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• Which programming language to choose? (for a specific problem/domain, details inside)

  - by Bijan

  I am building a trading portfolio management system that is responsible for production, optimization, and simulation of non-high frequency trading portfolios (dealing with 1min or 3min bars of data, not tick data). I plan on employing Amazon web services to take on the entire load of the application. I have four choices that I am considering as language. a) Java b) C++ c) C# d) Python Here is the scope of the extremes of the project scope. This isn't how it will be, maybe ever, but it's within the scope of the requirements: Weekly simulation of 10,000,000 trading systems. (Each trading system is expected to have its own data mining methods, including feature selection algorithms which are extremely computationally-expensive. Imagine 500-5000 features using wrappers. These are not run often by any means, but it's still a consideration) Real-time production of portfolio w/ 100,000 trading strategies Taking in 1 min or 3 min data from every stock/futures market around the globe (approx 100,000) Portfolio optimization of portfolios with up to 100,000 strategies. (rather intensive algorithm) Speed is a concern, but I believe that Java can handle the load. I just want to make sure that Java CAN handle the above requirements comfortably. I don't want to do the project in C++, but I will if it's required. The reason C# is on there is because I thought it was a good alternative to Java, even though I don't like Windows at all and would prefer Java if all things are the same. Python - I've read somethings on PyPy and pyscho that claim python can be optimized with JIT compiling to run at near C-like speeds.... That's pretty much the only reason it is on this list, besides that fact that Python is a great language and would probably be the most enjoyable language to code in, which is not a factor at all for this project, but a perk. To sum up: - real time production - weekly simulations of a large number of systems - weekly/monthly optimizations of portfolios - large numbers of connections to collect data from There is no dealing with millisecond or even second based trades. The only consideration is if Java can possibly deal with this kind of load when spread out of a necessary amount of EC2 servers. Thank you guys so much for your wisdom.

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• Performance of looping over an Unboxed array in Haskell

  - by Joey Adams

  First of all, it's great. However, I came across a situation where my benchmarks turned up weird results. I am new to Haskell, and this is first time I've gotten my hands dirty with mutable arrays and Monads. The code below is based on this example. I wrote a generic monadic for function that takes numbers and a step function rather than a range (like forM_ does). I compared using my generic for function (Loop A) against embedding an equivalent recursive function (Loop B). Having Loop A is noticeably faster than having Loop B. Weirder, having both Loop A and B together is faster than having Loop B by itself (but slightly slower than Loop A by itself). Some possible explanations I can think of for the discrepancies. Note that these are just guesses: Something I haven't learned yet about how Haskell extracts results from monadic functions. Loop B faults the array in a less cache efficient manner than Loop A. Why? I made a dumb mistake; Loop A and Loop B are actually different. Note that in all 3 cases of having either or both Loop A and Loop B, the program produces the same output. Here is the code. I tested it with ghc -O2 for.hs using GHC version 6.10.4 . import Control.Monad import Control.Monad.ST import Data.Array.IArray import Data.Array.MArray import Data.Array.ST import Data.Array.Unboxed for :: (Num a, Ord a, Monad m) => a -> a -> (a -> a) -> (a -> m b) -> m () for start end step f = loop start where loop i | i <= end = do f i loop (step i) | otherwise = return () primesToNA :: Int -> UArray Int Bool primesToNA n = runSTUArray $ do a <- newArray (2,n) True :: ST s (STUArray s Int Bool) let sr = floor . (sqrt::Double->Double) . fromIntegral $ n+1 -- Loop A for 4 n (+ 2) $ \j -> writeArray a j False -- Loop B let f i | i <= n = do writeArray a i False f (i+2) | otherwise = return () in f 4 forM_ [3,5..sr] $ \i -> do si <- readArray a i when si $ forM_ [i*i,i*i+i+i..n] $ \j -> writeArray a j False return a primesTo :: Int -> [Int] primesTo n = [i | (i,p) <- assocs . primesToNA $ n, p] main = print $ primesTo 30000000

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• Need Help with Consolidating RoR Google Map Results

  - by Kevin

  I have a project that returns geocoded results within 20 miles of the user. I want these results grouped on the map by zip code, then within the info window show the individual results. The code posted below works, but for some reason it only displays the 1.png rather than looking at the results and using the correct .png icon associated with the number. When I look at the infowindows, it displays the correct png like "/images/2.png" or "/images/5.png" but the actual image is always 1. @ziptickets = Ticket.find(:all, :origin => coords, :select => 'DISTINCT zip, lat, lng', :within => @user.distance_to_travel, :conditions => "status_id = 1") for t in @ziptickets zips = Ticket.find(:all, :conditions => ["zip = ?", t.zip]) currentzip = t.zip.to_s tixinzip = zips.size.to_s imagelocation = "/images/" + tixinzip + ".png" shadowlocation = "/images/" + tixinzip + "s.png" @map.icon_global_init(GIcon.new(:image => imagelocation, :shadow => shadowlocation, :shadow_size => GSize.new(60,40), :icon_anchor => GPoint.new(20,20), :info_window_anchor => GPoint.new(9,2)), "test") newicon = Variable.new("test") new_marker = GMarker.new([t.lat, t.lng], :icon => newicon, :title => imagelocation, :info_window => currentzip) @map.overlay_init(new_marker) end I tried changing the last part of the mapicon from: :info_window_anchor => GPoint.new(9,2)), "test") newicon = Variable.new("test") to: :info_window_anchor => GPoint.new(9,2)), currentzip) newicon = Variable.new(currentzip) but the strangest thing is that any string that has numbers in it causes the map to fail to render in the view and just show a blank screen... same if I replace it with :info_window_anchor => GPoint.new(9,2)), "123") newicon = Variable.new("123") Any advice would be helpful... also it runs a bit slower than my previous code which just set up 4 standard icons and used them outside of the loop so any hints as to speed up execution would be appreciated greatly. Thanks!

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• ArithmeticException thrown during BigDecimal.divide

  - by polygenelubricants

  I thought java.math.BigDecimal is supposed to be The Answer™ to the need of performing infinite precision arithmetic with decimal numbers. Consider the following snippet: import java.math.BigDecimal; //... final BigDecimal one = BigDecimal.ONE; final BigDecimal three = BigDecimal.valueOf(3); final BigDecimal third = one.divide(three); assert third.multiply(three).equals(one); // this should pass, right? I expect the assert to pass, but in fact the execution doesn't even get there: one.divide(three) causes ArithmeticException to be thrown! Exception in thread "main" java.lang.ArithmeticException: Non-terminating decimal expansion; no exact representable decimal result. at java.math.BigDecimal.divide It turns out that this behavior is explicitly documented in the API: In the case of divide, the exact quotient could have an infinitely long decimal expansion; for example, 1 divided by 3. If the quotient has a non-terminating decimal expansion and the operation is specified to return an exact result, an ArithmeticException is thrown. Otherwise, the exact result of the division is returned, as done for other operations. Browsing around the API further, one finds that in fact there are various overloads of divide that performs inexact division, i.e.: final BigDecimal third = one.divide(three, 33, RoundingMode.DOWN); System.out.println(three.multiply(third)); // prints "0.999999999999999999999999999999999" Of course, the obvious question now is "What's the point???". I thought BigDecimal is the solution when we need exact arithmetic, e.g. for financial calculations. If we can't even divide exactly, then how useful can this be? Does it actually serve a general purpose, or is it only useful in a very niche application where you fortunately just don't need to divide at all? If this is not the right answer, what CAN we use for exact division in financial calculation? (I mean, I don't have a finance major, but they still use division, right???).

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• c++ quick sort running time

  - by chnet

  I have a question about quick sort algorithm. I implement quick sort algorithm and play it. The elements in initial unsorted array are random numbers chosen from certain range. I find the range of random number effects the running time. For example, the running time for 1, 000, 000 random number chosen from the range (1 - 2000) takes 40 seconds. While it takes 9 seconds if the 1,000,000 number chosen from the range (1 - 10,000). But I do not know how to explain it. In class, we talk about the pivot value can effect the depth of recursion tree. For my implementation, the last value of the array is chosen as pivot value. I do not use randomized scheme to select pivot value. int partition( vector<int> &vec, int p, int r) { int x = vec[r]; int i = (p-1); int j = p; while(1) { if (vec[j] <= x){ i = (i+1); int temp = vec[j]; vec[j] = vec[i]; vec[i] = temp; } j=j+1; if (j==r) break; } int temp = vec[i+1]; vec[i+1] = vec[r]; vec[r] = temp; return i+1; } void quicksort ( vector<int> &vec, int p, int r) { if (p<r){ int q = partition(vec, p, r); quicksort(vec, p, q-1); quicksort(vec, q+1, r); } } void random_generator(int num, int * array) { srand((unsigned)time(0)); int random_integer; for(int index=0; index< num; index++){ random_integer = (rand()%10000)+1; *(array+index) = random_integer; } } int main() { int array_size = 1000000; int input_array[array_size]; random_generator(array_size, input_array); vector<int> vec(input_array, input_array+array_size); clock_t t1, t2; t1 = clock(); quicksort(vec, 0, (array_size - 1)); // call quick sort int length = vec.size(); t2 = clock(); float diff = ((float)t2 - (float)t1); cout << diff << endl; cout << diff/CLOCKS_PER_SEC <<endl; }

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• An AuthLogic form is giving me incorrect validation errors -- why?

  - by sscirrus

  Hi everyone, I set up AuthLogic for Rails according to the AuthLogic example: http://github.com/binarylogic/authlogic_example. I can log on successfully to the system, but when accessing users/new.html.erb to register a new user, the form returns the following validation errors: Email is too short (minimum is 6 characters) Email should look like an email address. Login is too short (minimum is 3 characters) Login should use only letters, numbers, spaces, and .-_@ please. Password is too short (minimum is 4 characters) Password confirmation is too short (minimum is 4 characters) None of these errors exist in the data I am entering. # new.html.erb <%= form.label :login, nil, :class => "label" %><br /> <%= form.text_field :login, :class => "inputBox", :name => "login", :type => "text" %><br /> <%= form.label :password, form.object.new_record? ? nil : "Change password", :class => "label" %><br /> <%= form.password_field :password, :class => "inputBox", :name => "password", :type => "text" %><br /> <%= form.label "Confirm password", nil, :class => "label" %><br /> <%= form.password_field :password_confirmation, :class => "inputBox", :name => "password_confirmation", :type => "text" %><br /> <%= form.label :email, nil, :class => "label" %><br /> <%= form.text_field :email, :class => "inputBox", :name => "email", :type => "text" %><br /> # Users controller def new @user = User.new render :layout => "forms" end I think the problem is that the data isn't being transferred somehow and therefore AuthLogic doesn't think the inputs are sufficient. Do you have any idea why AuthLogic is telling me the data doesn't satisfy its validation?

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• How do I get the next token in a Cstring if I want to use it as an int? (c++)

  - by Van

  My objective is to take directions from a user and eventually a text file to move a robot. The catch is that I must use Cstrings(such as char word[];) rather than the std::string and tokenize them for use. the code looks like this: void Navigator::manualDrive() { char uinput[1]; char delim[] = " "; char *token; cout << "Enter your directions below: \n"; cin.ignore(); cin.getline (uinput, 256); token=strtok(uinput, delim); if(token == "forward") { int inches; inches=token+1; travel(inches); } } I've never used Cstrings I've never tokenized anything before, and I don't know how to write this. Our T.A.'s expect us to google and find all the answers because they are aware we've never been taught these methods. Everyone in my lab is having much more trouble than usual. I don't know the code to write but I know what I want my program to do. I want it to execute like this: 1) Ask for directions. 2) cin.getline the users input 3) tokenize the inputed string 4) if the first word token == "forward" move to the next token and find out how many inches to move forward then move forward 5) else if the first token == "turn" move to the next token. if the next token == "left" move to the next token and find out how many degrees to turn left I will have to do this for forward x, backward x, turn left x, turn right x, and stop(where x is in inches or degrees). I already wrote functions that tell the robot how to move forward an inch and turn in degrees. I just need to know how to convert the inputted strings to all lowercase letters and move from token to token and convert or extract the numbers from the string to use them as integers. If all is not clear you can read my lab write up at this link: http://www.cs.utk.edu/~cs102/robot_labs/Lab9.html If anything is unclear please let me know, and I will clarify as best I can.

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• UIScrollView Infinite Scrolling

  - by Ben Robinson

  I'm attempting to setup a scrollview with infinite (horizontal) scrolling. Scrolling forward is easy - I have implemented scrollViewDidScroll, and when the contentOffset gets near the end I make the scrollview contentsize bigger and add more data into the space (i'll have to deal with the crippling effect this will have later!) My problem is scrolling back - the plan is to see when I get near the beginning of the scroll view, then when I do make the contentsize bigger, move the existing content along, add the new data to the beginning and then - importantly adjust the contentOffset so the data under the view port stays the same. This works perfectly if I scroll slowly (or enable paging) but if I go fast (not even very fast!) it goes mad! Heres the code: - (void) scrollViewDidScroll:(UIScrollView *)scrollView { float pageNumber = scrollView.contentOffset.x / 320; float pageCount = scrollView.contentSize.width / 320; if (pageNumber > pageCount-4) { //Add 10 new pages to end mainScrollView.contentSize = CGSizeMake(mainScrollView.contentSize.width + 3200, mainScrollView.contentSize.height); //add new data here at (320*pageCount, 0); } //*** the problem is here - I use updatingScrollingContent to make sure its only called once (for accurate testing!) if (pageNumber < 4 && !updatingScrollingContent) { updatingScrollingContent = YES; mainScrollView.contentSize = CGSizeMake(mainScrollView.contentSize.width + 3200, mainScrollView.contentSize.height); mainScrollView.contentOffset = CGPointMake(mainScrollView.contentOffset.x + 3200, 0); for (UIView *view in [mainContainerView subviews]) { view.frame = CGRectMake(view.frame.origin.x+3200, view.frame.origin.y, view.frame.size.width, view.frame.size.height); } //add new data here at (0, 0); } //** MY CHECK! NSLog(@"%f", mainScrollView.contentOffset.x); } As the scrolling happens the log reads: 1286.500000 1285.500000 1284.500000 1283.500000 1282.500000 1281.500000 1280.500000 Then, when pageNumber<4 (we're getting near the beginning): 4479.500000 4479.500000 Great! - but the numbers should continue to go down in the 4,000s but the next log entries read: 1278.000000 1277.000000 1276.500000 1275.500000 etc.... Continiuing from where it left off! Just for the record, if scrolled slowly the log reads: 1294.500000 1290.000000 1284.500000 1280.500000 4476.000000 4476.000000 4473.000000 4470.000000 4467.500000 4464.000000 4460.500000 4457.500000 etc.... Any ideas???? Thanks Ben.

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• What is a proper way to store site-level global variables in a SharePoint site?

  - by ccomet

  One thing that has driven me nuts about SharePoint2007 is the apparent inability to have defineable settings that apply specifically to a site or site collection itself, and not the content. I mean, you have some pre-defined settings like the Site Logo, the Site Name, and various other things, but there doesn't appear to be anywhere to add new kinds of settings. The application I am working on needs to be able to create multiple kinds of "project site collections" that all follow a basic template, but have certain additional settings that apply specifically to that site collection and that one alone. In addition to the standard site name we also need to define the Project Number, the Project Name, and the Client Name. And given the requests of some of our clients, we also reach a point where we have to have configurable settings that alter how some of the workflows work, like whether files are marked with Letters or Numbers. Our current solution, which I'm hesitant about, has been to store an XML file on the SharePoint server. This file contains one node for each site collection, identified by the URL of the root site. Inside the node are all of the elements that need to be defined for that site collection. When we need them, we have to access the XML file (which will always require SPSecurity.RunWithElevatedPrivileges to access files right on the server) every time to load it and retrieve the data. There are a lot of automated processes which will have to do this, and I'm hesitant about the stability of this method when we reach hundreds of sites with thousands of files running tens of thousands of workflows, all wanting to access this file. Maybe they're unfounded worries, but I'd rather worry than risk everything breaking in a couple years. I was looking into the SPWeb object and found the AllProperties hashtable. It looks like just the kind of thing which might work, but I don't know how safe it is to be modifying this. I read through both MSDN and the WSS SDK but found nothing that clarified on adding completely new properties into AllProperties. Is it safe to use AllProperties for this kind of thing? Or is there yet another feature that I am missing, which could handle the concept of global variables at the site collection or site scope?

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• What is the most effective way to test for combined keyboard arrow direction in ActionScript 3.0?

  - by Relee

  I need to monitor the direction a user is indicating using the four directional arrow keys on a keyboard in ActionScript 3.0 and I want to know the most efficient and effective way to do this. I've got several ideas of how to do it, and I'm not sure which would be best. I've found that when tracking Keyboard.KEY_DOWN events, the event repeats as long as the key is down, so the event function is repeated as well. This broke the method I had originally chosen to use, and the methods I've been able to think of require a lot of comparison operators. The best way I've been able to think of would be to use bitwise operators on a uint variable. Here's what I'm thinking var _direction:uint = 0x0; // The Current Direction That's the current direction variable. In the Keyboard.KEY_DOWN event handler I'll have it check what key is down, and use a bitwise AND operation to see if it's already toggled on, and if it's not, I'll add it in using basic addition. So, up would be 0x1 and down would be 0x2 and both up and down would be 0x3, for example. It would look something like this: private function keyDownHandler(e:KeyboardEvent):void { switch(e.keyCode) { case Keyboard.UP: if(!(_direction & 0x1)) _direction += 0x1; break; case Keyboard.DOWN: if(!(_direction & 0x2)) _direction += 0x2; break; // And So On... } } The keyUpHandler wouldn't need the if operation since it only triggers once when the key goes up, instead of repeating. I'll be able to test the current direction by using a switch statement labeled with numbers from 0 to 15 for the sixteen possible combinations. That should work, but it doesn't seem terribly elegant to me, given all of the if statements in the repeating keyDown event handler, and the huge switch. private function checkDirection():void { switch(_direction) { case 0: // Center break; case 1: // Up break; case 2: // Down break; case 3: // Up and Down break; case 4: // Left break; // And So On... } } Is there a better way to do this?

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• Mysterious constraints problem with SQL Server 2000

  - by Ramon

  Hi all I'm getting the following error from a VB NET web application written in VS 2003, on framework 1.1. The web app is running on Windows Server 2000, IIS 5, and is reading from a SQL server 2000 database running on the same machine. System.Data.ConstraintException: Failed to enable constraints. One or more rows contain values violating non-null, unique, or foreign-key constraints. at System.Data.DataSet.FailedEnableConstraints() at System.Data.DataSet.EnableConstraints() at System.Data.DataSet.set_EnforceConstraints(Boolean value) at System.Data.DataTable.EndLoadData() at System.Data.Common.DbDataAdapter.FillFromReader(Object data, String srcTable, IDataReader dataReader, Int32 startRecord, Int32 maxRecords, DataColumn parentChapterColumn, Object parentChapterValue) at System.Data.Common.DbDataAdapter.Fill(DataSet dataSet, String srcTable, IDataReader dataReader, Int32 startRecord, Int32 maxRecords) at System.Data.Common.DbDataAdapter.FillFromCommand(Object data, Int32 startRecord, Int32 maxRecords, String srcTable, IDbCommand command, CommandBehavior behavior) at System.Data.Common.DbDataAdapter.Fill(DataSet dataSet, Int32 startRecord, Int32 maxRecords, String srcTable, IDbCommand command, CommandBehavior behavior) at System.Data.Common.DbDataAdapter.Fill(DataSet dataSet) The problem appears when the web app is under a high load. The system runs fine when volume is low, but when the number of requests becomes high, the system starts rejecting incoming requests with the above exception message. Once the problem appears, very few requests actually make it through and get processed normally, about 2 in every 30. The vast majority of requests fail, until a SQL Server restart or IIS reset is performed. The system then start processing requests normally, and after some time it starts throwing the same error. The error occurs when a data adapter runs the Fill() method against a SELECT statement, to populate a strongly-typed dataset. It appears that the dataset does not like the data it is given and throws this exception. This error occurs on various SELECT statements, acting on different tables. I have regenerated the dataset and checked the relevant constraints, as well as the table from which the data is read. Both the dataset definition and the data in the table are fine. Admittedly, the hardware running both the web app and SQL Server 2000 is seriously outdated, considering the numbers of incoming requests it currently receives. The amount of RAM consumed by SQL Server is dynamically allocated, and at peak times SQL Server can consume up to 2.8 GB out of a total of 3.5 GB on the server. At first I suspected some sort of index or database corruption, but after running DBCC CHECKDB, no errors were found in the database. So now I'm wondering whether this error is a result of the hardware limitations of the system. Is it possible for SQL Server to somehow mess up the data it's supposed to pass to the dataset, resulting in constraint violation due to, say, data type/length mismatch? I tried accessing the RowError messages of the data rows in the retrieved dataset tables but I kept getting empty strings. I know that HasErrors = true for the datatables in question. I have not set the EnableConstraints = false, and I don't want to do that. Thanks in advance. Ray

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• LINQ Query Returning Multiple Copies Of First Result

  - by Mike G

  I'm trying to figure out why a simple query in LINQ is returning odd results. I have a view defined in the database. It basically brings together several other tables and does some data munging. It really isn't anything special except for the fact that it deals with a large data set and can be a bit slow. I want to query this view based on a long. Two sample queries below show different queries to this view. var la = Runtime.OmsEntityContext.Positions.Where(p => p.AccountNumber == 12345678).ToList(); var deDa = Runtime.OmsEntityContext.Positions.Where(p => p.AccountNumber == 12345678).Select(p => new { p.AccountNumber, p.SecurityNumber, p.CUSIP }).ToList(); The first one should hand back a List. The second one will be a list of anonymous objects. When I do these queries in entities framework the first one will hand me back a list of results where they're all exactly the same. The second query will hand me back data where the account number is the one that I queried and the other values differ. This seems to do this on a per account number basis, ie if I were to query for one account number or another all the Position objects for one account would have the same value (the first one in the list of Positions for that account) and the second account would have a set of Position objects that all had the same value (again, the first one in it's list of Position objects). I can write SQL that is in effect the same as either of the two EF queries. They both come back with results (say four) that show the correct data, one account number with different securities numbers. Why does this happen??? Is there something that I could be doing wrong so that if I had four results for the first query above that the first record's data also appears in the 2-4th's objects??? I cannot fathom what would/could be causing this. I've searched Google for all kinds of keywords and haven't seen anyone with this issue. We partial class out the Positions class for added functionality (smart object) and some smart properties. There are even some constructors that provide some view model type support. None of this is invoked in the request (I'm 99% sure of this). However, we do this same pattern all over the app. The only thing I can think of is that the mapping in the EDMX is screwy. Is there a way that this would happen if the "primary keys" in the EDMX were not in fact unique given the way the view is constructed? I'm thinking that the dev who imported this model into the EDMX let the designer auto select what would be unique. Any help would give a haggered dev some hope!

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• Is there a scheduling algorithm that optimizes for "maker's schedules"?

  - by John Feminella

  You may be familiar with Paul Graham's essay, "Maker's Schedule, Manager's Schedule". The crux of the essay is that for creative and technical professionals, meetings are anathema to productivity, because they tend to lead to "schedule fragmentation", breaking up free time into chunks that are too small to acquire the focus needed to solve difficult problems. In my firm we've seen significant benefits by minimizing the amount of disruption caused, but the brute-force algorithm we use to decide schedules is not sophisticated enough to handle scheduling large groups of people well. (*) What I'm looking for is if there's are any well-known algorithms which minimize this productivity disruption, among a group of N makers and managers. In our model, There are N people. Each person pi is either a maker (Mk) or a manager (Mg). Each person has a schedule si. Everyone's schedule is H hours long. A schedule consists of a series of non-overlapping intervals si = [h1, ..., hj]. An interval is either free or busy. Two adjacent free intervals are equivalent to a single free interval that spans both. A maker's productivity is maximized when the number of free intervals is minimized. A manager's productivity is maximized when the total length of free intervals is maximized. Notice that if there are no meetings, both the makers and the managers experience optimum productivity. If meetings must be scheduled, then makers prefer that meetings happen back-to-back, while managers don't care where the meeting goes. Note that because all disruptions are treated as equally harmful to makers, there's no difference between a meeting that lasts 1 second and a meeting that lasts 3 hours if it segments the available free time. The problem is to decide how to schedule M different meetings involving arbitrary numbers of the N people, where each person in a given meeting must place a busy interval into their schedule such that it doesn't overlap with any other busy interval. For each meeting Mt the start time for the busy interval must be the same for all parties. Does an algorithm exist to solve this problem or one similar to it? My first thought was that this looks really similar to defragmentation (minimize number of distinct chunks), and there are a lot of algorithms about that. But defragmentation doesn't have much to do with scheduling. Thoughts? (*) Practically speaking this is not really a problem, because it's rare that we have meetings with more than ~5 people at once, so the space of possibilities is small.

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• Separating positive values from 'zero' values in an XSLT for-each statement

  - by danielle

  I am traversing an XML file (that contains multiple tables) using XSLT. Part of the job of the page is to get the title of each table, and present that title with along with the number of items that table contains (i.e. "Problems (5)"). I am able to get the number of items, but I now need to separate the sections with 0 (zero) items in them, and put them at the bottom of the list of table titles. I'm having trouble with this because the other items with positive numbers need to be left in their original order/not sorted. Here is the code for the list of titles: <ul> <xsl:for-each select="n1:component/n1:structuredBody/n1:component/n1:section/n1:title"> <li style="list-style-type:none;"> <div style = "padding:3px"><a href="#{generate-id(.)}"> <xsl:variable name ="count" select ="count(../n1:entry)"/> <xsl:choose> <xsl:when test = "$count != 0"> <xsl:value-of select="."/> (<xsl:value-of select="$count"/>) </xsl:when> <xsl:otherwise> <div id = "zero"><xsl:value-of select="."/> (<xsl:value-of select="$count"/>)</div> </xsl:otherwise> </xsl:choose> </a> </div> </li> </xsl:for-each> </ul> Right now, the "zero" div just marks each link as gray. Any help regarding how to place the "zero" divs at the bottom of the list would be greatly appreciated. Thank you!

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• difference between calling javascript function on body load or directly from script.

  - by Abbas

  i am using a javascript where in i am creating multiple div (say 5) at runtime, using javascript function, all the divs contain some text, which is again set at runtime, now i want to disable all the divs at runtime and have the page numbers in the bottom, so that whenever user clicks on the page number only that div should get visible else other should get disable, i have created a function, which accepts parameter, as page number, i enable the div whose page number is clicked and using a for loop, i disable all the other divs, now here my problem is i have created two functions, 1st (for adding divs and disabling all the divs except 1st) and writing content to it, and other for enabling the div whose page number is clicked, and i have called the Adding div function on body onload; now first time when i run, page everthing goes well, but next time when i click on any of the page number, it just gets enabled and again that AddDiv function, runs and re-enables all the divs.. Please reply why this is happening and how should i resolve my issue... Below is my script, content for the div are coming using Json. <body onload="JsonScript();"> <script language="javascript" type="text/javascript"> function JsonScript() { var existingDiv = document.getElementById("form1"); var newAnchorDiv = document.createElement("div"); newAnchorDiv.id = "anchorDiv"; var list = { "Article": articleList }; for(var i=0; i < list.Article.length; i++) { var newDiv = document.createElement("div"); newDiv.id = "div"+(i+1); newDiv.innerHTML = list.Article[i].toString(); newAnchorDiv.innerHTML += "<a href='' onclick='displayMessage("+(i+1)+")'>"+(i+1)+"</a>&nbsp;"; existingDiv.appendChild(newDiv); existingDiv.appendChild(newAnchorDiv); } for(var j = 2; j < list.Article.length + 1; j ++) { var getDivs = document.getElementById("div"+j); getDivs.style.display = "none"; } } function displayMessage(currentId) { var list = {"Article" : articleList} document.getElementById("div"+currentId).style.display = 'block'; for(var i = 1; i < list.Article.length + 1; i++) { if (i != currentId) { document.getElementById("div"+i).style.display = 'none'; } } } </script> Thanks and Regards

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• How to learn proper C++?

  - by Chris

  While reading a long series of really, really interesting threads, I've come to a realization: I don't think I really know C++. I know C, I know classes, I know inheritance, I know templates (& the STL) and I know exceptions. Not C++. To clarify, I've been writing "C++" for more than 5 years now. I know C, and I know that C and C++ share a common subset. What I've begun to realize, though, is that more times than not, I wind up treating C++ something vaguely like "C with classes," although I do practice RAII. I've never used Boost, and have only read up on TR1 and C++0x - I haven't used any of these features in practice. I don't use namespaces. I see a list of #defines, and I think - "Gracious, that's horrible! Very un-C++-like," only to go and mindlessly write class wrappers for the sake of it, and I wind up with large numbers (maybe a few per class) of static methods, and for some reason, that just doesn't seem right lately. The professional in me yells "just get the job done," the academic yells "you should write proper C++ when writing C++" and I feel like the point of balance is somewhere in between. I'd like to note that I don't want to program "pure" C++ just for the sake of it. I know several languages. I have a good feel for what "Pythonic" is. I know what clean and clear PHP is. Good C code I can read and write better than English. The issue is that I learned C by example, and picked up C++ as a "series of modifications" to C. And a lot of my early C++ work was creating class wrappers for C libraries. I feel like my own personal C-heavy background while learning C++ has sort of... clouded my acceptance of C++ in it's own right, as it's own language. Do the weathered C++ lags here have any advice for me? Good examples of clean, sharp C++ to learn from? What habits of C does my inner-C++ really need to break from? My goal here is not to go forth and trumpet "good" C++ paradigm from rooftops for the sake of it. C and C++ are two different languages, and I want to start treating them that way. How? Where to start? Thanks in advance! Cheers, -Chris

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• Supporting multiple instances of a plugin DLL with global data

  - by Bruno De Fraine

  Context: I converted a legacy standalone engine into a plugin component for a composition tool. Technically, this means that I compiled the engine code base to a C DLL which I invoke from a .NET wrapper using P/Invoke; the wrapper implements an interface defined by the composition tool. This works quite well, but now I receive the request to load multiple instances of the engine, for different projects. Since the engine keeps the project data in a set of global variables, and since the DLL with the engine code base is loaded only once, loading multiple projects means that the project data is overwritten. I can see a number of solutions, but they all have some disadvantages: You can create multiple DLLs with the same code, which are seen as different DLLs by Windows, so their code is not shared. Probably this already works if you have multiple copies of the engine DLL with different names. However, the engine is invoked from the wrapper using DllImport attributes and I think the name of the engine DLL needs to be known when compiling the wrapper. Obviously, if I have to compile different versions of the wrapper for each project, this is quite cumbersome. The engine could run as a separate process. This means that the wrapper would launch a separate process for the engine when it loads a project, and it would use some form of IPC to communicate with this process. While this is a relatively clean solution, it requires some effort to get working, I don't now which IPC technology would be best to set-up this kind of construction. There may also be a significant overhead of the communication: the engine needs to frequently exchange arrays of floating-point numbers. The engine could be adapted to support multiple projects. This means that the global variables should be put into a project structure, and every reference to the globals should be converted to a corresponding reference that is relative to a particular project. There are about 20-30 global variables, but as you can imagine, these global variables are referenced from all over the code base, so this conversion would need to be done in some automatic manner. A related problem is that you should be able to reference the "current" project structure in all places, but passing this along as an extra argument in each and every function signature is also cumbersome. Does there exist a technique (in C) to consider the current call stack and find the nearest enclosing instance of a relevant data value there? Can the stackoverflow community give some advice on these (or other) solutions?

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• Navigation bar(s) disappear when the window gets too small

  - by Leron

  The title maybe is a little misleading but I'm not 100% sure how this effect is called. I'm pretty sure what I meant is that my navigation bar is disappearing instead of collapsing. However my set up is this - I am working on the Layout view of ASP.NET MVC 4 project. I'm using bootstrap 3x but also have included jQuery libs so my <head> part is like this: @Scripts.Render("~/Scripts/bootstrap.min.js") @Styles.Render("~/Content/bootstrap.css") @Styles.Render("~/Content/themes/base/jquery.ui.smoothness.css") @Scripts.Render("~/Scripts/jquery-2.0.3.min.js") @Scripts.Render("~/Scripts/jquery-ui-1.10.3.min.js") //just skipped the standard stuff In the body I want to have two navbars and one side menu which will be the same for all my pages but I've noticed that when I start to narrow the window at some point instead of getting an effect similar to this example (noticed how the elements get repositioned) I just got both my navbars gone, I can't see them. The markup for my first navbar is this : <div class="navbar navbar-static-top navbar-inverse navbar-collapse collapse" role="navigation"> <ul class="nav navbar-nav "> <li><a href="#">Info</a></li> <li><a href="#">Info</a></li> </ul> </div> and the second one is : <div class="navbar navbar-collapse collapse" role="navigation" id="main-navigation-bar"> <ul class="nav nav-pills nav-justified"> <li style="border: 1px solid grey"><a href="#">Link</a></li> <li><a href="#">Link</a></li> <li><a href="#">Link</a></li> </ul> In fact the only thing left in my _Layout body is this: <div class="container-fluid"> @RenderBody() </div> which is just for compiling purposes and renders this view : <p>1</p> <p>2</p> <p>3</p> <p>4</p> <p>5</p> So when I make the window small enough so that my navbars disappear the only thing left is 1..5 numbers from the rendered view. I tested with only one navbar (commented the other) - no matter which one is commented, when I narrow the window I loose the navbar. How can I keep them using bootstrap 3x?

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• Quick question regarding this issue, Why doesnt it print out the second value(converted second value

  - by sil3nt

  Quick question, What have I done wrong here. The purpose of this code is to get the input into a string, the input being "12 34", with a space in between the "12" and "32" and to convert and print the two separate numbers from an integer variable known as number. Why doesn't the second call to the function copyTemp, not produce the value 34?. I have an index_counter variable which keeps track of the string index and its meant to skip the 'space' character?? what have i done wrong? thanks. #include <stdio.h> #include <string.h> int index_counter = 0; int number; void copyTemp(char *expr,char *temp); int main(){ char exprstn[80]; //as global? char tempstr[80]; gets(exprstn); copyTemp(exprstn,tempstr); printf("Expression: %s\n",exprstn); printf("Temporary: %s\n",tempstr); printf("number is: %d\n",number); copyTemp(exprstn,tempstr); //second call produces same output shouldnt it now produce 34 in the variable number? printf("Expression: %s\n",exprstn); printf("Temporary: %s\n",tempstr); printf("number is: %d\n",number); return 0; } void copyTemp(char *expr,char *temp){ int i; for(i = index_counter; expr[i] != '\0'; i++){ if (expr[i] == '0'){ temp[i] = expr[i]; } if (expr[i] == '1'){ temp[i] = expr[i]; } if (expr[i] == '2'){ temp[i] = expr[i]; } if (expr[i] == '3'){ temp[i] = expr[i]; } if (expr[i] == '4'){ temp[i] = expr[i]; } if (expr[i] == '5'){ temp[i] = expr[i]; } if (expr[i] == '6'){ temp[i] = expr[i]; } if (expr[i] == '7'){ temp[i] = expr[i]; } if (expr[i] == '8'){ temp[i] = expr[i]; } if (expr[i] == '9'){ temp[i] = expr[i]; } if (expr[i] == ' '){ temp[i] = '\0'; sscanf(temp,"%d",&number); index_counter = i+1; //skips? } } // is this included here? temp[i] = '\0'; }

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• Implementing Skip List in C++

  - by trikker

  [SOLVED] So I decided to try and create a sorted doubly linked skip list... I'm pretty sure I have a good grasp of how it works. When you insert x the program searches the base list for the appropriate place to put x (since it is sorted), (conceptually) flips a coin, and if the "coin" lands on a then that element is added to the list above it(or a new list is created with element in it), linked to the element below it, and the coin is flipped again, etc. If the "coin" lands on b at anytime then the insertion is over. You must also have a -infinite stored in every list as the starting point so that it isn't possible to insert a value that is less than the starting point (meaning that it could never be found.) To search for x, you start at the "top-left" (highest list lowest value) and "move right" to the next element. If the value is less than x than you continue to the next element, etc. until you have "gone too far" and the value is greater than x. In this case you go back to the last element and move down a level, continuing this chain until you either find x or x is never found. To delete x you simply search x and delete it every time it comes up in the lists. For now, I'm simply going to make a skip list that stores numbers. I don't think there is anything in the STL that can assist me, so I will need to create a class List that holds an integer value and has member functions, search, delete, and insert. The problem I'm having is dealing with links. I'm pretty sure I could create a class to handle the "horizontal" links with a pointer to the previous element and the element in front, but I'm not sure how to deal with the "vertical" links (point to corresponding element in other list?) If any of my logic is flawed please tell me, but my main questions are: How to deal with vertical links and whether my link idea is correct Now that I read my class List idea I'm thinking that a List should hold a vector of integers rather than a single integer. In fact I'm pretty positive, but would just like some validation. I'm assuming the coin flip would simply call int function where rand()%2 returns a value of 0 or 1 and if it's 0 then a the value "levels up" and if it's 0 then the insert is over. Is this incorrect? How to store a value similar to -infinite? Edit: I've started writing some code and am considering how to handle the List constructor....I'm guessing that on its construction, the "-infinite" value should be stored in the vectorname[0] element and I can just call insert on it after its creation to put the x in the appropriate place.

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• Matching array elements to get an array element at another index

  - by bccarlso

  I have a PHP array that I'm using to generate an HTML form. The PHP array is this: <?php $vdb = array ( array( "Alabama", 275), array( "Alaska", 197), array( "Arizona", 3322)); ?> The PHP to generate the HTML form is below. I need to have the value be the name of the state, because there is some AJAX I'm using to display which states a user has chosen. <?php echo "<table border='1'><thead><tr><th></th><th>State</th><th>Contacts</th><th>Email</th></tr></thead>"; for ($row = 0; $row < 42; $row++) { echo "<tr><td class='input_button'><input type='checkbox' name='vdb[]' value='".$vdb[$row][0]."' title='".$vdb[$row][1]."' /></td>"; echo "<td>".$vdb[$row][0]."</td>"; echo "<td>".$vdb[$row][1]."</td>"; } echo "</table>"; ?> What I'm trying to do is, on submission of the form, with the states the user selected, loop through the PHP array and total the numbers from the selected states. So if I checked Alabama and Alaska, I'd want to add 275 + 197. This is what I thought would have worked, but it's not: <?php $vendors = array(); if (isset($_POST["vdb"])) { $vendors = $_POST["vdb"]; } $ven_i = 0; $ven_j = 0; $ven_total = 0; foreach ($vendors as $value) { foreach ($vdb as $vdb_value) { if ($vendors[$ven_i] == $vdb[$ven_j][0]) { $ven_total += $vdb[$ven_j][1]; } $ven_j++; } $ven_i++; } ?> and then $ven_total should be the total I'm looking for. However, $ven_total just ends up being the first checkbox selected, and it ignores the rest. I am doing this correctly with the AJAX, displaying the total on the front end, but I don't know how to pass that on to the form submission. I'd rather not using GET and URL variables, because a user could type something into the URL and modify the count. Any idea what I'm doing wrong, or a better way to approach this that I would be able to understand? (Very much a novice programmer.)

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• tablednd post issue help please

  - by netrise

  Hi plz i got a terrible headache my script is very simple Why i can’t get $_POST['table-2'] after submiting update button, i want to get ID numbers sorted # index.php <head> <script src="jquery.js" type="text/javascript"></script><br /> <script src="jquery.tablednd.js" type="text/javascript"></script><br /> <script src="jqueryTableDnDArticle.js" type="text/javascript"></script><br /> </head> <body> <form method='POST' action=index.php> <table id="table-2" cellspacing="0" cellpadding="2"> <tr id="a"><td>1</td><td>One</td><td><input type="text" name="one" value="one"/></td></tr> <tr id="b"><td>2</td><td>Two</td><td><input type="text" name="two" value="two"/></td></tr> <tr id="c"><td>3</td><td>Three</td><td><input type="text" name="three" value="three"/></td></tr> <tr id="d"><td>4</td><td>Four</td><td><input type="text" name="four" value="four"/></td></tr> <tr id="e"><td>5</td><td>Five</td><td><input type="text" name="five" value="five"/></td></tr> </table> <input type="submit" name="update" value="Update"> </form> <?php $result[] = $_POST['table-2']; foreach($result as $value) { echo "$value<br/>"; } ?> </body> # jqueryTableDnDArticle.js …………. $(“#table-2?).tableDnD({ onDragClass: “myDragClass”, onDrop: function(table, row) { var rows = table.tBodies[0].rows; var debugStr = “Row dropped was “+row.id+”. New order: “; for (var i=0; i<rows.length; i++) { debugStr += rows[i].id+" "; } //$("#debugArea").html(debugStr); $.ajax({ type: "POST", url: "index.php", data: $.tableDnD.serialize(), success: function(html){ alert("Success"); } }); }, onDragStart: function(table, row) { $("#debugArea").html("Started dragging row "+row.id); } });

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• SSL Authentication with Certificates: Should the Certificates have a hostname?

  - by sixtyfootersdude

  Summary JBoss allows clients and servers to authenticate using certificates and ssl. One thing that seems strange is that you are not required to give your hostname on the certificate. I think that this means if Server B is in your truststore, Sever B can pretend to be any server that they want. (And likewise: if Client B is in your truststore...) Am I missing something here? Authentication Steps (Summary of Wikipeida Page) Client Server ================================================================================================= 1) Client sends Client Hello ENCRIPTION: None - highest TLS protocol supported - random number - list of cipher suites - compression methods 2) Sever Hello ENCRIPTION: None - highest TLS protocol supported - random number - choosen cipher suite - choosen compression method 3) Certificate Message ENCRIPTION: None - 4) ServerHelloDone ENCRIPTION: None 5) Certificate Message ENCRIPTION: None 6) ClientKeyExchange Message ENCRIPTION: server's public key => only server can read => if sever can read this he must own the certificate - may contain a PreMasterSecerate, public key or nothing (depends on cipher) 7) CertificateVerify Message ENCRIPTION: clients private key - purpose is to prove to the server that client owns the cert 8) BOTH CLIENT AND SERVER: - use random numbers and PreMasterSecret to compute a common secerate 9) Finished message - contains a has and MAC over previous handshakes (to ensure that those unincripted messages did not get broken) 10) Finished message - samething Sever Knows The client has the public key for the sent certificate (step 7) The client's certificate is valid because either: it has been signed by a CA (verisign) it has been self-signed BUT it is in the server's truststore It is not a replay attack because presumably the random number (step 1 or 2) is sent with each message Client Knows The server has the public key for the sent certificate (step 6 with step 8) The server's certificate is valid because either: it has been signed by a CA (verisign) it has been self-signed BUT it is in the client's truststore It is not a replay attack because presumably the random number (step 1 or 2) is sent with each message Potential Problem Suppose the client's truststore has certs in it: Server A Server B (malicous) Server A has hostname www.A.com Server B has hostname www.B.com Suppose: The client tries to connect to Server A but Server B launches a man in the middle attack. Since server B: has a public key for the certificate that will be sent to the client has a "valid certificate" (a cert in the truststore) And since: certificates do not have a hostname feild in them It seems like Server B can pretend to be Server A easily. Is there something that I am missing?

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• Simple RSA encryption (Java)

  - by jake blue

  This is simply for fun. This will not be used for any actual encryption. I'm only first year comp sci student and love cryptography. This took a long time to get working. At approximately N = 18, it begins breaking down. It won't encrypt messages properly after that point. I'm not sure why. Any insights? I'd also appreciate any links you could provide me to tutorials or interesting reading about Cryptography. import java.math.BigInteger; import java.security.SecureRandom; /** * Cryptography. * * Generates public and private keys used in encryption and * decryption * */ public class RSA { private final static BigInteger one = new BigInteger("1"); private final static SecureRandom random = new SecureRandom(); // prime numbers private BigInteger p; private BigInteger q; // modulus private BigInteger n; // totient private BigInteger t; // public key private BigInteger e; // private key private BigInteger d; private String cipherText; /** * Constructor for objects of class RSA */ public RSA(int N) { p = BigInteger.probablePrime(N/2, random); q = BigInteger.probablePrime(N/2, random); // initialising modulus n = p.multiply(q); // initialising t by euclid's totient function (p-1)(q-1) t = (p.subtract(one)).multiply(q.subtract(one)); // initialising public key ~ 65537 is common public key e = new BigInteger("65537"); } public int generatePrivateKey() { d = e.modInverse(t); return d.intValue(); } public String encrypt(String plainText) { String encrypted = ""; int j = 0; for(int i = 0; i < plainText.length(); i++){ char m = plainText.charAt(i); BigInteger bi1 = BigInteger.valueOf(m); BigInteger bi2 = bi1.modPow(e, n); j = bi2.intValue(); m = (char) j; encrypted += m; } cipherText = encrypted; return encrypted; } public String decrypt() { String decrypted = ""; int j = 0; for(int i = 0; i < cipherText.length(); i++){ char c = cipherText.charAt(i); BigInteger bi1 = BigInteger.valueOf(c); BigInteger bi2 = bi1.modPow(d, n); j = bi2.intValue(); c = (char) j; decrypted += c; } return decrypted; } }

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• OpenGL ES functions not accepting values originating outside of it's view

  - by Josh Elsasser

  I've been unable to figure this out on my own. I currently have an Open GLES setup where a view controller both updates a game world (with a dt), fetches the data I need to render, passes it off to an EAGLView through two structures (built of Apple's ES1Renderer), and draws the scene. Whenever a value originates outside of the Open GL view, it can't be used to either translate objects using glTranslatef, or set up the scene using glOrthof. If I assign a new value to something, it will work - even if it is the exact same number. The two structures I have each contain a variety of floating-point numbers and booleans, along with two arrays. I can log the values from within my renderer - they make it there - but I receive errors from OpenGL if I try to do anything with them. No crashes result, but the glOrthof call doesn't work if I don't set the camera values to anything different. Code used to set up scene: [EAGLContext setCurrentContext:context]; glBindFramebufferOES(GL_FRAMEBUFFER_OES, viewFramebuffer); //clears the color buffer bit glClear(GL_COLOR_BUFFER_BIT); glMatrixMode(GL_PROJECTION); //sets up the scene w/ ortho projection glViewport(0, 0, 320, 480); glLoadIdentity(); glOrthof(320, 0, dynamicData.cam_x2, dynamicData.cam_x1, 1.0, -1.0); glClearColor(1.0, 1.0, 1.0, 1.0); /*error checking code here*/ "dynamicData" (which is replaced every frame) is created within my game simulation. From within my controller, I call a method (w/in my simulation) that returns it, and pass the result on to the EAGLView, which passes it on to the renderer. I haven't been able to come up with a better solution for this - suggestions in this regard would be greatly appreciated as well. Also, this function doesn't work as well (values originate in the same place): glTranslatef(dynamicData.ship_x, dynamicData.ship_y, 0.0); Thanks in advance. Additional Definitions: Structure (declared in a separate header): typedef struct { float ship_x, ship_y; float cam_x1, cam_x2; } dynamicRenderData; Render data getter (and builder) (every frame) - (dynamicData)getDynRenderData { //d_rd is an ivar, zeroed on initialization d_rd.ship_x = mainShip.position.x; d_rd.ship_y = mainShip.position.y; d_rd.cam_x1 = d_rd.ship_x - 30.0f; d_rd.cam_x2 = d_rd.cam_x1 + 480.0f; return d_rd; } Zeroed at start. (d_rd.ship_x = 0;, etc…) Setting up the view. Prototype (GLView): - (void)draw: (dynamicRenderData)dynamicData Prototype (Renderer): - (void)drawView: (dynamicRenderData)dynamicData How it's called w/in the controller: //controller [glview draw: [world getDynRenderData]]; //glview (within draw) [renderer drawView: dynamicData];

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