User talk:RapidR

Hi,

As a regularly contributing UK Wikipedian, we were wondering if you wanted to contribute to the Oxford bid to host the 2010 Wikimania conference. Please see here for details of how to get involved, we need all the help we can get if we are to put in a compelling bid.

We are also in the process of forming a new UK Wikimedia chapter to replace the soon to be folded old one. If you are interested in helping shape our plans, showing your support or becoming a future member or board member, please head over to the Wikimedia UK v2.0 page and let us know. We plan on holding an election in the next month to find the initial board, who will oversee the process of founding the company and accepting membership applications. They will then call an AGM to formally elect a new board who after obtaining charitable status will start the fund raising, promotion and active support for the UK Wikimedian community for which the chapter is being founded.

You may also wish to attend the next London meet-up at which both of these issues will be discussed. If you can't attend this meetup, you may want to watch Wikipedia:Meetup, for updates on future meets.

We look forward to hearing from you soon, and we send our apologies for this automated intrusion onto your talk page!

Addbot (talk) 21:17, 30 August 2008 (UTC)[reply]

The September version of the WikiProject Earthquakes newsletter has been posted! Be sure to check it out! — Ceranthor [Formerly LordSunday] 14:13, 4 October 2008 (UTC)[reply]

Be sure to check out the October version of the WikiProject Earthquakes Newsletter for updates and news. Thanks, — Ceranthor  (Sing) 23:17, 30 October 2008 (UTC)[reply]

I don't dispute that the date for the 1556 Shaanxi earthquake is January 23 rather than February 14, which is the date that was on the article until today, but could you provide some citation? Thanks. Interlingua 05:01, 24 January 2009 (UTC)[reply]

Hi RapidR, Thanks for your help in sorting out this list. If you want to rename it '21st century' I've no real objection although I don't see an urgent need only nine years into the century. I was beginning to wonder if anyone had noticed the fairly major changes I was making to the various earthquake lists, so your contribution came as a relief.

The last change I have planned is to the List of earthquakes which is now almost completely redundant. My suggestion is to remove the USGS significant quake list (now fully duplicated), perhaps keep the two top ten lists but otherwise just keep it as a 'list of lists' for earthquakes, renaming it as Lists of earthquakes. I would appreciate your views on this. Cheers, Mikenorton (talk) 15:10, 1 June 2009 (UTC)[reply]

OK, that's all fine with me, pretty much what I was thinking. Have fun with the 2008 list, I almost lost the will to live going through that:-), I think that there's a lot of non-notable stuff there, at least for a global list, Cheers Mikenorton (talk) 20:20, 1 June 2009 (UTC)[reply]

I'm going to try and hurry the 1989 Loma Prieta earthquake article through both GA and FA to see if I can get it as the Featured Article on the Main Page in time for its 20-year anniversary on October 18, 2009. Care to help a little or a lot? Binksternet (talk) 02:40, 30 August 2009 (UTC)[reply]

The WikiProject Earthquakes newsletter for September 2009 has been released. Be sure to check on our status. ceranthor 11:42, 31 August 2009 (UTC)[reply]

Hi. I tried to fix the dead links in 'Railway electrification in Great Britain', but there was one that I couldn't fix. I marked it with {{Dead link}}. Can you help fix the last dead link?

Dead: http://www.nedrailways.com/html/merseyrailkeyfacts.html

• You added this in July 2008.
• I tried to load this link on 30 March, 1 April, 3 April and today, but it never worked.
• I looked in The Wayback Machine and WebCite but I couldn't find a suitable replacement.

Please take a look at that article and fix what you can. Thank you!

PS- you can opt-out of these notifications by adding {{Bots |deny=BlevintronBot}} to your user page or user talk page. BlevintronBot (talk) 03:08, 7 April 2012 (UTC)[reply]

I saw the wiki page, but I couldn't find any examples using actual numbers evaluating the formula. Could you give some examples of convolution, please? Mathijs Krijzer (talk) 22:13, 9 March 2013 (UTC)[reply]

Definition[edit]

The convolution of f and g is written f∗g, using an asterisk or star. It is defined as the integral of the product of the two functions after one is reversed and shifted. As such, it is a particular kind of integral transform:

${\displaystyle (f*g)($t)\ \ \,}	${\displaystyle {\stackrel {\mathrm {def} }{=}}\ \int _{-\infty }^{\infty }f(\tau )\,g(t-\tau )\,d\tau }$
	${\displaystyle =\int _{-\infty }^{\infty }f(t-\tau )\,g(\tau )\,d\tau .}$       (commutativity)

Domain of definition[edit]

The convolution of two complex-valued functions on R^d

${\displaystyle (f*g)($x)=\int _{\mathbf {R} ^{d}}f(y)g(x-y)\,dy}

is well-defined only if f and g decay sufficiently rapidly at infinity in order for the integral to exist. Conditions for the existence of the convolution may be tricky, since a blow-up in g at infinity can be easily offset by sufficiently rapid decay in f. The question of existence thus may involve different conditions on f and g.

Circular discrete convolution[edit]

When a function g_N is periodic, with period N, then for functions, f, such that f∗g_N exists, the convolution is also periodic and identical to:

${\displaystyle (f*g_{N})[$n]\equiv \sum _{m=0}^{N-1}\left(\sum _{k=-\infty }^{\infty }{f}[m+kN]\right)g_{N}[n-m].\,}

Circular convolution[edit]

When a function g_T is periodic, with period T, then for functions, f, such that f∗g_T exists, the convolution is also periodic and identical to:

${\displaystyle (f*g_{T})($t)\equiv \int _{t_{0}}^{t_{0}+T}\left[\sum _{k=-\infty }^{\infty }f(\tau +kT)\right]g_{T}(t-\tau )\,d\tau ,}

where t_o is an arbitrary choice. The summation is called a periodic summation of the function f.

Discrete convolution[edit]

For complex-valued functions f, g defined on the set Z of integers, the discrete convolutionoff and g is given by:

${\displaystyle (f*g)[$n]\ {\stackrel {\mathrm {def} }{=}}\ \sum _{m=-\infty }^{\infty }f[m]\,g[n-m]}

${\displaystyle =\sum _{m=-\infty }^{\infty }f[n-m]\,g[$m].}       (commutativity)

When multiplying two polynomials, the coefficients of the product are given by the convolution of the original coefficient sequences, extended with zeros where necessary to avoid undefined terms; this is known as the Cauchy product of the coefficients of the two polynomials.

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