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  • Best way to have unique key over 500M varchar(255) records in mysql/innodb?

    - by taw
    I have url column with unique key over it - but its performance on updates is absolutely atrocious. I suspect that's because the index doesn't all fit in memory. So I was thinking, how about adding a column of md5(url) with 16 bytes of binary data and unique-keying that instead. What would be the best datatype for that? I'd love to be able to just see 32-character hex hash, while mysql would convert it to/from 16 binary bytes and index that, as programs using the database might have some troubles with arbitrary binary data that I'd rather avoid if possible (also I'm a bit afraid that mysql might get some strange ideas about character sets and for example overalocating storage for that by 3:1 because it thinks it might need utf8, how do I avoid that for cure?).

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  • Is there a way to set the value of $? in a mock in Ruby?

    - by rleber
    I am testing some scripts that interface with system commands. Their logic depends on the return code of the system commands, i.e. the value of $?. So, as a simplified example, the script might say: def foo(command) output=`#{command}` if $?==0 'succeeded' else 'failed' end end In order to be able to test these methods properly, I would like to be able to stub out the Kernel backquote call, and set $? to an arbitrary value, to see if I get appropriate behavior from the logic in the method after the backquote call. I can't figure out a way to do this. (In case it matters, I'm testing using Test::Unit and Mocha.)

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  • transform file/directory structure into 'tree' in javascript

    - by dave
    I have an array of objects that looks like this: [{ name: 'test', size: 0, type: 'directory', path: '/storage/test' }, { name: 'asdf', size: 170, type: 'directory', path: '/storage/test/asdf' }, { name: '2.txt', size: 0, type: 'file', path: '/storage/test/asdf/2.txt' }] There could be any number of arbitrary path's, this is the result of iterating through files and folders within a directory. What I'm trying to do is determine the 'root' node of these. Ultimately, this will be stored in mongodb and use materialized path to determine it's relationships. In this example, /storage/test is a root with no parent. /storage/test/asdf has the parent of /storage/test which is the parent to /storage/test/asdf/2.txt. My question is, how would you go about iterating through this array, to determine the parent's and associated children? Any help in the right direction would be great! Thank you

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  • How to save an order (permutation) in an sql db

    - by Bendlas
    I have a tree structure in an sql table like so: CREATE TABLE containers ( container_id serial NOT NULL PRIMARY KEY, parent integer REFERENCES containers (container_id)) Now i want to define an ordering between nodes with the same parent. I Have thought of adding a node_index column, to ORDER BY, but that seem suboptimal, since that involves modifying the index of a lot of nodes when modifying the stucture. That could include adding, removing, reordering or moving nodes from some subtree to another. Is there a sql datatype for an ordered sequence, or an efficient way to emulate one? Doesn't need to be fully standard sql, I just need a solution for mssql and hopefully postgresql EDIT To make it clear, the ordering is arbitrary. Actually, the user will be able to drag'n'drop tree nodes in the GUI

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  • Multiple Linked List in C

    - by LuckySlevin
    I have a problem about Linked Lists. I already know how to create structures and linked list. But now I have to create arbitrary number of linked list which are also be kept in another structure. Which means : struct list{int x, struct list *next; }; struct parent{int x, struct list *head, struct parent *next;} And after lists are created when i enter this input for example "123134 linked list should look like : 1 - 2 - 3 - 4 And for example 1 will contain 2-3 list inside of it, 3 will contain 1-4 list inside of it. I need a starting point and a spark from you. So how can i do this?

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  • Extract substructure from a text file using bash or python

    - by Werner
    Hi, I have a huge text file, which follows the structure: SET TAG1 ... ... SET ... SET TAG2 ... ... SET ... ... I would like to extract for a specific TAG, (i.e. TAG54) its individual "substructure", which would be SET TAG54 ... ... SET Each substructure, for a given TAG_i contains always: first line:SET second line:TAG_i (in this case TAG54) an arbitrary number of lines last line:SET I wonder what would be the best way to do this, whether in bash or python, so for a given TAG, one can "extract" this substructure. Thanks

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  • Loop through non-integer rows using SQL

    - by Jesse
    I know how to accomplish my task with .NET, but I wanted to do this just in SQL. I need to loop through all of the rows where the primary key is somewhat arbitrary. It can be a number or a series of letters, and probably any number of unusual things. I know I could do something like this... DECLARE @numRows INT SET @numRows = (SELECT COUNT(pkField) FROM myTable) DECLARE @I INT SET @I = 1 WHILE (@I <= @numRows) BEGIN --Do what I need to here SET @I = @I + 1 END ...if my rows were indexed in a contiguous fashion, but I don't know enough about SQL to do that if they're not. I keep coming across the use of "cursors," but I come across just as much reading about avoiding cursors. I found this SO solution but I'm not sure if that's what I'm needing? I appreciate any ideas.

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  • Why do I have to set the max length of every damn text column in the database?

    - by John Leidegren
    Why is it that every RDBMS insists that you tell it what the max length of a text field is going to be... why can't it just infer this information form the data that's put into the database? I've mostly worked with MS SQL Server, but every other database I know also demands that you set these arbitrary limits on your data schema. The reality is that this is not particulay helpful or friendly to work with becuase the business requirements change all the time and almost every day some end-user is trying to put a lot of text into that column. Does any one with some inner working knowledge of a RDBMS know why we just don't infer the limits from the data that's put into the storage? I'm not talking about guessing the type information, but guessing the limits of a particular text column. I mean, there's a reason why I don't use nvarchar(max) on every text column in the database.

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  • How to schedule hundreds of thousands of tasks?

    - by wehriam
    We have hundreds of thousands of tasks that need to be run at a variety of arbitrary intervals, some every hour, some every day, and so on. The tasks are resource intensive and need to be distributed across many machines. Right now tasks are stored in a database with an "execute at this time" timestamp. To find tasks that need to be executed, we query the database for jobs that are due to be executed, then update the timestamps when the task is complete. Naturally this leads to a substantial write load on the database. As far as I can tell, we are looking for something to release tasks into a queue at a set interval. (Workers could then request tasks from that queue.) What is the best way to schedule recurring tasks at scale? For what it's worth we're largely using Python, although we have no problems using components (RabbitMQ?) written in other languages.

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  • Any ORMs that easily support access to raw table schema?

    - by fizil
    I work with a ASP.NET UI framework that pulls fields for a particular screen off a database. These fields can be associated with particular data fields in another database for binding. The idea with this setup is that if a client needs a new column on a table, they can easily add it, and create a UI field that binds to it without any sort of application restart or recompile. The problem I've always had with this is that it has meant I'm always having to work with untyped datasets in my code. Are there any ORM libraries for .NET out there that could easily accommodate the requirement of being able to access arbitrary columns in the table schema over and above ones mapped to strongly typed fields?

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  • How can I represent URL (possibly including query string) as a filename in Java without obscuring the original URL?

    - by jerluc
    Is there any real way to represent a URL (which more than likely will also have a query string) as a filename in Java without obscuring the original URL completely? My first approach was to simply escape invalid characters with arbitrary replacements (for example, replacing "/" with "_", etc). The problem is, as in the example of replacing with underscores is that a URL such as "app/my_app" would become "app_my_app" thus obscuring the original URL completely. I have also attempted to encode all the special characters, however again, seeing crazy %3e %20 etc is really not clear. Thank you for any suggestions.

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  • How do I find the viewable area of a WPF RichTextBox?

    - by shoe
    I'm working on an app where I have a bunch of text in a RichTextBox. I'm jumping to various positions within the text, (hopping to an arbitrary paragraph for example) which seems to work by send the caret to that position but I can't seem to control where in the viewable area the caret ends up. Sometimes the caret ends up at the top of the RichTextBox and sometimes at the bottom. This would be fine if I was only interested in the line that the caret is on but I'm interested in the entire paragraph.Ideally I'd like to get the caret in the middle of the RichTextBox everytime. Unless the Paragraph is longer than the viewable area. My question. Is there a way to determine the viewable area of a RichTextBox and so do a calculation on how to position the caret properly? If I had that value I can then decided whether to put the caret in the middle (and know where the middle is) or at the top. Thanks for you help.

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  • Parsing a string for dates in PHP

    - by nickf
    Given an arbitrary string, for example ("I'm going to play croquet next Friday" or "Gadzooks, is it 17th June already?"), how would you go about extracting the dates from there? If this is looking like a good candidate for the too-hard basket, perhaps you could suggest an alternative. I want to be able to parse Twitter messages for dates. The tweets I'd be looking at would be ones which users are directing at this service, so they could be coached into using an easier format, however I'd like it to be as transparent as possible. Is there a good middle ground you could think of?

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  • How to implement a tiered "selection tree" in Swing? (Or: is there an existing implementation?)

    - by Sbodd
    I need a Swing component that will let me display a tree-structured list of items, and allow the user to select or de-select an arbitrary subset of those items, with the ability to select or deselect an entire subtree's worth of components by picking that subtree's parent. (Basically, something similar to the Eclipse "Export JAR file's" dialog (an image of the relevant dialog is here - I basically want the "Select resources to export" component, but for a Swing application.) I know I can do this by creating a custom TreeCellRenderer, a custom TreeCellEditor, and a custom TreeModel - but that seems like an awful lot of work. Are there any good off-the-shelf implementations that I can use? Thanks!

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  • You have an error in your SQL syntax; check the manual that corresponds to your MySQL

    - by LuisEValencia
    I am trying to run a mysql query to find all occurences of a text. I have a syntax error but dont know where or how to fix it I am using sqlyog to execute this script DECLARE @url VARCHAR(255) SET @url = '1720' SELECT 'select * from ' + RTRIM(tbl.name) + ' where ' + RTRIM(col.name) + ' like %' + RTRIM(@url) + '%' FROM sysobjects tbl INNER JOIN syscolumns col ON tbl.id = col.id AND col.xtype IN (167, 175, 231, 239) -- (n)char and (n)varchar, there may be others to include AND col.length > 30 -- arbitrary min length into which you might store a URL WHERE tbl.type = 'U' -- user defined table 1 queries executed, 0 success, 1 errors, 0 warnings Query: declare @url varchar(255) set @url = '1720' select 'select * from ' + rtrim(tbl.name) + ' where ' + rtrim(col.name) + ' like %' ... Error Code: 1064 You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'declare @url varchar(255)

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  • Is there a way to write a Python script that creates and executes code?

    - by KaliMa
    Is there a way in Python to create Python code inside the Python script and then execute/test it? My function has the following type of form (as an example) def f(n): if n<=3: return [0, 0, 6, 12][n] return 2*f(n-1) - 4*f(n-2) - 5*f(n-3) + 15*f(n-4) But I want to be able to create these kinds of functions dynamically (or any arbitrary function for that matter) and then test their outputs during runtime (as opposed to copying/pasting this function into the script and then manually testing it). Not sure if this makes sense, please ask for elaboration if needed. I've already looked into eval and exec but couldn't get them to work with entire function definitions, just basic statements like 1+2, etc.

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  • Use of .apply() with 'new' operator. Is this possible?

    - by Premasagar
    In JavaScript, I want to create an object instance (via the new operator), but pass an arbitrary number of arguments to the constructor. Is this possible? What I want to do is something like this (but the code below does not work): function Something(){ // init stuff } function createSomething(){ return new Something.apply(null, arguments); } var s = createSomething(a,b,c); // 's' is an instance of Something The Answer From the responses here, it became clear that there's no in-built way to call .apply() with the new operator. However, people suggested a number of really interesting solutions to the problem. My preferred solution was this one from Matthew Crumley (I've modified it to pass the arguments property): var createSomething = (function() { function F(args) { return Something.apply(this, args); } F.prototype = Something.prototype; return function() { return new F(arguments); } })();

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  • Effectively implementing a game view using java

    - by kdavis8
    I am writing a 2d game in java. The game mechanics are similar to the Pokémon game boy advance series e.g. fire red, ruby, diamond and so on. I need a way to draw a huge map maybe 5000 by 5000 pixels and then load individual in game sprites to across the entirety of the map, like rendering a scene. Game sprites would be things like terrain objects, trees, rocks, bushes, also houses, castles, NPC's and so on. But i also need to implement some kind of camera view class that focuses on the player. the camera view class needs to follow the characters movements throughout the game map but it also needs to clip the rest of the map away from the user's field of view, so that the user can only see the arbitrary proximity adjacent to the player's sprite. The proximity's range could be something like 500 pixels in every direction around the player’s sprite. On top of this, i need to implement an independent resolution for the game world so that the game view will be uniform on all screen sizes and screen resolutions. I know that this does sound like a handful and may fall under the category of multiple questions, but the questions are all related and any advice would be very much appreciated. I don’t need a full source code listing but maybe some pointers to effective java API classes that could make doing what i need to do a lot simpler. Also any algorithmic/ design advice would greatly benefit me as well. example of what i am trying to do in source code form below package myPackage; /** * The Purpose of GameView is to: Render a scene using Scene class, Create a * clipping pane using CameraView class, and finally instantiate a coordinate * grid using Path class. * * Once all of these things have been done, GameView class should then be * instantiated and used jointly with its helper classes. CameraView should be * used as the main drawing image. CameraView is the the window to the game * world.Scene passes data constantly to CameraView so that the entire map flows * smoothly. Path uses the x and y coordinates from camera view to construct * cells for path finding algorithms. */ public class GameView { // Scene is a helper class to game view. it renders the entire map to memory // for the camera view. Scene scene; // Camera View is a helper class to game view. It clips the Scene into a // small image that follows the players coordinates. CameraView Camera; // Path is a helper class to game view. It observes and calculates the // coordinates of camera view and divides them into Grids/Cells for Path // finding. Path path; // this represents the player and has a getSprite() method that will return // the current frame column row combination of the passed sprite sheet. Sprite player; }

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  • The softer side of BPM

    - by [email protected]
    BPM and RTD are great complementary technologies that together provide a much higher benefit than each of them separately. BPM covers the need for automating processes, making sure that there is uniformity, that rules and regulations are complied with and that the process runs smoothly and quickly processes the units flowing through it. By nature, this automation and unification can lead to a stricter, less flexible process. To avoid this problem it is common to encounter process definition that include multiple conditional branches and human input to help direct processing in the direction that best applies to the current situation. This is where RTD comes into play. The selection of branches and conditions and the optimization of decisions is better left in the hands of a system that can measure the results of its decisions in a closed loop fashion and make decisions based on the empirical knowledge accumulated through observing the running of the process.When designing a business process there are key places in which it may be beneficial to introduce RTD decisions. These are:Thresholds - whenever a threshold is used to determine the processing of a unit, there may be an opportunity to make the threshold "softer" by introducing an RTD decision based on predicted results. For example an insurance company process may have a total claim threshold to initiate an investigation. Instead of having that threshold, RTD could be used to help determine what claims to investigate based on the likelihood they are fraudulent, cost of investigation and effect on processing time.Human decisions - sometimes a process will let the human participants make decisions of flow. For example, a call center process may leave the escalation decision to the agent. While this has flexibility, it may produce undesired results and asymetry in customer treatment that is not based on objective functions but subjective reasoning by the agent. Instead, an RTD decision may be introduced to recommend escalation or other kinds of treatments.Content Selection - a process may include the use of messaging with customers. The selection of the most appropriate message to the customer given the content can be optimized with RTD.A/B Testing - a process may have optional paths for which it is not clear what populations they work better for. Rather than making the arbitrary selection or selection by committee of the option deeped the best, RTD can be introduced to dynamically determine the best path for each unit.In summary, RTD can be used to make BPM based process automation more dynamic and adaptable to the different situations encountered in processing. Effectively making the automation softer, less rigid in its processing.

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  • Camera rotation - First Person Camera using GLM

    - by tempvar
    I've just switched from deprecated opengl functions to using shaders and GLM math library and i'm having a few problems setting up my camera rotations (first person camera). I'll show what i've got setup so far. I'm setting up my ViewMatrix using the glm::lookAt function which takes an eye position, target and up vector // arbitrary pos and target values pos = glm::vec3(0.0f, 0.0f, 10.0f); target = glm::vec3(0.0f, 0.0f, 0.0f); up = glm::vec3(0.0f, 1.0f, 0.0f); m_view = glm::lookAt(pos, target, up); i'm using glm::perspective for my projection and the model matrix is just identity m_projection = glm::perspective(m_fov, m_aspectRatio, m_near, m_far); model = glm::mat4(1.0); I send the MVP matrix to my shader to multiply the vertex position glm::mat4 MVP = camera->getProjection() * camera->getView() * model; // in shader gl_Position = MVP * vec4(vertexPos, 1.0); My camera class has standard rotate and translate functions which call glm::rotate and glm::translate respectively void camera::rotate(float amount, glm::vec3 axis) { m_view = glm::rotate(m_view, amount, axis); } void camera::translate(glm::vec3 dir) { m_view = glm::translate(m_view, dir); } and i usually just use the mouse delta position as the amount for rotation Now normally in my previous opengl applications i'd just setup the yaw and pitch angles and have a sin and cos to change the direction vector using (gluLookAt) but i'd like to be able to do this using GLM and matrices. So at the moment i have my camera set 10 units away from the origin facing that direction. I can see my geometry fine, it renders perfectly. When i use my rotation function... camera->rotate(mouseDeltaX, glm::vec3(0, 1, 0)); What i want is for me to look to the right and left (like i would with manipulating the lookAt vector with gluLookAt) but what's happening is It just rotates the model i'm looking at around the origin, like im just doing a full circle around it. Because i've translated my view matrix, shouldn't i need to translate it to the centre, do the rotation then translate back away for it to be rotating around the origin? Also, i've tried using the rotate function around the x axis to get pitch working, but as soon as i rotate the model about 90 degrees, it starts to roll instead of pitch (gimbal lock?). Thanks for your help guys, and if i've not explained it well, basically i'm trying to get a first person camera working with matrix multiplication and rotating my view matrix is just rotating the model around the origin.

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  • VSDB to SSDT part 4 : Redistributable database deployment package with SqlPackage.exe

    - by Etienne Giust
    The goal here is to use SSDT SqlPackage to deploy the output of a Visual Studio 2012 Database project… a bit in the same fashion that was detailed here : http://geekswithblogs.net/80n/archive/2012/09/12/vsdb-to-ssdt-part-3--command-line-deployment-with-sqlpackage.exe.aspx   The difference is we want to do it on an environment where Visual Studio 2012 and SSDT are not installed. This might be the case of your Production server.   Package structure So, to get started you need to create a folder named “DeploymentSSDTRedistributable”. This folder will have the following structure :         The dacpac and dll files are the outputs of your Visual Studio 2012 Database project. If your database project references another database project, you need to put their dacpac and dll here too, otherwise deployment will not work. The publish.xml file is the publish configuration suitable for your target environment. It holds connexion strings, SQLVARS parameters and deployment options. Review it carefully. The SqlDacRuntime folder (an arbitrary chosen name) will hold the SqlPackage executable and supporting libraries   Contents of the SqlDacRuntime folder Here is what you need to put in the SqlDacRuntime folder  :      You will be able to find these files in the following locations, on a machine with Visual Studio 2012 Ultimate installed : C:\Program Files (x86)\Microsoft SQL Server\110\DAC\bin : SqlPackage.exe Microsoft.Data.Tools.Schema.Sql.dll  Microsoft.Data.Tools.Utilities.dll Microsoft.SqlServer.Dac.dll C:\Windows\Microsoft.NET\assembly\GAC_MSIL\Microsoft.SqlServer.TransactSql.ScriptDom\v4.0_11.0.0.0__89845dcd8080cc91 Microsoft.SqlServer.TransactSql.ScriptDom.dll   Deploying   Now take your DeploymentSSDTRedistributable deployment package to your remote machine. In a standard command window, place yourself inside the DeploymentSSDTRedistributable  folder.   You can first perform a check of what will be updated in the target database. The DeployReport task of SqlPackage.exe will help you do that. The following command will output an xml of the changes:   "SqlDacRuntime/SqlPackage.exe" /Action:DeployReport /SourceFile:./Our.Database.dacpac /Profile:./Release.publish.xml /OutputPath:./ChangesToDeploy.xml      You might get some warnings on Log and Data file like I did. You can ignore them. Also, the tool is warning about data loss when removing a column from a table. By default, the publish.xml options will prevent you from deploying when data loss is occuring (see the BlockOnPossibleDataLoss inside the publish.xml file). Before actual deployment, take time to carefully review the changes to be applied in the ChangesToDeploy.xml file.    When you are satisfied, you can deploy your changes with the following command : "SqlDacRuntime/SqlPackage.exe" /Action:Publish /SourceFile:./Our.Database.dacpac /Profile:./Release.publish.xml   Et voilà !  Your dacpac file has been deployed to your database. I’ve been testing this on a SQL 2008 Server (not R2) but it should work on 2005, 2008 R2 and 2012 as well.   Many thanks to Anuj Chaudhary for his article on the subject : http://www.anujchaudhary.com/2012/08/sqlpackageexe-automating-ssdt-deployment.html

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  • Excel Solver vs Solver Foundation

    - by JoshReuben
    I recently read a book http://www.amazon.com/Scientific-Engineering-Cookbook-Cookbooks-OReilly/dp/0596008791/ref=sr_1_1?ie=UTF8&s=books&qid=1296593374&sr=8-1 - the Excel Scientific and Engineering Cookbook.     The 2 main tools that this book leveraged were the Data Analysis Pack and Excel Solver. I had previously been aquanted with Microsoft Solver Foundation - this is a full fledged API for solving optimization problems, and went beyond being a mere Excel plugin - it exposed a C# programmatic interface for in process and a web service interface for out of process integration. were they the same? apparently not!   2 different solver frameworks for Excel: http://www.solver.com/index.html http://www.solverfoundation.com/ I contacted both vendors to get their perspectives.   Heres what the Excel Solver guys had to say:   "The Solver Foundation requires you to learn and use a very specific modeling language (OML). The Excel solver allows you to formulate your optimization problems without learning any new language simply by entering the formulas into cells on the Excel spreadsheet, something that nearly everyone is already familiar with doing.   The Excel Solver also allows you to seamlessly upgrade to products that combine Monte Carlo Simulation capabilities (our Risk Solver Premium and Risk Solver Platform products) which allow you to include uncertainty into your models when appropriate.   Our advanced Excel Solver Products also have a number of built in reporting tools for advanced analysis of the your model and it's results"           And Heres what the Microsoft Solver Foundation guys had to say:   "  With the release of Solver Foundation 3.0, Solver Foundation has the same kinds of solvers (plus a few more) than what is found in Excel Solver. I think there are two main differences:   1.      Problems are described differently. In Excel Solver the goals and constraints are specified inside the spreadsheet, in formulas. In Solver Foundation they are described either in .Net code that uses the Solver Foundation Services API, or using the OML modeling language in Excel. 2.      Solver Foundation’s primary strength is on solving large linear, mixed integer, and constraint models. That is, models that contain arbitrary nonlinear functions (such as trig functions, IF(), powers, etc) are handled a bit better by the Excel Solver at this point. "

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  • Will HTML5 make Silverlight redundant?

    - by Laila
    One of the great features of Adobe AIR v2 that was launched this month was its support for some of the 2008 draft of HTML5. The HTML5 specification was started in 2004, but the full spec will probably not be approved by W3C until around 2022. One might have thought that it would take years yet from now to reach the point where any browsers were remotely HTML5-compliant, but enough of HTML5 is published and agreed to make a lot of it possible, and Safari and Adobe have got there thanks to Apple's open-source WebKit. The race for HTML 5 has been fuelled by the demand by Apple and Google for advanced graphics, typography, animations and transitions without having to rely on third party browser plug-ins such as Adobe Flash or Silverlight. There is good reason for this haste: Flash doesn't support touch-devices and has been slow in supporting hardware video decoders such as H.264. There is a strong requirement to do all that Flash can do in an open-standards way. Those with proprietary solutions remain sniffy. In AIR 2, Adobe pointedly disables the HTML5 and tags that allow basic playing of media content, saying that the specification is not final and there is still no standard for the supported formats, and adding that Safari implements a 'disjoint set' of codecs. Microsoft also has little interest in HTML 5 as it has so much invested in Silverlight. Google stands to gain by the Adobe AIR for Android as it will allow a lot of applications to be migrated easily to the platform, so sees Apple's war on Flash as a way of gaining market share. Why do we care? It is because HTML5/CSS3 provides facilities much far beyond HTML4, bring the reality of browser-based applications a lot closer. Probably most generally useful is the advanced typography: Safari and AIR already both support a way of reflowing text in a container across an arbitrary number of columns; Page-specific fonts can also be specified. Then there is 2D drawing, video, transitions, local storage, AJAX navigation and mutable DOM prototypes. HTML5 is likely to provide base functionality that is required but it is too early to be certain that it will render Flash, Silverlight or JavaFX obsolete. In the meantime, Adobe Air provides the best vehicle for developing HTML5/CSS3 applications without a twinge of worry about browser incompatibilities. Cheers, Laila

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  • Which is the most practical way to add functionality to this piece of code?

    - by Adam Arold
    I'm writing an open source library which handles hexagonal grids. It mainly revolves around the HexagonalGrid and the Hexagon class. There is a HexagonalGridBuilder class which builds the grid which contains Hexagon objects. What I'm trying to achieve is to enable the user to add arbitrary data to each Hexagon. The interface looks like this: public interface Hexagon extends Serializable { // ... other methods not important in this context <T> void setSatelliteData(T data); <T> T getSatelliteData(); } So far so good. I'm writing another class however named HexagonalGridCalculator which adds some fancy pieces of computation to the library like calculating the shortest path between two Hexagons or calculating the line of sight around a Hexagon. My problem is that for those I need the user to supply some data for the Hexagon objects like the cost of passing through a Hexagon, or a boolean flag indicating whether the object is transparent/passable or not. My question is how should I implement this? My first idea was to write an interface like this: public interface HexagonData { void setTransparent(boolean isTransparent); void setPassable(boolean isPassable); void setPassageCost(int cost); } and make the user implement it but then it came to my mind that if I add any other functionality later all code will break for those who are using the old interface. So my next idea is to add annotations like @PassageCost, @IsTransparent and @IsPassable which can be added to fields and when I'm doing the computation I can look for the annotations in the satelliteData supplied by the user. This looks flexible enough if I take into account the possibility of later changes but it uses reflection. I have no benchmark of the costs of using annotations so I'm a bit in the dark here. I think that in 90-95% of the cases the efficiency is not important since most users wont't use a grid where this is significant but I can imagine someone trying to create a grid with a size of 5.000.000.000 X 5.000.000.000. So which path should I start walking on? Or are there some better alternatives? Note: These ideas are not implemented yet so I did not pay too much attention to good names.

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  • How to implement an intelligent enemy in a shoot-em-up?

    - by bummzack
    Imagine a very simple shoot-em-up, something we all know: You're the player (green). Your movement is restricted to the X axis. Our enemy (or enemies) is at the top of the screen, his movement is also restricted to the X axis. The player fires bullets (yellow) at the enemy. I'd like to implement an A.I. for the enemy that should be really good at avoiding the players bullets. My first idea was to divide the screen into discrete sections and assign weights to them: There are two weights: The "bullet-weight" (grey) is the danger imposed by a bullet. The closer the bullet is to the enemy, the higher the "bullet-weight" (0..1, where 1 is highest danger). Lanes without a bullet have a weight of 0. The second weight is the "distance-weight" (lime-green). For every lane I add 0.2 movement cost (this value is kinda arbitrary now and could be tweaked). Then I simply add the weights (white) and go to the lane with the lowest weight (red). But this approach has an obvious flaw, because it can easily miss local minima as the optimal place to go would be simply between two incoming bullets (as denoted with the white arrow). So here's what I'm looking for: Should find a way through bullet-storm, even when there's no place that doesn't impose a threat of a bullet. Enemy can reliably dodge bullets by picking an optimal (or almost optimal) solution. Algorithm should be able to factor in bullet movement speed (as they might move with different velocities). Ways to tweak the algorithm so that different levels of difficulty can be applied (dumb to super-intelligent enemies). Algorithm should allow different goals, as the enemy doesn't only want to evade bullets, he should also be able to shoot the player. That means that positions where the enemy can fire at the player should be preferred when dodging bullets. So how would you tackle this? Contrary to other games of this genre, I'd like to have only a few, but very "skilled" enemies instead of masses of dumb enemies.

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