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  • Can C++ do something like an ML case expression?

    - by Nathan Andrew Mullenax
    So, I've run into this sort of thing a few times in C++ where I'd really like to write something like case (a,b,c,d) of (true, true, _, _ ) => expr | (false, true, _, false) => expr | ... But in C++, I invariably end up with something like this: bool c11 = color1.count(e.first)>0; bool c21 = color2.count(e.first)>0; bool c12 = color1.count(e.second)>0; bool c22 = color2.count(e.second)>0; // no vertex in this edge is colored // requeue if( !(c11||c21||c12||c22) ) { edges.push(e); } // endpoints already same color // failure condition else if( (c11&&c12)||(c21&&c22) ) { results.push_back("NOT BICOLORABLE."); return true; } // nothing to do: nodes are already // colored and different from one another else if( (c11&&c22)||(c21&&c12) ) { } // first is c1, second is not set else if( c11 && !(c12||c22) ) { color2.insert( e.second ); } // first is c2, second is not set else if( c21 && !(c12||c22) ) { color1.insert( e.second ); } // first is not set, second is c1 else if( !(c11||c21) && c12 ) { color2.insert( e.first ); } // first is not set, second is c2 else if( !(c11||c21) && c22 ) { color1.insert( e.first ); } else { std::cout << "Something went wrong.\n"; } I'm wondering if there's any way to clean all of those if's and else's up, as it seems especially error prone. It would be even better if it were possible to get the compiler complain like SML does when a case expression (or statement in C++) isn't exhaustive. I realize this question is a bit vague. Maybe, in sum, how would one represent an exhaustive truth table with an arbitrary number of variables in C++ succinctly? Thanks in advance.

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  • Level of detail algorithm not functioning correctly

    - by Darestium
    I have been working on this problem for months; I have been creating Planet Generator of sorts, after more than 6 months of work I am no closer to finishing it then I was 4 months ago. My problem; The terrain does not subdivide in the correct locations properly, it almost seems as if there is a ghost camera next to me, and the quads subdivide based on the position of this "ghost camera". Here is a video of the broken program: http://www.youtube.com/watch?v=NF_pHeMOju8 The best example of the problem occurs around 0:36. For detail limiting, I am going for a chunked LOD approach, which subdivides the terrain based on how far you are away from it. I use a "depth table" to determine how many subdivisions should take place. void PQuad::construct_depth_table(float distance) { tree[0] = -1; for (int i = 1; i < MAX_DEPTH; i++) { tree[i] = distance; distance /= 2.0f; } } The chuncked LOD relies on the child/parent structure of quads, the depth is determined by a constant e.g: if the constant is 6, there are six levels of detail. The quads which should be drawn go through a distance test from the player to the centre of the quad. void PQuad::get_recursive(glm::vec3 player_pos, std::vector<PQuad*>& out_children) { for (size_t i = 0; i < children.size(); i++) { children[i].get_recursive(player_pos, out_children); } if (this->should_draw(player_pos) || this->depth == 0) { out_children.emplace_back(this); } } bool PQuad::should_draw(glm::vec3 player_position) { float distance = distance3(player_position, centre); if (distance < tree[depth]) { return true; } return false; } The root quad has four children which could be visualized like the following: [] [] [] [] Where each [] is a child. Each child has the same amount of children up until the detail limit, the quads which have are 6 iterations deep are leaf nodes, these nodes have no children. Each node has a corresponding Mesh, each Mesh structure has 16x16 Quad-shapes, each Mesh's Quad-shapes halves in size each detail level deeper - creating more detail. void PQuad::construct_children() { // Calculate the position of the Quad based on the parent's location calculate_position(); if (depth < (int)MAX_DEPTH) { children.reserve((int)NUM_OF_CHILDREN); for (int i = 0; i < (int)NUM_OF_CHILDREN; i++) { children.emplace_back(PQuad(this->face_direction, this->radius)); PQuad *child = &children.back(); child->set_depth(depth + 1); child->set_child_index(i); child->set_parent(this); child->construct_children(); } } else { leaf = true; } } The following function creates the vertices for each quad, I feel that it may play a role in the problem - I just can't determine what is causing the problem. void PQuad::construct_vertices(std::vector<glm::vec3> *vertices, std::vector<Color3> *colors) { vertices->reserve(quad_width * quad_height); for (int y = 0; y < quad_height; y++) { for (int x = 0; x < quad_width; x++) { switch (face_direction) { case YIncreasing: vertices->emplace_back(glm::vec3(position.x + x * element_width, quad_height - 1.0f, -(position.y + y * element_width))); break; case YDecreasing: vertices->emplace_back(glm::vec3(position.x + x * element_width, 0.0f, -(position.y + y * element_width))); break; case XIncreasing: vertices->emplace_back(glm::vec3(quad_width - 1.0f, position.y + y * element_width, -(position.x + x * element_width))); break; case XDecreasing: vertices->emplace_back(glm::vec3(0.0f, position.y + y * element_width, -(position.x + x * element_width))); break; case ZIncreasing: vertices->emplace_back(glm::vec3(position.x + x * element_width, position.y + y * element_width, 0.0f)); break; case ZDecreasing: vertices->emplace_back(glm::vec3(position.x + x * element_width, position.y + y * element_width, -(quad_width - 1.0f))); break; } // Position the bottom, right, front vertex of the cube from being (0,0,0) to (-16, -16, 16) (*vertices)[vertices->size() - 1] -= glm::vec3(quad_width / 2.0f, quad_width / 2.0f, -(quad_width / 2.0f)); colors->emplace_back(Color3(255.0f, 255.0f, 255.0f, false)); } } switch (face_direction) { case YIncreasing: this->centre = glm::vec3(position.x + quad_width / 2.0f, quad_height - 1.0f, -(position.y + quad_height / 2.0f)); break; case YDecreasing: this->centre = glm::vec3(position.x + quad_width / 2.0f, 0.0f, -(position.y + quad_height / 2.0f)); break; case XIncreasing: this->centre = glm::vec3(quad_width - 1.0f, position.y + quad_height / 2.0f, -(position.x + quad_width / 2.0f)); break; case XDecreasing: this->centre = glm::vec3(0.0f, position.y + quad_height / 2.0f, -(position.x + quad_width / 2.0f)); break; case ZIncreasing: this->centre = glm::vec3(position.x + quad_width / 2.0f, position.y + quad_height / 2.0f, 0.0f); break; case ZDecreasing: this->centre = glm::vec3(position.x + quad_width / 2.0f, position.y + quad_height / 2.0f, -(quad_height - 1.0f)); break; } this->centre -= glm::vec3(quad_width / 2.0f, quad_width / 2.0f, -(quad_width / 2.0f)); } Any help in discovering what is causing this "subdivding in the wrong place" would be greatly appreciated.

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  • Doing Master'S at Home.

    - by Demla Pawan
    I mean,as I'm a computer science student at present,soon I'm going to get job at somewhere,But I wish to go for higher studies in MS,My interests are automation of things using web app's, and I wish to research in AI,as I think it may resolve most of ours present problem's. So,I'm thinking of, is there anyway to do MS like studies and research in organised manner at home only, as a part-time research work,bcoz I like learn new things anytime. So,Finally can you tell me what's the pattern of MS studies and which MS field suits me, as I'm interested in web and Mobility solution like mobiles. and along with that is there a correspondence MS possible,from where.

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  • How should I structure my turn based engine to allow flexibility for players/AI and observation?

    - by Reefpirate
    I've just started making a Turn Based Strategy engine in GameMaker's GML language... And I was cruising along nicely until it came time to handle the turn cycle, and determining who is controlling what player, and also how to handle the camera and what is displayed on screen. Here's an outline of the main switch happening in my main game loop at the moment: switch (GameState) { case BEGIN_TURN: // Start of turn operations/routines break; case MID_TURN: switch (PControlledBy[Turn]) { case HUMAN: switch (MidTurnState) { case MT_SELECT: // No units selected, 'idle' UI state break; case MT_MOVE: // Unit selected and attempting to move break; case MT_ATTACK: break; } break; case COMPUTER: // AI ROUTINES GO HERE break; case OBSERVER: // OBSERVER ROUTINES GO HERE break; } break; case END_TURN: // End of turn routines/operations, and move Turn to next player break; } Now, I can see a couple of problems with this set-up already... But I don't have any idea how to go about making it 'right'. Turn is a global variable that stores which player's turn it is, and the BEGIN_TURN and END_TURN states make perfect sense to me... But the MID_TURN state is baffling me because of the things I want to happen here: If there are players controlled by humans, I want the AI to do it's thing on its turn here, but I want to be able to have the camera follow the AI as it makes moves in the human player's vision. If there are no human controlled player's, I'd like to be able to watch two or more AI's battle it out on the map with god-like 'observer' vision. So basically I'm wondering if there are any resources for how to structure a Turn Based Strategy engine? I've found lots of writing about pathfinding and AI, and those are all great... But when it comes to handling the turn structure and the game states I am having trouble finding any resources at all. How should the states be divided to allow flexibility between the players and the controllers (HUMAN, COMPUTER, OBSERVER)? Also, maybe if I'm on the right track I just need some reassurance before I lay down another few hundred lines of code...

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  • Doing Master's at Home

    - by parmanand
    I'm a computer science student at present, soon I'm going to get job at somewhere. But I wish to go for higher studies in MS. My interests are automation of things using web apps, and I wish to research in AI, as I think it may resolve most of ours present problem's. Is there any way to do MS like studies and research in organised manner at home only, as a part-time research work? Because I like to learn new things anytime. Finally can you tell me what's the pattern of MS studies and which MS field suits me, as I'm interested in web and Mobility solution like mobiles. And along with that is a correspondence MS possible and if so, from where?

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  • Enum types, FlagsAttribute & Zero value – Part 2

    - by nmgomes
    In my previous post I wrote about why you should pay attention when using enum value Zero. After reading that post you are probably thinking like Benjamin Roux: Why don’t you start the enum values at 0x1? Well I could, but doing that I lose the ability to have Sync and Async mutually exclusive by design. Take a look at the following enum types: [Flags] public enum OperationMode1 { Async = 0x1, Sync = 0x2, Parent = 0x4 } [Flags] public enum OperationMode2 { Async = 0x0, Sync = 0x1, Parent = 0x2 } To achieve mutually exclusion between Sync and Async values using OperationMode1 you would have to operate both values: protected void CheckMainOperarionMode(OperationMode1 mode) { switch (mode) { case (OperationMode1.Async | OperationMode1.Sync | OperationMode1.Parent): case (OperationMode1.Async | OperationMode1.Sync): throw new InvalidOperationException("Cannot be Sync and Async simultaneous"); break; case (OperationMode1.Async | OperationMode1.Parent): case (OperationMode1.Async): break; case (OperationMode1.Sync | OperationMode1.Parent): case (OperationMode1.Sync): break; default: throw new InvalidOperationException("No default mode specified"); } } but this is a by design constraint in OperationMode2. Why? Simply because 0x0 is the neutral element for the bitwise OR operation. Knowing this singularity, replacing and simplifying the previous method, you get: protected void CheckMainOperarionMode(OperationMode2 mode) { switch (mode) { case (OperationMode2.Sync | OperationMode2.Parent): case (OperationMode2.Sync): break; case (OperationMode2.Parent): default: break; } This means that: if both Sync and Async values are specified Sync value always win (Zero is the neutral element for bitwise OR operation) if no Sync value specified, the Async method is used. Here is the final method implementation: protected void CheckMainOperarionMode(OperationMode2 mode) { if (mode & OperationMode2.Sync == OperationMode2.Sync) { } else { } } All content above prove that Async value (0x0) is useless from the arithmetic perspective, but, without it we lose readability. The following IF statements are logically equals but the first is definitely more readable: if (OperationMode2.Async | OperationMode2.Parent) { } if (OperationMode2.Parent) { } Here’s another example where you can see the benefits of 0x0 value, the default value can be used explicitly. <my:Control runat="server" Mode="Async,Parent"> <my:Control runat="server" Mode="Parent">

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  • Would you see any use of a Trilean (True, False, ??)

    - by Sybiam
    I don't know if I'm alone but sometimes I have a function that should return true or false. But in some case there would be a third result that would make more sense. In some language theses cases would be handled with integers or with exception. For exemple you want to handle the age of a user if he is over 18 years old. And you have a function like this. if(user.isAdult(country_code)){ //Go On }else{ // Block access or do nothing } But in some case depending how your app is built I could see case where the birthday field is incomplete. Then this function should return something undetermined. switch(user.isAdult()){ case true: // go on break; case undetermined: //Inform user birthday is incomplete case false: //Block access } As i said we can handle that with Exceptions and Int, but I would find it quite sexy to have a true, false, undetermined embeded in the language instead of using some home defined constants.

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  • Changing the background color of a view in real-time.

    - by Tarmon
    Hey Everyone, I am trying to implement a ListView that is composed of rows that contain a View on the left followed by a TextView to the right of that. I want to be able to change the background color of the first View based on it's position in the ListView. Below is what I have at this point but it doesn't seem to due anything. public class Routes extends ListActivity { String[] ROUTES; TextView selection; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); ROUTES = getResources().getStringArray(R.array.routes); setContentView(R.layout.routes); setListAdapter(new IconicAdapter()); selection=(TextView)findViewById(R.id.selection); } public void onListItemClick(ListView parent, View v, int position, long id) { selection.setText(ROUTES[position]); } class IconicAdapter extends ArrayAdapter<String> { IconicAdapter() { super(Routes.this, R.layout.row, R.id.label, ROUTES); } } public View getView(int position, View convertView, ViewGroup parent) { LayoutInflater inflater = getLayoutInflater(); View row = inflater.inflate(R.layout.row, parent, false); TextView label = (TextView) row.findViewById(R.id.label); label.setText(ROUTES[position]); View icon = (View) row.findViewById(R.id.icon); switch(position){ case 0: icon.setBackgroundColor(R.color.Red); break; case 1: icon.setBackgroundColor(R.color.Red); break; case 2: icon.setBackgroundColor(R.color.Green); break; case 3: icon.setBackgroundColor(R.color.Green); break; case 4: icon.setBackgroundColor(R.color.Blue); break; case 5: icon.setBackgroundColor(R.color.Blue); break; case 6: icon.setBackgroundColor(R.color.Gray); break; case 7: icon.setBackgroundColor(R.color.Yellow); break; case 8: icon.setBackgroundColor(R.color.Brown); break; case 9: icon.setBackgroundColor(R.color.Brown); break; case 10: icon.setBackgroundColor(R.color.Brown); break; case 11: icon.setBackgroundColor(R.color.Purple); break; case 12: icon.setBackgroundColor(R.color.Red); break; case 13: icon.setBackgroundColor(R.color.Gold); break; case 14: icon.setBackgroundColor(R.color.Orange); break; } return(row); } } Any input is appreciated and if you have any questions don't hesitate to ask! Thanks, Rob

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  • How can I modify my Shunting-Yard Algorithm so it accepts unary operators?

    - by KingNestor
    I've been working on implementing the Shunting-Yard Algorithm in JavaScript for class. Here is my work so far: var userInput = prompt("Enter in a mathematical expression:"); var postFix = InfixToPostfix(userInput); var result = EvaluateExpression(postFix); document.write("Infix: " + userInput + "<br/>"); document.write("Postfix (RPN): " + postFix + "<br/>"); document.write("Result: " + result + "<br/>"); function EvaluateExpression(expression) { var tokens = expression.split(/([0-9]+|[*+-\/()])/); var evalStack = []; while (tokens.length != 0) { var currentToken = tokens.shift(); if (isNumber(currentToken)) { evalStack.push(currentToken); } else if (isOperator(currentToken)) { var operand1 = evalStack.pop(); var operand2 = evalStack.pop(); var result = PerformOperation(parseInt(operand1), parseInt(operand2), currentToken); evalStack.push(result); } } return evalStack.pop(); } function PerformOperation(operand1, operand2, operator) { switch(operator) { case '+': return operand1 + operand2; case '-': return operand1 - operand2; case '*': return operand1 * operand2; case '/': return operand1 / operand2; default: return; } } function InfixToPostfix(expression) { var tokens = expression.split(/([0-9]+|[*+-\/()])/); var outputQueue = []; var operatorStack = []; while (tokens.length != 0) { var currentToken = tokens.shift(); if (isNumber(currentToken)) { outputQueue.push(currentToken); } else if (isOperator(currentToken)) { while ((getAssociativity(currentToken) == 'left' && getPrecedence(currentToken) <= getPrecedence(operatorStack[operatorStack.length-1])) || (getAssociativity(currentToken) == 'right' && getPrecedence(currentToken) < getPrecedence(operatorStack[operatorStack.length-1]))) { outputQueue.push(operatorStack.pop()) } operatorStack.push(currentToken); } else if (currentToken == '(') { operatorStack.push(currentToken); } else if (currentToken == ')') { while (operatorStack[operatorStack.length-1] != '(') { if (operatorStack.length == 0) throw("Parenthesis balancing error! Shame on you!"); outputQueue.push(operatorStack.pop()); } operatorStack.pop(); } } while (operatorStack.length != 0) { if (!operatorStack[operatorStack.length-1].match(/([()])/)) outputQueue.push(operatorStack.pop()); else throw("Parenthesis balancing error! Shame on you!"); } return outputQueue.join(" "); } function isOperator(token) { if (!token.match(/([*+-\/])/)) return false; else return true; } function isNumber(token) { if (!token.match(/([0-9]+)/)) return false; else return true; } function getPrecedence(token) { switch (token) { case '^': return 9; case '*': case '/': case '%': return 8; case '+': case '-': return 6; default: return -1; } } function getAssociativity(token) { switch(token) { case '+': case '-': case '*': case '/': return 'left'; case '^': return 'right'; } } It works fine so far. If I give it: ((5+3) * 8) It will output: Infix: ((5+3) * 8) Postfix (RPN): 5 3 + 8 * Result: 64 However, I'm struggling with implementing the unary operators so I could do something like: ((-5+3) * 8) What would be the best way to implement unary operators (negation, etc)? Also, does anyone have any suggestions for handling floating point numbers as well? One last thing, if anyone sees me doing anything weird in JavaScript let me know. This is my first JavaScript program and I'm not used to it yet.

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  • How do I mock an object in this case? no obvious way to replace object with mock

    - by Tristan
    Hi there, Suppose I have this very simple method in Store's model: def geocode_address loc = Store.geocode(address) self.lat = loc.lat self.lng = loc.lng end If I want to write some test scripts that aren't affected by the geocoding service, which may be down, have limitations or depend on my internet connection, how do I mock out the geocoding service? If I could pass a geocoding object into the method, it would be easy, but I don't see how I could do it in this case. Thanks! Tristan

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  • Is it possible for BeautifulSoup to work in a case-insensitive manner?

    - by Nitin
    I am trying to extract Meta Description for fetched webpages. But here I am facing the problem of case sensitivity of BeautifulSoup. As some of the pages have <meta name="Description and some have <meta name="description. My problem is very much similar to that of Question on Stackoverflow The only difference is that I can't use lxml .. I have to stick with Beautifulsoup.

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  • Scala: is it possible to override default case class constructor?

    - by adam77
    Just wondering if this is possible. What I would actually like to do is check and possibly modify one of the arguments before it is stored as a val. Alternatively, I could use an overload and make the default constructor private. In which case I would also like to make private the default factory constructor in the companion object, how would I do that? Many thanks. Adam

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  • How do you search between two columns using a parameter and a case when statement? SQL Server

    - by Kip Birgen
    I would like to search between to columns in a s query or a table depending on the variable on a paramenter e.g Declare @SelectAll as interger Set @SelectAll = 1 Declare @Column as interger Select mt.Column1, mtColumn2 From MyTable as mt Where Case When @SelectAll = 1 Then mt.Column1 IN(@Column) and mt.Column2 (' Selecting all") When @SelectAll = 1 Then mt.Column2 IN(@Column) and mt.Column1 (' Selecting all") End The purpose of this query is to allow the user to search between the column they choose. Further more the use of parameter is for the purposes of writing reporting services reports.

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  • How to give sentence case to sentences through CSS or javascript?

    - by jitendra
    How to give sentence case to sentences through CSS or javascript? I've tried these CSS properties but these are different capitalize Transforms the first character of each word to uppercase uppercase Transforms all characters to uppercase lowercase Transforms all characters to lowercase Edit: 19 FEB 2010 is there any option in jquery to achieve this?

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  • 'Attempt to call private method' error when trying to change change case of db entires in migration

    - by Senthil
    class AddTitleToPosts < ActiveRecord::Migration def self.up add_column :posts, :title, :string Post.find(:all).each do |post| post.update(:title => post.name.upcase) end end def self.down end end Like you can nothing particularly complicated, just trying to add new column title by changing case of name column already in db. But I get attempt to call private method error. I'm guessing it has something to do with 'self'? Thanks for your help.

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  • facebook .net and mvc - Unrecognized attribute 'ApiKey'. Note that attribute names are case-sensitive

    - by vondip
    Hi all, I'm trying to build a small fb application using asp.net mvc 2, and facebook C# .net From some reason, the code from the sample application doesn't seem to work for me. Here's the exception I am receiving from my web.config file. Unrecognized attribute 'apiKey'. Note that attribute names are case-sensitive. Source Error: <facebookSettings apiKey="XXXX" apiSecret="XXXX" appId="XXXX" /> Any ideas?

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  • Is there an use case for non-blocking receive when I have threads?

    - by Gabriel Šcerbák
    I know non-blocking receive is not used as much in message passing, but still some intuition tells me, it is needed. Take for example GUI event driven applications, you need some way to wait for a message in a non-blocking way, so your program can execute some computations. One of the ways to solve this is to have a special thread with message queue. Is there some use case, where you would really need non-blocking receive even if you have threads?

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  • How can I recreate a SQL statement using NHibernate that has an inner select case?

    - by brianberns
    I am trying to recreate something like the following SQL using NHibernate criteria: select Range, count(*) from ( select case when ent.ID between 'A' and 'N' then 'A-M' else 'Other' end as Range from Subject ) tbl group by tbl.Range I am able to create the inner select as follows: session.CreateCriteria<Subject>() .SetProjection( Projections.Conditional( Expression.Between("Name", "A", "N"), Projections.Constant("A-M"), Projections.Constant("Other"))) .List(); However, I can't figure out how to pipe those results into a grouping by row count.

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  • How to prove worst-case number of inversions in a heap is O(nlogn)?

    - by Jacques
    I am busy preparing for exams, just doing some old exam papers. The question below is the only one I can't seem to do (I don't really know where to start). Any help would be appreciated greatly. Use the O(nlogn) comparison sort bound, the theta(n) bound for bottom-up heap construction, and the order complexity if insertion sort to show that the worst-case number of inversions in a heap is O(nlogn).

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