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• Get Angle to Tangent that Intersects Point

  - by Christian Stewart

  I have a circle around a given point, call this point (x1, y1). I know the radius of the circle around this point. I also have a second point (x2, y2), that is a distance away, outside the radius of the circle. I need a algebraic way through code to calculate the heading (angle from vertical) needed to intersect the circle at 90* to the center point (I.E. get the angle of the tangent intersecting line 2) around the point (x1, y1) from the second point (x2, y2) A bit of background: Essentially the two points are GPS coordinates on a 2D map, I need to know the target heading to intersect the circle in order to follow its path around the center point. Thanks! Christian

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• filesystem compatible with freenas and windows

  - by Daniel

  Hi all, I'm planning on using FreeNAS (was considering openfiler but freenas seems simpler) for my home NAS box running off ESXI. I have managed to get local sata drives to mount in ESXI (http://serverfault.com/questions/216902/esxi-add-datastore-without-partitioning). I've had one of the drives fail on my before and I was able to retrieve most of the data off it using windows tools (I'm not much of a linux guy I know enough to be dangerous!). If I go the freenas route in the event that something goes bad what would be the best file system to use so that I could pop the drive out of the freenas box (vm) and put it in another pc running windows so I could try and run various recovery tools to get the data back. All in all its not a major problem if I lose the data just would be a bit annoying, so I'm not looking for suggestions around backing up etc. I was considering using NTFS that the drives are already formatted as but it appears that while freenas does support NTFS that its a bit buggy and not 100% reliable, anyone know if this is still true? Read that on a forum somewhere.

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• How do you calculate the reflex angle given to vectors in 3D space?

  - by Reimund

  I want to calculate the angle between two vectors a and b. Lets assume these are at the origin. This can be done with theta = arccos(a . b / |a| * |b|) However arccos gives you the angle in [0, pi], i.e. it will never give you an angle greater than 180 degrees, which is what I want. So how do you find out when the vectors have gone past the 180 degree mark? In 2D I would simply let the sign of the y-component on one of the vectors determine what quadrant the vector is in. But what is the easiest way to do it in 3D?

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• Is there a faster alternative to using textures in XNA?

  - by Matthew Bowen

  I am writing a map editing program for a 2D game using XNA. To create a Texture2D for all of the tiles that a map requires takes too long. Are there any alternatives to using textures for drawing with XNA? I attempted to create just one texture per tile set instead of a texture for every tile in a tile set, but there is a limit to the size of textures and I could not fit all the tiles of a tile set into one texture. Currently the program contains all the would-be textures in memory as Bitmap objects. Is there a way to simply draw a Bitmap object to the screen in XNA? I have searched but I cannot find any information on this. This approach would avoid having to create textures altogether, however any tinting or effects I would have to do to the bitmap directly. Any help would be very much appreciated. Thanks

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• How to use Haar wavelet to detect LINES on an image?

  - by Ole Jak

  So I have Image like this I want to get something like this (I hevent drawn all lines I want but I hope you can get my idea) I want to use SURF ( (Speeded Up Robust Features) is a robust image descriptor, first presented by Herbert Bay et al. in 2006 ) or something that is based on sums of 2D Haar wavelet responses and makes an efficient use of integral images for finding all straight lines on image. I want to get relative to picture pixel coords start and end points of lines. So on this picture to find all lines between tiles and thouse 2 black lines on top. Is there any such Code Example (with lines search capability) to start from? I love C and C++ but any other readable code will probably work for me=)

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• Solving iPhone/iPad out of memory issues

  - by Joonas Trussmann

  I have a strange issue where I'm scrolling through a paged UIScrollView which displays the pages of a PDF document (using Quartz 2D and CATiledLayer). When I page through memory allocation looks fine with it going up with a few initial pages and then keeping it steady as it obviously releases the memory kept for earlier pages. Upon hitting page x (not a certain PDF page or a certain number per se) memory usage goes from a couple of megs to 308 megs and the app crashes. So my question is: how to best try to find what's causing this? The object alloc tool in instruments shows the memory as simply going to malloc. (in huge chunks).

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• How can I write automated tests for iptables?

  - by Phil Frost

  I am configuring a Linux router with iptables. I want to write acceptance tests for the configuration that assert things like: traffic from some guy on the internet is not forwarded, and TCP to port 80 on the webserver in the DMZ from hosts on the corporate LAN is forwarded. An ancient FAQ alludes to a iptables -C option which allows one to ask something like, "given a packet from X, to Y, on port Z, would it be accepted or dropped?" Although the FAQ suggests it works like this, for iptables (but maybe not ipchains as it uses in the examples) the -C option seems to not simulate a test packet running through all the rules, but rather checks for the existence for an exactly matching rule. This has little value as a test. I want to assert that the rules have the desired effect, not just that they exist. I've considered creating yet more test VMs and a virtual network, then probing with tools like nmap for effects. However, I'm avoiding this solution due to the complexity of creating all those additional virtual machines, which is really quite a heavy way to generate some test traffic. It would also be nice to have an automated testing methodology which can also work on a real server in production. How else might I solve this problem? Is there some mechanism I might use to generate or simulate arbitrary traffic, then know if it was (or would be) dropped or accepted by iptables?

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• What is the RSA SecurID packet format?

  - by bmatthews68

  I am testing a client application that authenticates using RSA SecurID hardware tokens. The authentication is failing and I am not finding any useful information in the log files. I am using Authentication Manager 8.0 and the Java SDK. I have a traffic capture which I would like to analyze with Wireshark to and from port 5500 on the authentication agent. But I can't find the packet format searching the internet or on the the RSA SecurCare knowledge base. Can anybody direct me to the packet format? Here is an extract from the rsa_api_debug.log file which dumps the UDP payload of the request and the response: [2013-11-06 15:11:08,602] main - b.a():? - Sending 508 bytes to 192.168.10.121; contents: 5c 5 0 3 3 5 0 0 2 0 0 0 0 0 1 ea 71 ee 50 6e 45 83 95 8 39 4 72 e 55 cf cc 62 6d d5 a4 10 79 89 13 d5 23 6a c1 ab 33 8 c3 a1 91 92 93 4f 1e 4 8d 2a 22 2c d0 c3 7 fc 96 5f ba bf 0 80 60 60 9d 1d 9c b9 f3 58 4b 43 18 5f e0 6d 5e f5 f4 5d df bf 41 b9 9 ae 46 a0 a9 66 2d c7 6 f6 d7 66 f1 4 f8 ad 8a 9f 4d 7e e5 9c 45 67 16 15 33 70 f0 1 d5 c0 38 39 f5 fd 5e 15 4f e3 fe ea 70 fa 30 c9 e0 18 ab 64 a9 fe 2c 89 78 a2 96 b6 76 3e 2e a2 ae 2e e0 69 80 8d 51 9 56 80 f4 1a 73 9a 70 f3 e7 c1 49 49 c3 41 3 c6 ce 3e a8 68 71 3f 2 b2 9b 27 8e 63 ce 59 38 64 d1 75 b7 b7 1f 62 eb 4d 1d de c7 21 e0 67 85 b e6 c3 80 0 60 54 47 e ef 3 f9 33 7b 78 e2 3e db e4 8e 76 73 45 3 38 34 1e dd 43 3e 72 a7 37 72 5 34 8e f4 ba 9d 71 6c e 45 49 fa 92 a f6 b bf 5 b 4f dc bd 19 0 7e d2 ef 94 d 3b 78 17 37 d9 ae 19 3a 7e 46 7d ea e4 3a 8c e1 e5 9 50 a2 eb df f2 57 97 bc f2 c3 a7 6f 19 7f 2c 1a 3f 94 25 19 4b b2 37 ed ce 97 f ae f ec c9 f5 be f0 8f 72 1c 34 84 1b 11 25 dd 44 8b 99 75 a4 77 3d e1 1d 26 41 58 55 5f d5 27 82 c d3 2a f8 4 aa 8d 5e e4 79 0 49 43 59 27 5e 15 87 a f4 c4 57 b6 e1 f8 79 3b d3 20 69 5e d0 80 6a 6b 9f 43 79 84 94 d0 77 b6 fc f 3 22 ca b9 35 c0 e8 7b e9 25 26 7f c9 fb e4 a7 fc bb b7 75 ac 7b bc f4 bb 4f a8 80 9b 73 da 3 94 da 87 e7 94 4c 80 b3 f1 2e 5b d8 2 65 25 bb 92 f4 92 e3 de 8 ee 2 30 df 84 a4 69 a6 a1 d0 9c e7 8e f 8 71 4b d0 1c 14 ac 7c c6 e3 2a 2e 2a c2 32 bc 21 c4 2f 4d df 9a f3 10 3e e5 c5 7f ad e4 fb ae 99 bf 58 0 20 0 0 0 0 0 0 0 0 0 0 [2013-11-06 15:11:08,602] main - b.b():? - Enterring getResponse [2013-11-06 15:11:08,618] main - b.a():? - Enterring getTimeoutValue(AceRequest AceAuthV4Request[AbstractAceRequest[ hdr=AcePacketHeader[Type=92 Ver=5 AppID=3 Enc=ENCRYPT Hi-Proto=5 Opt=0 CirID=0] created=1383750668571 trailer=AcePackeTrailer[nonce=39e7a607b517c4dd crc=722833884]] user=bmatthews node-sec-req=0 wpcodes=null resp-mac=0 m-resp-mac=0 client=192.168.10.3 passcode==ZTmY|? sec-sgmt=AceSecondarySegments[ cnt=3] response=none]) [2013-11-06 15:11:08,618] main - b.a():? - acm base timeout: 5 [2013-11-06 15:11:08,618] main - b.b():? - Timeout is 5000 [2013-11-06 15:11:08,618] main - b.b():? - Current retries: 0 [2013-11-06 15:11:10,618] main - b.b():? - Received 508 bytes from 192.168.10.121; contents: 6c 5 0 3 3 6 0 0 0 0 0 1 4d 18 55 ca 18 df 84 49 70 ee 24 4a a5 c3 1c 4e 36 d8 51 ad c7 ef 49 89 6e 2e 23 b4 7e 49 73 4 15 d f4 d5 c0 bf fc 72 5b be d1 62 be e0 de 23 56 bf 26 36 7f b f0 ba 42 61 9b 6f 4b 96 88 9c e9 86 df c6 82 e5 4c 36 ee dc 1e d8 a1 0 71 65 89 dc ca ee 87 ae d6 60 c 86 1c e8 ef 9f d9 b9 4c ed 7 55 77 f3 fc 92 61 f9 32 70 6f 32 67 4d fc 17 4e 7b eb c3 c7 8c 64 3f d0 d0 c7 86 ad 4e 21 41 a2 80 dd 35 ba 31 51 e2 a0 ef df 82 52 d0 a8 43 cb 7c 51 c 85 4 c5 b2 ec 8f db e1 21 90 f5 d7 1b d7 14 ca c0 40 c5 41 4e 92 ee 3 ec 57 7 10 45 f3 54 d7 e4 e6 6e 79 89 9a 21 70 7a 3f 20 ab af 68 34 21 b7 1b 25 e1 ab d 9f cd 25 58 5a 59 b1 b8 98 58 2f 79 aa 8a 69 b9 4c c1 7d 36 28 a3 23 f5 cc 2b ab 9e f a1 79 ab 90 fd 5f 76 9f d9 86 d1 fc 4c 7a 4 24 6d de 64 f1 53 22 b0 b7 91 9a 7c a2 67 2a 35 68 83 74 6a 21 ac eb f8 a2 29 53 21 2f 5a 42 d6 26 b8 f6 7f 79 96 5 3b c2 15 3a b d0 46 42 b7 74 4e 1f 6a ad f5 73 70 46 d3 f8 e a3 83 a3 15 29 6e 68 2 df 56 5c 88 8d 6c 2f ab 11 f1 5 73 58 ec 4 5f 80 e3 ca 56 ce 8 b9 73 7c 79 fc 3 ff f1 40 97 bb e3 fb 35 d1 8d ba 23 fc 2d 27 5b f7 be 15 de 72 30 b e d6 5c 98 e8 44 bd ed a4 3d 87 b8 9b 35 e9 64 80 9a 2a 3c a2 cf 3e 39 cb f6 a2 f4 46 c7 92 99 bc f7 4a de 7e 79 9d 9b d9 34 7f df 27 62 4f 5b ef 3a 4c 8d 2e 66 11 f7 8 c3 84 6e 57 ba 2a 76 59 58 78 41 18 66 76 fd 9d cb a2 14 49 e1 59 4a 6e f5 c3 94 ae 1a ba 51 fc 29 54 ba 6c 95 57 6b 20 87 cc b8 dc 5f 48 72 9c c0 2c dd 60 56 4e 4c 6c 1d 40 bd 4 a1 10 4e a4 b1 87 83 dd 1c f2 df 4c [2013-11-06 15:11:10,618] main - a.a():? - Response status is: 1 [2013-11-06 15:11:10,618] main - a.a():? - Authenticaton failed for bmatthews ! [2013-11-06 15:11:10,618] main - AuthSessionFactory.shutdown():? - RSA Authentication API shutdown invoked [2013-11-06 15:11:10,618] main - AuthSessionFactory.shutdown():? - RSA Authentication API shutdown successful

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• Errors/warnings passing int/char arrays by reference

  - by Ankur Banerjee

  I'm working on a program where I try to pass parameters by reference. I'm trying to pass a 2D int array and a 1D char array by reference. Function prototype: void foo (int* (&a)[2][2], char* (&b)[4]) Function call: foo (a, b); However, when I compile the code with -ansi and -Wall flags on gcc, I get the following errors: foo.c: At top level: error: expected ‘)’ before ‘&’ token error: expected ‘;’, ‘,’ or ‘)’ before ‘char’ foo.c: In function ‘main’: error: too many arguments to function ‘foo’ I've stripped out the rest of the code of my program and concentrated on the bits which throw up the errors. I've searched around on StackOverflow and tried out different ways to pass the parameters, but none of them seem to work. (I took this way of passing parameters from the discussion on StackOverflow here.) Could you please tell me where I'm going wrong?

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• How to avoid HTML Canvas auto-stretching

  - by Tom

  I have the following piece of HTML: <style type="text/css"> #c{width:200px;height:500px} </style> <canvas id="c"></canvas> <script type="text/javascript"> var i = new Image(); i.onload = function () { var ctx = document.getElementById('c').getContext('2d'); ctx.drawImage(i, 0, 0); } i.width = i.height = 20; // actual size of square.png i.src = 'square.png'; </script> The issue is that the drawn image is automatically stretched (resized) proportionally with the size of the canvas. I have tried using all available parameters (drawImage(i, 0, 0, 20, 20, 0, 0, 20, 20)) and that didn't help. What is causing my drawing to stretch and how can I prevent that? Thanks, Tom

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• Some math and animation

  - by Ockonal

  Hello, I have a grass texture: I use it in my 2d-game. I want to animate it by code, without any predefined animations. The grass should interact with wind. So when the wind is stronger, the grass should stoop into need side more. First version of animation I made using sinusoid function, but such animation is a bit ugly, because the base of the grass moves left/right like all another part of picture. And with sinusoid I'm not able to regulate stoop of the image. Any advices?

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• Unkillable console windows

  - by rep_movsd

  I'm developing an OpenGL based 2d simulation with GLUT under Visual C++ 2008, sometimes when I have an assert() or unhandled exception and break into the debugger, the GLUT display window closes, but the console window remains open.They just cant be killed!!! They do not show up with Task manager, Process Explorer or any other tool, I cannot find the window handle using the Spy++ tool either. Worst thing is they prevent my system (Windows XP) from shutting down, I have to manually poweroff (and of course I have to run chkdsk on my drives and invariably it finds and fixes minor errors after bad shutdowns) Has anyone come across such an issue?

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• My New Dell Workstation T-7500 gives electric shock

  - by Dan

  Just bought Dell T-7500 Workstation. When installation technician came to Install the workstation, he got an electric shock when he touched the Start Button. He also got shock when he touched Front Panel. No shock when touching rest of the Chassis. He called Dell Support & tried to troubleshoot by taking out various wires etc but did not help. I touched the same places & I also got shock. We checked everything possible including connecting to various outlets but it didn't solve the problem. Installation subcontractor said that they are not supposed to troubleshoot anything on new system, just install it & they made notes & left. I called my sales guy & it was weekend so he said he will take care of it on Monday. Here are my concerns : (1) Why does that happen ? Although it is a mild shock & it won't kill you but might damage other parts of workstation ? (2) Is this common for workstations ? (3) What should I do ? Of course Dell will try to troubleshoot again but should I let them do that OR ask for a New System ? (4) Wheat would happen if I continue using it till the new system arrives ? Thank You.

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• How to access Windows Server 2008 R2 file shares from a different subnet

  - by Lloyd Cotten

  We have a couple of severs that used to be Windows Server 2003 that we recently upgraded to Windows Server 2008 R2. A couple of details to set the situation up: We wiped the OS and re-installed. These servers are on one subnet (172.16.x.x) and we are trying to access some file shares on them from another subnet (10.34.x.x). Firewall is disabled on these servers. Trying to access with UNC "\172.16.x.x\sharename" and net use \172.16.x.x However, we're having problems doing this. We are getting "The network path was not found". Here's some of the things we've tried so far and the result: Tried accessing the share from other (non-2008) servers on the same subnet... Success! Ping servers from different subnet... Success! Telnet connection into port 139 from different subnet... Success! Took a scan through Local Security Policies to see if something obvious needed to be enabled / disabled / configured... Fail I'm not sure where to look next. I know that the router between the two subnets is locked down pretty good, but this did work for our 2003 servers. Has anything changed in the way of ports used for UNC / file share access in 2008? Maybe I'm missing some security policy setting? Hoping somebody can take pity on a poor programming guy that can't figure out something really simple. :-) Thanks!

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• How do I randomly fill an array in Java?

  - by Kat

  I'm writing a program that creates a 2D array from a integer n. I then have to fill the array with values from 1 to the n*n array size and check to see if it is a magic square. The way I am doing it now fills the array in order from 1 to n*n array size. How can I make that random? My code: System.out.print("Enter an whole number: "); int n = scan.nextInt(); int [][] magic = new int [n][n]; for (int row = 0; row < magic.length; row++) { for(int col = 0; col < magic[row].length; col++) magic[row][col] = ((row * n) + 1) + col; }

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• Coordinates in distorted grid

  - by Carsten

  I have a grid in a 2D system like the one in the before image where all points A,B,C,D,A',B',C',D' are given (meaning I know the respective x- and y-coordinates). I need to calculate the x- and y-coordinates of A(new), B(new), C(new) and D(new) when the grid is distorted (so that A' is moved to A'(new), B' is moved to B'(new), C' is moved to C'(new) and D' is moved to D'(new)). The distortion happens in a way in which the lines of the grid are each divided into sub-lines of equal length (meaning for example that AB is divided into 5 parts of the equal length |AB|/5 and A(new)B(new) is divided into 5 parts of the equal length |A(new)B(new)|/5). The distortion is done with the DistortImage class of the Sandy 3D Flash engine. (My practical task is to distort an image using this class where the handles are not positioned at the corners of the image like in this demo but somewhere within it).

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• Matrix multiplication in java (RE-POST)

  - by Chapax

  Apologies for the re-post; the earlier time I'd posted I did not have all the details. My colleague, who quit the firm was a C# programmer, was forced to write Java code that involved (large, dense) matrix multiplication. He's coded his own DataTable class in Java, in order to be able to a) create indexes to sort and join with other DataTables b) do matrix multiplication. The code in its current form is NOT maintainable/extensible. I want to clean up the code, and thought using something like R within Java will help me focus on business logic rather than sorting, joining, matrix multiplication, etc. Plus, I'm very new to the concept of DataTable; I just want to replace the DataTable with 2D arrays, and let R handle the rest. (I currently do not know how to join 2 large datasets in java very efficiently Please let me know what you think. Also, are there any simple examples that I can take a look at?

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• How much more complex is it to draw simple curves, lines and circles in OpenGL ES rather than in Qua

  - by mystify

  Is OpenGL ES really so much faster? Why? And is it really so horrible complicated to draw such simple things in OpenGL ES compared to drawing these in Quartz 2D? For example, I have a UIView subclass with -drawRect: implemented, where I draw some lines, curves and circles. Just simple paths, with some shadow. What would I do in OpenGL ES? Isn't there this nice EAGLView layer thing? One thing that comes to mind is how do touch events go into OpenGL ES? Maybe that's the complex thing about it? Are there tutorials on basic drawing operations in OpenGL ES?

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• What are some techniques to create scrollable areas?

  - by Omega

  I'm getting started with OpenGL ES on Android and I'd looking to learn some techniques to have a game map larger than the visible area. I'm assuming I've somehow got to ensure that the system isn't rendering the entire scene, including what's outside of the visible area. I'm just not sure how I'd go about designing this! This is for simple 2D top-down tile based rendering. No real 3D except what's inherent in OpenGL ES itself. Would anyone be able to get me started on the right path? Are there options that might scale nicely when I decide to start tilting my perspective and doing 3D?

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• What kind of icon should I deploy with my Android 1.x and 2.x application?

  - by licorna

  The thing is this, in Android 1.5 and 1.6 we had the Icon Design Guidelines. In this guide there are specifications for application icons. Every application should conform to this. However, in recent Android versions (2.0 and 2.1) icons have changed from the old to this new flat 2D style. Every icon in Nexus One has this style, so not even Google is conforming to the guideline. To see the differences between high and low density icons see this image and compare Evernote icon with the rest. I've been able to use different icons by using two directories with different icons: drawables-hdpi/icon.png and drawables/icon.png, BUT not every Android 2.x is going to be HDPI and not every 1.x Android device is going to be low pixel density. So the question is: Should I deploy different icons for different Android platform version within my apk file? and if I should, How do I do it?

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• Can't access certain web sites - reset router, any ideas?

  - by IniTech

  EDIT: This problem was resolved by my ISP - had to do with damaged fiber in one of their locations. Thanks to everyone that helped. Not sure if this is the right site (I'm a StackOverflow user) so I thought I'd give it a shot. I'm having trouble connecting to certain sites on any of the 3 machines that are on my LAN. The following sites are returning "Problem Loading Page - The connection has timed out" Sourceforge.net CNet.com Microsoft.com OpenDNS.com even my company's webiste I was worried about possible malware/virus, but I don't think that is the case (given the inability to access my company's site and the fact that all 3 machines are having the same issues.) I've tried with IE8, FF, and Chrome I have reset my router (WRT54G) and my machine(s) multiple times. EDIT: It is also worth noting that this page spins constantly and no avatars show up (I'm assuming it is trying to access gravatar.com with no success.) EDIT: I have the same issues directly connected to the modem. So, any router config is probably not the issue I'm a programmer, not a network guy - any ideas?

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• SQL Server 2008 Bring Database Online trying to open a file from a drive that doesn't exist

  - by Nai

  This is my error I am facing TITLE: Microsoft.SqlServer.Smo Set offline failed for Database 'Go3D_Retailer ------------------------------ ADDITIONAL INFORMATION: An exception occurred while executing a Transact-SQL statement or batch. (Microsoft.SqlServer.ConnectionInfo) Unable to open the physical file "E:\Program Files\Microsoft SQL Server\MSSQL10.MSSQLSERVER\MSSQL\DATA\ftrow_Go3D_catalog.ndf". Operating system error 2: "2(failed to retrieve text for this error. Reason: 15105)". Database 'Go3D_Retailer' cannot be opened due to inaccessible files or insufficient memory or disk space. See the SQL Server errorlog for details. ALTER DATABASE statement failed. (Microsoft SQL Server, Error: 5120) Background to this error I've been trying to move my destination logshipping database to another physical server for analysis purposes. Because I do not have domain keys and active directory set up, I had to hack my process by using the same username/password for both the source and destination servers to get the process to work. Following that, I used this guy's solution to move the destination database to another server. However, this error occurs when I try to bring the database back online. I don't have an E drive on my server and I have no idea why it's trying to open a file from E drive. I have over a 100gb left on my hard disk so it's definitely not a space issue. This sounds like a bug... Any ideas?

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• Does C99 guarantee that arrays are contiguous ?

  - by kriss

  Following an hot comment thread in another question, I came to debate of what is and what is not defined in C99 standard about C arrays. Basically when I define a 2D array like int a[5][5], does the standard C99 garantee or not that it will be a contiguous block of ints, can I cast it to (int *)a and be sure I will have a valid 1D array of 25 ints. As I understand the standard the above property is implicit in the sizeof definition and in pointer arithmetic, but others seems to disagree and says casting to (int*) the above structure give an undefined behavior (even if they agree that all existing implementations actually allocate contiguous values). More specifically, if we think an implementation that would instrument arrays to check array boundaries for all dimensions and return some kind of error when accessing 1D array, or does not give correct access to elements above 1st row. Could such implementation be standard compilant ? And in this case what parts of the C99 standard are relevant.

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• Variable alpha blending in pylab

  - by Hooked

  How does one control the transparency over a 2D image in pylab? I'd like to give two sets of values (X,Y,Z,T) where X,Y are arrays of positions, Z is the color value, and T is the transparency to a function like imshow but it seems that the function only takes alpha as a scalar. As a concrete example, consider the code below that attempts to display two Gaussians. The closer the value is to zero, the more transparent I'd like the plot to be. from pylab import * side = linspace(-1,1,100) X,Y = meshgrid(side,side) extent = (-1,1,-1,1) Z1 = exp(-((X+.5)**2+Y**2)) Z2 = exp(-((X-.5)**2+(Y+.2)**2)) imshow(Z1, cmap=cm.hsv, alpha=.6, extent=extent) imshow(Z2, cmap=cm.hsv, alpha=.6, extent=extent) show() Note: I am not looking for a plot of Z1+Z2 (that would be trivial) but for a general way to specify the alpha blending across an image.

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• NumPy: how to quickly normalize many vectors?

  - by EOL

  How can a list of vectors be elegantly normalized, in NumPy? Here is an example that does not work: from numpy import * vectors = array([arange(10), arange(10)]) # All x's, then all y's norms = apply_along_axis(linalg.norm, 0, vectors) # Now, what I was expecting would work: print vectors.T / norms # vectors.T has 10 elements, as does norms, but this does not work The last operation yields "shape mismatch: objects cannot be broadcast to a single shape". How can the normalization of the 2D vectors in vectors be elegantly done, with NumPy? Edit: Why does the above not work while adding a dimension to norms does work (as per my answer below)?

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