Wikipedia:Reference desk/Archives/Computing/2007 September 23

= September 23 =

Saving Flash files
On the miscellaneous sight I had asked about saving a file from youtube. Someone had written that I could go to temporary internet files and copy a file from there that I had just seen and open it with another program. But, when I went there I didn't see any files resembling a youtube file. How can I do this and copy to an external drive to place on another computer? ( would like to avoid downloading a program to acomplish this if possible.) —Preceding unsigned comment added by 67.127.99.245 (talk) 00:45, 23 September 2007 (UTC)


 * Use something like FLV Downloader instead. --antilivedT 04:43, 23 September 2007 (UTC)


 * The download helper extension for firefox is my tool of choice - very easy to use and access whilst browsing --Fir0002 11:02, 23 September 2007 (UTC)

So it wouldn't be possible to copy a file from the temporary internet file folder? —Preceding unsigned comment added by 67.121.105.34 (talk) 04:57, 23 September 2007 (UTC)
 * It might be, but you'd have to figure out which file it was (it may not have the FLV ending, and there may be many of such files there). It is easier to just get a downloader. --24.147.86.187 15:23, 23 September 2007 (UTC)


 * UnPlug --h2g2bob (talk) 10:53, 23 September 2007 (UTC)

use diagram for vehicle identification
VISION:one should be able to identify vehicle and owner information using the identification mechanism.could be useful for police for theft checking and reduction,insurance companies could use it for physical verification of the vehicle,vehicle workshops could use it to better the customer service vehicle information could be accessible within punching of a button or even maybe moment the vehicle enters a premise or is near any tracker hardware —Preceding unsigned comment added by 219.64.121.42 (talk) 08:53, 23 September 2007 (UTC)


 * Do you have a question? — Matt Eason (Talk &#149; Contribs) 10:29, 23 September 2007 (UTC)


 * Would appear to be from here - The Great Mind Challenge - 2007. At the risk of not assuming good faith maybe someone wants us to come up with an answer so they can enter it? If I'm feeling more charitable maybe they'd like us to enter ourselves as a team effort! Exxolon 13:31, 23 September 2007 (UTC)


 * The basic programming challenge doesn't seem so difficult, design a database keyed on the VIN for each car, which has fields for all the relevent info. The real challenge would be in getting all the different people involved, from manufacturers, dealerships, insurers, and consumers to commit to keeping the records up to date.  I can't see how you would make this happen.  For comparison, I recently bought a car, and each dealership is responsible for keeping their own database of cars up to date so you can do a "dealer search" to find the dealership which has the desired vehicle on the lot.  However, I found the database was so out of date as to be useless, and had to go back to calling each and every dealership in my area.  In that case, there is a direct profit motive for each dealership to keep the database current, yet they still fail to do so.  If they won't do so then, why on earth would they do so when there is no profit motive ?  As a result, I'd expect only the automated parts to be updated reliably.  For example, when a dealership orders a car from a manufacturer, that request can be assigned a VIN and automatically entered into the system.


 * Also, be aware that there is a "Big Brother" aspect to this. People applying for insurance don't necessarily want all their info available to the insurance companies, especially for unrelated vehicles.  And used car dealerships would be angry if customers knew the real history of the car that they said was "only driven on Sundays by a little old lady from Pasadena", so you may find people have an interest in sabotaging the database and entering false data. StuRat 16:21, 23 September 2007 (UTC)

openssh question
I have two unix machine, A and B.

I have setup the ssh servers on machine B to accept both publickey authentication and password authentication.

Usually, when I use an ssh client on machine A to scp a file into machine B, it uses the publickey authentication and does not asks for a password.

However, for some special occasions, I want to be prompted for a password. How can I get the openssh client on machine A to tell the openssh server on machine B to use password authentication instead of publickey authentication?

I usually type


 * scp filename B:/somedirectory/filename

How do I force it to use the password instead of the publickey (which it is using at the moment).
 * 202.168.50.40 00:02, 24 September 2007 (UTC)


 * Add the option -o PreferredAuthentications=password --tcsetattr (talk / contribs) 00:24, 24 September 2007 (UTC)

Dormant programs
Is dormant programs consume resources of the computer?Give support to the answer. —Preceding unsigned comment added by 122.162.105.73 (talk) 12:24, 23 September 2007 (UTC)
 * This sounds suspiciously like a homework question. I'd guess you should try reading Background_(computer_software), but "dormant program" is a vague term. Exxolon 13:29, 23 September 2007 (UTC)
 * They do; that's why your computer slows down if you have too many apps running at the same time, or if your PC has spyware on it. The RAM that you have and the processor installed can contribute to that... Blake Gripling 08:16, 25 September 2007 (UTC)

Functional and imperative programming time-equivalent
Both the functional and imperative (random-access) models of computation are Turing-complete, but are they time equivalent? For example, I just wrote a breadth-first search in Haskell, where I would use an array to mark vertices as visited in an imperative language, but I had to use a Set, where insertions take O(log n) time instead of O(1). Are there clever tricks that could (theoretically) be used to bring the functional algorithm into the same efficiency class as the imperative one?

BTW, do Computer Science questions belong in Computing (which seems to consist mostly of "I think my iPod has a virus") or Mathematics? --Taejo|대조 12:29, 23 September 2007 (UTC)


 * The order of a function is dependent only on the algorithm, and all algorithms that can be implemented in one turing-complete system can be implemented in all the others (because they're turing equivalent). Haskell has an array type, which has O(1) insertions. 217.42.190.82 14:25, 23 September 2007 (UTC)


 * This is wrong. Turing reduction requires only finiteness. You would need a linear time reduction (where is the freaking article?) from haskell programs to register machine programs. I suppose one exists, otherwise nobody would want to use haskell. —Preceding unsigned comment added by 84.187.32.213 (talk) 16:42, 23 September 2007 (UTC)


 * There was a paper proving that a certain problem can be solved asymptotically faster with a mutating algorithm than with any non-mutating algorithm, subject to some assumptions which I can't remember. A followup paper showed that there is a lazily evaluated non-mutating algorithm with the same efficiency as the mutating algorithm (so I guess one of the assumptions of the original paper was eager evaluation). I can track down the references if you're interested.


 * I must say, though, that these big-O comparisons are pretty dubious to begin with. Array access isn't really O(1), because the size of the array indices grows without bound. For sufficiently large n there has to be a factor of log n in the imperative algorithm to account for the extra cost of working with all those bits. In practice, of course, array indices are a fixed width, which means that log n is bounded above and array access is O(1). But then the functional lookup is O(1) too. In fact, every algorithm is O(1)! It's hard to make sense of typical big-O bounds as true expressions of asymptotic complexity. Most of the time what they're really about is the growth for "medium-sized" n, but I don't know how to formalize that. Also, the whole notion of sending fixed-length addresses over the bus is tied to the von Neumann architecture. Implementations of functional languages have to run on such architectures, but I can almost imagine that, if untold trillions of dollars had been spent on speeding up functional algorithms instead, we might have a totally different architecture in which (for example) selecting the left or right branch of a binary tree node would only require transmitting one bit. -- BenRG 20:12, 23 September 2007 (UTC)


 * The formalization is a special cost model for the register machine (I don't know the correct english term, something like armotized costs or so). Every operation requires log(x) cost, where x is the size of the largest of the 3 numbers stored in the touched registers (two input, one output). The model is always implicitly assumed, but it is rarely needed directly, because the constant cost model gives the same result in O notation for most algorithms. —Preceding unsigned comment added by 84.187.9.141 (talk) 19:49, 24 September 2007 (UTC)


 * Any ideas where I could find the paper? --Taejo|대조 21:03, 23 September 2007 (UTC)

No Videos on Temporary Internet Diles Folder
I watched a couple of different videos on Youtube and none of them are showing up in my temporary internet files folder. Is there some way to do this? —Preceding unsigned comment added by 67.122.137.214 (talk) 14:43, 23 September 2007 (UTC)


 * If your goal is to save the video files, try Video Downloader. —Keenan Pepper 15:09, 23 September 2007 (UTC)

Norton SystemWorks
Hello. Does Norton SystemWorks block cookies at the point of entry to my computer? Thanks in advance. --Mayfare 16:19, 23 September 2007 (UTC)


 * Norton Internet Security and Norton Personal Firewall both do. --  k a i n a w &trade; 19:27, 23 September 2007 (UTC)

self made billionaire
are the three facebook founders youngest self made billionaires? —Preceding unsigned comment added by 59.92.102.198 (talk) 16:38, 23 September 2007 (UTC)


 * See Facebook. There is one founder.  He has brought in people to help - not necessarily "found" Facebook.  He has turned down a billion dollar offer to buy Facebook, indicating that it is worth $8 billion.  That doesn't necessarily mean that he is worth a billion. --  k a i n a w &trade; 19:25, 23 September 2007 (UTC)


 * How doesn't that necessarily mean he's worth a billion? --⁪frotht 22:07, 23 September 2007 (UTC)


 * Just because the owner of a company claims that his company is worth a certain amount, does not mean it is worth that amount. Someone has to be willing to pay what is asked (and nobody is offering $8 billion for Facebook that I know of).  Also, the value of a company does not equal the worth of the company's owner.  He retroactively named others as "co-founders", implying that they get a cut of the company's worth (even though they weren't really "founders").  There are also 300 or so employees, all getting paid.  The estimated income for the company in 2006 was around $100 million.  If he pocketed all the income of the company himself, he'd still need another $900 million to make a billion, right? --  k a i n a w &trade; 22:28, 23 September 2007 (UTC)


 * "He has turned down a billion dollar offer to buy Facebook" ... "Someone has to be willing to pay what is asked" ... how is he not worth a billion? Someone's willing to pay it apparently --⁪frotht 00:19, 24 September 2007 (UTC)
 * Who wouldn't turn down a billion - my guess is that in reality - the money's not there and it's all bullshit - would you pay 1,000,000,000$ for a 'crappy' networking site? - which has no physical products and income is reliant on advertising.. For that money I could buy France (smile)83.100.254.150 07:19, 24 September 2007 (UTC)
 * I don't understand how facebook could be worth so much. How on Earth do they make any money? It must cost them millions just to keep it running. —Preceding unsigned comment added by 84.12.143.75 (talk) 22:44, 23 September 2007 (UTC)


 * Someone offered to buy Facebook for a billion dollars. Nobody offered to buy the founder of Facebook for a billion dollars.  Therefore, Facebook has a value of around a billion dollars, but that doesn't necessarily mean that the founder is worth a billion dollars.  To make that leap, you have to demonstrate that the entire value of Facebook is passed on to the founder.  I've demonstrated that the value is spread among multiple "founders" and many employees.  I do not know how to state it any clearer that the founder of Facebook is not Facebook.  One is a person, the other is a company. --  k a i n a w &trade; 12:03, 24 September 2007 (UTC)


 * According to our article it's mainly from advertising and sponsored groups. They also make money from people purchasing gifts, flyers and polls. — Matt Eason (Talk &#149; Contribs) 23:47, 23 September 2007 (UTC)


 * It's quite possible that they are selling (or intend to sell, at some future time) user-data - whether personally identifiable or aggregate statistics. Market research such as this can be quite valuable; it is very likely that the company value stems from the potential to capitalize on its huge information resources.  Finally, the large amount of capital investment in infrastructure cannot be discounted - i.e. the total value of all their servers, processors, networking gear (let alone non-technical items such as office space) must be reasonably large.  In the hypothetical "liquidate everything" scenario, those assets would add considerable value to the net worth of the company.  Nimur 04:27, 24 September 2007 (UTC)


 * Wouldn't it be illegal to sell that data? A.Z. 07:23, 24 September 2007 (UTC)


 * The reference desk cannot give legal advice. The Terms of Use shed some light on what you agree to as a member of the website.  The company probably has legal advisers or employs attorneys to determine the legal limits of their policies.  Nimur 15:03, 24 September 2007 (UTC)


 * No, it wouldn't necessarily be illegal — practically every for-profit online site sells demographic data for targeted advertising purposes. Facebook is pretty straightforward about the type of data they collect and would use for profit purposes, and anyone who is made queasy by that shouldn't sign up. --24.147.86.187 15:37, 24 September 2007 (UTC)

I read somewere Mark Zuckerberg, holds 30-33% stake in facebook. so, I think if facebook is sold for $3bn, he is youngest billionaire. Given roumours at 8 bn $s, he may already gone past 1 bn mark —Preceding unsigned comment added by 59.92.122.76 (talk) 17:37, 24 September 2007 (UTC)


 * If you read this (and believe it), Facebook is in negotiations for a $10-$15 billion purchase by Microsoft. If the purchase goes through, it states that it will equate to $300-$500 million for the company.  Then, Zuckerberg can take a cut of that.  I hope this makes it clear, as I stated repeatedly above, the sale-price of Facebook is not Zuckerberg's personal worth. --  k a i n a w &trade; 15:01, 25 September 2007 (UTC)
 * Everyone knows that facebook is merely [ a shell] for the US government in an attempt to get otherwise normal people to give up mass amounts of personal information for their direct use. Equity?  Market value?  Zuckerberg?  Who cares! --Jmeden2000 17:27, 25 September 2007 (UTC)

10 ± 0.001 on a TI89?
Is the \pm symbol on the TI89 functional, or is it just treated like an undefined variable/special character?-- VectorPotential Talk 18:54, 23 September 2007 (UTC)
 * I'm not sure I understand the question. Pressing that key will change the sign of the current number, sort of like a macro for "take buffer and multiply by -1". --Mdwyer 03:32, 24 September 2007 (UTC)
 * I'm referring to the combined ± key, not the individual + or - keys. Obviously adding either + or - in front of a number changes its sign. What I was wondering is if I could write a number as 10 ± 0.001 and have the calculator understand that the second number is the error, since there is a key for ±, but it seems to just treat ± as an undefined character. And yes, I'm expecting a lot in terms of understanding from a simple machine.-- VectorPotential Talk 12:36, 24 September 2007 (UTC)
 * What Mdwyer is saying is that if you have a number on screen and you press it, it reverses the sign, rather than being used in the way you want. Sorry. Kuronue | Talk 15:25, 24 September 2007 (UTC)
 * What Mdwyer is saying is relevant to many calculators that do not operate on lines of input but rather immediately react to keypresses; the TI-89 is in the former category. From my experience it is treated like an operator (correctly), not a variable, but it does not have any rules associated with it (so that $$(5\pm1)+(4\pm2)$$ doesn't evaluate to anything simpler).  This makes a certain amount of sense: error propagation is complicated and there's no one correct formula.  I don't have one in front of me, but I believe what it can't do is understand $$\pm1$$ (as opposed to $$0\pm1$$) as a known quantity with unknown sign (or a sign that depends on context); thus the $$\{1,-1\}$$ suggestion (note braces) from LarryMac below.  --Tardis 15:19, 25 September 2007 (UTC)


 * I am looking at a diagram of the keypad in the User's Guide (page 16), and I don't see a \pm anywhere. However, it's been a long day and I don't have my glasses, so I might be missing it.  Searching on Google for TI89 "plus/minus" was not very successful either, except to learn that "the list (1, -1) can be used in place of plus/minus".  -- LarryMac  | Talk  20:32, 24 September 2007 (UTC)
 * I was going to say the same when I originally saw the question, but never having owned a real TI-89, I was afraid I was missing something vital here. I must have spent ten minutes looking at that picture but couldn't find a \pm symbol anywhere on the calculator. Perhaps the answerer has never heard of the TI-89 but instead answered in the context of your average 5 € basic calculators. J I P  | Talk 15:52, 27 September 2007 (UTC)

HDMI everyday benefits?
Besides the convenience of one-cable wiring, does HDMI deliver any other benefits to the average user? I know about deep color, and 7.1 surround and all that ultra high-end marketing BS. But to the everyday average consumer watching 720p stereo, is there any advantage over using HDMI vs. component cables? --72.202.150.92 20:40, 23 September 2007 (UTC)
 * You sate the lust for control of the DRM cabal, allowing you to watch AACS-encrypted content. --⁪frotht 22:11, 23 September 2007 (UTC)
 * What content today requires HDMI and is unviewable with component cables? --24.249.108.133 18:55, 25 September 2007 (UTC)
 * A bit like scart pressing play on your dvd player can cause the tv to automatically change channels see Hdmi83.100.254.150 06:45, 24 September 2007 (UTC)

File extension .do
What sort of file ends in .do? It appears to be used on webpages as some kind of script, similar to PHP, but I can't find any specifics. —Preceding unsigned comment added by 81.151.250.111 (talk) 23:11, 23 September 2007 (UTC)


 * I've only seen those on the IBM WebSphere server. It is a web-based application (Java, I believe). --  k a i n a w &trade; 23:16, 23 September 2007 (UTC)
 * I've seen those within JBoss. --Mdwyer 03:30, 24 September 2007 (UTC)
 * This may help. --MZMcBride 23:42, 23 September 2007 (UTC)

Java, huh? Which leads me to my next question... Is there any way to view server-side scripts? The default action is for the server to execute the script, but surely there must be a way to request the actual file. —Preceding unsigned comment added by 81.151.250.111 (talk) 00:10, 24 September 2007 (UTC)
 * Surely not. It's not possible and it shouldn't be- servers are black boxes that take inputs and serve you outputs. As far as the client is concerned, it's all done by a guy with a TV-typewriter and a pad of paper.. what do you mean script? Black box. --⁪frotht 00:22, 24 September 2007 (UTC)
 * Never mind, that was my idiocy and inexperience talking. By scripts, I'm thinking mainly of PHP scripts, which I remember hearing there was a way of reverse-engineering. —Preceding unsigned comment added by 81.151.250.111 (talk) 00:34, 24 September 2007 (UTC)
 * That's only possible if the server has enabled viewable source for the PHP script. In most recent distributions, this option is disabled (to fit in to the "black box" paradigm).  Nimur 04:24, 24 September 2007 (UTC)
 * (note that while that's technically correct, "most" basically means "all but a very few") --⁪frotht 06:30, 24 September 2007 (UTC)