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  • Useless variable name in C struct type definition

    - by user1210233
    I'm implementing a linked list in C. Here's a struct that I made, which represents the linked list: typedef struct llist { struct lnode* head; /* Head pointer either points to a node with data or NULL */ struct lnode* tail; /* Tail pointer either points to a node with data or NULL */ unsigned int size; /* Size of the linked list */ } list; Isn't the "llist" basically useless. When a client uses this library and makes a new linked list, he would have the following declaration: list myList; So typing llist just before the opening brace is practically useless, right? The following code basically does the same job: typedef struct { struct lnode* head; /* Head pointer either points to a node with data or NULL */ struct lnode* tail; /* Tail pointer either points to a node with data or NULL */ unsigned int size; /* Size of the linked list */ } list;

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  • Splitting a list based on another list values in Mathematica

    - by Max
    In Mathematica I have a list of point coordinates size = 50; points = Table[{RandomInteger[{0, size}], RandomInteger[{0, size}]}, {i, 1, n}]; and a list of cluster indices these points belong to clusterIndices = {1, 1, 1, 1, 1, 1, 1, 2, 2, 1, 2, 1, 2, 1, 1, 1, 1, 1, 1, 1}; what is the easiest way to split the points into two separate lists based on the clusterIndices values?

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  • R graphics plotting a linegraph with date/time horizontally along x-axis

    - by user2978586
    I want to get a linegraph in R which has Time along x and temperature along y. Originally I had the data in dd/mm/yyyy hh:mm format, with a time point every 30 minutes. https://www.dropbox.com/s/q35y1rfila0va1h/Data_logger_S65a_Ania.csv Since I couldn't find a way of reading this into R, I formatted the data to make it into dd/mm/yyyy and added a column 'time' with 1-48 for all the time points for each day https://www.dropbox.com/s/65ogxzyvuzteqxv/temp.csv This is what I have so far: temp<-read.csv("temp.csv",as.is=T) temp$date<-as.Date(temp$date, format="%d/%m/%Y") #inputting date in correct format plot(temperature ~ date, temp, type="n") #drawing a blank plot with axes, but without data lines(temp$date, temp$temperature,type="o") #type o is a line overlaid on top of points. This stacks the points up vertically, which is not what I want, and stacks all the time points (1-48) for each day all together on the same date. Any advice would be much appreciated on how to get this horizontal, and ordered by time as well as date.

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  • Write a SQL Query to replace values and include all the Dates.

    - by VJ
    Well I have this - Table DimDate- Date Table Employee- Id,Name,Points,Date Now the Employee table has points for everyday unless they did not come...so the Date does not have all the Dates entries... I mean for e.g in a week he did not come for 2 days the Employee table has only 5 rows...so I have this dimdate table which has all the dates till 2050 which I want to join with and add Zeros for the dates he does not have points. So I have written this query but does not work - Select E.EmployeeId,D.Date,isNull(E.Points,0) from DimDate D left join Employee E on D.Date between '01-01-2009'and '06-01-2009' where E.EmployeeId=1 The above query give multiple dates and I tried group by on Date but does not work.

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  • database design help for game / user levels / progress

    - by sprugman
    Sorry this got long and all prose-y. I'm creating my first truly gamified web app and could use some help thinking about how to structure the data. The Set-up Users need to accomplish tasks in each of several categories before they can move up a level. I've got my Users, Tasks, and Categories tables, and a UserTasks table which joins the three. ("User 3 has added Task 42 in Category 8. Now they've completed it.") That's all fine and working wonderfully. The Challenge I'm not sure of the best way to track the progress in the individual categories toward each level. The "business" rules are: You have to achieve a certain number of points in each category to move up. If you get the number of points needed in Cat 8, but still have other work to do to complete the level, any new Cat 8 points count toward your overall score, but don't "roll over" into the next level. The number of Categories is small (five currently) and unlikely to change often, but by no means absolutely fixed. The number of points needed to level-up will vary per level, probably by a formula, or perhaps a lookup table. So the challenge is to track each user's progress toward the next level in each category. I've thought of a few potential approaches: Possible Solutions Add a column to the users table for each category and reset them all to zero each time a user levels-up. Have a separate UserProgress table with a row for each category for each user and the number of points they have. (Basically a Many-to-Many version of #1.) Add a userLevel column to the UserTasks table and use that to derive their progress with some kind of SUM statement. Their current level will be a simple int in the User table. Pros & Cons (1) seems like by far the most straightforward, but it's also the least flexible. Perhaps I could use a naming convention based on the category ids to help overcome some of that. (With code like "select cats; for each cat, get the value from Users.progress_{cat.id}.") It's also the one where I lose the most data -- I won't know which points counted toward leveling up. I don't have a need in mind for that, so maybe I don't care about that. (2) seems complicated: every time I add or subtract a user or a category, I have to maintain the other table. I foresee synchronization challenges. (3) Is somewhere in between -- cleaner than #2, but less intuitive than #1. In order to find out where a user is, I'd have mildly complex SQL like: SELECT categoryId, SUM(points) from UserTasks WHERE userId={user.id} & countsTowardLevel={user.level} groupBy categoryId Hmm... that doesn't seem so bad. I think I'm talking myself into #3 here, but would love any input, advice or other ideas.

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  • What happens if I give more inputs in estimateRigidTransform or getAffineTransform?

    - by user3531608
    I am using estimateRigidTransform with about two vectors of 100 points and is working FINE. But somehow getAffineTransform doesn't work. I know that findHomography finds the best matrix using RANSAC and getPerspectiveTransform needs only 4 points. My question is what happens if I give more inputs in estimateRigidTransform or getAffineTransform? Does it take only 4 points from input matrix? Or do some kind of RANSAC?

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  • Hell: NTFS "Restore previous versions"...

    - by ttsiodras
    The hell I have experienced these last 24h: Windows 7 installation hosed after bluetooth driver install. Attempting to recover using restore points via "Repair" on the bootable Win7 installation CD. Attempting to go back one day in the restore points. No joy. Attempting to go back two days in the restore points. No joy. Attempting to go back one week in the restore points. Stil no joy. Windows won't boot. Apparently something is REALLY hosed. And then it hits me - PANIC - the restore points somehow reverted DATA files to their older versions! Word, Powerpoint, SPSS, etc document versions are all one week old now. Using the "freshest" restore point. Failed to restore yesterday's restore point!!! I am stuck at old versions of the data!!! Booting KNOPPIX, mounting NTFS partition as read-only under KNOPPIX. Checking. Nope, the data files are still the one week old versions. Booting Win7 CD, Recovery console - Cmd prompt - navigating - yep, data files are still one week old. Removing the drive, mounting it under other Win7 installation. Still old data. Running NTFS undelete on the drive (read-only scan), searching for file created yesterday. Not found. Despair. At this point, idea: I will install a brand new Windows installation, keeping the old one in Windows.old (default behaviour of Windows installs). I boot the new install, I go to my C:\Data\ folder, I choose "Restore previous versions", click on yesterday's date, and click open... YES! It works! I can see the latest versions of my files (e.g. from yesterday). Thank God. And then, I try to view the files under the "yesterday snapshot-version" of c:\Users\MyAccount\Desktop ... And I get "Permission Denied" as soon as I try to open "Users\MyAccount". I make sure I am an administrator. No joy. Apparently, the new Windows installation does not have access to read the "NTFS snapshots" or "Volume Shadow Snapshots" of my old Windows account! Cross-installation permissions? I need to somehow tell the new Windows install that I am the same "old" user... So that I will be able to access the "Users\MyAccount" folder of the snapshot of my old user account. Help?

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  • Why not use JavaScript but libraries instead?

    - by shareef
    I read this article Unobtrusive JavaScript with jQuery and I noticed these points in the slide page 11 some companies strip JavaScript at the firewall some run the NoScript Firefox extension to protect themselves from common XSS and CSRF attacks many mobile devices ignore JavaScript entirely screen readers do execute JavaScript but accessibility issues mean you may not want them to I did not understand the fourth point. What does it mean? I need your comment and responses on these points. Is not using JavaScript and switching to libraries like jQuery worth it?

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  • MCP 70-536 Acquired

    - by dave
    Yeah...   Today I passed the 70-536 exam, so my way to 70-562 (ASP.NET 3.5) is open. Points: 815 Points needed for pass:700 Strarting to read new book :)

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  • Routes on a sphere surface - Find geodesic?

    - by CaNNaDaRk
    I'm working with some friends on a browser based game where people can move on a 2D map. It's been almost 7 years and still people play this game so we are thinking of a way to give them something new. Since then the game map was a limited plane and people could move from (0, 0) to (MAX_X, MAX_Y) in quantized X and Y increments (just imagine it as a big chessboard). We believe it's time to give it another dimension so, just a couple of weeks ago, we began to wonder how the game could look with other mappings: Unlimited plane with continous movement: this could be a step forward but still i'm not convinced. Toroidal World (continous or quantized movement): sincerely I worked with torus before but this time I want something more... Spherical world with continous movement: this would be great! What we want Users browsers are given a list of coordinates like (latitude, longitude) for each object on the spherical surface map; browsers must then show this in user's screen rendering them inside a web element (canvas maybe? this is not a problem). When people click on the plane we convert the (mouseX, mouseY) to (lat, lng) and send it to the server which has to compute a route between current user's position to the clicked point. What we have We began writing a Java library with many useful maths to work with Rotation Matrices, Quaternions, Euler Angles, Translations, etc. We put it all together and created a program that generates sphere points, renders them and show them to the user inside a JPanel. We managed to catch clicks and translate them to spherical coords and to provide some other useful features like view rotation, scale, translation etc. What we have now is like a little (very little indeed) engine that simulates client and server interaction. Client side shows points on the screen and catches other interactions, server side renders the view and does other calculus like interpolating the route between current position and clicked point. Where is the problem? Obviously we want to have the shortest path to interpolate between the two route points. We use quaternions to interpolate between two points on the surface of the sphere and this seemed to work fine until i noticed that we weren't getting the shortest path on the sphere surface: We though the problem was that the route is calculated as the sum of two rotations about X and Y axis. So we changed the way we calculate the destination quaternion: We get the third angle (the first is latitude, the second is longitude, the third is the rotation about the vector which points toward our current position) which we called orientation. Now that we have the "orientation" angle we rotate Z axis and then use the result vector as the rotation axis for the destination quaternion (you can see the rotation axis in grey): What we got is the correct route (you can see it lays on a great circle), but we get to this ONLY if the starting route point is at latitude, longitude (0, 0) which means the starting vector is (sphereRadius, 0, 0). With the previous version (image 1) we don't get a good result even when startin point is 0, 0, so i think we're moving towards a solution, but the procedure we follow to get this route is a little "strange" maybe? In the following image you get a view of the problem we get when starting point is not (0, 0), as you can see starting point is not the (sphereRadius, 0, 0) vector, and as you can see the destination point (which is correctly drawn!) is not on the route. The magenta point (the one which lays on the route) is the route's ending point rotated about the center of the sphere of (-startLatitude, 0, -startLongitude). This means that if i calculate a rotation matrix and apply it to every point on the route maybe i'll get the real route, but I start to think that there's a better way to do this. Maybe I should try to get the plane through the center of the sphere and the route points, intersect it with the sphere and get the geodesic? But how? Sorry for being way too verbose and maybe for incorrect English but this thing is blowing my mind! EDIT: This code version is related to the first image: public void setRouteStart(double lat, double lng) { EulerAngles tmp = new EulerAngles ( Math.toRadians(lat), 0, -Math.toRadians(lng)); //set route start Quaternion qtStart.setInertialToObject(tmp); //do other stuff like drawing start point... } public void impostaDestinazione(double lat, double lng) { EulerAngles tmp = new AngoliEulero( Math.toRadians(lat), 0, -Math.toRadians(lng)); qtEnd.setInertialToObject(tmp); //do other stuff like drawing dest point... } public V3D interpolate(double totalTime, double t) { double _t = t/totalTime; Quaternion q = Quaternion.Slerp(qtStart, qtEnd, _t); RotationMatrix.inertialQuatToIObject(q); V3D p = matInt.inertialToObject(V3D.Xaxis.scale(sphereRadius)); //other stuff, like drawing point ... return p; } //mostly taken from a book! public static Quaternion Slerp(Quaternion q0, Quaternion q1, double t) { double cosO = q0.dot(q1); double q1w = q1.w; double q1x = q1.x; double q1y = q1.y; double q1z = q1.z; if (cosO < 0.0f) { q1w = -q1w; q1x = -q1x; q1y = -q1y; q1z = -q1z; cosO = -cosO; } double sinO = Math.sqrt(1.0f - cosO*cosO); double O = Math.atan2(sinO, cosO); double oneOverSinO = 1.0f / senoOmega; k0 = Math.sin((1.0f - t) * O) * oneOverSinO; k1 = Math.sin(t * O) * oneOverSinO; // Interpolate return new Quaternion( k0*q0.w + k1*q1w, k0*q0.x + k1*q1x, k0*q0.y + k1*q1y, k0*q0.z + k1*q1z ); } A little dump of what i get (again check image 1): Route info: Sphere radius and center: 200,000, (0.0, 0.0, 0.0) Route start: lat 0,000 °, lng 0,000 ° @v: (200,000, 0,000, 0,000), |v| = 200,000 Route end: lat 30,000 °, lng 30,000 ° @v: (150,000, 86,603, 100,000), |v| = 200,000 Qt dump: (w, x, y, z), rot. angle°, (x, y, z) rot. axis Qt start: (1,000, 0,000, -0,000, 0,000); 0,000 °; (1,000, 0,000, 0,000) Qt end: (0,933, 0,067, -0,250, 0,250); 42,181 °; (0,186, -0,695, 0,695) Route start: lat 30,000 °, lng 10,000 ° @v: (170,574, 30,077, 100,000), |v| = 200,000 Route end: lat 80,000 °, lng -50,000 ° @v: (22,324, -26,604, 196,962), |v| = 200,000 Qt dump: (w, x, y, z), rot. angle°, (x, y, z) rot. axis Qt start: (0,962, 0,023, -0,258, 0,084); 31,586 °; (0,083, -0,947, 0,309) Qt end: (0,694, -0,272, -0,583, -0,324); 92,062 °; (-0,377, -0,809, -0,450)

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  • runtime error: invalid memory address or nil pointer dereference

    - by Klink
    I want to learn OpenGL 3.0 with golang. But when i try to compile some code, i get many errors. package main import ( "os" //"errors" "fmt" //gl "github.com/chsc/gogl/gl33" //"github.com/jteeuwen/glfw" "github.com/go-gl/gl" "github.com/go-gl/glfw" "runtime" "time" ) var ( width int = 640 height int = 480 ) var ( points = []float32{0.0, 0.8, -0.8, -0.8, 0.8, -0.8} ) func initScene() { gl.Init() gl.ClearColor(0.0, 0.5, 1.0, 1.0) gl.Enable(gl.CULL_FACE) gl.Viewport(0, 0, 800, 600) } func glfwInitWindowContext() { if err := glfw.Init(); err != nil { fmt.Fprintf(os.Stderr, "glfw_Init: %s\n", err) glfw.Terminate() } glfw.OpenWindowHint(glfw.FsaaSamples, 1) glfw.OpenWindowHint(glfw.WindowNoResize, 1) if err := glfw.OpenWindow(width, height, 0, 0, 0, 0, 32, 0, glfw.Windowed); err != nil { fmt.Fprintf(os.Stderr, "glfw_Window: %s\n", err) glfw.CloseWindow() } glfw.SetSwapInterval(1) glfw.SetWindowTitle("Title") } func drawScene() { for glfw.WindowParam(glfw.Opened) == 1 { gl.Clear(gl.COLOR_BUFFER_BIT) vertexShaderSrc := `#version 120 attribute vec2 coord2d; void main(void) { gl_Position = vec4(coord2d, 0.0, 1.0); }` vertexShader := gl.CreateShader(gl.VERTEX_SHADER) vertexShader.Source(vertexShaderSrc) vertexShader.Compile() fragmentShaderSrc := `#version 120 void main(void) { gl_FragColor[0] = 0.0; gl_FragColor[1] = 0.0; gl_FragColor[2] = 1.0; }` fragmentShader := gl.CreateShader(gl.FRAGMENT_SHADER) fragmentShader.Source(fragmentShaderSrc) fragmentShader.Compile() program := gl.CreateProgram() program.AttachShader(vertexShader) program.AttachShader(fragmentShader) program.Link() attribute_coord2d := program.GetAttribLocation("coord2d") program.Use() //attribute_coord2d.AttribPointer(size, typ, normalized, stride, pointer) attribute_coord2d.EnableArray() attribute_coord2d.AttribPointer(0, 3, false, 0, &(points[0])) //gl.DrawArrays(gl.TRIANGLES, 0, len(points)) gl.DrawArrays(gl.TRIANGLES, 0, 3) glfw.SwapBuffers() inputHandler() time.Sleep(100 * time.Millisecond) } } func inputHandler() { glfw.Enable(glfw.StickyKeys) if glfw.Key(glfw.KeyEsc) == glfw.KeyPress { //gl.DeleteBuffers(2, &uiVBO[0]) glfw.Terminate() } if glfw.Key(glfw.KeyF2) == glfw.KeyPress { glfw.SetWindowTitle("Title2") fmt.Println("Changed to 'Title2'") fmt.Println(len(points)) } if glfw.Key(glfw.KeyF1) == glfw.KeyPress { glfw.SetWindowTitle("Title1") fmt.Println("Changed to 'Title1'") } } func main() { runtime.LockOSThread() glfwInitWindowContext() initScene() drawScene() } And after that: panic: runtime error: invalid memory address or nil pointer dereference [signal 0xb code=0x1 addr=0x0 pc=0x41bc6f74] goroutine 1 [syscall]: github.com/go-gl/gl._Cfunc_glDrawArrays(0x4, 0x7f8500000003) /tmp/go-build463568685/github.com/go-gl/gl/_obj/_cgo_defun.c:610 +0x2f github.com/go-gl/gl.DrawArrays(0x4, 0x3, 0x0, 0x45bd70) /tmp/go-build463568685/github.com/go-gl/gl/_obj/gl.cgo1.go:1922 +0x33 main.drawScene() /home/klink/Dev/Go/gogl/gopher/exper.go:85 +0x1e6 main.main() /home/klink/Dev/Go/gogl/gopher/exper.go:116 +0x27 goroutine 2 [syscall]: created by runtime.main /build/buildd/golang-1/src/pkg/runtime/proc.c:221 exit status 2

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  • Tool for creating complex paths?

    - by TerryB
    I want to create some fairly complex predefined paths for my AI sprites to follow. I'll need to use curves, splines etc to get the effect I want. Is there a drawing tool out there that will allow me to draw such curves, "mesh" them by placing lots of points along them at some defined density and then output the coordinates of all of those points for me? I could write this tool myself but hopefully one of the drawing packages can do this? Cheers!

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  • Google I/O Sandbox Case Study: HistoryPin

    Google I/O Sandbox Case Study: HistoryPin We interviewed HistoryPin at the Google I/O Sandbox on May 10, 2011 and they explained to their new technology and the benefits of integrating with Google Maps. HistoryPin lets you upload historical photos of places onto their respective points on Google Maps, enabling users to see what cities looked like at different points in time. For more information about developing on Google Maps visit: code.google.com For more information on HistoryPin, visit: www.historypin.com From: GoogleDevelopers Views: 90 0 ratings Time: 01:28 More in Science & Technology

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  • It is CX a new concept?

    - by Isabel F. Peñuelas
    The Marketing Industry and the Web Industry are talking about CX since some time. However it is only very recently that the concept has reached some common meaning accepted by the analysts’ and the IT community. The new CX model depends on two previous facts: the expansion of the social media, and the impact of the new advanced features of mobile devices regarding brand-customer interaction. CXsers vs UXers First there is some need of disambiguity between User Experience and Customer Experience. User Experience -UX, is a much well established concept related with the design of user interactions for particular devices. UX people are interested on multiple touch points of digital interfaces while CX people are interested on all kind of interfaces including physical ones. UX is an evolution of Web Usability, while CX is a marketing concept. UX is an instrument of User Experience. CX in fact is all about Connections and Interactions. Connections Dan Draper, the creative director Mad Men, understands very well that to market effectively means to connect with people, and the best way to connect to people is to use the connections people have with other people: understanding Social Media connections and taking the customer pulse of customers on those medias, and are strong facilitators of CX strategies.  Interactions We can very simply define CX as the relationship that a customer establishes with a brand through multiple touch points (interactions, channels) through the entire life cycle of his relationship- direct or indirect with the brand. Interactions can be grouped on Customer Journeys through multiple touch points defined as the path a customer follows to achieve a goal. Processes A customer journey today usually starts at the moment he surfs the Web, then he takes a purchase decision; purchases the product;  request a particular service and finally recommends or do not recommends the product.  Customer Journeys are processes, and to analyze customer journeys there exists today a broad offering of modern Customer Journey tools very similar actually to the use cases or UML activity diagrams for IT systems design. As a summary CX is nothing more and nothing less than applying process analysis methods for better understanding how to create value through customer interactions across the multiple user´s touch points with the brand.

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  • XNA 4.0 Point Vertex Rendering

    - by luis
    I have a buffer of about 134 million particles and a very powerful computer to render them smoothly but I am getting an error when trying to render them as primitive lines it says I cannot render more than around 1 million. I wonder how can I do this, also if is there a better way to render this other than with lines, I'm comfortable with having 1 pixel points or anything as long as the vertices are shown all the time. I'm basically just plotting the points. thanks.

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  • Making a clone of Starcraft legal?

    - by user782220
    My question is similar to a previous question. Consider the following clone of Starcraft: Change the artwork, sound, music, change the names of units. However, leave the unit hit points unchanged, unit damage unchanged, unit movement speed unchanged, change ability names but not ability effects. Is that considered illegal? In other words, is copying the unit hit points, damage, etc. considered illegal even if everything else is changed?

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  • Is there a library that handles hexagon tiled 2D maps?

    - by Pete Mancini
    It would represent a map that is semi-square of arbitrary size. It would have a simple system for representation of the map coordinates such as 0101 (first column, 1st hex). I'd want the map to be able to tell me the distance between two points, and what other hexes lay between those two points as a list or array. I don't care as much about the language but c# or python would be ideal. Does one exist?

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  • Changing coordinate system from Z-up to Y-up

    - by Jari Komppa
    Blender's coordinate system is different from what I'm used to, in that Z points upwards instead of Y. What would be the simplest way of converting all the world data (so that all animations, texture coordinates, etc still work) so that Y points upwards? Clarification: Object positions are defined as matrices, so just switching translation/rotation/scale information in matrices is not a trivial task.

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  • POSH-y SQL Disk Space Monitoring

    - by merrillaldrich
    In a prior post I expressed my dismay that apparently Operations Manager (which I dig in other respects) has no love for SQL Server storage that uses mount points. Herewith, henceforth, forthwith is a PowerShell workaround I am using until I find out I am wrong, or there’s a management pack fix. The crux of the issue, I think, is that SQL Server itself has basically no visibility to the disks mounted using mount points, and that blind spot carries through to the management pack. That much is well...(read more)

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  • Passoker Online Betting Use of Oracle NoSQL Database

    - by Charles Lamb
    Here's an Oracle NoSQL Database customer success story for Passoker, an online betting house. http://www.oracle.com/us/corporate/customers/customersearch/passoker-1-nosql-ss-1863507.html There are a lot of great points made in the Solutions section, but as a developer the one I like the most is this one: Eliminated daily maintenance related to single-node points-of-failure by moving to Oracle NoSQL Database, which is designed to be resilient and hands-off, thus minimizing IT support costs

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  • How to write a real time data acquisition program [closed]

    - by Tosin Awe
    I have to write a program in assembly language that will monitor temperature continuously, and I have no idea where to begin. The temperature must be displayed in BCD format, and the high and low set points will be programmed into the system. if the set points are exceeded then an alarm will be indicated. The low point is 20 degrees Celsius, and the high point is 24 degrees Celsius. Can somebody give me some hints on how to complete this task?

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  • Will a SQL Server client alias survive a sysprep?

    - by shufler
    I want to sysprep a Windows Server 2008 R2 SP1 machine that has SQL Server 2008 R2 SP1 installed (for reference, SQL Server 2008 R2 has a new sysprep feature that allows the instance to be sysprepped). On the server is a SQL Server client alias that points to the default SQL Server database engine instance. For reference, the alias is called Alias-SQLServer and has been configured in both 32-bit and 64-bit cliconfig versions (that is, both registry keys exist) The alias points to the local instance as the image will be used to create development VMs and the installation script for the application that is being developed will use the SQL Server client alias in order to generalize the installation scripts. I can't seem to find information about whether the sysprep tool will update the SQL Server client alias's registry keys with the server's new name once it's unsealed. My guess is that it is not; how is sysprep to know that the server name the alias points to will be different for each image? Right? Perhaps if the alias points to localhost instead of the server name this will work?

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  • Apache: Setting up local test server with subdomains

    - by RC
    Hi everyone, I have XAMPP running on my desktop machine, and I do all my work on it with no issue. http://localhost ---> points to public_html http://site1.localhost ---> points to site 1 http://site2.localhost ---> points to site 2 http://site3.localhost ---> points to site 3 Entering the above URLs in my web browser on the machine with Apache works great, and I can work on multiple sites within distinct subdomains. But what I want to do now is to transfer Apache and all the files to another Windows 7 machine within the LAN, but still be able to view the subdomains from my main development machine. With a vanilla XAMPP installation on the new hosting machine, entering the IP address of that machine (e.g. 192.168.1.10) into my development computer would send me to the main public_html folder. But how do I set up subdomains such that I can access it externally? For example, http://site1.devmachine Thanks for any help.

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  • Physics System ignores collision in some rare cases

    - by Gajoo
    I've been developing a simple physics engine for my game. since the game physics is very simple I've decided to increase accuracy a little bit. Instead of formal integration methods like fourier or RK4, I'm directly computing the results after delta time "dt". based on the very first laws of physics : dx = 0.5 * a * dt^2 + v0 * dt dv = a * dt where a is acceleration and v0 is object's previous velocity. Also to handle collisions I've used a method which is somehow different from those I've seen so far. I'm detecting all the collision in the given time frame, stepping the world forward to the nearest collision, resolving it and again check for possible collisions. As I said the world consist of very simple objects, so I'm not loosing any performance due to multiple collision checking. First I'm checking if the ball collides with any walls around it (which is working perfectly) and then I'm checking if it collides with the edges of the walls (yellow points in the picture). the algorithm seems to work without any problem except some rare cases, in which the collision with points are ignored. I've tested everything and all the variables seem to be what they should but after leaving the system work for a minute or two the system the ball passes through one of those points. Here is collision portion of my code, hopefully one of you guys can give me a hint where to look for a potential bug! void PhysicalWorld::checkForPointCollision(Vec2 acceleration, PhysicsComponent& ball, Vec2& collisionNormal, float& collisionTime, Vec2 target) { // this function checks if there will be any collision between a circle and a point // ball contains informations about the circle (it's current velocity, position and radius) // collisionNormal is an output variable // collisionTime is also an output varialbe // target is the point I want to check for collisions Vec2 V = ball.mVelocity; Vec2 A = acceleration; Vec2 P = ball.mPosition - target; float wallWidth = mMap->getWallWidth() / (mMap->getWallWidth() + mMap->getHallWidth()) / 2; float r = ball.mRadius / (mMap->getWallWidth() + mMap->getHallWidth()); // r is ball radius scaled to match actual rendered object. if (A.any()) // todo : I need to first correctly solve the collisions in case there is no acceleration return; if (V.any()) // if object is not moving there will be no collisions! { float D = P.x * V.y - P.y * V.x; float Delta = r*r*V.length2() - D*D; if(Delta < eps) return; Delta = sqrt(Delta); float sgnvy = V.y > 0 ? 1: (V.y < 0?-1:0); Vec2 c1(( D*V.y+sgnvy*V.x*Delta) / V.length2(), (-D*V.x+fabs(V.y)*Delta) / V.length2()); Vec2 c2(( D*V.y-sgnvy*V.x*Delta) / V.length2(), (-D*V.x-fabs(V.y)*Delta) / V.length2()); float t1 = (c1.x - P.x) / V.x; float t2 = (c2.x - P.x) / V.x; if(t1 > eps && t1 <= collisionTime) { collisionTime = t1; collisionNormal = c1; } if(t2 > eps && t2 <= collisionTime) { collisionTime = t2; collisionNormal = c2; } } } // this function should step the world forward by dt. it doesn't check for collision of any two balls (components) // it just checks if there is a collision between the current component and 4 points forming a rectangle around it. void PhysicalWorld::step(float dt) { for (unsigned i=0;i<mObjects.size();i++) { PhysicsComponent &current = *mObjects[i]; Vec2 acceleration = current.mForces * current.mInvMass; float rt=dt; // stores how much more the world should advance while(rt > eps) { float collisionTime = rt; Vec2 collisionNormal = Vec2(0,0); float halfWallWidth = mMap->getWallWidth() / (mMap->getWallWidth() + mMap->getHallWidth()) / 2; // we check if there is any collision with any of those 4 points around the ball // if there is a collision both collisionNormal and collisionTime variables will change // after these functions collisionTime will be exactly the value of nearest collision (if any) // and if there was, collisionNormal will report in which direction the ball should return. checkForPointCollision(acceleration,current,collisionNormal,collisionTime,Vec2(floor(current.mPosition.x) + halfWallWidth,floor(current.mPosition.y) + halfWallWidth)); checkForPointCollision(acceleration,current,collisionNormal,collisionTime,Vec2(floor(current.mPosition.x) + halfWallWidth, ceil(current.mPosition.y) - halfWallWidth)); checkForPointCollision(acceleration,current,collisionNormal,collisionTime,Vec2( ceil(current.mPosition.x) - halfWallWidth,floor(current.mPosition.y) + halfWallWidth)); checkForPointCollision(acceleration,current,collisionNormal,collisionTime,Vec2( ceil(current.mPosition.x) - halfWallWidth, ceil(current.mPosition.y) - halfWallWidth)); // either if there is a collision or if there is not we step the forward since we are sure there will be no collision before collisionTime current.mPosition += collisionTime * (collisionTime * acceleration * 0.5 + current.mVelocity); current.mVelocity += collisionTime * acceleration; // if the ball collided with anything collisionNormal should be at least none zero in one of it's axis if (collisionNormal.any()) { collisionNormal *= Dot(collisionNormal, current.mVelocity) / collisionNormal.length2(); current.mVelocity -= 2 * collisionNormal; // simply reverse velocity along collision normal direction } rt -= collisionTime; } // reset all forces for current object so it'll be ready for later game event current.mForces.zero(); } }

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  • How to associate Wi-Fi beacon info with a virtual "location"?

    - by leander
    We have a piece of embedded hardware that will sense 802.11 beacons, and we're using this to make a map of currently visible bssid -> signalStrength. Given this map, we would like to make a determination: Is this likely to be a location I have been to before? If so, what is its ID? If not, I should remember this location: generate a new ID. Now what should I store (and how should I store it) to make future determinations easier? This is for an augmented-reality app/game. We will be using it to associate particular characters and events with "locations". The device does not have internet or cellular access, so using a geolocation service is out of consideration for the time being. (We don't really need to know where we are in reality, just be able to determine if we return there.) It isn't crucial that it be extremely accurate, but it would be nice if it was tolerant to signal strength changes or the occasional missing beacon. It should be usable in relatively low numbers of access points (e.g. rural house with one wireless router) or many (wandering around a dense metropolis). In the case of a city, it should change location every few minutes of walking (continuously-overlapping signals make this a bit more tricky in naive code). A reasonable number of false positives (match a location when we aren't actually there) is acceptable. The wrong character/event showing up just adds a bit of variety. False negatives (no location match) are a bit more troublesome: this will tend to add a better-matching new location to the saved locations, masking the old one. While we will have additional logic to ensure locations that the device hasn't seen in a while will "orphan" any associated characters or events (if e.g. you move to a different country), we'd prefer not to mask and eventually orphan locations you do visit regularly. Some technical complications: signalStrength is returned as 1-4; presumably it's related to dB, but we are not sure exactly how; in my experiments it tends to stick to either 1 or 4, but occasionally we see numbers in between. (Tech docs on the hardware are sparse.) The device completes a scan of one-quarter of the channel space every second; so it takes about 4-5 seconds to get a complete picture of what's around. The list isn't always complete. (We are making strides to fix this using some slight sampling period randomization, as recommended by the library docs. We're also investigating ways to increase the number of scans without killing our performance; the hardware/libs are poorly behaved when it comes to saturating the bus.) We have only kilobytes to store our history. We have a "working" impl now, but it is relatively naive, and flaky in the face of real-world Wi-Fi behavior. Rough pseudocode: // recordLocation() -- only store strength 4 locations m_savedLocations[g_nextId++] = filterForStrengthGE( m_currentAPs, 4 ); // determineLocation() bestPoints = -inf; foreach ( oldLoc in m_savedLocations ) { points = 0.0; foreach ( ap in m_currentAPs ) { if ( oldLoc.has( ap ) ) { switch ( ap.signalStrength ) { case 3: points += 1.0; break; case 4: points += 2.0; break; } } } points /= oldLoc.numAPs; if ( points > bestPoints ) { bestLoc = oldLoc; bestPoints = points; } } if ( bestLoc && bestPoints > 1.0 ) { if ( bestPoints >= (2.0 - epsilon) ) { // near-perfect match. // update location with any new high-strength APs that have appeared bestLoc.addAPs( filterForStrengthGE( m_currentAPs, 4 ) ); } return bestLoc; } else { return NO_MATCH; } We record a location currently only when we have NO_MATCH and the app determines it's time for a new event. (The "near-perfect match" code above would appear to make it harder to match in the future... It's mostly to keep new powerful APs from being associated with other locations, but you'd think we'd need something to counter this if e.g. an AP doesn't show up in the next 10 times I match a location.) I have a feeling that we're missing some things from set theory or graph theory that would assist in grouping/classification of this data, and perhaps providing a better "confidence level" on matches, and better robustness against missed beacons, signal strength changes, and the like. Also it would be useful to have a good method for mutating locations over time. Any useful resources out there for this sort of thing? Simple and/or robust approaches we're missing?

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