User talk:Bob K

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Welcome!

Hello, Bob K, and welcome to Wikipedia! Thank you for your contributions. I hope you like the place and decide to stay. Here are a few good links for newcomers:

I hope you enjoy editing here and being a Wikipedian! Please sign your name on talk pages using four tildes (~~~~); this will automatically produce your name and the date. If you need help, check out Wikipedia:Where to ask a question, ask me on my talk page, or place {{helpme}} on your talk page and someone will show up shortly to answer your questions. Again, welcome!  DV8 2XL 11:38, 19 November 2005 (UTC)

Finding subpages[edit]

Is there any way to list all the subpages of a specific page?

To find all subpages of Manifold, for instance, go to Special:Allpages and type "manifold/" in the box labelled "Display all pages starting with:" (I learned this trick from R. Koot) -- Jitse Niesen

Moved images[edit]

[1]

I also went there and changed PD to PD-self, but I didn't realize that I was not logged in, because I wasn't a member of commons. It seemed to work anyway. Is that true? And did I need to do that? If so, shouldn't someone have notified me?... like maybe the person who moved the image? Is is going to stay in one place now? Should I have uploaded it differently than I did? -- Bob K
Since the image contains English text not suitable to http://simple.wikipedia.org/ I think User:Tiaguito's move to commons was wrong, and your original upload was fine. It's not a problem since it still shows up fine in the articles. -- Jeandré, 2006-01-11t11:00z

Convolution[edit]

Hi, your edit summary said that some characters do not appear correctly in Internet Explorer. They seem fine on my copy, which has no special fonts installed. But if this is generally a problem for people running internet explorer, then something should be done to make changes across several articles. Is it possible to get a screen shot to see what it looks like on your copy? Thenub314 (talk) 11:04, 19 January 2009 (UTC)

When User:Bdmy changed ƒ*gT to ƒ∗gT, the asterisk became an empty square (aka "box") on my IE screen. Upon further reading, such as Talk:Set_(mathematics)#Box-fixing and Template_talk:SpecialChars#Internet_Explorer, I learned that the problem is associated with IE. I have Firefox, and it works, but I use IE for everything else, as do many other readers.
--Bob K (talk) 14:28, 19 January 2009 (UTC)
This is good to know. I when I tried IE on my vista machine it worked fine, when I tried on my XP machine it displayed a box. I wonder why they only fixed the bug on Vista? Oddly, as an a side, on my XP system the PNG graphics also looked very pixelated. I am surprised the issue about boxes has never come up on the WT:WPM. I will try to keep this in mind when editing articles, and make sure to use * instead of ∗. Thenub314 (talk) 15:05, 19 January 2009 (UTC)
Ah Ha! I discovered an easy fix. I changed Times New Roman to Lucida Sans Unicode in a pull down menu at Tools -> Internet Options -> Fonts -> Webpage Font:.  That fixes the problem for me. But how do we disseminate that information to the readership?
--Bob K (talk) 14:55, 19 January 2009 (UTC)
Well, one could include a link on the special characters template that discusses possible fixes. Thenub314 (talk) 15:05, 19 January 2009 (UTC)
Yes, I was just looking into that. But I haven't figured out where the "fix" page should exist. Any suggestions?
--Bob K (talk) 15:20, 19 January 2009 (UTC)
More progress... I just created section Changing Internet Explorer's (IE) default font
--Bob K (talk) 17:03, 19 January 2009 (UTC)
Nice work! It is looking much better. Thenub314 (talk) 19:07, 19 January 2009 (UTC)

Disambiguation link notification for November 19[edit]

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Single-sideband_modulation answer on my biggest Question of life[edit]

Спасибо! Привет тебе из России. Не хворай ;-) http://translate.google.com/#ru/en/ Xakepp35 (talk) 20:03, 7 February 2013 (UTC)

You're very welcome. I'm glad to know the answer actually reached you. And thanks for the well wishes. --Bob K (talk) 21:21, 8 February 2013 (UTC)

Examples of convolution[edit]

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) 22:14, 9 March 2013 (UTC)

Definition[edit]

The convolution of f and g is written fg, 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:

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

Domain of definition[edit]

The convolution of two complex-valued functions on Rd

(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 gN is periodic, with period N, then for functions, f, such that fgN exists, the convolution is also periodic and identical to:

(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]

Main article: Circular convolution

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

(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 to 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 convolution of f and g is given by:

(f * g)[n]\ \stackrel{\mathrm{def}}{=}\ \sum_{m=-\infty}^\infty f[m]\, g[n - m]
= \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.

Disambiguation link notification for May 2[edit]

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Some bubble tea for you![edit]

Bubble Tea.png I thought your comment on the technical sophistication of a signls processing article I was reading was very sensible.
David Lloyd-Jones (talk) 22:26, 4 February 2014 (UTC)

Renaming of Star transform article[edit]

Please explain the criteria for your assertion that (quote): ""starred transform" receives the higher percentage of relevant hits on the internet", which was your argument for renaming the article "star transform". Consider the following results:

  • "star transform"
    • Google Scholar: 125 results
    • IEEE Xplore: 4 results
  • "starred transform"
    • Google Scholar: 36 results
    • IEEE Xplore: 1 result

Based on these results, I expect you to revert your changes. --Sagie (talk) 13:04, 6 February 2014 (UTC)

I saw the Google Scholar results, but my informal inspection of the hits revealed that the "star transform" hits were mostly about text compression algorithms, which I assume are irrelevant here. There were many other irrelevant hits as well.
--Bob K (talk) 14:32, 6 February 2014 (UTC)

Your contributions to Z-transform and Star transform[edit]

While your contribution to said articles is very appreciated, you have also been systematically deleting information from them. Specifically, you have deleted (twice) information about relationship between the Z-transform and the Laplace transform, by means of the star transform:

  1. in your first edits that relationship was removed altogether.
  2. in your last edits (following my retrieval of said information) you've removed information regarding the conversion from a continuous-time Laplace representation to a discrete time Z/star representation, which is what the star transform is all about, since from before it was even known as star/starred transform (see E. Jury, "Analysis and Synthesis of Sampled-Data Control Systems", Sept. 1954)

While the information about star transform could probably have been presented more succinctly in the Z-transform article, I find removing it altogether is completely unacceptable. I'd appreciate your reinstating of the removed information.

--Sagie (talk) 13:09, 6 February 2014 (UTC)

Regarding the second point I made, note that you've removed this information from both articles (Z-transform and Star transform)
--Sagie (talk) 13:11, 6 February 2014 (UTC)


Comparing the current version of Starred transform to the 23Mar'13 version, it appears that what you're concerned about is merely this:

x(t) \rightarrow X^*(s) \rightarrow x^*(t)

Really?

--Bob K (talk) 15:41, 6 February 2014 (UTC)

I don't know why you're playing dumb. Your changes to said article are far more than the above mentioned deletion. What I'm mainly concerned about is you deleting the following paragraph, which the main way to convert between the transforms:
The star transform can be related to the Laplace transform, by taking the residues of the Laplace transform of a function, as such:
X^*(s) = \sum \bigg[\text{residues of }X(\lambda)\frac{1}{1-e^{-T(s-\lambda)}}\bigg]_{\text{at poles of }X(\lambda)},
--Sagie (talk) 12:30, 19 February 2014 (UTC)

First of all, your point no. 1 is irrelevant. It's quibbling about the route I took, rather than the result. Regarding your point no. 2, indeed I seem to have made a mistake when I tried to compare the Feb 6 version (https://en.wikipedia.org/w/index.php?title=Starred_transform&oldid=594159008) version with the Mar 2013 version (https://en.wikipedia.org/w/index.php?title=Starred_transform&oldid=546556726). Had I done it correctly, my suggestion would have been to better-support the deleted, isolated fragment, as you have now apparently done (Starred_transform#Relation_to_Laplace_transform) on your own. Better. Not sure if your text changes are an improvement though. Not sure that I really care anymore. Perhaps others are watching who will weigh in.
--Bob K (talk) 17:09, 19 February 2014 (UTC)

Instantaneous phase[edit]

Question for you on [Instantaneous phase]]. Does it make sense to you that in the figure, the y-axis has different scale in the top vs the bottom graphs? Thanks. 22:06, 16 June 2014 (UTC)

Since they are being compared side-by-side, one can certainly make a good case for using one scale for both. And by-the-way, phase unwrapping algorithms are not fool-proof when looking at angle-modulated signals with possible smeared 180 degree phase shifts. The approach I've used in systems since the 1970's, is to simply stack three "copies" of the wrapped phase plot vertically, and label the y-axis [-3π,3π]... works like a charm. Another good trick is to not try to "connect the dots" of the graph. Instead, vertically elongate each dot (for instance 1 pixel wide and 8 pixels high), which tends to make them look connected without having to make error-prone algorithmic decisions.
--Bob K (talk) 11:35, 17 June 2014 (UTC)
Thanks for that, and for the extra advice too! Jytdog (talk) 11:59, 17 June 2014 (UTC)

Proposed deletion of A derivation of the discrete Fourier transform[edit]

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The article A derivation of the discrete Fourier transform has been proposed for deletion because of the following concern:

Unsourced alternative-pov content fork of discrete Fourier transform, written in an essay-like and unencyclopedic way, not suitable for merging.

While all constructive 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 {{proposed deletion/dated}} 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 {{proposed deletion/dated}} will stop the proposed deletion process, but other deletion processes exist. In particular, the speedy deletion process can result in deletion without discussion, and articles for deletion allows discussion to reach consensus for deletion. —David Eppstein (talk) 00:42, 9 February 2015 (UTC)

FFT of the Window functions[edit]

Hello Bob K,

I've read your posts in the section: Talk:Window function. I posted a question yesterday in that section under the title identical to this post. I would appreciate if you could take a look at it. Thanks much. --AboutFace 22 (talk) 14:50, 17 June 2015 (UTC)