# User talk:Loisel

I am no longer editing Wikipedia at this time (15 September 2008), although I may return in the future. Messages here will not be read.

## Refactored Riemann integral

Mmmhhh I have refactored the first section of Riemann integral... I think the animation is not what I would call "flashy"... Mmmhhh... I'd better take it out, but... Pfortuny 19:21, 17 Apr 2004 (UTC)

## Math tags

Hello. Could you please restrict the use of TeX to "displayed" math rather than math embedded in text? It looks horribly ugly on nearly all browsers. (I just cleaned up some of this in Fourier series. Michael Hardy 20:02, 17 Apr 2004 (UTC)

I don't care to do it either way, but every time I switch math-tag protocol, someone else complains. Loisel 03:25, 18 Apr 2004 (UTC)

## About computer algebra systems in integral

Hi Loisel, I'd like to mention that I think you did a great job on the bit about computer algebra systems in integral. There is certainly a lot to say on that topic & I think you did a good job of summarizing it. -- FWIW I'm in favor of using LaTeX notation only in displayed eqns. That's essentially a work around for a shortcoming in the rendering but it seems unlikely to change for the foreseeable future. Regards & happy editing, Wile E. Heresiarch 16:38, 21 Jun 2004 (UTC)

## Sturm-Liouville theory

Loisel, many thanks on your edits in Sturm-Liouville theory. The article is much clearer now. I don't know enough to contribute myself; Sturm-Liouville theory has for some time been high on the list of things to study. I do however have some remarks which you could perhaps take onboard. I found the transition from Lu = λu to Lu = f quite abrupt; are you trying to say that the inhomogeneous problem can be solved by reducing it to the eigenvalue problem? Could you also specify the "assumptions on L" in the section "Some highly technical details"? While I applaud your efforts to keep the article readable for many people, I think that we do need to be precise. I hope you don't mind my criticism, and thank you again for your contributions. -- Jitse Niesen 11:31, 11 Jul 2004 (UTC)

The passage starting with "Indeed, from the technical property that..." explains how to use the eigenanalysis to solve the Lu=f problem. I may add this to the example later.

The assumptions on p and q can be difficult to state in full generality. To solve in H^2, say, you'd want q to be in L^2 and probably p to be in H^1 (because it gets differentiated.) This guarantees that L is continuous from H^2 to L^2, however, it may still be that A is not continuous (in fact L need not be injective, so that A wouldn't be well defined.) If p≤0 and q≥c>0, for instance, then L is uniformly strongly elliptic or something to that effect. There is an associated bilinear form; this bilinear form will be symmetric (which is what the article is referring to when it discusses that L is hermitian) continuous and coercive on H^1; hence, it defines an inner product on H^1 equivalent to the natural inner product. Using the Riesz representation theorem for Hilbert spaces (the Lax-Milgram theorem isn't as precise and not needed in the hermitian case) you can get the existence and uniqueness of a solution to Lu=f. The eigenvalue problem would translate these hypotheses to the operator L-λ. At any rate, the coerciveness and continuity constants become the reciprocal of the continuity and coerciveness constants of A, respectively.

The positivity/negativity constraints on p and q are sufficient but not necessary. I don't know of any necessary and sufficient criteria for the Riesz rep th argument to work. When the RRT argument fails, it is still possible to give certain rules of the game; the Fredholm alternative is such an example. The alternative exists in very sophisticated settings, but it is sometimes difficult to describe.

Loisel 10:46, 16 Jul 2004 (UTC)

Thanks for the reply. I have used it to amend the article, hopefully making it clearer. Feel free to change my additions (of course). -- Jitse Niesen 20:44, 17 Jul 2004 (UTC)

I am assuming you meant p≤c<0 and q≥0. -- Jitse Niesen 21:18, 17 Jul 2004 (UTC)

## More Sobolev notations

Loisel, any favorite notation for the Sobolev norm? $||f||_{k,p}$? $||f||^{k,p}$? Something else? Gadykozma 16:31, 27 Aug 2004 (UTC) (you can reply here)

I usually put them in subscripts. However, I use so many norms that I have resorted to putting the whole vector space in the subscript, as in $||f||_{W^{k,p}(\Omega)}$. In the context of a concise article on Sobolev spaces, I guess I'd go for the ||f||_{k,p} one. Loisel 06:38, 6 Sep 2004 (UTC)

I didn't wait for you answer :-O, I just went ahead and refactored the Sobolev space article. Please check it! I am bound to have inserted mistakes, and you seem to be the most likely to find them. Gadykozma 12:18, 6 Sep 2004 (UTC)

## Article Licensing

To allow us to track those users who muli-license their contributions, many users copy and paste the "{{DualLicenseWithCC-BySA-Dual}}" template into their user page, but there are other options at Template messages/User namespace. The following examples could also copied and pasted into your user page:

Option 1
I agree to [[Wikipedia:Multi-licensing|multi-license]] all my contributions, with the exception of my user pages, as described below:

OR

Option 2
I agree to [[Wikipedia:Multi-licensing|multi-license]] all my contributions to any [[U.S. state]], county, or city article as described below:

Or if you wanted to place your work into the public domain, you could replace "{{DualLicenseWithCC-BySA-Dual}}" with "{{MultiLicensePD}}". If you only prefer using the GFDL, I would like to know that too. Please let me know what you think at my talk page. It's important to know either way so no one keeps asking. -- Ram-Man (comment| talk)

## Unverified image

Thanks for uploading Image:Aliased.png! I noticed that it currently doesn't have an image copyright tag. Could you add one to let us know its copyright status? (You can use {{gfdl}} if you release it under the GNU Free Documentation License, {{fairuse}} if you claim fair use, etc.) If you don't know what any of this means, just let me know at my talk page where you got the images and I'll tag them for you. Thanks so much. Ricky81682 (talk) 07:52, Dec 22, 2004 (UTC)

## Article for deletion

You may wish to be aware that one of your articles is being considered for deletion at Wikipedia:Articles for deletion/Matlab code for the simulation of detection of radius of stars Regards--AYArktos 00:11, 19 September 2005 (UTC)

The result of the vote was to delete the article. Since it was your work, I've copied it to your userpage, where it may be retained. · Katefan0(scribble) 17:55, 26 September 2005 (UTC)

## Chavez consensus

As a recent editor on Hugo Chávez, can you review developments on Talk:Hugo Chávez and let us know which version you think we should move forward with, considering that either version we pick will need work? Thanks ! Sandy 14:36, 13 June 2006 (UTC)

Thanks ! Sandy 19:54, 13 June 2006 (UTC)

"get yourself a blog dude." Thanks for the edit and the smile: I think I'd run out of reverts :-) We sure could use some help. I'm having a heck of a time balancing the need to reference every bloody statement versus the need to shorten the article via Summary Style. Could sure use a fresh set of eyes. (See the Sandy Summarization section of the talk page.) Sandy 22:51, 5 July 2006 (UTC)

The pleasure is mine! Loisel 05:58, 6 July 2006 (UTC)

## Chavez graphs

Thanks very much for the graphs. At times Wikipedia can seem like a drag, dealing with idealogues, trolls and edit warriors half the time. It's at rare times like this when it is pleasure to log on and see other editors good work. Well done!--Zleitzen 23:55, 9 September 2006 (UTC)

The pleasure is mine. Loisel 00:58, 10 September 2006 (UTC)
Now we just have to put them in Economy of Venzuela, where they belong, and reduce and summarize the already too long article :-) Sandy 09:26, 13 September 2006 (UTC)

## Help with FAR

Loisel, I was hoping you'd have a moment to look at Eigenvalue, eigenvector and eigenspace which is up for a featured article review. Detailed concerns may be found here. It's to the point that it needs a good copy edit, having more English/prose problems than math problems: are you able to help? It's a shame that the article should be de-featured because of prose problems, and I suspect you could fix it quickly. Regards, Sandy 09:26, 13 September 2006 (UTC)

Sure, I'll take a look this weekend. Loisel 13:46, 13 September 2006 (UTC)
Thanks, Loisel. If you find the article to be in very bad shape, rather than taking too much time to work on it, you can vote on the FARC (either Keep the article FA, or Remove) - you might want to enter a vote in either case? Sandy 13:56, 13 September 2006 (UTC)
You're going to hate me :-) Here's another FAC on Leonhard Euler, you might want to look at, work on, or vote on. Sandy 19:32, 13 September 2006 (UTC)
Thanks, Loisel -- your comments helped gel the consensus -- the problem wasn't the math, but the English. There's a new math FAR, recently nominated, a month to fix it: Ackermann function. Sandy 19:46, 19 September 2006 (UTC)

Somebody undid your edits to File sharing in Canada. You might want to keep on eye on this article so it doesn't get screwed up. Suoerh2 23:16, 27 September 2006 (UTC)

Thanks for letting me know. Loisel 02:57, 28 September 2006 (UTC)

I undid your edits because they were sloppy and simply repeated information that was already presented in a later section. If you vandalize the page again, you WILL be reported. 207.112.76.138 03:48, 18 October 2006 (UTC)Alex

## your edits to Numerical analysis

Hi, adding examples is welcome, but could you do it without zapping some excellent exposition? Perhaps you could put your examples in subsections after the introductory exposition, naming the subsections Example. --Jtir 20:30, 29 September 2006 (UTC)

I am being bold WP:BB, which is policy. My examples are meant to replace the vague exposition that precede it. The style I intend is to start with an example, and end with some sort of general statement that resembles the previous text. I also intend to do that to the rest of the article. Loisel 17:39, 30 September 2006 (UTC)
Thanks for choosing to merge. The wikitables are a good idea.
For future complex edits, here are some things you can do to smooth the process:
• You can use the talk page to say what you plan to do and why. This way you invite editors to work with you.
• You can create a proposed revision of the article in a sandbox under your user page.
• You can give a brief edit summary for each edit using neutral language. [1] [2] [3] [4]
• You can place an Edit lock template such as {{inuse}} at the top of the article to notify readers and editors that the article is being heavily edited.
--Jtir 07:14, 1 October 2006 (UTC)
Point by point:
• I could, and I sometimes do. But sometimes I don't. I hold WP:BB dear.
• I am unlikely to do that, see WP:BB.
• WP:NPOV is for article contents, not talk pages or modification comments. My edits to mathematical articles are necessarely NPOV and my edits to non-mathematical articles are purely factual. The exception is reverts. If a modification is significantly worse than the original article, I revert it, even if the original article is POV.
• I'll keep that tag in mind, but in my 5+ years of editing Wikipedia, some of these protocols have changed often enough that I'm having a hard time keeping track. For instance, math tags has been in and out of favor for their entire existence.
Loisel 07:31, 1 October 2006 (UTC)

By the way, the Hugo Chavez, that's not what I reverted. Sandy, whom I think does not like Chavez, requested that Luxgratia's anti-Chavez essay under Criticism be reverted. I concurred and reverted it. The actual edit that I reverted was this: [5]. The revert had an appropriate comment attached to it. I don't know what you're complaining about. Loisel 08:08, 1 October 2006 (UTC)
Thanks for pointing this out. I might have said simply "rm pov" in the edit summary so that the summary could not be so easily misinterpreted. [6] --Jtir 12:27, 1 October 2006 (UTC)

## Edit summary etc

Thanks for your edits to numerical analysis. Two suggestions though. One is to use an edit summary, it really helps others to see what you changed. Second, could you please hold off modifying that article until it is decided on talk what to do about the article? Thanks. You can reply here if you have comments. Oleg Alexandrov (talk) 20:09, 30 September 2006 (UTC)

## created Fixed point iteration

I have created Fixed point iteration as a mathematics stub. Hope my definition isn't too far off. --Jtir 00:58, 8 October 2006 (UTC)

Hi, could you give your opinion on whether there should be a separate article on FPI?
FYI, I quoted you here.
--Jtir 04:30, 9 October 2006 (UTC)

I don't think so. Loisel 15:59, 9 October 2006 (UTC)

## Riemann integrability

Hi Loisel. Regarding this edit you made, from what I remember from calculus the statement you removed is true. See also a google books statement (I hope you can see that page). It appears that you don't even need to assume that f is Lebesgue integrable. Boundedness plus a set of discontinuities of measure zero, are enough to guarantee Riemann integrability (and hence Lebesgue integrability too). You can reply here if you have comments. I'll keep your talk page on my watchlist. Oleg Alexandrov (talk) 15:20, 25 March 2007 (UTC)

Wow, I blame the wine. I totally misread that as saying that Lebesgue integrable functions were a.e. continuous. Loisel 20:39, 25 March 2007 (UTC)
We should institute new rules stating that an editor may not edit if his alcohol concentration in blood is above certain threshold. :) Oleg Alexandrov (talk) 01:53, 26 March 2007 (UTC)

## elliptic boundary value problem

Loisel, great work on the discussion of elliptic operators! Since you're evidently the one who has the best overview of that article, I thought I'd point out what I think is a typo, namely, the nondivergence form of the general elliptic operator in matrix notation: the "\div (a\nabla a)" term appears in both the divergence and non-divergence form. Since I'm not really sure what you intended, I hesited to edit it myself. -- J.G. —The preceding unsigned comment was added by Gagelman (talkcontribs) 09:35, 13 April 2007 (UTC).

Thanks for letting me know. The error is now fixed. Loisel 18:42, 13 April 2007 (UTC)

An image or media file that you uploaded or altered, Image:Zoomed-star-radius-error.png, has been listed at Wikipedia:Images and media for deletion. Please see the discussion to see why this is (you may have to search for the title of the image to find its entry), if you are interested in it not being deleted. Thank you. User:Gay Cdn (talk) (Contr) 21:13, 4 June 2007 (UTC)

## Impressed

Just to say, I'm impressed by your calm and constructive responses to a number of challenging comments and edits. Of course this does not mean I agree with everything ;) but I like your approach. Geometry guy 01:11, 19 June 2007 (UTC)

Yeah, sometimes it's hard to please everyone. I just hope nobody invokes any of those rules on me in the future. (Famous last words.) Loisel 01:52, 19 June 2007 (UTC)

## Collision detection

Actually, it isn't that helpful to try to subdivide time using Newton's method to find the exact time of contact. Remember, this is usually a real-time problem; what matters is the worst case, not the average case. When simulating free flight, Newton's method will work, but the compute load is low then. During complex contact, when the compute load is high, there's enough nonlinearity that Newton's method won't help you much and can make things worse, especially if the sign of the second derivative is changing. Binary search has a simple upper bound. --John Nagle 16:15, 19 June 2007 (UTC)

I'm not pushing either method. The point here is that this editor does not think this has anything to do with root finding, whether it's binary search or Newton's.

Loisel 16:23, 19 June 2007 (UTC)

## Note

Why French? You can reply here. Thanks. Oleg Alexandrov (talk) 07:40, 10 January 2008 (UTC)

The original is in French. I just like the books with the quotes in the original language, especially, as in this case, when it's entirely possible to understand what's being said without speaking the language at all.

You don't like it?

Loisel (talk) 07:48, 10 January 2008 (UTC)

I respectfully disagree. I do know French, and I understood what it said, but while a refined French expression can make a fine point in a conversation or an article about art, a pedestrian article about Fourier series better use English, to not distract from understanding the mathematics, which is after all what matters. That is, I see your point, but I think it is not the right place for that. Oleg Alexandrov (talk) 07:51, 10 January 2008 (UTC)
OK, I don't care very much about it, I'll change it back. Loisel (talk) 08:03, 10 January 2008 (UTC)
Merci beaucoup mon cher. :) Oleg Alexandrov (talk) 16:30, 10 January 2008 (UTC)

## Chavez Graph

Salut, pourrais-tu traduire ton graphique sur la politique économique de Chavez (http://en.wikipedia.org/wiki/Image:Venezuela_Economic_Indicators.png) en français, je l'ai fait de mon côté mais je n'arrive pas à l'exporter en fichier image. Merci.88.166.140.196 (talk) 21:06, 12 March 2008 (UTC)

## Unspecified source for Image:Blurry-star-fourier.png

Thanks for uploading Image:Blurry-star-fourier.png. I noticed that the file's description page currently doesn't specify who created the content, so the copyright status is unclear. If you did not create this file yourself, then you will need to specify the owner of the copyright. If you obtained it from a website, then a link to the website from which it was taken, together with a restatement of that website's terms of use of its content, is usually sufficient information. However, if the copyright holder is different from the website's publisher, then their copyright should also be acknowledged.

As well as adding the source, please add a proper copyright licensing tag if the file doesn't have one already. If you created/took the picture, audio, or video then the {{GFDL-self}} tag can be used to release it under the GFDL. If you believe the media meets the criteria at Wikipedia:Fair use, use a tag such as {{non-free fair use in|article name}} or one of the other tags listed at Wikipedia:Image copyright tags#Fair use. See Wikipedia:Image copyright tags for the full list of copyright tags that you can use.

If you have uploaded other files, consider checking that you have specified their source and tagged them, too. You can find a list of files you have uploaded by following this link. Unsourced and untagged images may be deleted one week after they have been tagged, as described on criteria for speedy deletion. If the image is copyrighted under a non-free license (per Wikipedia:Fair use) then the image will be deleted 48 hours after 05:53, 23 April 2008 (UTC). If you have any questions please ask them at the Media copyright questions page. Thank you. Do you want to opt out of receiving this notice? Kelly hi! 05:53, 23 April 2008 (UTC)

## Unspecified source for Image:Blurry-star.png

Thanks for uploading Image:Blurry-star.png. I noticed that the file's description page currently doesn't specify who created the content, so the copyright status is unclear. If you did not create this file yourself, then you will need to specify the owner of the copyright. If you obtained it from a website, then a link to the website from which it was taken, together with a restatement of that website's terms of use of its content, is usually sufficient information. However, if the copyright holder is different from the website's publisher, then their copyright should also be acknowledged.

As well as adding the source, please add a proper copyright licensing tag if the file doesn't have one already. If you created/took the picture, audio, or video then the {{GFDL-self}} tag can be used to release it under the GFDL. If you believe the media meets the criteria at Wikipedia:Fair use, use a tag such as {{non-free fair use in|article name}} or one of the other tags listed at Wikipedia:Image copyright tags#Fair use. See Wikipedia:Image copyright tags for the full list of copyright tags that you can use.

If you have uploaded other files, consider checking that you have specified their source and tagged them, too. You can find a list of files you have uploaded by following this link. Unsourced and untagged images may be deleted one week after they have been tagged, as described on criteria for speedy deletion. If the image is copyrighted under a non-free license (per Wikipedia:Fair use) then the image will be deleted 48 hours after 05:53, 23 April 2008 (UTC). If you have any questions please ask them at the Media copyright questions page. Thank you. Do you want to opt out of receiving this notice? Kelly hi! 05:53, 23 April 2008 (UTC)

## Your Request for a Picture of a Vibrating Drum

On Wikipedia:Requested_pictures/Science#Mathematics you request some images of a vibrating drum. There are some here. Are these sufficient? There doesn't seem to be any with 3-fold radial vibrations. If not can you give a bit more detail of what you had in mind. Those images appear to have been generated via [Mathematic] or [Matlab] and shouldn't be too hard to generate some similar ones if desired. Yvori (talk) 03:03, 25 April 2008 (UTC)

That was for Fourier series, and I got a picture now. I don't remember who did it, one of the math people. Loisel (talk) 04:14, 25 April 2008 (UTC)

Actually, the ones you found is the one I have, and I think it was Oleg who pointed me to them. Loisel (talk) 04:15, 25 April 2008 (UTC)

## Easy as pi?: Making mathematics articles more accessible to a general readership

The discussion, to which you contributed, has been archived, with very much additional commentary,
at Wikipedia:Village pump (proposals)/Archive 35#Easy as pi? (subsectioned and sub-subsectioned).
A related discussion is at
(Temporary link) Talk:Mathematics#Making mathematics articles more accessible to a general readership and
(Permanent link) Talk:Mathematics (Section "Making mathematics articles more accessible to a general readership"). Another related discussion is at
(Temporary link) Wikipedia talk:WikiProject Mathematics#Making mathematics articles more accessible to a general readership and
(Permanent link) Wikipedia talk:WikiProject Mathematics (Section "Making mathematics articles more accessible to a general readership").
-- Wavelength (talk) 01:38, 29 September 2008 (UTC)