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• How important is Discrete Mathematics for a Computer Scientist?

  - by mort

  As the title says, How important is Discrete Mathematics for a Computer Scientist? Background: I'm pursuing a Master's degree with a focus on fundamentals such as Algorithms, Complexity and Computability Theory and Programming Languages to get a good foundation for working in the field of Parallel Computing. Some more background: My university grants a lot of freedom in the choices of courses for my Master's degree. It's officially called "Software Engineering", but due to a the broad range of electives, a different focus is possible. Interestingly, none of the electives is a lecture in Math! I'm thinking about doing a course about Discrete Mathematics that would take half a semester to complete successfully, even if I can't use it for my degree. So with this question I'm trying to find out if the effort is justifiable.

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• Get Hands On with Raspberry Pi via Free OS-Building Course

  - by Jason Fitzpatrick

  Cambridge University is now offering a free 12-segment course that will guide you through building an OS from scratch for the tiny Raspberry Pi development board–learn the ins and outs of basic OS design on the cheap. You’ll need a Raspberry Pi board, a computer running Windows, OS X, or Linux, and an SD card, as well as a small amount of free software. The 12-part tutorial starts you off with basic OS theory and then walks you through basic control of the board, graphics manipulation, and, finally, creating a command line interface for your new operating system. Hit up the link below to read more and check out the lessons. Baking Pi – Operating Systems Development HTG Explains: What The Windows Event Viewer Is and How You Can Use It HTG Explains: How Windows Uses The Task Scheduler for System Tasks HTG Explains: Why Do Hard Drives Show the Wrong Capacity in Windows?

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• Open a File Browser From Your Current Command Prompt/Terminal Directory

  - by The Geek

  Ever been doing some work at the command line when you realized… it would be a lot easier if I could just use the mouse for this task? One command later, you’ll have a window open to the same place that you’re at. This same tip works in more than one operating system, so we’ll detail how to do it in every way we know how. Open a File Browser in Windows We’ve actually covered this before when we told you how to open an Explorer window from the command prompt’s current directory, but we’ll briefly review: Just type the follow command into your command prompt: explorer . Note: You could actually just type “start .” instead. And you’ll then see a file browsing window set to the same directory you were previous at. And yes, this screenshot is from Vista, but it works the same in every version of Windows. If that wasn’t good enough, you should really read how you can navigate in the File Open/Save dialogs with just the keyboard—now that’s a Stupid Geek Trick! Open a File Browser in Linux For this exercise, we’re going to assume that you’re using Gnome under a Linux flavor like Ubuntu, because that’s the most common. From your terminal window, just type in the following command: nautilus . And the next thing you know, you’ll have a file browser window open at the current location. You’ll see some type of error message at the prompt, but you can pretty much ignore that. You can also use “gnome-open .” if you want. Open Finder in Mac OS X All the Mac computers in this office are running Linux, so we haven’t had a chance to verify, but you should be able to use the following command on OS X to open Finder in the current terminal location: open . Open Dolphin on Linux KDE4 dolphin . Got any extra tips to help out your fellow readers? How do you do the same thing in KDE3? What about OS X? Leave your savvy advice in the comments, and maybe we’ll update the article. Or not. Either way, it’ll help somebody! Similar Articles Productive Geek Tips Keyboard Ninja: Concatenate Multiple Text Files in WindowsStupid Geek Tricks: Open an Explorer Window from the Command Prompt’s Current DirectoryHow to automate FTP uploads from the Windows Command LineShell Geek: Rename Multiple Files At OnceAdd "Open with gedit" to the right click menu in Ubuntu TouchFreeze Alternative in AutoHotkey The Icy Undertow Desktop Windows Home Server – Backup to LAN The Clear & Clean Desktop Use This Bookmarklet to Easily Get Albums Use AutoHotkey to Assign a Hotkey to a Specific Window Latest Software Reviews Tinyhacker Random Tips DVDFab 6 Revo Uninstaller Pro Registry Mechanic 9 for Windows PC Tools Internet Security Suite 2010 Home Networks – How do they look like & the problems they cause Check Your IMAP Mail Offline In Thunderbird Follow Finder Finds You Twitter Users To Follow Combine MP3 Files Easily QuicklyCode Provides Cheatsheets & Other Programming Stuff Download Free MP3s from Amazon

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• Trying to detect collision between two polygons using Separating Axis Theorem

  - by Holly

  The only collision experience i've had was with simple rectangles, i wanted to find something that would allow me to define polygonal areas for collision and have been trying to make sense of SAT using these two links Though i'm a bit iffy with the math for the most part i feel like i understand the theory! Except my implementation somewhere down the line must be off as: (excuse the hideous font) As mentioned above i have defined a CollisionPolygon class where most of my theory is implemented and then have a helper class called Vect which was meant to be for Vectors but has also been used to contain a vertex given that both just have two float values. I've tried stepping through the function and inspecting the values to solve things but given so many axes and vectors and new math to work out as i go i'm struggling to find the erroneous calculation(s) and would really appreciate any help. Apologies if this is not suitable as a question! CollisionPolygon.java: package biz.hireholly.gameplay; import android.graphics.Canvas; import android.graphics.Color; import android.graphics.Paint; import biz.hireholly.gameplay.Types.Vect; public class CollisionPolygon { Paint paint; private Vect[] vertices; private Vect[] separationAxes; CollisionPolygon(Vect[] vertices){ this.vertices = vertices; //compute edges and separations axes separationAxes = new Vect[vertices.length]; for (int i = 0; i < vertices.length; i++) { // get the current vertex Vect p1 = vertices[i]; // get the next vertex Vect p2 = vertices[i + 1 == vertices.length ? 0 : i + 1]; // subtract the two to get the edge vector Vect edge = p1.subtract(p2); // get either perpendicular vector Vect normal = edge.perp(); // the perp method is just (x, y) => (-y, x) or (y, -x) separationAxes[i] = normal; } paint = new Paint(); paint.setColor(Color.RED); } public void draw(Canvas c, int xPos, int yPos){ for (int i = 0; i < vertices.length; i++) { Vect v1 = vertices[i]; Vect v2 = vertices[i + 1 == vertices.length ? 0 : i + 1]; c.drawLine( xPos + v1.x, yPos + v1.y, xPos + v2.x, yPos + v2.y, paint); } } /* consider changing to a static function */ public boolean intersects(CollisionPolygon p){ // loop over this polygons separation exes for (Vect axis : separationAxes) { // project both shapes onto the axis Vect p1 = this.minMaxProjection(axis); Vect p2 = p.minMaxProjection(axis); // do the projections overlap? if (!p1.overlap(p2)) { // then we can guarantee that the shapes do not overlap return false; } } // loop over the other polygons separation axes Vect[] sepAxesOther = p.getSeparationAxes(); for (Vect axis : sepAxesOther) { // project both shapes onto the axis Vect p1 = this.minMaxProjection(axis); Vect p2 = p.minMaxProjection(axis); // do the projections overlap? if (!p1.overlap(p2)) { // then we can guarantee that the shapes do not overlap return false; } } // if we get here then we know that every axis had overlap on it // so we can guarantee an intersection return true; } /* Note projections wont actually be acurate if the axes aren't normalised * but that's not necessary since we just need a boolean return from our * intersects not a Minimum Translation Vector. */ private Vect minMaxProjection(Vect axis) { float min = axis.dot(vertices[0]); float max = min; for (int i = 1; i < vertices.length; i++) { float p = axis.dot(vertices[i]); if (p < min) { min = p; } else if (p > max) { max = p; } } Vect minMaxProj = new Vect(min, max); return minMaxProj; } public Vect[] getSeparationAxes() { return separationAxes; } public Vect[] getVertices() { return vertices; } } Vect.java: package biz.hireholly.gameplay.Types; /* NOTE: Can also be used to hold vertices! Projections, coordinates ect */ public class Vect{ public float x; public float y; public Vect(float x, float y){ this.x = x; this.y = y; } public Vect perp() { return new Vect(-y, x); } public Vect subtract(Vect other) { return new Vect(x - other.x, y - other.y); } public boolean overlap(Vect other) { if( other.x <= y || other.y >= x){ return true; } return false; } /* used specifically for my SAT implementation which i'm figuring out as i go, * references for later.. * http://www.gamedev.net/page/resources/_/technical/game-programming/2d-rotated-rectangle-collision-r2604 * http://www.codezealot.org/archives/55 */ public float scalarDotProjection(Vect other) { //multiplier = dot product / length^2 float multiplier = dot(other) / (x*x + y*y); //to get the x/y of the projection vector multiply by x/y of axis float projX = multiplier * x; float projY = multiplier * y; //we want to return the dot product of the projection, it's meaningless but useful in our SAT case return dot(new Vect(projX,projY)); } public float dot(Vect other){ return (other.x*x + other.y*y); } }

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• How do I get the child of a unique parent in ActionScript?

  - by Koen

  My question is about targeting a child with a unique parent. For example. Let's say I have a box people can move called box_mc and 3 platforms it can jump on called: Platform_1 Platform_2 Platform_3 All of these platforms have a child element called hit. Platform_1 Hit Platform_2 Hit Platform_3 Hit I use an array and a for each statement to detect if box_mc hits one of the platforms childs. var obj_arr:Array = [Platform_1, Platform_2, Platform_3]; for each(obj in obj_arr){ if(box_mc.hitTestObject(obj.hit)){ trace(obj + " " + obj.hit); box_mc.y = obj.hit.y - box_mc.height; } } obj seems to output the unique parent it is hitting but obj.hit ouputs hit, so my theory is that it is applying the change of y to all the childs called hit in the stage. Would it be possible to only detect the child of that specific parent?

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• Game Object Factory: Fixing Memory Leaks

  - by Bunkai.Satori

  Dear all, this is going to be tough: I have created a game object factory that generates objects of my wish. However, I get memory leaks which I can not fix. Memory leaks are generated by return new Object(); in the bottom part of the code sample. static BaseObject * CreateObjectFunc() { return new Object(); } How and where to delete the pointers? I wrote bool ReleaseClassType(). Despite the factory works well, ReleaseClassType() does not fix memory leaks. bool ReleaseClassTypes() { unsigned int nRecordCount = vFactories.size(); for (unsigned int nLoop = 0; nLoop < nRecordCount; nLoop++ ) { // if the object exists in the container and is valid, then render it if( vFactories[nLoop] != NULL) delete vFactories[nLoop](); } return true; } Before taking a look at the code below, let me help you in that my CGameObjectFactory creates pointers to functions creating particular object type. The pointers are stored within vFactories vector container. I have chosen this way because I parse an object map file. I have object type IDs (integer values) which I need to translate them into real objects. Because I have over 100 different object data types, I wished to avoid continuously traversing very long Switch() statement. Therefore, to create an object, I call vFactoriesnEnumObjectTypeID via CGameObjectFactory::create() to call stored function that generates desired object. The position of the appropriate function in the vFactories is identical to the nObjectTypeID, so I can use indexing to access the function. So the question remains, how to proceed with garbage collection and avoid reported memory leaks? #ifndef GAMEOBJECTFACTORY_H_UNIPIXELS #define GAMEOBJECTFACTORY_H_UNIPIXELS //#include "MemoryManager.h" #include <vector> template <typename BaseObject> class CGameObjectFactory { public: // cleanup and release registered object data types bool ReleaseClassTypes() { unsigned int nRecordCount = vFactories.size(); for (unsigned int nLoop = 0; nLoop < nRecordCount; nLoop++ ) { // if the object exists in the container and is valid, then render it if( vFactories[nLoop] != NULL) delete vFactories[nLoop](); } return true; } // register new object data type template <typename Object> bool RegisterClassType(unsigned int nObjectIDParam ) { if(vFactories.size() < nObjectIDParam) vFactories.resize(nObjectIDParam); vFactories[nObjectIDParam] = &CreateObjectFunc<Object>; return true; } // create new object by calling the pointer to the appropriate type function BaseObject* create(unsigned int nObjectIDParam) const { return vFactories[nObjectIDParam](); } // resize the vector array containing pointers to function calls bool resize(unsigned int nSizeParam) { vFactories.resize(nSizeParam); return true; } private: //DECLARE_HEAP; template <typename Object> static BaseObject * CreateObjectFunc() { return new Object(); } typedef BaseObject*(*factory)(); std::vector<factory> vFactories; }; //DEFINE_HEAP_T(CGameObjectFactory, "Game Object Factory"); #endif // GAMEOBJECTFACTORY_H_UNIPIXELS

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• Error in my Separating Axis Theorem collision code

  - by Holly

  The only collision experience i've had was with simple rectangles, i wanted to find something that would allow me to define polygonal areas for collision and have been trying to make sense of SAT using these two links Though i'm a bit iffy with the math for the most part i feel like i understand the theory! Except my implementation somewhere down the line must be off as: (excuse the hideous font) As mentioned above i have defined a CollisionPolygon class where most of my theory is implemented and then have a helper class called Vect which was meant to be for Vectors but has also been used to contain a vertex given that both just have two float values. I've tried stepping through the function and inspecting the values to solve things but given so many axes and vectors and new math to work out as i go i'm struggling to find the erroneous calculation(s) and would really appreciate any help. Apologies if this is not suitable as a question! CollisionPolygon.java: package biz.hireholly.gameplay; import android.graphics.Canvas; import android.graphics.Color; import android.graphics.Paint; import biz.hireholly.gameplay.Types.Vect; public class CollisionPolygon { Paint paint; private Vect[] vertices; private Vect[] separationAxes; int x; int y; CollisionPolygon(Vect[] vertices){ this.vertices = vertices; //compute edges and separations axes separationAxes = new Vect[vertices.length]; for (int i = 0; i < vertices.length; i++) { // get the current vertex Vect p1 = vertices[i]; // get the next vertex Vect p2 = vertices[i + 1 == vertices.length ? 0 : i + 1]; // subtract the two to get the edge vector Vect edge = p1.subtract(p2); // get either perpendicular vector Vect normal = edge.perp(); // the perp method is just (x, y) => (-y, x) or (y, -x) separationAxes[i] = normal; } paint = new Paint(); paint.setColor(Color.RED); } public void draw(Canvas c, int xPos, int yPos){ for (int i = 0; i < vertices.length; i++) { Vect v1 = vertices[i]; Vect v2 = vertices[i + 1 == vertices.length ? 0 : i + 1]; c.drawLine( xPos + v1.x, yPos + v1.y, xPos + v2.x, yPos + v2.y, paint); } } public void update(int xPos, int yPos){ x = xPos; y = yPos; } /* consider changing to a static function */ public boolean intersects(CollisionPolygon p){ // loop over this polygons separation exes for (Vect axis : separationAxes) { // project both shapes onto the axis Vect p1 = this.minMaxProjection(axis); Vect p2 = p.minMaxProjection(axis); // do the projections overlap? if (!p1.overlap(p2)) { // then we can guarantee that the shapes do not overlap return false; } } // loop over the other polygons separation axes Vect[] sepAxesOther = p.getSeparationAxes(); for (Vect axis : sepAxesOther) { // project both shapes onto the axis Vect p1 = this.minMaxProjection(axis); Vect p2 = p.minMaxProjection(axis); // do the projections overlap? if (!p1.overlap(p2)) { // then we can guarantee that the shapes do not overlap return false; } } // if we get here then we know that every axis had overlap on it // so we can guarantee an intersection return true; } /* Note projections wont actually be acurate if the axes aren't normalised * but that's not necessary since we just need a boolean return from our * intersects not a Minimum Translation Vector. */ private Vect minMaxProjection(Vect axis) { float min = axis.dot(new Vect(vertices[0].x+x, vertices[0].y+y)); float max = min; for (int i = 1; i < vertices.length; i++) { float p = axis.dot(new Vect(vertices[i].x+x, vertices[i].y+y)); if (p < min) { min = p; } else if (p > max) { max = p; } } Vect minMaxProj = new Vect(min, max); return minMaxProj; } public Vect[] getSeparationAxes() { return separationAxes; } public Vect[] getVertices() { return vertices; } } Vect.java: package biz.hireholly.gameplay.Types; /* NOTE: Can also be used to hold vertices! Projections, coordinates ect */ public class Vect{ public float x; public float y; public Vect(float x, float y){ this.x = x; this.y = y; } public Vect perp() { return new Vect(-y, x); } public Vect subtract(Vect other) { return new Vect(x - other.x, y - other.y); } public boolean overlap(Vect other) { if(y > other.x && other.y > x){ return true; } return false; } /* used specifically for my SAT implementation which i'm figuring out as i go, * references for later.. * http://www.gamedev.net/page/resources/_/technical/game-programming/2d-rotated-rectangle-collision-r2604 * http://www.codezealot.org/archives/55 */ public float scalarDotProjection(Vect other) { //multiplier = dot product / length^2 float multiplier = dot(other) / (x*x + y*y); //to get the x/y of the projection vector multiply by x/y of axis float projX = multiplier * x; float projY = multiplier * y; //we want to return the dot product of the projection, it's meaningless but useful in our SAT case return dot(new Vect(projX,projY)); } public float dot(Vect other){ return (other.x*x + other.y*y); } }

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• How to write a network game? [closed]

  - by Tom Wijsman

  Based on Why is so hard to develop a MMO?: Networked game development is not trivial; there are large obstacles to overcome in not only latency, but cheat prevention, state management and load balancing. If you're not experienced with writing a networked game, this is going to be a difficult learning exercise. I know the theory about sockets, servers, clients, protocols, connections and such things. Now I wonder how one can learn to write a network game: How to balance load problems? How to manage the game state? How to keep things synchronized? How to protect the communication and client from reverse engineering? How to work around latency problems? Which things should be computed local and which things on the server? ... Are there any good books, tutorials, sites, interesting articles or other questions regarding this? I'm looking for broad answers, but specific ones are fine too to learn the difference.

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• Handling different screen densities in Android Devices?

  - by DevilWithin

  Well, i know there are plenty of different-sized screens in devices that run Android. The SDK I code with deploys to all major desktop platforms and android. I am aware i must have special cares to handle the different screen sizes and densities, but i just had an idea that would work in theory, and my question is exactly about that method, How could it FAIL ? So, what I do is to have an ortho camera of the same size for all devices, with possible tweaks, but anyway that would grant the proper positioning of all elements in all devices, right? We can assume everything is drawn in OpenGLES and input handling is converted to the proper camera coordinates. If you need me to improve the question, please tell me.

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• Resources on learning to program in machine code?

  - by AceofSpades

  I'm a student, fresh into programming and loving it, from Java to C++ and down to C. I moved backwards to the barebones and thought to go further down to Assembly. But, to my surprise, a lot of people said it's not as fast as C and there is no use. They suggested learning either how to program a kernel or writing a C compiler. My dream is to learn to program in binary (machine code) or maybe program bare metal (program micro-controller physically) or write bios or boot loaders or something of that nature. The only possible thing I heard after so much research is that a hex editor is the closest thing to machine language I could find in this age and era. Are there other things I'm unaware of? Are there any resources to learn to program in machine code? Preferably on a 8-bit micro-controller/microprocessor. This question is similar to mine, but I'm interested in practical learning first and then understanding the theory.

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• The Chemistry of Fireworks [Video]

  - by Jason Fitzpatrick

  Fireworks are the dazzling and loud end result of complex chemical process. Watch this video to see the chemistry behind a fireworks display explained by none other than the father of modern pyrotechnics, John Conkling. Courtesy of Bytesize Science: From the sizzle of the fuse to the boom and burst of colors, this video brings you all of the exciting sights and sounds of Fourth of July fireworks, plus a little chemical knowhow. The video features John A. Conkling, Ph.D., who literally wrote the book on fireworks — he is the author of The Chemistry of Pyrotechnics, Basic Principles and Theory. Conkling shows how the familiar rockets and other neat products that light up the night sky all represent chemistry in action. [via Geeks Are Sexy] How to Use an Xbox 360 Controller On Your Windows PC Download the Official How-To Geek Trivia App for Windows 8 How to Banish Duplicate Photos with VisiPic

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• Why aren't there automated translators from one programming language to another?

  - by serg

  Most programming languages are Turing complete, which means that any task that can be solved in one language can be solved in another one, or even on Turing machine. Then why aren't there automatic translators that can convert programs from any given language to any other language? I've seen couple attempts for two languages, but they always work only on a limited subset of a language and can hardly be used for converting real projects. Is it possible, at least in theory, to write 100% correct translator between all languages? What are the challenges in practice? Are there any existing translators that work?

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• What tool do you use to organise your tasks?

  - by Gearóid

  Hi, I've been a web developer for four years now and I've yet to come across a nice piece of software that allows me to manage my day to day tasks well. In theory, I should be able to just pull up a textfile and write: write test scripts check code into svn remember to go home But obviously this isnt very usable. I've tried stuff like Ta-da List but it feels quite limited. JIRA is great for bug tracking but what if I have to remember to go to the bank at 2pm. Is there anything piece of software out there that helps organise programmers? I'm really interested in hearing what you guys have to say on this one. Thanks.

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• I'm having trouble learning

  - by Gavin Sapp

  I'm only 13 but i'm genuinely interested in CS and would really like it if I could actually accomplish it. I've read books on C++ and C#, but ALL of them are the same!! They all say "Ok so since you have no prior knowledge in this what so ever, write a snippet that will do this and then make a GUI and then throw it into the Priafdhsu hfad then add the program and then program your own compiler to do some stuff". It's really getting annoying. I've payed near $40 (via Paypal) on ebooks that supposedly taught people to program with no prior knowledge. ALL OF THEM EXPECT ME TO ALREADY KNOW THE LANGUAGE. Is there something that I'm missing or am I suppose to be born with the property of CS? I would very much appreciate it if someone could explain this to me or possibly refer me to a tutorial on Programming Theory that starts from below ground zero as I have know knowledge in CS at all.

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• Absolute Top Programming Tips [closed]

  - by Eric

  I'm very intersted in the stuff that REALLY makes a critical difference to career in programming, other than intrinsic stuff like how smart your are, where you were born, etc... Some ideas: 1) Best approach to managing small, medium, and large teams. 2) Most important books to read. 3) Most important skills to know. 4) Correct balance of learning theory vs. just writing code. 5) A good approach to estimating time and cost of a project. 6) Etc... Please limit your answers. If you see somebody has already written your idea, please just vote for their response. I'd like to see what the community thinks are the true indicators of a successful career in our field.

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• Retrofit Certification

  - by Bill Evjen

  Impact of Regulations on Cabin Systems Installation John Courtright, Structural Integrity Engineering There are “heightened” FAA attention to technical issues related to IFE and Wi-Fi Systems Installations The Aging Aircraft Safety Rule – EWIS & Damage Tolerance Analysis The Challenge: Maximize Flight Safety While Minimizing Costs Issue Papers & Testing, Testing, Testing The role of Airworthiness Directives (ADs) on the design of many IFE systems and all antenna systems. Goal is safety AND cost-effective maintenance intervals and inspection techniques The STC Process Briefly Stated Type Certifications (TC) Supplemental Type Certifications (STC) The STC Process Project Specific Certification Plan (PSCP) Managed by FAA Aircraft Certification Office (ACO) Type of Project (Electrical/Mechanical Systems or Structural) Specific Type of Aircraft Being Modified Schedule Design & Installation Location What does the STC Plan (PSCP) Cover? System Description – What does the system do? System qualification – Are the components qualified? Certification requirements – What FARs are applicable? Installation detail – what is being modified? Prototype installation – What is new? Functional hazard Assessment (FHA) – is it safe? EZAP-EWIS Requirements – Any aging aircraft issues? Certification Data – How is compliance achieved? Delegation and FAA involvement – Who is doing the work? Proposed certification schedule – When is the installation? Certification documentation – What the FAA Expects to see Cabin Systems Certification Concerns In addition to meeting the requirements for DO-160, Cabin System Certification needs to address issues related to: Power management: Generally, IFE and Wi-Fi Systems are classified as “Non-Essential Equipment” from a certification viewpoint. Connected to “non-essential” power buses Must be able to shed IFE & Wi-Fi Systems in a smoke/fire event or Other electrical emergency (FAA Policy 00-111-160) FAA is more relaxed with testing wi-fi. It used to be that you had to have 150 seats with laptops running wi-fi, but now it is down to around 50. Aging aircraft concerns – electrical and structural Issue papers addressing technical concerns involving: “Structural Certification Criteria for Large Antenna Installations” Antenna “Vibration/Buffeting Compliance Criteria” DO-160 : Environmental Test Procedures DO 160 – “Environmental Conditions and Test Procedures for Airborne Equipment”, Issued by RTCA Provides guidance to equipment manufacturers as to testing requirements Temperature: –40C to +55C Vibration and Shock Contaminant susceptibility – fluids and dust Electro-magnetic Interference Cabin systems are generally classified as “non-essential” Swissair 111 crashed (in part) due to non-standard wiring practices. EWIS Design Implications Installation design must take EWIS Requirements into account. This generally means: Aircraft surveys are needed to identify proper wire routing Ensure existing wiring diagrams are correct Identify primary/Secondary/Tertiary bus locations Verify proper separation of wire bundles exist Required separation from fuel quantity indicator system (FQIS) to prevent fuel tang ignition Enhanced Zonal Analysis Procedure (EZAP) Performed EZAP was developed by the Aging Transport Systems Rulemaking Advisory Committee (ATSRAC) EZAP is the method for analyzing airplane zones with an emphasis on evaluating wiring systems and the existence of combustibles  in the cabin. Certification Considerations for Wi-Fi Systems Electrical – All existing DO 160 testing required Issue papers required Onboard EMI testing – any interference with aircraft systems when multiple wi-fi users are logged on? Vibration/Buffeting compliance criteria – what is the effect of the antenna on aircraft flight characteristics? Structural certification criteria – what are the stress loads on the aircraft at the antenna location and what is the impact on maintenance inspection criteria for the airline? Damage tolerance analysis required Goal – minimize maintenance inspection intervals

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• How should I interpret these DirectX Caps Viewer values?

  - by tobi

  Briefly asking - what do the nodes mean and what the difference is between them in DirectX Caps Viewer? DXGI Devices Direct3D9 Devices DirectDraw Devices The most interesting for me is 1 vs 2. In the Direct3D9 Devices under HAL node I can see that my GeForce 8800GT supports PixelShaderVersion 3.0. However, under DXGI Devices I have DX 10, DX 10.1 and DX 11 having Shader model 4.0 (actually why DX 11? My card is not compatible with DX 11). I am implementing a DX 11 application (including d3d11.h) with shaders compiled in 4.0 version, so I can clearly see that 4.0 is supported. What is the difference between 1 and 2? Could you give me some theory behind the nodes?

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• RemoveHandler Issues with Custom Events

  - by Jeff Certain

  This is a case of things being more complicated that I thought they should be. Since it took a while to figure this one out, I thought it was worth explaining and putting all of the pieces to the answer in one spot. Let me set the stage. Architecturally, I have the notion of generic producers and consumers. These put items onto, and remove items from, a queue. This provides a generic, thread-safe mechanism to load balance the creation and processing of work items in our application. Part of the IProducer(Of T) interface is: 1: Public Interface IProducer(Of T) 2: Event ItemProduced(ByVal sender As IProducer(Of T), ByVal item As T) 3: Event ProductionComplete(ByVal sender As IProducer(Of T)) 4: End Interface Nothing sinister there, is there? In order to simplify our developers’ lives, I wrapped the queue with some functionality to manage the produces and consumers. Since the developer can specify the number of producers and consumers that are spun up, the queue code manages adding event handlers as the producers and consumers are instantiated. Now, we’ve been having some memory leaks and, in order to eliminate the possibility that this was caused by weak references to event handles, I wanted to remove them. This is where it got dicey. My first attempt looked like this: 1: For Each producer As P In Producers 2: RemoveHandler producer.ItemProduced, AddressOf ItemProducedHandler 3: RemoveHandler producer.ProductionComplete, AddressOf ProductionCompleteHandler 4: producer.Dispose() 5: Next What you can’t see in my posted code are the warnings this caused. The 'AddressOf' expression has no effect in this context because the method argument to 'AddressOf' requires a relaxed conversion to the delegate type of the event. Assign the 'AddressOf' expression to a variable, and use the variable to add or remove the method as the handler.  Now, what on earth does that mean? Well, a quick Bing search uncovered a whole bunch of talk about delegates. The first solution I found just changed all parameters in the event handler to Object. Sorry, but no. I used generics precisely because I wanted type safety, not because I wanted to use Object. More searching. Eventually, I found this forum post, where Jeff Shan revealed a missing piece of the puzzle. The other revelation came from Lian_ZA in this post. However, these two only hinted at the solution. Trying some of what they suggested led to finally getting an invalid cast exception that revealed the existence of ItemProducedEventHandler. Hold on a minute! I didn’t create that delegate. There’s nothing even close to that name in my code… except the ItemProduced event in the interface. Could it be? Naaaaah. Hmmm…. Well, as it turns out, there is a delegate created by the compiler for each event. By explicitly creating a delegate that refers to the method in question, implicitly cast to the generated delegate type, I was able to remove the handlers: 1: For Each producer As P In Producers 2: Dim _itemProducedHandler As IProducer(Of T).ItemProducedEventHandler = AddressOf ItemProducedHandler 3: RemoveHandler producer.ItemProduced, _itemProducedHandler 4:  5: Dim _productionCompleteHandler As IProducer(Of T).ProductionCompleteEventHandler = AddressOf ProductionCompleteHandler 6: RemoveHandler producer.ProductionComplete, _productionCompleteHandler 7: producer.Dispose() 8: Next That’s “all” it took to finally be able to remove the event handlers and maintain type-safe code. Hopefully, this will save you the same challenges I had in trying to figure out how to fix this issue!

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• Lean/Kanban *Inside* Software (i.e. WIP-Limits, Reducing Queues and Pull as Programming Techniques)

  - by Christoph

  Thinking about Kanban, I realized that the queuing-theory behind the SW-development-methodology obviously also applies to concurrent software. Now I'm looking for whether this kind of thinking is explicitly applied in some area. A simple example: We usually want to limit the number of threads to avoid cache-thrashing (WIP-Limits). In the paper about the disruptor pattern[1], one statement that I found interesting was that producer/consumers are rarely balanced so when using queues, either consumers wait (queues are empty), or producers produce more than is consumed, resulting in either a full capacity-constrained queue or an unconstrained one blowing up and eating away memory. Both, in lean-speak, is waste, and increases lead-time. Does anybody have examples of WIP-Limits, reducing/eliminating queues, pull or single piece flow being applied in programming? http://disruptor.googlecode.com/files/Disruptor-1.0.pdf

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• Solving a probabilistic problem

  - by ????????????

  So I am interested in Computational Investing and came across this problem on a wiki page: Write a program to discover the answer to this puzzle:"Let's say men and women are paid equally (from the same uniform distribution). If women date randomly and marry the first man with a higher salary, what fraction of the population will get married?" I don't have much knowledge in probability theory, so I'm not really sure how to implement this in code. My thinking: Populate two arrays(female,male) with random salary values from a uniform distribution. Randomly pair one female and one male array element and see if condition of higher salary is met. If it is, increment a counter. Divide counter by population and get percentage. Is this the correct logic? Do woman continually date until there is no males left with higher salaries than women?

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• Is it a good idea to use a formula to balance a game's complexity, in order to keep players in constant flow?

  - by user1107412

  I read a lot about Flow theory and its applications to video games, and I got an idea sticking in my mind. If a number of weight values are applied to different parameters of a certain game level (i.e. the size of the level, the number of enemies, their overal strength, the variance in their behavior, etc), then it should be technically possible to find an overal score mechanism for each level in the game. If a constant ratio of complexity increase were empirically defined, for instance 1,3333, or say, the Golden Ratio, would it be a good idea to arrange the levels in such an order that the increase of overal complexity tends to increase that much? Has somebody tried it?

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• Learn Many Languages

  - by Jeff Foster

  My previous blog, Deliberate Practice, discussed the need for developers to “sharpen their pencil” continually, by setting aside time to learn how to tackle problems in different ways. However, the Sapir-Whorf hypothesis, a contested and somewhat-controversial concept from language theory, seems to hold reasonably true when applied to programming languages. It states that: “The structure of a language affects the ways in which its speakers conceptualize their world.” If you’re constrained by a single programming language, the one that dominates your day job, then you only have the tools of that language at your disposal to think about and solve a problem. For example, if you’ve only ever worked with Java, you would never think of passing a function to a method. A good developer needs to learn many languages. You may never deploy them in production, you may never ship code with them, but by learning a new language, you’ll have new ideas that will transfer to your current “day-job” language. With the abundant choices in programming languages, how does one choose which to learn? Alan Perlis sums it up best. “A language that doesn‘t affect the way you think about programming is not worth knowing“ With that in mind, here’s a selection of languages that I think are worth learning and that have certainly changed the way I think about tackling programming problems. Clojure Clojure is a Lisp-based language running on the Java Virtual Machine. The unique property of Lisp is homoiconicity, which means that a Lisp program is a Lisp data structure, and vice-versa. Since we can treat Lisp programs as Lisp data structures, we can write our code generation in the same style as our code. This gives Lisp a uniquely powerful macro system, and makes it ideal for implementing domain specific languages. Clojure also makes software transactional memory a first-class citizen, giving us a new approach to concurrency and dealing with the problems of shared state. Haskell Haskell is a strongly typed, functional programming language. Haskell’s type system is far richer than C# or Java, and allows us to push more of our application logic to compile-time safety. If it compiles, it usually works! Haskell is also a lazy language – we can work with infinite data structures. For example, in a board game we can generate the complete game tree, even if there are billions of possibilities, because the values are computed only as they are needed. Erlang Erlang is a functional language with a strong emphasis on reliability. Erlang’s approach to concurrency uses message passing instead of shared variables, with strong support from both the language itself and the virtual machine. Processes are extremely lightweight, and garbage collection doesn’t require all processes to be paused at the same time, making it feasible for a single program to use millions of processes at once, all without the mental overhead of managing shared state. The Benefits of Multilingualism By studying new languages, even if you won’t ever get the chance to use them in production, you will find yourself open to new ideas and ways of coding in your main language. For example, studying Haskell has taught me that you can do so much more with types and has changed my programming style in C#. A type represents some state a program should have, and a type should not be able to represent an invalid state. I often find myself refactoring methods like this… void SomeMethod(bool doThis, bool doThat) { if (!(doThis ^ doThat)) throw new ArgumentException(“At least one arg should be true”); if (doThis) DoThis(); if (doThat) DoThat(); } …into a type-based solution, like this: enum Action { DoThis, DoThat, Both }; void SomeMethod(Action action) { if (action == Action.DoThis || action == Action.Both) DoThis(); if (action == Action.DoThat || action == Action.Both) DoThat(); } At this point, I’ve removed the runtime exception in favor of a compile-time check. This is a trivial example, but is just one of many ideas that I’ve taken from one language and implemented in another.

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• Checking form input data on submit with pure PHP [migrated]

  - by Leron

  I have some experience with PHP but I have never even try to do this wit pure PHP, but now a friend of mine asked me to help him with this task so I sat down and write some code. What I'm asking is for opinion if this is the right way to do this when you want to use only PHP and is there anything I can change to make the code better. Besides that I think the code is working at least with the few test I made with it. Here it is: <?php session_start(); // define variables and initialize with empty values $name = $address = $email = ""; $nameErr = $addrErr = $emailErr = ""; $_SESSION["name"] = $_SESSION["address"] = $_SESSION["email"] = ""; $_SESSION["first_page"] = false; if ($_SERVER["REQUEST_METHOD"] == "POST") { if (empty($_POST["name"])) { $nameErr = "Missing"; } else { $_SESSION["name"] = $_POST["name"]; $name = $_POST["name"]; } if (empty($_POST["address"])) { $addrErr = "Missing"; } else { $_SESSION["address"] = $_POST["address"]; $address = $_POST["address"]; } if (empty($_POST["email"])) { $emailErr = "Missing"; } else { $_SESSION["email"] = $_POST["email"]; $email = $_POST["email"]; } } if ($_SESSION["name"] != "" && $_SESSION["address"] != "" && $_SESSION["email"] != "") { $_SESSION["first_page"] = true; header('Location: http://localhost/formProcessing2.php'); //echo $_SESSION["name"]. " " .$_SESSION["address"]. " " .$_SESSION["email"]; } ?> <DCTYPE! html> <head> <style> .error { color: #FF0000; } </style> </head> <body> <form method="POST" action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]);?>"> Name <input type="text" name="name" value="<?php echo htmlspecialchars($name);?>"> <span class="error"><?php echo $nameErr;?></span> <br /> Address <input type="text" name="address" value="<?php echo htmlspecialchars($address);?>"> <span class="error"><?php echo $addrErr;?></span> <br /> Email <input type="text" name="email" value="<?php echo htmlspecialchars($email);?>"> <span class="error"><?php echo $emailErr;?></span> <br /> <input type="submit" name="submit" value="Submit"> </form> </body> </html>

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• Why is Lubuntu default desktop environment

  - by John

  So I just wanted to try things out on 14.04, so I did sudo apt-get install lxde sudo apt-get install lubuntu-desktop When I get to the greeter, it reads Lubuntu (Default) Lubuntu Netbook LXDE Openbox Ubuntu Why is Lubuntu default? I don't know if its because its the last thing I installed or if its because it is in alphabetical order. I'm tempted to test this theory by installing Xubuntu and see if it becomes default. I'd like it to read Ubuntu (Default) and have the Ubuntu splash instead. When I open lightdm.conf, there is no line "user-session" nor "greeter-session". They are missing. Is this normal and I have to add it manually?

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• PHP code works on Chrome, but not on Firefox or IE (send email via HTML form) [on hold]

  - by Cachirro

  My brother has this form: <form id="lista" action="lista2.php" method="post"> <input name="cf_name" type="text" size="50" hidden="yes" class="obscure"> <input name="cf_email" type="text" size="50" hidden="yes" class="obscure"> <textarea name="cf_message" cols="45" rows="10" hidden="yes" class="obscure"> </textarea> <input type="image" name="submit" value="Enviar Lista por Email" src="imagens/lista_email.png" width="40" height="40" onclick="this.form.elements['cf_message'].value = lista_mail;this.form.elements['cf_name'].value = prompt('Escreva o seu nome:', '');this.form.elements['cf_email'].value = prompt('Escreva o seu email:', '');"> <input name="submit2" type="submit" value="Enviar" hidden="yes" class="obscure"> </form> That calls this PHP file: <?php if ( isset($_POST['submit']) ) { // Dados de autenticacao SMTP $smtpinfo['host'] = 'localhost'; $smtpinfo['port'] = '25'; $smtpinfo['auth'] = true; $smtpinfo['username'] = 'xxx'; $smtpinfo['password'] = 'xxx'; // Dados recebidos do formulario $nome = $_POST['cf_name']; $email = $_POST['cf_email']; $mensagem = $_POST['cf_message']; // Inclusão de ficheiro PEAR. Certifique-se que o PEAR está activado no seu alojamento require_once "Mail.php"; // Corpo da mensagem $body = "Nome: ".$nome; $body.= "\n\n"; $body.= nl2br($mensagem); $headers = array ('From' => $email, 'To' => $smtpinfo["username"], 'Subject' => 'Encomenda Website'); $mail_object = Mail::factory('smtp', $smtpinfo); $mail = $mail_object->send($smtpinfo["username"], $headers, $body); if ( PEAR::isError($mail) ) { echo ("<p>" . $mail->getMessage() . "</p>"); } else { echo ('<b><font color="FFFF00">Mensagem enviada com sucesso.<br><br></b>Seu email: ' . $email . '<br><br></font>'); }} ?> This basically sends an email with some selected products, name and email. The problem is that it works perfectly on Chrome, but not on FF or IE. When the submit image is pressed, the URL changes to the PHP file, but it displays a blank page. After display errors activated: ini_set('display_errors',1); ini_set('display_startup_errors',1); error_reporting(-1) FF/IE display blank page and email isn't sent, Chrome sends the email and displays this: Strict Standards: Non-static method Mail::factory() should not be called statically in /var/www/vhosts/[site url]/httpdocs/lista2.php on line 33 Strict Standards: Non-static method PEAR::isError() should not be called statically, assuming $this from incompatible context in /usr/share/php/Mail/smtp.php , dont know if it helps So, what is causing the email to be sent on chrome and not on FF or IE? Thank you.

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