43, 25 July 2008 (UTC)

The current contents and name are not notable. What does that leave? — Arthur Rubin (talk) 20:46, 25 July 2008 (UTC)

Haha, I cannot argue with your logic! I was thinking expanding the article's focus on "slew". Currently slew redirects to something in electrical engineering. I was thinking maybe this could either become slew (spaceflight) or could be linked from a section of that article. I think if this article was part of a larger series of articles on spaceflight, then it would be more clear how intrinsically notable and important the topic is! I know nothing about space, so I can't really put forth a better position than this (for not merging to a math article). If someone with more subject expertise in space flight could give an opinion it would probably be more helpful. Without such an opinion I see two options:

• Let the original editor work on it, and assume WikiProject Space will handle it
• Basically delete the whole "space" context from the article by merging it into a mathematics (or at best physics, but certainly not aerospace engineering article), like rotation matrix or vector (spatial).

I propose the former, but I can't really argue much with the latter. JackSchmidt (talk) 20:55, 25 July 2008 (UTC)

After checking wikt:slew, it appears that the term may be used at ESA, but not ever at NASA. "Slew" was considered slang, rather than jargon, in the 1970s, when I was working at JPL. — Arthur Rubin (talk) 20:51, 25 July 2008 (UTC)

And if *you* are an informed "space kind of guy", then I'm happy deferring to you as a representative of the spaceflight interests. Could you check if we have any articles on steering spacecraft (or whatever "slew" is)? JackSchmidt (talk) 20:55, 25 July 2008 (UTC)

Well, I found a slew article, and I'm willing to believe it's used in telescope steering, as they have a jargon of their own. Perhaps I'll create a disambiguation at slew, and see if anyone notices. — Arthur Rubin (talk) 21:17, 25 July 2008 (UTC)

Awesome. Slewing definitely needs more content. Reading over my reply here, I think it could use a much shorter summary: "I think the steering of space craft is an interesting topic and important aspect of this article. I think merging only to mathematical articles would lose this important aspect, so suggest we find an appropriate aerospace article to absorb the content as well." I actually have no idea if telescopes and spaceships are related, so I'll step out of the debate as one unqualified to speak on it. I think my short summary is a good general principal, but I cannot help beyond that. JackSchmidt (talk) 21:25, 25 July 2008 (UTC)

I think that the merging could be done by giving Rotation matrix a new text that is more useful for applied mathematicians/spacecraft engineers. See the "Talk page" of Rotation matrix where I make a proposal.

Stamcose (talk) 18:04, 29 July 2008 (UTC)

Spacecraft attitude control

This seems to be a subject that is treated surprisingly little in Wikipedia! There is an article Attitude dynamics and control that is a start but neither "3 axis stabilisation" nor "slew" is explicitly mentioned! This article is a start but:

it pretends that attitude control of ships, aircraft and spacecraft have anything in common that could be treated in one single article (in reality it is just about spacecraft!)

neither "3 axis stabilisation" nor "slew" is explicitly mentioned (what I would like to reference from the "Eigenvector slew" article)

Any special editor in charge of this domain? Could the autor of Attitude dynamics and control be pursuaded to expand the subject a bit?

Stamcose (talk) 18:35, 26 July 2008 (UTC)

I see your point. Either propose a split there, or work up your own article for the spacecraft. Because of the current disputes, it would be less disruptive if you prepared it as a subpage of your usage page, such as User:Stamcose/Spacecraft attitude dynamics and control, and we'll see what develops. You seem to have trouble meeting Wikipedia style guidelines, so that working in the main space might be counter-productive, even if we could get agreement that your article structure would be an improvement. — Arthur Rubin (talk) 19:19, 27 July 2008 (UTC)