Wikipedia:Reference desk archive/Computing/2006 July 29

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Problem in Scheme with Let[edit]

Okay, I'm trying to write a function that will generate all of the "co-matrices" (essentially a co-matrix of an n*n matrix will be an (n-1)*(n-1) matrix with a given row and column removed) of a matrix in Scheme, here is the working code to generate a given co-matrix

(define co-matrix
  (let ((answer ()))
    (lambda (matrix row iteration)
        ((= iteration 0)
        ((> ( + 1 row) (length matrix))
         ;if this is true, we want to go start of matrix
         (append answer (cons (cdar (get-list 0 matrix)) (co-matrix matrix 1 (- iteration 1)))))  
         (append answer (cons (cdar (get-list row matrix)) (co-matrix matrix (+ 1 row) (- iteration 1))))))))) 

Here's the nonworking (but probably would if I could figure a way around the let statement stuff) code to generate all the co-matrices when we fix a row and remove each row.

(define co-matrices
  (let ((answer ()))
    (lambda (matrix iteration)
        ((not (= iteration (length matrix)))
         (append answer (list (append (co-matrix matrix iteration (- (length matrix) 1))
                                      (co-matrices matrix (+ 1 iteration))))))
        (else answer))

Why is it that my code for dot-product (below)

(define dot-product
  (let ((result 0))
  (lambda (vector1 vector2)
      ;we take the product of the two vectors, add it to the result and then add the dot product of the cdrs of both lists to the result recursively.
      ((not (and (equal? vector1 ()) (equal? vector2 () ))) 
       ( + result ( + (* (car vector1) (car vector2)) 
                      (dot-product (cdr vector1) (cdr vector2)))))
      ;if we're at the end of both vectors, return result
      (else result)))))

works but the co-matrix stuff does not?

I'm not a Scheme expert (I tend to use ELisp instead), but it seems to me that you should interchange your lets and your lambdas. Otherwise your variable initializations are occurring during the definition of your functions rather than during their execution. Does that help? --Tardis 23:00, 31 July 2006 (UTC)

It does actually! Thanks so much.

Help Customize The Dell I Intend To Purchase[edit]

I'm about to buy a new system, and these are the specs. I request that someone help me out in deciding if I made the right decision in choosing this setup. Sorry about the long post, but I'd really appreciate some help so I don't get ripped off, overkill, underkill, etc. M@$+@ Ju ~ 05:22, 29 July 2006 (UTC)

Dell Dimension E510 Series: Pentium® D Processor 940 with Dual Core Technology (3.2GHz, 800FSB)

Operating System: Genuine Windows® XP Home Edition

Memory: 2GB Dual Channel DDR2 SDRAM at 533MHz (4x512M)

Keyboard: Dell USB Keyboard

Monitor: 20 inch UltraSharp™ 2007FPW Widescreen Digital Flat Panel

Video Card: 256MB PCI Express™ x16 (DVI/VGA/TV-out) ATI Radeon X600 SE HyperMemory

Hard Drive: 250GB Serial ATA 3Gb/s Hard Drive (7200RPM) w/ 8MB cache

Floppy Drive and Media Reader: 13 in 1 Media Card Reader and External USB 1.44MB Floppy Drive

Mouse: Dell Optical USB Mouse

Network Card: Integrated Intel® PRO 10/100 Ethernet

Modem: 56K PCI Data Fax Modem

Adobe Software: Adobe® Acrobat® Reader 6.0

CD or DVD Drive: Dual Drives: 16x DVD-ROM Drive + 16x DVD+/-RW w/dbl layer write capability

Sound: Sound Blaster® X-Fi™ XtremeMusic (D), w/Dolby® Digital 5.1

Speakers: No speakers (Speakers are required to hear audio from your system)

Office Software (not included in Windows XP): No Productivity Suite - Corel WordPerfect® word processor only

Anti-Virus/Security Suite (Pre-installed): No Security Subscription

Hardware Warranty: 1Yr Ltd Warranty, 1Yr At-Home Service, and 1Yr HW Warranty Support

Dial-Up Internet Access: 6 Months of America Online Membership Included

Miscellaneous: Award Winning Service and Support

Future Operating Systems: Windows Vista™ Capable

Operating System Re-Installation CD: Genuine Windows® XP Home Edition re-installation CD

Dell Digital Entertainment: Starter Entertainment Pack -Basic digital Music, Photo, and Casual Gaming


  • "Made the right decision" sounds like you already bought it. In case you can still change stuff, here's what I think. "No Security Subscription" is no good and it doesn't describe what anti-virus software the system has (only that you are not subscribed for updates). You need to know if this means you haven't got any protection, or that you need to download updates manually. If it isn't included, either get it or download a free option. Whether a system is right for you depends on how you want to use it. Are you an avid gamer? To play the more recent games, I recommend you get a 3D video card. - Mgm|(talk) 05:53, 29 July 2006 (UTC)
  • Oh, and AOL and Wikipedia don't mesh well. Unless you're on dial-up, stick with whatever provider you have now. - Mgm|(talk) 05:54, 29 July 2006 (UTC)
You need to tell us a little bit about what you plan to use the system for, before we can advise you on whether it will meet your needs. I see you have chosen Windows XP Home as your operating system - presumably this is the cheapest operating system available. If you plan on wiping it to install Linux, let us know, as we may be able to find a system for you that comes with Linux preinstalled, or without an OS entirely. You have chosen Corel WordPerfect, again presumably because it's the cheapest option available. If you have the option of dumping it for less cost, is free and probably at least as capable. You have a modem included, which will be of no use if you plan to use broadband. You have a floppy disk drive specified - is this because you want one or because you can't order the system without it. Telling us what country you are in may help too, and what currency is that final price in?-gadfium 06:01, 29 July 2006 (UTC)
I like Dell PCs. Anyway, I would recommend AVG Anti-Virus (commonly known as AVG) for your security and I assume it is coming shipped with XP SP2? That includes a firewall, too. Iolakana|T 14:22, 29 July 2006 (UTC)
    • AOL and Wikipedia don't mesh well? I've been using AOL and Wikipedia for years now with no ill effects. User:Zoe|(talk) 02:54, 30 July 2006 (UTC)
It's okay. But as mentioned, what are you going to be using it for? If you plan on gaming, then it's a moderate build. --Proficient 20:38, 29 July 2006 (UTC)
  • Since you bought it from Dell, I'd recommend you reformat the hard drive and install your choice of Windows (Personally, I like Server 2003)from or Linux. Then, get a firewall, buy yourself a broadband router with NAT+SPI, and install anything else you might need. The hardware seems competent, even overkill (2 GB RAM? Even Alienwares usually ship with 1GB).--Frenchman113 on wheels! 15:11, 30 July 2006 (UTC)
  • Now that I think of it, GET SOME SPEAKERS! That 5.1 channel sound card isn't doing you a lot of good without speakers. Now that I think of it, you should also dump that Adobe Acrobat Reader for something lightweight like Foxit Reader. And, if you need a broadband ISP, sign up under Speakeasy if possible.--Frenchman113 on wheels! 15:16, 30 July 2006 (UTC)
  • Also, why do you happen to need a 250GB hard drive?--Frenchman113 on wheels! 15:19, 30 July 2006 (UTC)

Hey guys, well I intended on setting it up for gaming, but maybe I wasn't totally clear. I won't be using AOL, but they do not give you the option to get rid of it. I would get my own speaker system that isn't their make, and as for the graphics card, it was the highest end they offered in this computer. I was using a coupon code that made the price alot lower, so it isn't just a cheap setup, in total it's about 1,500+ but was reduced. Do you think I'd do better calling them with the specs I want? M@$+@ Ju ~ 16:12, 31 July 2006 (UTC)
Probably. However, you may have to pay slightly higher for a custom system. You should consider Dell's N series PCs though, they don't come preinstalled with junk (or Windows for that matter, see and are a couple hundred cheaper. You'll have to ask for that specifically, licensing deals with MSFT don't let them advertise it.--Frenchman113 on wheels! 17:31, 31 July 2006 (UTC)
Ha, I called Dell and had them give me a quote, and I dunno how it happened, but it would end up costing me about $300 more! Either way, I've changed the specs a bit but I'll spare you the details. I think I'll buy a seperate video card that is a higher end model and that should make the computer pretty nice. Thanks for your help guys. M@$+@ Ju ~ 19:38, 31 July 2006 (UTC)

Checksum for backups onto DVD[edit]

Hello! I am in the process of backing up my documents, music, e-mail and so forth onto DVD+R. I also have an old set of backups (covering a similar range of data) from a year ago. My questions:

  1. Is there a way of checking the integrity of the old backups without opening every single file on there manually? There are several thousands of them, this would take too long. I just want to know if all the files are still readable/intact - or is this impossible without a 'true' copy to compare them to (this isn't possible anymore, as obviously the contents of my documents have changed in the past year)?
  2. If #1 is difficult/impossible to do, is there something I can to my current round of backups to ensure that, in future, I can test their integrity more easily? A checksum of some sort, perhaps? If anyone has any suggestions for programs I could use, that would be greatly appreciated. I am relatively computer-savvy, but run Windows. — QuantumEleven 10:38, 29 July 2006 (UTC)
  1. I think you should Google for "DVD integrity check" or something similar.
  2. In the Unix world, people would probably use md5sum for that. In the Windows world, I've heard that some people use Parchive. --Kjoonlee 17:35, 29 July 2006 (UTC)
If you can't find an integrity checker, I guess you could run md5sum twice on your set of backups, and try seeing if any MD5 sums differ. I'm sure there's an MD5 checker for Windows with logging support that you can use to check directories recursively. You could examine the two logs later on to see if you're getting any faulty reads. --Kjoonlee 18:31, 29 July 2006 (UTC)
FSUM. I think you can use something similar to the following. --Kjoonlee 18:40, 29 July 2006 (UTC)
fsum -r -jm e:\*.* > check.md5
fsum -c check.md5

Microsoft Word and ligature/accented glyphs[edit]

I have never used Word in the past, but I have to deal with Word documents now at work. When I found that Word doesn't cope with TrueType ligature glyphs, I at first refused to believe it. I mean, TrueType has been in use since when, 1991? Then I found out that OpenOffice supports them without problem. It is simply beyond me how a $230 application can lack such basic functionality, especially seeing that it is provided by its $0 competition as a matter of course. Now it appears that Uniscribe has some support for context shaping. It apparently just refuses to apply it to Latin script. Can I conceivably trick Word somehow into using a font's ligature/precomposed glyphs repertoire, e.g. by making it believe the script is not Latin or similar? This may not be straightforward, as the fontforge manual tells us that

Microsoft tries to document what features they apply for which scripts in Uniscribe, but that isn't very helpful since Word and Office have quite different behavior than the default.

That seems to mean that Microsoft documents one thing, and their applications do something entirely different. This reduces me to trial and error. Is there any information available surrounding this? dab () 18:47, 29 July 2006 (UTC)

I've never heard of TrueType ligature glyphs, and I am sure it doesn't surprise many people that it's not supported by MS Word. --Proficient 20:40, 29 July 2006 (UTC)
I am unsure, I might mean OpenType (a Microsoft format!). Fact is that I save my font as TrueType (.ttf, hence I don't think I am using OpenType functionality) in FontForge, and the ligatures (defined as being of the "liga" 'standard ligature' type) work in OpenOffice, but not in Word. dab () 22:04, 29 July 2006 (UTC)
I found this help page on the Microsoft site. It explains how to use fonts and how to "embed True Type fonts" in Word and Powerpoint. I hope this is helpful. Road Wizard 22:32, 29 July 2006 (UTC) I have crossed this comment out as, after more research, it doesn't seem to tackle the specific issue of ligatures. However, I will leave the link there in case others are having difficulty with True Type fonts. Road Wizard 22:42, 29 July 2006 (UTC)


what are some ways to get better download times on torrent files?

Leave your PC on for longer periods of time, and upload more. — QuantumEleven 20:25, 29 July 2006 (UTC)
Sometimes uploading less can increase download speed (if the upload cap is set too high or too many connections are allowed it can eat up all the bandwidth). digfarenough (talk) 15:18, 30 July 2006 (UTC)

Try portforwarding, this should help you with this problem.--Sangeeth 20:31, 29 July 2006 (UTC)

Download torrents that are being seeded by a large amount of people. Also, portforward as mentioned. --Proficient 17:43, 1 August 2006 (UTC)

Power Caliberation Error[edit]

Hai...I use Nero 6 Version for burning DVDs and CDs of general types(DVD-R,+R,RW...etc.Right from the begining with some mid range quality discs(CD-Rs as well as DVD-R and DVD+R) I've seen a lot of such complaint"Power Caliberation Failed" and my burning process becomes failed.I tried to look for the description of it in nero itself but I ended up with their statement that my drive needed some Firmware upgrade and Blaa....blaa...blaa....But I believe it's not the case since when I burnt those same discs but with reduced speeds...I was able to succesfully burn but this though didnt happen all the time..So what does this mean and what could be the cause?...My drives are a brand new one which I purchased before a couple of weeks.It's a Samsung CD-Writer and Sony DVD-Writer DWQ-120A.What should I need exactly to avoid this error and what exactly this means?..Help Needed guys

Hi.. the problem you have got now is very common click here [1] i hope you found what you are looking for.--Sangeeth 21:36, 29 July 2006 (UTC)

Hey Sangeeth,Thanks about that link but that was just one step more than one big piece of mess..I could possible find people bursting their tears about the same problem of mine but no solutions were provided till todate...I returned empty now....any more?..

hi... OPC (Optical Power Calibration) errors are related to the drive trying to test how strong to make the burning laser. If you recieve this error, the piece of media you are using may have problems. Once the error occurs once on any piece of media, click past the error messages. This will return to the burn screen and eject the media from the drive. Insert the SAME blank media again, then click refresh. The status in XCopy should change to green and give a message of ready to burn again. Click burn, and the burn process should continue as normal. If the error occurs again, please make sure that the blank media you are using is on the compatibility list for your drive, and that you are not running any software listed on the DVDXCopy Black List.

Also, if you recently had the DVD burner installed you will want to make sure you have a strong enough power supply to power all of your system devices. Newer PC's with high end processors need more power and are more likely to need a higher wattage power supply. If there is not enough wattage to go around, the drive cannot muster enough laser power to burn the disk. Sangeeth

graphics card builtin[edit]


I have a graphics card builtin (SiS 661FX_760_741_M661FX_M760_M741) into my motherboard. I want to change the graphics card is it possible ????

thank you

Yes it's quite possible if your motherboard allows peripheral expansion.But if it's a quite old model,then you may no longer change it because of the unavailability and no supporting softwares(rare cases).But your in-built video processing unit can only be disabled prior to the installation of your new graphics card.You need to have a proper graphic slot interface in your motherboard for this purpose.Check your moher board PCB side and look for some slots or either way you can check out the manuals of main board.Changin the graphics card depends upon your mother board type.If it's very older,I bet you can never get one.If you know the motherboard model number,then I recommend you to try looking for upgrading information in the internet through google search first.

If you have a SiS 661FX then your board is reasonably new (I think the FX bit refers to hyperthreading, but that's a vaguely-remember bit of info). Then you should have an AGP (accelerated graphics port) slot, or if you're really new a PCI Express slot. Since you mention SiS 661FX_760_741_M661FX_M760_M741, it seems that you have a manual for your machine. One needs the specific model name of the motherboard to give more info, but SiS 661fx refers to a chipset, not a motherboard. In the absence of documentation, find the model name of the motherboard by first switching off mains power, then opening the case and looking on the board. The model name is printed on the board itself, and is the largest lettering on the board. If you have all sorts of cards and connectors already plugged in, it's usually easier if you use a bright torch and go over the board systematically, gently moving aside wires as you go. Once you have the name (e.g. something like "GT-80" or "PBX-7" or whatever) then you can ask any computer shop to help you find a suitable card (or come back here - without that name we are guessing). Remember that just getting a fancier graphics card does not necessarily solve all problems related to the display of graphics intensive programs. Sometimes getting the newest driver for your onboard graphics does the trick for you, and at the other extreme nothing less than a new machine may do what you want. --Seejyb 14:43, 30 July 2006 (UTC)
Translation for other side of pond: "bright torch" = "bright flashlight". Please, no open flames! :-)
Also be warned that AGP has gone through several revisions, and naming is diverse and confusing. Not all AGP cards work with all AGP slots, so be careful. Also, every PC has PCI slots; these are not the same as PCI express slots. --KSmrqT 18:46, 30 July 2006 (UTC

thank u for u r information....


Err, I think I f-ed my windows install[edit]

I kind of deleted the i386 directory on my Windows partition, with system restore off. My PC seems to be running fine, but is something gonna come back and bite me in the rear later on?-- 22:26, 29 July 2006 (UTC)

No, but you will now have to find a Windows CD when you are installing Windows components. The i386 folder stores the files that would be found on a Windows installation CD. 23:50, 29 July 2006 (UTC)
(after edit conflict) The i386 directory usually holds a copy of the installation files for Windows. Without it, Windows may need to prompt you for the original Windows CD if you want to install more Windows features. If you don't have the original Windows CD, then you have limited your options. Most likely, you will not need to install such features, so this may never be a problem for you. I suggest you do turn on system restore, so that any future corruption of the operating system can be rolled back.-gadfium 23:52, 29 July 2006 (UTC)
If you have a valid Windows licence ( sticker on pc), I think it should be possible to get a replacement cd. Else there would be stil the possible way to get one from a Peer to Peer network. helohe (talk) 02:48, 30 July 2006 (UTC)
There should be a warning: "Don't feed the windows install". DirkvdM 06:52, 30 July 2006 (UTC)