Wikipedia:Reference desk/Archives/Computing/2012 February 17

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February 17

Vector Spaces over Finite Vector Spaces

I was wondering if anybody here knows of a good reference like a textbook perhaps to study finite fields and vector spaces over those finite fields. I thought maybe these topics are relevant to computer science (like cryptography and error detection/correction codes) so there may be a well known text or something. Every time I search anywhere I keep getting "finite DIMENSIONAL vector spaces". I can imagine most of the theory is the same as real/complex vector spaces but there are some subtle differences which I want to explore. Thanks! - Looking for Wisdom and Insight! (talk) 00:45, 17 February 2012 (UTC)

You would probably do better to ask this in the Maths section. Rojomoke (talk) 14:32, 17 February 2012 (UTC)

I can't make a recommendation based on personal experience, but maybe I can help you find what you're looking for. I recalled that a common example in computer science is to use vector spaces over F_2, the field of two elements. Googling /binary vector space/ returned this nice webpage of lecture notes, full of content and exercises [1]. For more general search terms /vector space "finite field"/ returned this book [2] which is probably not quite what you're looking for, but does have a chapter on vector spaces over finite fields. If you have access to a good library, these, terms, plus maybe "encoding" or "computer science" should get you going. SemanticMantis (talk) 19:36, 17 February 2012 (UTC)

I agree about asking at the math desk. These vector spaces up in in coding theory and Galois theory and other places too, but I hadn't thought of them as a subject in their own right. 67.117.145.9 (talk) 22:59, 18 February 2012 (UTC)

Finding extensions

Sometimes you have files that you want to open them but you don't know the extension! How would you open them? for example some tmp files or someone who Gziped a file, but didn't added the extension... or if someone used binhex on it and you extract the hqx file but don't know what to do with the file.. How would you find the extension? 190.60.93.218 (talk) 18:04, 17 February 2012 (UTC)

It sounds like you want to find the file's type and then change the extension to match, so it automatically opers with the appropriate program? On Mac OS-X and Linux you can use the file command. 46.208.44.141 (talk) 18:31, 17 February 2012 (UTC)

You can grab a win32 build of file from gnuwin32.sf.net. It is a command line application, though, so to get the most use out of it, you'll want to add the directory of executables it creates (by default %programfiles%\GnuWin32\bin [or %programfiles(x86)%\GnuWin32\bin for a 64-bit system, since it's a 32-bit binary]) to your path. Then to utilize it, at least in recent versions of Windows, you can SHIFT+right_mouse_click on a directory to get a convenient 'Open command window here', and run file nameOfFile. ¦ Reisio (talk) 23:49, 17 February 2012 (UTC)

Try opening the file using Notepad or a hex editor. The first few characters of the file are usually the name of the program that created it.--Shantavira|^{feed me} 19:03, 17 February 2012 (UTC)

Unless it is some really obscure format, just trying different programs until you find one that works is usually good enough. 7zip will open most archive formats, Irfanview will open most picture formats, VLC will open most media formats, and open office will open many document formats. If none of those work, it's probably an .exe 82.45.62.107 (talk) 19:58, 17 February 2012 (UTC)

Windows has an option to hide file types, which I absolutely hate. The assumption is that the computer will know what to do with the file, so you don't need to know the type. That assumption often fails in the real world, though. Besides, just knowing how to open it isn't all the file type tells you. Different graphics formats are used for different purposes, for example, some with lossy compression, some with lossless, some with no compression at all. StuRat (talk) 17:26, 18 February 2012 (UTC)

I had thought about giving this answer but decided the original poster wasn't suffering from this "feature". In case I was wrong, the place to turn it off is Control Panel -> Folder Options -> View, and there's an option called "Hide extensions for known file types". Comet Tuttle (talk) 18:56, 18 February 2012 (UTC)

No, no no.. I don't need to know what is the extension of the file, becuase the file itself has .001 extension. and neither wnrar, vlc, notepad obviously opens it, it says some text. and beyond that it's binary. it's a strange format... meh.. I'll try to use that build that finds file types.. though. 190.158.184.192 (talk) 20:58, 19 February 2012 (UTC)

If that fails, I suggest you list the text portion here. Somebody might recognize that as part of a standard file header. StuRat (talk) 22:21, 19 February 2012 (UTC)