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• What technologies to use for a particle system with enormous calculation demand?

  - by Amir Rezaei

  I have a particle system with X particles. Each particle tests for collision with other particles. This gives X*X = X^2 collision tests per frame. For 60f/s, this corresponds to 60*X^2 collision detection per second. What is the best technological approach for these intensive calculations? Should I use F#, C, C++ or C#, or something else? The following are constraints The code is written in C# with the latest XNA Multi-threaded may be considered No special algorithm that tests the collision with the nearest neighbors or that reduces the problem The last constraint may be strange, so let me explain. Regardless constraint 3, given a problem with enormous computational requirement what would be the best approach to solve the problem. An algorithm reduces the problem; still the same algorithm may behave different depending on technology. Consider pros and cons of CLR vs native C.

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• Getting "too many rows" error inside a "for" cursor loop

  - by Will

  I have a trigger that contains two cursors loops, one nested inside the other like this: FOR outer_rec IN outer_cursor LOOP FOR inner_rec IN inner_cursor LOOP -- Do some calculations END LOOP; END LOOP; Somewhere in this it is throwing the following error: ORA-01422: exact fetch returns more than requested number of rows I've been trying to determine where it's coming from for an hour or so.. but should this error never happen? Also.. I am assuming the inner loop automatically closes and opens itself again every time the outer loop goes the next record, i hope this is correct.

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• problem reading a csv file in python

  - by Hossein

  Hi, I am trying to read a very simple but somehow large(800Mb) csv file using the csv library in python. The delimiter is a single tab and each line consists of some numbers. Each line is a record, and I have 20681 rows in my file. I had some problems during my calculations using this file,it always stops at a certain row. I got suspicious about the number of rows in the file.I used the code below to count the number of row in this file: tfdf_Reader = csv.reader(open('v2-host_tfdf_en.txt'),delimiter=' ') c = 0 for row in tfdf_Reader: c = c + 1 print c To my surprise c is printed with the value of 61722!!! Why is this happening? What am I doing wrong?

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• Is It Worth Using Bitwise Operators In Methods?

  - by user1626141

  I am very new to Java (and programming in general, my previous experience is with ActionScript 2.0 and some simple JavaScript), and I am working my way slowly and methodically through Java: A Beginner's Guide by Herbert Schildt. It is an incredible book. For one thing, I finally understand more-or-less what bitwise operators (which I first encountered in ActionScript 2.0) do, and that they are more efficient than other methods for certain sums. My question is, is it more efficient to use a method that uses, say, a shift right, to perform all your divisions/2 (or divisions/even) for you in a large program with many calculations (in this case, a sprawling RPG), or is it more efficient to simply use standard mathematical operations because the compiler will optimise it all for you? Or, am I asking the wrong question entirely?

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• Are there any well-known algorithms or computer models that computer scientists use to predict FIFA

  - by Khnle

  Occasionally I read news articles that mention about some computer models that computer scientists use to predict winners of some sporting events or the odds for betting which I think there must be a mathematical model behind it. I never bothered to think twice even though I am a "pseudo computer scientist" myself. With the 2010 FIFA World Cup just underway, and since I am also a "pseudo football/soccer player" myself, I just started to wonder about these calculations algorithms. For example, I know one factor is determining the strength of opponents, so that a win against a strong opponent can count more than a win against a weak opponent. But it now kind of gets in a circular loop, or at least how does one determine the strength of a team in the first place, before that team can be considered strong or weak? If it's based on a historical data then there's no way that could be accurate, because those players of the past are no longer on the fields so their impact is none (except maybe if they become coaches like Maradona) Anyway, long question short, if you're happen to be working in this field or have some knowledge, please shed some lights.

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• Forced to use too many hidden fields; looking for an alternative approach

  - by harisri786

  I am looking for a better approach to do this. I have around 70 to 80 hidden fields in my page. This hidden fields are initialized at the server side and then used at the client side for validations, calculations, etc,. using java script. I wanted to know if there is any other alternative approach to using hidden fields in asp.net. I guess, these many hidden fields are increasing the page size and hence affecting the performance of my web page and I want to do away with it. FYI: I am working on an asp.net web application.

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• MySql returning multiple rows from stored procedure / function

  - by pistacchio

  Hi, I need to make a stored procedure or function that returns a set of rows. I've noted that in a stored procedure i can SELECT * FROM table with success. If i fetch rows in a loop and SELECT something, something_other FROM table once per loop execution, I only get one single result. What I need to do is looping, doing some calculations and returning a rowset. What's the best way to do this? A temporary table? Stored functions? Any help appreciated.

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• Javascript: parseInt() with trailing characters

  - by chris_l

  parseInt("7em", 10); returns 7 in all browsers I tested [*]. But can I rely on this? The reason I ask is, that I want to perform some calculations based on em, like /* elem1.style.top uses em units */ elem2.style.top = parseInt(elem1.style.top, 10) + 1 + "em"; I could do this with regular expressions, but parseInt is easier to use, and probably a bit faster. Or is there another solution (maybe using jQuery)? [*] Tested so far on: IE 6, IE 8, Safari 4, Firefox 3.6, Opera 10.5

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• 2D Game: Fast(est) way to find x closest entities for another entity - huge amount of entities, high

  - by Pygmy

  I'm working on a 2D game that has a huge amount of dynamic entities. For fun's sake, let's call them soldiers, and let's say there are 50000 of them (which I just randomly thought up, it might be much more or much less :)). All these soldiers are moving every frame according to rules - think boids / flocking / steering behaviour. For each soldier, to update it's movement I need the X soldiers that are closest to the one I'm processing. What would be the best spatial hierarchy to store them to facilitate calculations like this without too much overhead ? (All entities are updated/moved every frame, so it has to handle dynamic entities very well)

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• How to pass parameters with spaces via cstdlib system

  - by buchtak

  Hi, I have this windows console app which takes a file, do some calculations, and then writes the output to a specified file. The input is specified in "app.exe -input fullfilename" format. I need to call this application from my C++ program, but I have a problem with spaces in paths to files. When I call the app directly from cmd.exe by typing (without specifying output file for clarity) "c:\first path\app.exe" -input "c:\second path\input.file" everything works as expected. But, when I try using cstdlib std::system() function, i.e. std::system(" \"c:\\first path\\app.exe\" -input \"c:\\second path\\input.file\" "); the console prints out that c:\first is not any valid command. It's probably common mistake and has simple solution, but I have been unable to find any. Thx for any help.

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• How to represent datetime of different time zomes in C#

  - by Mohoch

  I have a .NET WebService (written in C#), that is supposed to serve people around the world. With each request I get the user's datetime in his own time zone with the format : yyyy/MM/dd HH:mm ZZZZ. I have to convert the string to something representing the original date and time and specifying the time zone in GMT. I have to make some logical calculations and keep it in the database. The regular DateTime doe's not support this. it does not have a property specifying the time zone. When I try to convert my string into DateTime - it simply converts it to my local time. I do not want to keep my time in UTC, because I have some logic that has to run per user by his own time. Does anyone know a C# class that handles this?

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• How to use GPS data like the double value returned by getLatitude()?

  - by Dan

  I have been searching quite a bit for an answer, but maybe I'm just not using the correct terminology. I am creating an app that will access a database to return a list of other users that are within a certain distance of the users location. I've never worked with this type of data, and I don't really know what the values mean. I'd like to do all the calculations on the backend with either MySQL or PHP. Currently, I am storing the latitude and longitude as doubles within the database. I can access them and store them, but I have no idea how I might be able to sort them based on distance. Perhaps I should be using a different type or some technique that is common in this area. TIA.

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• C# Dispatcher {"The calling thread cannot access this object because a different thread owns it."}

  - by user359446

  Hi, first I need to say that I´m noob with WPF and C#. Application: Create Mandelbrot Image (GUI) My disptacher works perfektly this this case: private void progressBarRefresh(){ while ((con.Progress) < 99) { progressBar1.Dispatcher.Invoke(DispatcherPriority.Send, new Action(delegate { progressBar1.Value = con.Progress; } )); } } I get the Message (Title) when tring to do this with the below code: bmp = BitmapSource.Create(width, height, 96, 96, pf, null, rawImage, stride); this.Dispatcher.Invoke(DispatcherPriority.Send, new Action(delegate { img.Source = bmp; ViewBox.Child = img; //vllt am schluss } )); I will try to explain how my program works. I created a new Thread (because GUI dont response) for the calculation of the pixels and the colors. In this Thread(Mehtod) I´m using the Dispatcher to Refresh my Image in the ViewBox after the calculations are ready. When I´m dont put the calculation in a seperate Thread then I can refresh or build my Image. PS: Sry for my bad english

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• Threading and cores

  - by Matt

  If I have X cores on my machine and I start X threads. Let's assume for the sake of argument that each thread is completely separated in terms of the memory, hdd, etc it uses. Is the OS going to know to send each thread to a core or do more time slicing on one core for multiple threads. What the question boils down to, is if I have X cores and my program must do independent calculations, should I start X threads, will they each get piped to a core, or is the presumption that because I have X cores I can start X threads completely wrong? I'm thinking it is. This is with C# --

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• How to mimic an excel spreadsheet on a website in vb.net?

  - by user1439659

  I am building a website to capture data. I have many spreadsheets that are used for data entry or capture. Now I want to mimic these complex spreadsheets on the web forms but I am unsure of the correct control to use. Data entry must be allowed and live calculations also need to be made similar to formulas on normal excel spreadsheets. Later on the data must be captured into an SQL table. What would be the best control to use or method to mimic that functionality, albeit that the spreadsheet component is no longer available in visual studio 2010. Is it a data grid? Thanks

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• Hosted Continuous Application Monitoring Services

  - by Ian Silber

  Does anybody know of a good service or tool for continuos application monitoring? I'm looking specifically for something that is hosted, so we don't have to worry to much about the fact that the monitoring tool is actually running. Specifically, we have a few e-commerce customers that we would like to provide detailed monitoring services for. We don't want to simply monitor uptime, we'd like to go through the entire checkout process once a day or even more often to ensure everything's working (adding to cart, shipping calculations, payment processing, etc). We've tried site24x7.com but their recording tool just doesn't seem to offer the level of customization we need. Does anybody have any recommendations?

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• SSRS Performance Mystery

  - by user101654

  I have a stored procedure that returns about 50000 records in 10sec using at most 2 cores in SSMS. The SSRS report using the stored procedure was taking 20min and would max out the processor on an 8 core server for the entire time. The report was relatively simple (i.e. no graphs, calculations). The report did not appear to be the issue as I wrote the 50K rows to a temp table and the report could display the data in a few seconds. I tried many different ideas for testing altering the stored procedure each time, but keeping the original code in a separate window to revert back to. After one Alter of the stored procedure, going back to the original code, the report and server utilization started running fast, comparable to the performance of the stored procedure alone. Everything is fine for now, but I am would like to get to the bottom of what caused this in case it happens again. Any ideas?

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• Rotating Viewbox contents smoothly

  - by user204562

  I'm looking to teach myself better methods of doing things in WPF that I would normally do manually. In this case, I have a ViewBox with an image in it. I also have a button that uses a DoubleAnimation to rotate the image 90 to the right. This animation works fine, but obviously because it's square as it turns, the image does a "best fit" to the ViewBox which makes the rotation look quite bad, as it gets larger and smaller as its longest edge shrinks or grows to fit to that particular rotation angle. I am looking for any advice on the best way to handle this using appropriate WPF methods. Obviously I could do all the calculations manually, but I would be more interested in finding a way to use the controls and methods built into the .NET architecture. Thanks for your help.

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• Shortest distance between points on a toroidally wrapped (x- and y- wrapping) map?

  - by mstksg

  I have a toroidal-ish Euclidean-ish map. That is the surface is a flat, Euclidean rectangle, but when a point moves to the right boundary, it will appear at the left boundary (at the same y value), given by x_new = x_old % width Basically, points are plotted based on: (x_new, y_new) = ( x_old % width, y_old % height) Think Pac Man -- walking off one edge of the screen will make you appear on the opposite edge. What's the best way to calculate the shortest distance between two points? The typical implementation suggests a large distance for points on opposite corners of the map, when in reality, the real wrapped distance is very close. The best way I can think of is calculating Classical Delta X and Wrapped Delta X, and Classical Delta Y and Wrapped Delta Y, and using the lower of each pair in the Sqrt(x^2+y^2) distance formula. But that would involve many checks, calculations, operations -- some that I feel might be unnecessary. Is there a better way?

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• C++ for small, individual projects (i.e. hobby programming)

  - by Ygam

  I recently started C++. I am using PHP right now and decided to take a look at C++. Web programming had me working with a couple of languages, with a couple of people. I wanted to do programming where I only had to bother with one language and create small utility apps (mostly not web-based). I wanted a compiled, strongly-type language without memorizing a tome of classes. Basically I wanted to learn C++ for the following: mobile programming (I don't ever want to go touching Java, and I don't have a Mac for Objective C or IPhone SDK) small desktop apps like DTRs, POSs creating small desktop-based games creating small Air-like applications that can access the web for additional content I heard that C++ is not beginner-friendly and is mostly used for huge projects with lots of calculations and fine details (like 3D games). Is it practical or even possible for me to use C++ for the above cases? (Sorry, I haven't delved on C++ that much yet, so aside from "huge, monolithic project", I don't know any other uses for it)

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• Qt: How to force a hidden widget to calculate its layout?

  - by Chris

  What I am trying to do is render a qwidget onto a different window (manually using a QPainter) I have a QWidget (w) with a layout and a bunch of child controls. w is hidden. Until w is shown, there is no layout calculations happening, which is expected. When I call w->render(painter, w->mapToGlobal(QPoint(0,0)), I get a bunch of controls all overlapping each other. w->layout()->activate();w->layout()->update() doesn't seem to do anything. Is there a way to force the layout to happen without showing w?

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• WPF-to stroke arc with two different brushes

  - by user1914725

  i am new to geometric drawing in wpf. i have a volmeter arc that needs to have alert value. The section of the arc beyond that alert value has to be done with a different color than the rest of the arc. hence the arc is brushed with 2 different colors. a path has one brush at a time.hence how i apply two different pens to the same arc? the alert value is obtained with a lot of pain by doing calculations like gemetry.getpointatfraction.it won't easy to apply triggers any suggestions /approach?

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• Are there any real life uses for the Java byte primitive type?

  - by Thorbjørn Ravn Andersen

  For some inexplicable reason the byte primitive type is signed in Java. This mean that valid values are -128..127 instead of the usual 0..255 range representing 8 significant bits in a byte (without a sign bit). This mean that all byte manipulation code usually does integer calculations and end up masking out the last 8 bits. I was wondering if there is any real life scenario where the Java byte primitive type fits perfectly or if it is simply a completely useless design decision? EDIT: The sole actual use case was a single-byte placeholder for native code. In other words, not to be manipulated as a byte inside Java code.

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• How to create a snapshot or clone of PHP, MySQL page... Inspiration needed

  - by jimbo

  Hi, We have a web application that creates a dynamic PHP page with all the MySQL stored details a user has entered via a number a forms. So far so good, but we want this information stored some how to be refereed to at a later date, as an administrator can make changes to the data, which reflects on calculations that are worked out from this saved data. When going back over this saved data we need to be able to see all the information submitted for that particular calculation, so if that data has changed we will see what is was relating to that calculation. Now we have thought about maybe a snapshot when the calculation is done, pdf of the webpage or something similar would do, but is this simple to do? I hope this makes sense...

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• Database that accesses a website.?

  - by Alec

  Hi Guys What application should I use that is able to automatically access a website to gather information? Basically I have a database that completes calculations for me; however I have to manually gather the parameters from a website and input these into my database. What I would like is have an application that will take my input say the name of a product, access the website, add this name into a search box on a website, complete the search and then extract the desired information from the web page returning the results to my application to complete the calculation thus presenting me with the result. This is a little out of my depth but I’m willing to learn no matter how complicated the software. Cheers for your help.

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