User talk:Nbarth/Archive 2009

Utility and all that
One wants to be very cautious about attributing the origin of notions of utility functions and of marginal utility to the work of Cramer or of Bernoulli on the St Petersburg Paradox. On the one hand, some read Aristoteles as having a concept of marginal utility; on the other hand, many later thinkers arrived at such notions independently of any concern with this particular paradox. —SlamDiego&#8592;T 18:01, 1 January 2009 (UTC)

BTW, quite a while back, I was in repeated conflict with an editor at that article who wanted to replace every reference to diminishing marginal utility with a reference to risk aversion. Perhaps you already see the problem there in full, but part of it is that Cramer and Bernoulli specifically conceptualized things in terms of diminishing marginal utility, and part of it is that, while diminishing marginal utility can be expected to imply risk aversion, it is really only equivalent to risk aversion on the assumption of something like the strong independence axiom (id est, that expected utility is linear in the probabilities). (Some technically define “risk aversion” to be equivalent to diminishing marginal utility, but this turns what was a description into a mere name, dangerously separated from ordinary language.) —SlamDiego&#8592;T 06:27, 2 January 2009 (UTC)

Maximum of a discrete uniform distribution / German tank problem

 * See: User_talk:Michael_Hardy

Horribly misleading sentence

 * See: User talk:Michael Hardy

At Studentized residual, you wrote:
 * This adjusts for scale, yielding a dimensionless quantity which can be compared between different sample sets
 * This adjusts for scale, yielding a dimensionless quantity which can be compared between different sample sets

That seems horribly misleading, because it seems likely to leave the reader under the impression that comparability across data sets, resulting from dimensionlessness, is the point.

That is wrong.

In typical linear regression problems, even when all of the errors have the same variance, the variances of residuals vary greatly. That is the main point! Think of a very simple regression problem: just a scatterplot in the plane, to which you fit a line. If an x-value is extreme, then the corresponding residual is highly sensitive to the estimated slope, and thus has a large variance; by contrast, for a nearly average x-value, the residual is relatively insensitive to the estimated slope. Errors, in contrast to residuals, on the other hand, in no way depend on the estimated slope. Thus when errors have the same variance, residuals don't. Michael Hardy (talk) 00:54, 21 February 2009 (UTC)


 * Now I see what I had forgotten: in the article it said:
 * The fact that the variances of the residuals differ, even though the variances of the true errors are all equal to each other, is the principal reason for the need for studentization.
 * That is actually set in bold. Michael Hardy (talk) 00:58, 21 February 2009 (UTC)

About Frame of a vector space
Hi, I'v written some comments about your edits on the Talk:Frame of a vector space page. --KYN (talk) 08:42, 2 April 2009 (UTC)


 * Thanks for the note, and sorry for the hassle – fixed and replied there!
 * —Nils von Barth (nbarth) (talk) 18:48, 2 April 2009 (UTC)

Reverted and remove ringing assertion
I think you significantly misrepresented the cited source on ringing and windowing. Please take another look, and if you need help interpreting it, ask. Dicklyon (talk) 02:52, 29 March 2009 (UTC)


 * Hi Dick,
 * I don’t understand your objection – page 2 of Mastering Windows: Improving Reconstruction reads:
 * Simple truncation causes severe ringing artifacts. …
 * To reduce artifacts originating from truncation the ideal reconstruction filters can be multiplied with appropriate functions which drop off more smoothly at the edges.
 * We will discuss…these…windows.
 * I don’t see how my wording:
 * In image processing applications, windowing often causes ringing artifacts, and different choices of windowing function can significantly affect a filter.
 * significantly differs from it.
 * Should I write instead: “Simple truncation causes ringing artifacts, which can be mitigated by different choices of windowing functions”?
 * …or are you saying something else?
 * —Nils von Barth (nbarth) (talk) 03:02, 29 March 2009 (UTC)


 * I'd say the more sensible interpretation is that windowing reduces ringing artifacts. An unwindowed sinc, or a truncated sinc, has ringing artifacts; a tight window that cuts off negative lobes will have no ringing at all.  The windowing doesn't cause ringing – it reduces it.  Unfortunately that particular source doesn't say what happens with an unwindowed filter.  And it is not clear why you put the mention of ringing into the context of images.  Dicklyon (talk) 03:39, 29 March 2009 (UTC)


 * Good point about truncation being the main cause, and windowing reducing this – that’s a better way of putting it, and I’ve incorporated it.
 * I’ve rewritten (in rather more detail) the contributions to the various pages, drawing on the sources and adding another reference for Lanczos. Do they look better?
 * —Nils von Barth (nbarth) (talk) 15:26, 29 March 2009 (UTC)


 * Truncation isn't the main cause, either, as it never adds negative lobes that weren't there already. Ringing is caused by filter impulse responses that ring, corresponging to sharp frequency-domain cutoffs; windowing reduces the negative lobes and smears out the f-domain transitions, reducing ringing.  But I wouldn't focus too much on ringing in the context of windowing; the frequency-domain view of windowing is usually more important.  I haven't looked at your new contribs yet, and probably don't have time right now, but later.  You can reply here without the talkback thing and I'll see it.  Dicklyon (talk) 16:03, 29 March 2009 (UTC)


 * Ok – thanks for clarifying.
 * So if I understand what you’re saying, brick-wall filters cause ringing, due to the discontinuity (sharp cutoff) in the frequency domain.
 * Thus sinc, the time-domain view of a brick-wall low-pass filter, causes ringing, even ideally?
 * …and this is reflected (in the time-domain) in the negative lobes?
 * Are there any references you might recommend?
 * The authors of the paper are either confused or unclear though, as they attribute ringing artifacts to truncation, as in the quote – they don’t say that truncation fails to fix the artifact.
 * From doing a little reading, it seems people attribute ringing to the Gibbs phenomenon, i.e., discontinuities in the signal.
 * Regardless, ringing is not the emphasis of the revised changes.
 * —Nils von Barth (nbarth) (talk) 20:49, 29 March 2009 (UTC)


 * Right, that source is very unclear on that point; it should say that the rectangular window does little to reduce ringing (and has other bad properties when viewed in the frequency domain). Also, if you're going to reference that paper, you need to say where it's published; a link to a PDF that doesn't say really doesn't quality as a reliable source.  As for Gibbs, yes, that's pretty much what a brick-wall filter is.  Here are some books you look at. Dicklyon (talk) 22:13, 29 March 2009 (UTC)


 * I took out all that stuff you added to Lanczos filter. From the figures in the paper it appears that the authors just got very confused. Their plots do not show it as one of the ones with negative frequency-domain lobes.  I think you should read some of those books and base your edits on better sources.  Dicklyon (talk) 22:56, 29 March 2009 (UTC)


 * Actually, I mis-characterized the problem. Looking with more zoom, I do see a slight negative lobe on the Lanczos plot.  But the conclusions that it causes "severe artifacts" and that it's "unsuitable for reconstruction" are not justified.  If there's something about the 3D "reconstruction" problem that makes it a lot different from image reconstruction, they haven't explained that.  And the figures at the end suggest that they didn't bother trying the Lanczos filter.  If you want to cite the published opinion of these authors anyway, you need to at least show that they are credible experts first.  Dicklyon (talk) 23:17, 29 March 2009 (UTC)

Ringing (signal)
This is an automated message from CorenSearchBot. I have performed a web search with the contents of Ringing (signal), and it appears to be very similar to another Wikipedia page: Ringing. It is possible that you have accidentally duplicated contents, or made an error while creating the page&mdash; you might want to look at the pages and see if that is the case. If you are intentionally moving or duplicating content, please be sure you have followed the procedure at Splitting by acknowledging the duplication of material in edit summary to preserve attribution history.

This message was placed automatically, and it is possible that the bot is confused and found similarity where none actually exists. If that is the case, you can remove the tag from the article and it would be appreciated if you could drop a note on the maintainer's talk page. 209.51.196.26 (talk) 23:15, 12 April 2009 (UTC)

Invitation
I would like to commend you for your substantial contributions to articles in the telecommunications and signal processing area. I would also like to invite you to Wikiproject Telecommunicaitons WP:TEL. Mange01 (talk) 20:32, 14 April 2009 (UTC)


 * Thanks! Glad to be helpful – I’ve added myself as part-time.
 * —Nils von Barth (nbarth) (talk) 21:03, 14 April 2009 (UTC)

Fourier analysis
Nils, I removed again the bit about Babylonians' sums and differences being Fourier transforms – it's too much of a stretch to say such a thing without an explicit source; the wikipedia page you linked was itself unsourced, and removed it from there, too. I'm worried too about the Lagrange resolvents; I can't find anything in the books you cited that connect the resolvents with an order-3 DFT. Can you tell me what pages to check? Dicklyon (talk) 02:56, 21 April 2009 (UTC)


 * Hi Dick,
 * The Lagrange resolvents for the cubic are (obviously) the order-3 DFT, though people don’t tend to refer to them as such (separate culture of algebraists and analysts/signal processing).
 * I don’t have a reference to hand that explicitly links them, so you’re welcome to remove them if you feel uncomfortable, though mathematically they are identical.
 * OTOH, digging around, I’ve actually found several references that explain how the Babylonians used (continuous) Fourier series in astronomy – I’ll add those (referenced); also mentioned earlier 18th century Fourier theory.
 * —Nils von Barth (nbarth) (talk) 03:08, 21 April 2009 (UTC)


 * We can't be using our own observation of similar function form to make such claims about the order-3 DFT; if it's not sourced, let's leave it out. I've looked at the some of those refs that mention Babylonian and Fourier and Neugebauer, but I don't find any explicit support for the statement in the article that the Babylonians used a form of Fourier analysis.  Can you point to anything that actually says so?  Dicklyon (talk) 03:39, 21 April 2009 (UTC)


 * Re: order-3 DFT – ok, feel free to take it out.
 * Re: statement that the Babylonians used Fourier analysis.
 * “Babylonians used a primitive kind of Fourier series for the prediction of celestial events.” The evolution of applied harmonic analysis, p. 62
 * In addition, I’ve added (sourced) mentions of use of DFT by Clairhaut and FFT by Gauss.
 * —Nils von Barth (nbarth) (talk) 03:43, 21 April 2009 (UTC)


 * Actually, hold on – I found a ref for resolvents – this gives references for all statements; will include shortly.
 * —Nils von Barth (nbarth) (talk) 03:45, 21 April 2009 (UTC)


 * I’ve added a reference for resolvents being Fourier theory, and reworded it to accord with what the source says (Knapp calls it “a Fourier decomposition relative to a cyclic group”, though he doesn’t call it a DFT).
 * —Nils von Barth (nbarth) (talk) 03:53, 21 April 2009 (UTC)


 * Digging more, I’ve found a source that discusses (with facsimile copy of Lagrange’s paper!) a further use of the DFT by Lagrange (“The DFT” book), which I’ve included with reference.
 * —Nils von Barth (nbarth) (talk) 04:10, 21 April 2009 (UTC)


 * Well, the rest look pretty marginal, but that one looks good. Thanks for working on it.  I added some missing titles. Dicklyon (talk) 04:25, 21 April 2009 (UTC)


 * No worries, and thanks for helping – it looks rather better than before.
 * —Nils von Barth (nbarth) (talk) 04:36, 21 April 2009 (UTC)

Inappropriate moves?
Recently, you moved some articles to new names which are inappropriate according to Naming conventions. It says "Generally, article naming should prefer what the greatest number of English speakers would most easily recognize, with a reasonable minimum of ambiguity, while at the same time making linking to those articles easy and second nature.". In particular, I noticed that you moved Lambert quadrilateral to Ibn al-Haytham–Lambert quadrilateral and Saccheri quadrilateral to Khayyam–Saccheri quadrilateral. JRSpriggs (talk) 14:12, 20 April 2009 (UTC)


 * Hi JRSpriggs – thanks for the note.
 * AFAICT, there’s a conflict between “Common naming” versus “Neutral naming” (Neutral point of view), which I was trying to resolve: while the European-only names are common in English, the Persian-European names are used in the literature, and preferred in the historical literature, as discussed in the references. Hence mentioning both, particularly in light of the centuries of historical precedence and significant and earlier contribution, and use in the historical literature, seems a more neutral position. (For the purpose of linking it’s of course moot.)
 * Wikiproject Mathematics only mentions naming in Naming conventions (theorems), which just says “use lowercase”, and doesn’t address proper names.
 * A case can be made for either naming (as mentioned), though the Persian-European names seem more defensible to me.
 * —Nils von Barth (nbarth) (talk) 14:30, 20 April 2009 (UTC)


 * The move was inappropriate and due to your misunderstanding of Neutral point of view, which explicitly states that proper names should be descriptive and go with the common English name. See Wikipedia_talk:WikiProject_Mathematics if you wish to debate this point further.  --C S (talk) 01:06, 1 May 2009 (UTC)


 * Thanks for notifying me, C S.
 * —Nils von Barth (nbarth) (talk) 01:23, 1 May 2009 (UTC)

PTP and DCF
Nils, your recent edits suggest that PTP and DCF are somehow linked, but I can find no evidence for that. Do you have some sources that indicate some connection between them? The fact that most cameras implement both might be worth mentioning, if we have a source that says so, but as far as I know it doesn't go beyond that. Dicklyon (talk) 18:23, 3 May 2009 (UTC)


 * Hi Dick,
 * I figured that if one were interested in how images are stored on a camera or transfered between them, one would likely wish to know about both PTP and DCF, so I linked them.
 * Sorry if my edit suggests that they are linked more strongly than that; I’ve elaborated at Picture Transfer Protocol, with ref (PTP was designed to work with DCF, Exif, etc., though it’s a different layer) – how d’you like it now?
 * —Nils von Barth (nbarth) (talk) 20:27, 3 May 2009 (UTC)


 * Better; but I tweaked it a bit more, as the stuff on access is really pretty unrelated to DCF. Dicklyon (talk) 20:33, 3 May 2009 (UTC)


 * Sure thing!
 * —Nils von Barth (nbarth) (talk) 21:46, 3 May 2009 (UTC)

Brunnian/Borromean
You could look also at the Knot Atlas, http://katlas.math.toronto.edu/wiki/Brunnian_link etc., which could probably also benefit from attention... AnonMoos (talk) 01:12, 8 May 2009 (UTC)


 * Thanks for the tip!
 * —Nils von Barth (nbarth) (talk) 01:18, 8 May 2009 (UTC)

International Monetary Systems
Great addition. Just as the latest G8 was kicking off in Italy. There was a slight issues with the number of pics which I explained on the articles talk page. FeydHuxtable (talk) 12:34, 9 July 2009 (UTC)
 * Thanks for your kind words…
 * I’ve made a montage as you’ve suggested, and replied in more detail at Talk:International Monetary Systems – hope y’all like it!
 * —Nils von Barth (nbarth) (talk) 15:37, 9 July 2009 (UTC)

Paraboloid and Church Army Chapel, Blackheath
I'm contacting you as you have contributed to Paraboloid, and I hope you don't mind me asking you a purely hypothetical question about maths and the wooden hyperbolic paraboloid roof on the Church Army Chapel, Blackheath. We know the roof is a wooden structure as it was thus described by Terry Peck of Capital Roofing, who re-surfaced it last year. It was important to know this as, if I remember rightly, they were often made of carbon fibre and had a tendency to blow off the roof if a gale occurred during transport to site or fixing. Also, carbon fibre roofs don't support spires. So the idea of a wooden version makes sense. But how was it done?

My question is - is it possible to construct a hyperbolic paraboloid using straight lines (e.g. wooden beams) only? Forgive me - I have no mathematical knowledge - but the drawings on the Paraboloid page have lines delineating curves only, so any straight-line element within the shape can't be seen in the illustrations.

I am also interested to know whether - if the roof could have been constructed entirely with straight beams - the roof would be rigid enough to support a fairly lightweight but tall aluminium spire? I suspect that most of the required strength and rigidity would be for keeping the spire steady in a gale, and not quite so much for supporting weight.

I am also wondering if such a structure would be rigid by the same principle as the Mathematical Bridge. I don't understand the rigidity-principle of the bridge myself, but I do appreciate that if there is a named principle which could also be applied to a wooden hyperbolic paraboloid roof structure, then even a dumbo like me would have simple language by which to demonstrate that the roof could theoretically be rigid enough to stabilise the spire.

Please forgive me for all these questions - I appreciate that you may not be interested in the question, and I quite understand if you don't feel like answering. My problem is that the plans are missing and I am not an architect, so I have to look for other means of understanding the building. I shall be attempting to visit it next week, so any advice on what too look for or photograph would be gratefully received.

Cheers.--Storye book (talk) 11:31, 23 July 2009 (UTC)


 * Hi Storye book – no worries re: question (fair game)!
 * Hyperbolic-paraboloid.jpg To your first question – yes, a hyperbolic paraboloid can be built using only straight beams, a so-called saddle roof – that’s the practical meaning of being a doubly ruled surface. I’ve added the attached image to Paraboloid: Properties so one needn’t dig through 2 or 3 levels of links to learn this.
 * Regarding rigidity – I’m no engineer, but I believe that saddle roofs are rigid (i.e., like triangles, which don’t flex, unlike squares, which do), and I believe that you are correct that the key issue with light-weight spires is keeping them steady in wind, not supporting them.
 * Mathematical Bridge, Cambridge, large.jpg [[Mathematical Bridge]] is built by an entirely different principle – it has a weak curved bridge surface, supported by external trussing.
 * The difference can be seen as follows: in a saddle roof, the straight beams are part of the curved surface (tangent lines to the surface lies inside the surface, in the 2 directions that form the rulings), while in the Mathematical Bridge, the straight lines are not part of the curved surface, but rather project out and form the trussing.
 * Hope these replies help!
 * You may find the Reference desk most helpful in answering questions, since it seems to be peopled by friendly folk for just this purpose!
 * And regarding photographs of Church Army Chapel, perhaps a photo of the roof from some angle and height that shows its shape to good effect (shadows help, of course) to contribute to the roof section of the article, together with an overall photograph of the chapel, and of any notable details, since there are no photos of the church at the current article.
 * Enjoy your visit!
 * —Nils von Barth (nbarth) (talk) 13:36, 23 July 2009 (UTC)


 * Yay! Thank you so much for all your help. This is really appreciated.--Storye book (talk) 15:54, 23 July 2009 (UTC)
 * I've updated Church Army Chapel, Blackheath with your information. Of course you are welcome to edit it if you see fit. I worry that my new para could get deleted on the grounds of being opinion, however the architect's own drawing at the top does appear to show straight beams on the roof, and the beams go in the same direction as the ones in your image. Meanwhile I have just been given a new lead towards a possible copy of the plans. You never know, we may be lucky. Thanks again.--Storye book (talk) 17:07, 23 July 2009 (UTC)


 * Glad to help!
 * I’ve updated your edits; you were being timid, saying that it is “possibly” a saddle roof (hyperbolic paraboloid) – it is obviously a saddle roof – as you note, it’s built with straight beams – so I’ve stated it more directly, and also clarified some points.
 * Good luck finding the plans!
 * —Nils von Barth (nbarth) (talk) 00:32, 24 July 2009 (UTC)


 * Thank you very much indeed for your careful edits - the article is much improved now - and more importantly we are closer to understanding the building. Cheers.--Storye book (talk) 10:58, 24 July 2009 (UTC)

List of knot theory topics
I've just added Link group to the list of knot theory topics. If you know of others that should be there and are not, could you add those too? Michael Hardy (talk) 17:07, 23 July 2009 (UTC)
 * Will do – I’ve added link concordance (other knot theory articles on which I’ve worked lately were already included) and a link to Category:Knot theory for reference.
 * —Nils von Barth (nbarth) (talk) 20:46, 23 July 2009 (UTC)

Weak/strong cobordism
I have not come across this terminology before: is there a reference? Unless I am misunderstanding the definition, oriented cobordism is strong, not weak as claimed. ranicki (talk) 14:20, 24 July 2009 (UTC)


 * Oops, sorry! This was me confusing myself: in an old edit, I had replaced “a very simple theory” with “weak theory” (as this sounded more formal), and then in a later edit thought “hey, this term should be more prominent!”
 * I’ve fixed this, removing all weak/strong words.
 * Regarding the distinction, it’s basically “cohomology theories that geometric topologists care about (unoriented, oriented cobordism)” and “cohomology theories that algebraic topologists care about (complex cobordism and related)”.
 * As I understand it, the distinction is that the oriented and unoriented cobordism Thom spectra are products of Eilenberg-MacLane spaces: $$MO = H(\pi_*(MO))$$ and $$MSO = H(\pi_*(MSO)),$$ and this is what is meant by “reduce to ordinary (co)homology”.
 * If I recall correctly, oriented cobordism is exactly characteristic classes (or rather, characteristic numbers): the cobordism class is not determined by the (ordinary) cohomology ring – they are/include normal data (classifying map) – but the representing object is just ordinary cohomology.
 * Is this correct? (And perhaps it could be made clearer at the page.)
 * —Nils von Barth (nbarth) (talk) 17:36, 24 July 2009 (UTC)
 * Also, shouldn’t you be preparing your Fringe show, “Algebraic Surgery Theory Cabaret”? It’s almost August you know.
 * —Nils von Barth (nbarth) (talk) 17:36, 24 July 2009 (UTC)
 * Thanks for fixing this. Unoriented cobordism is a product of Eilenberg-MacLane spaces (or rather spectra), but oriented cobordism is such a product only at the prime 2, i.e. if odd torsion is ignored. However, both unoriented and oriented cobordism are determined by characteristic numbers: Stiefel-Whitney in the unoriented case, Stiefel-Whitney and Pontrjagin in the oriented case. The Edinburgh Fringe has all kinds of esoteric shows, but not (as yet) anything quite as esoteric as algebraic surgery! ranicki (talk) 07:41, 26 July 2009 (UTC)
 * No problem – and I’ve clarified/elaborated that while oriented cobordism is determined by characteristic numbers, the ring is complicated to describe.
 * —Nils von Barth (nbarth) (talk) 21:15, 26 July 2009 (UTC)

Generalized cohomology theory redirect
Hello Nbarth, back in January you retargeted from homology theory to Cohomology, but that section has since disappeared. I would be inclined to just retarget it to Cohomology, but I am not familiar with the field, and I thought that you might have a better target in mind (possibly even something from List of cohomology theories). -- ToET 08:55, 15 September 2009 (UTC)

We have a similar situation with: -- ToET 18:37, 16 September 2009 (UTC)
 * → Cohomology
 * → Cohomology


 * Thanks ToE!
 * A vandal removed the section on Sep 13 (see history); I got my WikiGnome on and restored it, fixing these redirects. (As you perspicaciously suggest, "List of Coho" is referenced.)
 * —Nils von Barth (nbarth) (talk) 23:08, 16 September 2009 (UTC)

Logarithmic prior
Hello again! Back in February, you created the template targeting material you had just added. Unfortunately, an editor removed this material four days, later leaving this note: Talk:Jeffreys prior. What should we do here? -- ToET 15:56, 16 September 2009 (UTC)
 * → Jeffreys prior &bull; (links to redirect)
 * Thanks for advising me!
 * I did make a mistake in my edit (the log prior is not the only Jeffreys prior on the positive reals). I've fixed the mistake and incorporated a correct discussion of log prior on the page.
 * —Nils von Barth (nbarth) (talk) 22:57, 16 September 2009 (UTC)
 * Thank you for fixing this (and those above). Wikipedia's mathematics is amongst the best it has to offer, perhaps because it is, ironically enough,  the field where WP:OR in general and WP:SYN in particular is most acceptable, as everything correct is just a "routine calculation" (for someone) from verifiable material.  -- ToET 00:28, 17 September 2009 (UTC)
 * Glad you like 'em!
 * Your philosophical points on WP mathematics are well-taken; conversely, one could argue that WP's math articles are some of the least well-referenced, since everyone just figures it out themselves, half-remembered, rather than turning to the bookshelf. This also points to how much of math knowledge is oral - "everyone knows that" (mathematical folklore).
 * This has been present for me lately in contributions to economics articles - economics is a more scholarly and contentious field than math, so references are more prized and more necessary. For "obvious" or "well-known" statements, Google scholar and the (quite active) economics blogosphere have been invaluable; the former often reveals that concepts are centuries older than commonly understood, while the latter helps transcribe the folklore and the divisions.
 * Thanks again, and feel free to advise me on other nigh-insoluble problems!
 * —Nils von Barth (nbarth) (talk) 01:12, 17 September 2009 (UTC)

Computing Weighted Average Life from Amortized Payment
On the following page: Weighted-average life

you have a formula for computing the WAL without knowing the amortization schedule. Do you have a source for that formula you can share with me? I see it has been some time since you updated that page, but I'd appreciate any help you can provide.

Thanks.
 * unsigned comment by Sixhertz (talk) 9:28, 2009 September 18


 * Hi Sixhertz,
 * Are you referring to Weighted-average life?
 * I don't have a reference to hand (it's just a restatement of "Total Interest = WAL * interest * principal"), but you might find Fabozzi helpful -- I've added him as a ref to WAL; hope this helps.
 * —Nils von Barth (nbarth) (talk) 03:28, 19 September 2009 (UTC)

Golden age / long boom
Hi there. If you have time please check the merge discussion you started at Talk:Long boom with a view to merging Golden age of capitalism with long boom. Im hoping we can close the discussion with a view that the Golden age article will be kept with its current title, i dont mind whats decided about the other articles. FeydHuxtable (talk) 12:42, 10 September 2009 (UTC)


 * Hi Feyd,
 * Thanks for sorting this and your extensive research -- agree with conclusion that long boom should be a disambig, as Yvwv has done.
 * Pursuant to this, I've started a merge discussion at Talk:Golden Age of Capitalism, with the main question to my eye being whether to call the merged article "Golden Age" or "Post-War" -- perhaps you could weigh in?
 * —Nils von Barth (nbarth) (talk) 22:02, 16 September 2009 (UTC)
 * You're welcome. I replied over at the discussion. FeydHuxtable (talk) 11:02, 20 September 2009 (UTC)
 * I’ve merged the articles, as per discussion. The merged article is at Post-World War II economic boom, which was not your preferred title; I’ve suggested resolutions there, if you feel strongly that it should be “Golden Age” instead.
 * Thanks for your contributions to discussion and article!
 * —Nils von Barth (nbarth) (talk) 01:35, 12 October 2009 (UTC)
 * Great work on the merge, the article's looking much more well balanced and well organised now. Shame about the name, but one cant have everything. FeydHuxtable (talk) 13:13, 27 October 2009 (UTC)

Planimeter
You introduced the section "polar coordinates" in the article about the planimeter. I do not understand this section. Maybe you can give a more explicit explanation. Nijdam (talk) 11:51, 25 October 2009 (UTC)
 * Ok, will do – apologies for the unclear explanation, and thanks for the feedback.
 * —Nils von Barth (nbarth) (talk) 18:50, 25 October 2009 (UTC)
 * I've re-written the section some, though I grant that it's not terribly clear; it's just making the connection of planimeter to Green's theorem in polar coordinates instead of vector calculus, which I find clearer. Hope it helps though.
 * —Nils von Barth (nbarth) (talk) 06:41, 13 November 2009 (UTC)

Thanks for your recent changes!
Thanks for your recent edits!! - You helped the world today in some way... maybe a little bit, but wrong is doing nothing at all. 189.217.171.135 (talk) 01:52, 31 October 2009 (UTC)

Too much TeX

 * I’ve now made a project, at WP:WPMATHTYPE.

I just spent some time getting rid of some of the "inline" TeX in Automorphisms of the symmetric and alternating groups. Some of this was in section headings. When you put TeX in a section heading, it is invisible in the table of contents. That means you had a section heading appearing in the T.O.C. as follows:
 * The exceptional outer automorphism of

That's it: it ended with "of". When it's not in a section heading, you get things like $$2^3$$ in which the "2" appears lower than the surrounding letters and the characters are between two and four times the size of the surrounding letters, whereas 23 matches the surrounding letters perfectly. You need TeX to write things like
 * $$ \int_0^\infty \sum_{n=0}^u 1\,dx.$$

You don't need TeX to write 6!/120 = 1. Michael Hardy (talk) 05:31, 31 October 2009 (UTC)


 * Sorry about that!
 * I didn’t realize the problem with the section heading; I will avoid it in future, and I’ve made a note at the Manual of Style.
 * —Nils von Barth (nbarth) (talk) 00:01, 1 November 2009 (UTC)


 * To the other point…
 * Regarding LaTeX vs. HTML – your point regarding the poor typesetting of simple inline LaTeX is well-taken.
 * That said, use of LaTeX vs. HTML is a debated and contentious point – I find LaTeX markup much easier to write and edit (compare X \to Y to  X&amp;nbsp;&amp;rarr;&amp;nbsp;Y ), and more semantically correct.
 * The specific rendering problems you mention, while vexing, are technical issues, and are solved by better rendering.
 * My suggestion is to use LaTeX inline, and fix the rendering if necessary – this ensures consistent style and simplifies edition (and makes your life easier!) – and regardless, we’d like LaTeX rendition to be good.
 * Specifically:
 * I have no baseline problem with basic formulae.
 * The “math is too big” is due to the use of font-size: 125% in Monobook.css, which was discussed at: MediaWiki talk:Monobook.css – it was designed to make serif math work better with sans-serif text, but as you note, it breaks for many (myself included).
 * Removing the 125% fixes all problems for me (middle is HTML, two ends are LaTeX – right end removes the 125%, fixing the size); note that math is by default set in serif:
 * Aa $$2^3$$ Bb 23 Cc 2^3 Dd
 * Aa $$S_n$$ Bb Sn Cc S_n Dd

Aa $$2^3$$ Bb 23 Cc 2^3 Dd Aa $$S_n$$ Bb Sn Cc S_n Dd
 * Thanks for bringing this up; what I’d suggest concretely is:
 * Setup a WP:MATH subproject to discuss LaTeX rendering issues, as this is a big deal and warrants dedicated attention; I’d be happy to do so.
 * Discuss what WP:MATH would like the LaTeX-to-HTML rendering and style to do.
 * For example, LaTeX could render exactly as you desire (sans-serif, normal size) by making 2 small changes to
 * shared.css and
 * Monobook.css (search on texhtml).
 * So – shall I start a subproject page and a discussion?
 * —Nils von Barth (nbarth) (talk) 00:01, 1 November 2009 (UTC)

Probably couldn't hurt to start a subproject. These issues have been talked about since 2003. When TeX first became available on Wikipedia, "inline" TeX was formatted so that the bottom of the line of text aligned with the bottom of the TeX display, and that looked ridiculous in most cases. It was soon changed to centering, and that also looks ridiculous in some cases. I'm not sure there's been any progress since then. Michael Hardy (talk) 14:54, 1 November 2009 (UTC)

Systematic error
Howdy, your recent edits have introduced a systematic error: PGL is not the automorphism group of the incidence structure associated to projective geometry. It is similar but not isomorphic. The automorphism group of the projective plane is called the collineation group and is larger than the projective general linear group. Similar statements hold in higher dimensions. JackSchmidt (talk) 15:51, 31 October 2009 (UTC)


 * Oops‼ I thought they were identical!
 * Thanks for the catch – I’ll fix it and ref to and from collineation.
 * —Nils von Barth (nbarth) (talk) 00:07, 1 November 2009 (UTC)


 * Ok, fixed it at collineation and projective linear transformation, and linked these back and forth so it’s more discoverable; sorry about this, and thanks for correcting it.
 * —Nils von Barth (nbarth) (talk) 00:52, 2 November 2009 (UTC)

Invitation to participate in SecurePoll feedback and workshop
As you participated in the recent Audit Subcommittee election, or in one of two requests for comment that relate to the use of SecurePoll for elections on this project, you are invited to participate in the SecurePoll feedback and workshop. Your comments, suggestions and observations are welcome. For the Arbitration Committee, Risker (talk) 08:29, 12 November 2009 (UTC)

Covering trail off and citation
Howdy, thanks for splitting off the covering groups material.

The section Covering groups of the alternating and symmetric groups currently trails off with "As there are two pin groups, there are two distinct 2-fold covers of the symmetric group, but only one of these". From the lead, it looks like one wants to say "For the symmetric group, there are actually two different covers (corresponding to the two different Pin groups), but only one of these is of interest in classifying projective representations." but I'm not sure the comment about "interest" is accurate. Could a citation be added for this discounting of one of the covers? JackSchmidt (talk) 18:34, 18 November 2009 (UTC)


 * Oops, thanks -- got cut off editing (there's another diagram coming too). The statement discounting one of the covers is from the Encylopaedia of Mathematics (SpringerLink); I've added a citation. Unfortunately, they don't say *which* cover is of interest, and I can't find other refs (well, other than Schur, but looking through a 100-page article of 100-year old German mathematics is not exactly encouraging). Hope it looks better now!
 * —Nils von Barth (nbarth) (talk) 18:48, 18 November 2009 (UTC)

Autoreviewer
Hi Nbarth, after noticing one of your recent articles at NewPage patrol, I've set the Autoreviewer flag on for your account. So in future any articles you create will bypass the new page patrol process, as they will be automatically marked as patrolled. Take care and happy editing.  Ϣere Spiel  Chequers  14:38, 25 November 2009 (UTC)
 * Thank you for the flag and the explanation! (Now I can edit without fear of cluttering the New Page Patrol!)
 * —Nils von Barth (nbarth) (talk) 19:05, 25 November 2009 (UTC)
 * You're welcome:) More importantly than just new articles, I think that when and if flagged revisions come in the edits of Autoreviewers will be preflagged as not vandalism. So the more editors like you we can give the autoreviewer flag to the less likely it is that flagged revisions will break the wiki.  Ϣere Spiel  Chequers  21:29, 25 November 2009 (UTC)
 * OIC – thanks!
 * Over at Wiktionary, there’s a very active patrolling and autopatrolling culture and system, which y’all may find interesting – see WT:WL.
 * —Nils von Barth (nbarth) (talk) 00:46, 26 November 2009 (UTC)
 * Thanks, I've only made a couple of edits there so I'm not familiar with their culture, but I love the idea of a sysop based patrol of recent changes. We patrol both newpages and recent changes, but many, perhaps most, of our patrollers are not admins. At Newpage patrol we have a whole load of taggers who are not admins, and many of the admins just focus on stuff that others have tagged for deletion.  Ϣere Spiel  Chequers  22:51, 3 December 2009 (UTC)

Huh?
What did you have in mind with this edit? The sentence preceding the dash is false, and what comes after the dash seems to assume that infinitely divisible distributions cannot be decomposable; whereas in fact all infinitely divisible distributions are decomposable. Nor would it have made sense if you had said "need not be indecomposable", since in fact such distributions are NEVER indecomposable, immediately from the definition. Michael Hardy (talk) 23:28, 28 November 2009 (UTC)


 * Oops – it was a wording fix; I wanted to emphasize that indecomposable is clearly not closed under sum and emphasize that infinitely divisible is much stronger than decomposable, but I introduced an error in the process. Thanks for catching this; I’ve given another stab at wording in this edit, which is hopefully both clear and correct.
 * —Nils von Barth (nbarth) (talk) 23:37, 28 November 2009 (UTC)

Hyphenated name
Here's one of the hazard of Wikipedia: This is a hyphenated name of one person (I've moved it back). Michael Hardy (talk) 05:42, 30 November 2009 (UTC)


 * Oops! m(_ _)m
 * Sorry, and thanks for catching it; I fixed a few other instances of it. (Fortunately there isn’t a Borel–Harish-Chandra theorem or the hyphenation would be a mess.)
 * —Nils von Barth (nbarth) (talk) 21:15, 30 November 2009 (UTC)

I seem to recall having seen one or two like that. Michael Hardy (talk) 00:20, 1 December 2009 (UTC)

New article at Commuting matrices
hi, I saw your new article, and am impressed. I pointed out on the talk page that your internal link to commute contains no mathematical case of the word, but I think I'm the only one who's visited the talk page. Just thought I'd bring that to your attention. Cheers! —Preceding unsigned comment added by Throwaway85 (talk • contribs) 00:51, 3 December 2009 (UTC)
 * Fixed – thanks for bringing it to my attention!
 * —Nils von Barth (nbarth) (talk) 01:22, 3 December 2009 (UTC)
 * No problem. Keep up the good work! Throwaway85 (talk) 01:24, 3 December 2009 (UTC)

Proposed deletion of Efficient Recitation with Overlearning


The article Efficient Recitation with Overlearning has been proposed for deletion&#32; because of the following concern:
 * no evidence of notability

While all contributions to Wikipedia are appreciated, content or articles may be deleted for any of several reasons.

You may prevent the proposed deletion by removing the  notice, but please explain why in your edit summary or on the article's talk page.

Please consider improving the article to address the issues raised. Removing  will stop the Proposed Deletion process, but other deletion processes exist. The Speedy Deletion process can result in deletion without discussion, and Articles for Deletion allows discussion to reach consensus for deletion. &mdash; RHaworth 21:13, 5 December 2009 (UTC)


 * As noted on talk page, no objection – I was just cleaning up flashcard, and investigation shows no notability, as claimed.
 * —Nils von Barth (nbarth) (talk) 22:18, 5 December 2009 (UTC)

J-invariant

 * See: Talk:j-invariant: Confusing article

A criticism has been raised of an edit of yours on the talk page of the article J-invariant. You may like to read the criticism, and perhaps respond to it, even though it is now some years since you made the edit in question. JamesBWatson (talk) 11:44, 10 December 2009 (UTC)
 * Thanks for bringing this to my attention! (And for digging out that I wrote it.)
 * I’ve clarified the article and replied on the talk page.
 * —Nils von Barth (nbarth) (talk) 19:38, 10 December 2009 (UTC)
 * You are welcome. JamesBWatson (talk) 22:04, 10 December 2009 (UTC)
 * Oh, thanks for the Barnstar. JamesBWatson (talk) 22:10, 10 December 2009 (UTC)
 * No problem – you’re well deserving of that one!
 * —Nils von Barth (nbarth) (talk) 00:17, 11 December 2009 (UTC)

Deprecated parameters
I noticed in Equality (mathematics) and Isomorphism that you used the "day" parameter in citations. Please be informed that it is deprecated. The reason is that if you know a year, month and day, it obviously makes more sense to use the date parameter. Debresser (talk) 10:06, 13 December 2009 (UTC)
 * Thanks for the info!
 * (I’d assumed that explicit year/month/day was useful so that the date field didn’t need to be parsed, but as you say, it’s redundant, so I shaln’t need to include in future.)
 * —Nils von Barth (nbarth) (talk) 04:16, 14 December 2009 (UTC)
 * It is always confusing when parameters are being deprecated. That's why I dropped you a note. Good luck! Debresser (talk) 13:35, 14 December 2009 (UTC)

Money Creation
I just read your recent addition to Money creation. I don't think it fits there. Have you considered adding it to monetary policy and/or business cycles instead? thanks, LK (talk) 05:15, 21 December 2009 (UTC)
 * Hi Lawrence,
 * Thanks for the (too rare!) feedback!
 * The money creation articles are a bit of a mess – I’ve a long-standing to-do item to fix them – with information duplicated several places.
 * I’ve split money multiplier to its own page, as it’s currently 15k, which is rather long – hope you like it!
 * The point I was making, which is mentioned but often missed, is that the multiplier is a maximum, not an equality – though for long periods it functions as an equality, hence easily conflated. You’re right that this has important implications for monetary policy, though it is also important for the nature of the multiplier itself (Samuelson’s “no 5 for 1 [in a depression]” states this clearly), and I’ve reworded and retitled the section to reflect this (it was not “criticism” so much as “clarification”), and edited the article so that it reflects this.
 * I’ve also fixed the section in money creation so that it is written in summary style and defers to the main article, though I’ve not fixed the section at Fractional-reserve banking nor included relevant info at monetary policy, though you’re correct that something belongs there.
 * Hope this begins to address your concerns; I’ll be a bit busy over holidays, but I’ll try to continue integrating and cleaning up, and of course you’re quite welcome to do so yourself – we can review and reconcile when we’ve both time.
 * Enjoy holidays and take care!
 * —Nils von Barth (nbarth) (talk) 08:56, 21 December 2009 (UTC)


 * It's good that you're putting in the effort to clean up the money and banking articles. Thanks! You're right that they're in a bit of a mess. Part of the problem is the people who've read Rothbard and then decide to change the articles to reflect Rothbard's rather idiosyncratic viewpoint.
 * I've had a look at the money multiplier page you've put together, and it's nice. You're of course right that the classic 1/rr reflects a maximum for the money multiplier - there's a nice discussion of this in the Mankiw intermediate Macroeconomics textbook, Chapter 18 I think. The standard way to treat this is to define the money multiplier as the ratio between M2 and M0, and explain how it will be between 1 and 1/rr depending on the amount of currency that people decide to hold and the excess reserves kept by banks. I notice that your treatment is different - at some point I may wade in and change it a bit.
 * Unfortunately, I've been having a busy few months (putting together a new course, and just sent off a paper to a journal) and haven't really been contributing. But I do check for messages pretty regularly. Do let me know if I can help in any way.
 * regards, LK (talk) 14:47, 21 December 2009 (UTC)


 * No worries re: such an Augean task; I’ve added some references to Mankiw and Krugman, which should help, and mentioned M2 and M0, though it could certainly use revision (the worked re-lending example, in particular, is rather rough).
 * My main concern for the “Money multiplier” article itself is that readers are clear on the different ways this particular concept is used and defined, since the differences are subtle but have significant impact on monetary policy – hence I’ve fronted this issue, but started with the simple “reciprocal of reserve rate” definition. On other pages we needn’t (and shouldn’t) make a big point of it, as it obscures matters, but on this page we should – for example Krugman, Mankiw (Intro) and Mankiw (Macro) define it at least three different ways (reciprocal of reserve rate, empirical ratio, and component of model), sometimes in slightly different ways over the course of a few pages, and this can be very confusing.
 * Thanks for the warning about Austrians – agreed that while we want to include all significant views (and Austrian economics is a significant view, albeit heterodox), they shouldn’t dominate or distort main pages like Money; specialized pages like criticism of fractional-reserve banking are rather better places for such argument. I’ll try to avoid stepping on any golden toes!
 * Good luck with your course and paper!
 * —Nils von Barth (nbarth) (talk) 06:48, 22 December 2009 (UTC)


 * You asked if there was any way you might help; if you’ve time or familiarity with the literature on this,
 * one question that would be of particular interest to me is research that analyses the multiplier (presumably there’s something in Friedman & Schwartz, at least data), and especially the re-lending model of money creation; the only treatments beyond the intro “here’s $100 at 10% reserve rate – ta-da, geometric series!” with which I’m familiar are criticisms, in turn by monetary circuit theorists (rather different model), by financial practitioners (PIMCO, dismiss it as “textbook, not reality”), and by Kydland & Prescott (from econometric data/Real Business Cycle theory) – are there empirical studies that support the re-lending model, or is it mostly just used in textbooks (or in modeling?)?
 * —Nils von Barth (nbarth) (talk) 06:48, 22 December 2009 (UTC)


 * Deep questions. Unfortunately, I don't have the knowledge or expertise to answer them as well as I wish, and as you deserve.
 * First, for something a little more complicated than multiplier = 1/rr, Mankiw's intermediate macro textbook (chapter 18) has a simple model showing that the money multiplier depends on the actual reserve deposit ratio (which is equal to the mandatory reserve ratio plus the excess reserve ratio), and on the currency deposit ratio (the ratio of cash vs deposits that the public chooses to keep). Specifically, the actual multiplier will be equal to:
 * money multiplier =  CR + 1 / CR + RR
 * where CR is the currency deposit ratio, and RR is the actual reserve deposit ratio. Even if the mandatory reserve ratio remains constant, the money multiplier will tend to shrink as people hold more cash, and as banks hold more excess reserves. This happens during a financial crisis, which is why financial crisis were associated in the past with a shrinking money supply and economic depression (before the days of quantitative easing). This point was also brought up in Friedman & Schwartz in their "Monetary History of the United States".
 * Second, unfortunately I'm not familiar with criticisms from monetary circuit theorists or financial practitioners so can't comment on them. As for RBC ala Kydland & Prescott, the simple RBC models do not include money, and make no comment on the effect of money on the economy. However, no one can deny that an increase in the growth rate of money supply reduces nominal interest rates in the short run and increases it only in the long run, and so people working in the RBC literature have attempted to create models with money and the appropriate frictions to generate this result. The RBC and the new Keynesian models seem to be converging, in that as the RBC models add more and more frictions, and the new Keynesians try for more and more micro foundations, the models end up looking very similar to each other. As far as I know, the RBC people have no problems with the concept of a money multiplier, and would not disagree with the mainstream view that new money expands slowly into the economy as bank lending rises.
 * Third, a major strand of the post-Keynesian literature is on money, and the effect of money on the economy. They hold to a theory of 'endogenous money', which I understand to mean that the amount of money in the economy is actually very flexible, and subject to the demand for money and for bank lending. In the mainstream view, this would mean that both the money multiplier and the velocity of money are not constant, and are elastic to the demand for money. They also do work on credit cycles and economic bubbles. I am not very familiar with the post-Keynesian literature, but Paul Krugman has spoken of them approvingly.
 * Lastly, about an empirical literature on the money multiplier, there is work on how the multiplier shrinks when either banks or the public want to hold more cash. You can find this in the literature on financial crisis. Also, work on hyperinflations show that monetary injections affect broad money with a lag, essentially because it takes time for banks to relend the money out, and so when the money supply is accelerating very quickly (as happens in hyperinflationary environments) the money multiplier will tend to fall. Unfortunately, I do not have any handy citations available, as I read those papers a long time ago.
 * Hope this helps. If I wasn't clear about anything, please drop me a line asking me to clarify. best, LK (talk) 10:14, 29 December 2009 (UTC)
 * Thanks for the (detailed!) explanation and background! As and when I read up on money more (and work on the WP pages), I'll try to incorporate (and cite) the above, and whatever else I may find.
 * Meanwhile, best wishes for the new year!
 * —Nils von Barth (nbarth) (talk) 07:38, 30 December 2009 (UTC)