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• iPhone - Create non-persistent entities in core data

  - by ncohen

  Hi everyone, I would like to use entity objects but not store them... I read that I could create them like this: myElement = (Element *)[NSEntityDescription insertNewObjectForEntityForName:@"Element" inManagedObjectContext:managedObjectContext]; And right after that remove them: [managedObjectContext deleteObject:myElement]; then I can use my elements: myElement.property1 = @"Hello"; This works pretty well even though I think this is probably not the most optimal way to do it... Then I try to use it in my UITableView... the problem is that the object get released after the initialization. My table becomes empty when I move it! Thanks edit: I've also tried to copy the element ([myElement copy]) but I get an error...

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• Conting of objects created in stack and heap for many classes

  - by viswanathan

  What is the best way to count the total number of objects created in both stack and heap for different classes. I know that in C++ new and delete operators can be overloaded and hence in the default constructor and destructor the object count can be incremented or decremented as and when the objects get created or destroyed. Further if i am to extend the same thing for object counting of objects of different classes, then i can create a dummy class and write the object count code in that class and then when i create any new class i can derive it from the Dummy class. Is there any other optimal solution to the same problem.

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• Appropriate high level language to deal with binary data

  - by fortran

  Hi, I need to write a small tool that parses a textual input and generates some binary encoded data. I would prefer to stay away from C and the like, in favour of a higher level, (optionally) safer, more expressive and faster to develop language. My language of choice for this kind of tasks usually is Python, but for this case dealing with binary raw data can be problematic if one isn't very careful with the numbers being promoted to bignums, sign extensions and such. Ideally I would like to have records with named bitfields that are portable to be serialised in a consistent manner. (I know that there's a strong point in doing it in a language I already master, although it isn't optimal, but I think this could be a good opportunity to learn something new). Thanks.

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• Exclusive filtering by tag

  - by KaptajnKold

  I'm using rails 3.0 and MySql 5.1 I have these three models: Question, Tag and QuestionTag. Tag has a column called name. Question has many Tags through QuestionTags and vice versa. Suppose I have n tag names. How do I find only the questions that have all n tags, identified by tag name. And how do I do it in a single query. (If you can convince me that doing it in more than one query is optimal, I'll be open to that) A pure rails 3 solution would be preferred, but I am not adverse to a pure SQL solution either.

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• What techniques are available for filtering collections of objects when using zodb?

  - by Omega

  As the title says: What techniques are available for filtering objects when using zodb? The equivalent in SQL terms would be something like filtering results by a date range. Or only returning rows with a particular value set in a column. If I had a series of blog posts and only wanted ones done in the past month, what would I have to do? Is there any way to optimize these kinds of "queries"? My gut tells me iterating over all the objects in a relationship simply to perform a test is less than optimal.

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• Does Python Django support custom SQL and denormalized databases with no Foreign Key relationships?

  - by Jay

  I've just started learning Python Django and have a lot of experience building high traffic websites using PHP and MySQL. What worries me so far is Python's overly optimistic approach that you will never need to write custom SQL and that it automatically creates all these Foreign Key relationships in your database. The one thing I've learned in the last few years of building Chess.com is that its impossible to NOT write custom SQL when you're dealing with something like MySQL that frequently needs to be told what indexes it should use (or avoid), and that Foreign Keys are a death sentence. Percona's strongest recommendation was for us to remove all FKs for optimal performance. Is there a way in Django to do this in the models file? create relationships without creating actual DB FKs? Or is there a way to start at the database level, design/create my database, and then have Django reverse engineer the models file?

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• Any way to chunk gzip with Apache and PHP

  - by donatJ

  I have a web application on a site that takes a while (~10 seconds) to complete a portion of the page near the bottom - it has been as optimized as it can be, and caching is not an option. We have compression enabled on the server via an .htaccess directive SetOutputFilter DEFLATE the problem is this causes the whole page to be held until completion before it starts outputting to the user, this is not optimal as the user sees nothing until the page completes. I have also tried it via the php ob_start("ob_gzhandler"); method. Currently I have a <FilesMatch > in my .htaccess restricting this specific script from being compressed. Basically my question is this - Is there a way to say chunk gzip or deflate so that the user gets it in pieces, so they can see that the page has begun loading?

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• WithEvents LinkedList is it Impossible?

  - by serhio

  What is the optimal approach to a WithEvents Collection - VB.NET? Have you any remarks on the code bellow (skipping the Nothing verifications)? The problem is when I obtain the LinkedListNode(Of Foo) in a For Each block I can set myNode.Value = something, and here is a handlers leak... -Could I override the FooCollection's GetEnumerator in this case? -No. :( cause NotInheritable Class LinkedListNode(Of T) Class Foo Public Event SelectedChanged As EventHandler End Class Class FooCollection Inherits LinkedList(Of Foo) Public Event SelectedChanged As EventHandler Protected Overloads Sub AddFirst(ByVal item As Foo) AddHandler item.SelectedChanged, AddressOf OnSelectedChanged MyBase.AddFirst(item) End Sub Protected Overloads Sub AddLast(ByVal item As Foo) AddHandler item.SelectedChanged, AddressOf OnSelectedChanged MyBase.AddLast(item) End Sub ' ------------------- ' Protected Overloads Sub RemoveFirst() RemoveHandler MyBase.First.Value.SelectedChanged, _ AddressOf OnSelectedChanged MyBase.RemoveFirst() End Sub Protected Overloads Sub RemoveLast(ByVal item As Foo) RemoveHandler MyBase.Last.Value.SelectedChanged, _ AddressOf OnSelectedChanged MyBase.RemoveLast() End Sub ' ------------------- ' Protected Sub OnSelectedChanged(ByVal sender As Object, ByVal e As EventArgs) RaiseEvent SelectedChanged(sender, e) End Sub End Class

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• Enumerating combinations in a distributed manner

  - by Reyzooti

  I have a problem where I must analyse 500C5 combinations (255244687600) of something. Distributing it over a 10 node cluster where each cluster processes roughly 10^6 combinations per second means the job will be complete in about 7hours. The problem I have is distributing the 255244687600 combinations over the 10 nodes. I'd like to present each node with 25524468760, however the algorithms I'm using can only produce the combinations sequentially, I'd like to be able to pass the set of elements and a range of combination indicies eg: [0-10^7) or [10^7,2.0 10^7) etc and have the nodes themselves figure out the combinations. The algorithms I'm using at the moment are from the following: http://home.roadrunner.com/~hinnant/combinations.html A logical question I've considered using a master node, that enumerates each of the combinations and sends work to each of the nodes, however the overhead incurred in iterating the combinations from a single node and communicating back and forth work is enormous, and will subsequently lead to the master node becoming the bottleneck. Are there any good combination iterating algorithms geared up for efficient/optimal distributed enumeration?

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• Passing values across pages ASP.net

  - by GigaPr

  Hi i need to pass a long list of Ids from one page to another, i was thinking of using querystring but taking in consideration that the number of ids to be passed may reach 300 i think is not a good idea. an option from my understanding may be the use of session, this seems to me an optimal solution in my case but on the other hand I can certainly clear the session when the user performs a certain action and the list of ids is not longer needed, but if the user leaves the page without performing any action i want to clear the session, how can i do it? If multiple users are using the same functionality do i need the session's items to be confused or the session is for a single user? I am working in asp.net c# Thanks

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• What strategies are efficient to handle concurrent reads on heterogeneous multi-core architectures?

  - by fabrizioM

  I am tackling the challenge of using both the capabilities of a 8 core machine and a high-end GPU (Tesla 10). I have one big input file, one thread for each core, and one for the the GPU handling. The Gpu thread, to be efficient, needs a big number of lines from the input, while the Cpu thread needs only one line to proceed (storing multiple lines in a temp buffer was slower). The file doesn't need to be read sequentially. I am using boost. My strategy is to have a mutex on the input stream and each thread locks - unlocks it. This is not optimal because the gpu thread should have a higher precedence when locking the mutex, being the fastest and the most demanding one. I can come up with different solutions but before rush into implementation I would like to have some guidelines. What approach do you use / recommend ?

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• Visual Studio 2010 element names for theming

  - by Anthony Potts

  I am trying to figure out what the element name for the tooltip is in Visual studio so that I can change the style using the extension found here. Anyone know what that is? I am using the default theme which seems to have a white to light grey gradient on it. This is less than optimal since the text for the functions are also white. In a more general question (and perhaps better), is there anything that maps the names as they are found in the theme to where they are in the IDE.

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• How to use AutoLayout to position UIButtons in horizontal lines?

  - by thomers

  I need to create a couple of UIButtons programmatically in my app (iOS 6.0 and above). Each button should have the optimal width to display button label text (of various lenghts). I want to display the buttons in a "wrap around" style: Starting from the left edge, each button should be positioned next to each other horizontally (in a defined order), and if a button does not fit in the current "line", it should start a new line on the left edge below the previous line. I could manually calculate the frame of each button in my code, but should I use AutoLayout (with programmatically creates NSLayoutConstraints) instead? How exactly would I need to set it up?

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• iphone threading speed up startup of app

  - by BahaiResearch.com

  I have an app that must get data from the Sqlite database in order to display the first element to the User. I have created a domain object which wraps the DB access and is a thread safe singleton. Is this following strategy optimal to ensure the fastest load given the iPhone's file access and memory management capabilities in threaded apps: 1) In the AppDelegate's FinishedLaunching event the very first thing I do is create the domain singleton within a new thread. This will cause the domain object to go to Sqlite and get the data it needs without locking the UI thread. 2) I then call the standard Window methods to add the View and MakeKeyAndVisible etc. Is there an earlier stage in the AppDelegate where I should fire off the thread that creates the Domain Object and accesses Sqlite?

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• How Matlab calculates the camera view angle?

  - by iman

  I am using matlab to visualise a scene. In order to zoom in the scene, I can do that by eather: - Fix the cameraposition and the cameratarget and change the cameraviewangle.or - Fix the cameratarget and the cameraview angle and moving the camera along the viewing line (defined by the cameraPosition and the cameraTarget). I know how to set the values of cameraposition CameraTarget and viewangle, but I do not how to define the optimal view angle. In auto mode of cameraviewangle, matlab calculate the smalest view angle that capture all the scene from the specefied camera position. I appreciate any help in understanding this. Iman

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• Dynamic proxies to auto-save models

  - by atomman

  I'm trying to make some auto-magic happen in java using proxies to track objects and saving them when a set* method is called. I started of using java's built in Proxy, and everything works just fine, but from what I can understand I need a interface for every model, which is something that I'm trying to avoid. This is where CGLIB comes in, it allows me to create proxies of my models without the use of interfaces. BUT, how can I now retrieve the original object, the one I am trying to save? The optimal solution to be would be something like the EntityManager interface used by hibernate, where you keep your original object, but it is still tracked.

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• Searching for a complex and well-designed PHP OOP application to learn from

  - by Raveren

  Basically, I am diving ever deeper into complex programming practices. I've almost no friends that are experienced (or more experienced than me) programmers to learn from, so I am looking for the next best thing - learning from the work of strangers. Can anyone recommend a real world finished and working application written well and OOP-centered. I'd like to take and analyze its source. Bonus if it's based on Zend Framework. What I am interested most in is objects that unlike desktop applications, have only one real operation done to them (or to their representation in DB or session) during their lifetime (or pageload), like user-logIn(). I'm interested in optimal and reusable design patterns and their real life implementations.

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• Postgresql error: could not open segment 1 of relation base/20983/2416

  - by kokonut

  I'm running a Postgresql query and getting the following error: ActiveRecord::StatementInvalid (PGError: ERROR: could not open segment 1 of relation base/20983/24161 (target block 5046584): No such file or directory The query is of the format 'SELECT "locations".* FROM "locations" WHERE ("locations"."id" IN (115990, 78330, 77891, 78248, ...)' with about 600 ids in the IN clause - not an optimal query I know but it's what I have to work with for the moment! The server is running PostgreSQL 8.4.6 on x86_64-pc-linux-gnu, compiled by GCC gcc-4.4.real (Ubuntu 4.4.1-4ubuntu9) 4.4.1, 64-bit. Postgis 1.5 is also installed, and the locations table contains a geometry column. Anyone have any idea what could be causing the error? Thanks!

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• switching between one and two displays in visual studio

  - by WebDude

  Most of the time I work Visual Studio with two monitors. I setup my Visual Studio to sit nicely across both monitors with code on the one side and property windows etc. on the other. However, occasionally I need to remove into my work station from home where I only have one monitor. What ends up happening is I have to re-setup my entire workspace to be used on one monitor, and when I get back to my work station I have to undo this again to get to my optimal 2 monitor environment. Is there a way to save some set layouts in Visual Studio so I could quickly switch back and forward? Example: One Monitor Layout versus Two Monito Layout?

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• using NEWSEQUENTIALID() with UPDATE Trigger

  - by Ram

  I am adding a new GUID/Uniqueidentifier column to my table. ALTER TABLE table_name ADD VersionNumber UNIQUEIDENTIFIER UNIQUE NOT NULL DEFAULT NEWSEQUENTIALID() GO And when ever a record is updated in the table, I would want to update this column "VersionNumber". So I create a new trigger CREATE TRIGGER [DBO].[TR_TABLE_NAMWE] ON [DBO].[TABLE_NAME] AFTER UPDATE AS BEGIN UPDATE TABLE_NAME SET VERSIONNUMBER=NEWSEQUENTIALID() FROM TABLE_NAME D JOIN INSERTED I ON D.ID=I.ID/* some ID which is used to join*/ END GO But just realized that NEWSEQUENTIALID() can only be used with CREATE TABLE or ALTER TABLE. I got this error The newsequentialid() built-in function can only be used in a DEFAULT expression for a column of type 'uniqueidentifier' in a CREATE TABLE or ALTER TABLE statement. It cannot be combined with other operators to form a complex scalar expression. Is there a workaround for this ? Edit1: Changing NEWSEQUENTIALID() to NEWID() in the trigger solves this, but I am indexing this column and using NEWID() would be sub-optimal

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• How to implement low pass filter using java

  - by chai

  Hello Everyone, I am trying to implement a low pass filter in Java. My requirement is very simple,I have to eliminate signals beyond a particular frequency (Single dimension). Looks like Butterworth filter would suit my need. Now the important thing is that CPU time should be as low as possible. There would be close to a million sample the filter would have to process and our users don't like waiting too long. Are there any readymade implementation of Butterworth filters which has optimal algorithms for filtering. Regards, Chaitannya

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• iPhone - Create not persistant entities in core data

  - by ncohen

  Hi everyone, I would like to use entity objects but not store them... I read that I could create them like this: myElement = (Element *)[NSEntityDescription insertNewObjectForEntityForName:@"Element" inManagedObjectContext:managedObjectContext]; And right after that remove them: [managedObjectContext deleteObject:myElement]; then I can use my elements: myElement.property1 = @"Hello"; This works pretty well even though I think this is probably not the most optimal way to do it... Then I try to use it in my UITableView... the problem is that the object get released after the initialization. My table becomes empty when I move it! Thanks

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• Minimum number of training examples for Find-S/Candidate Elimination algorithms?

  - by Rich

  Consider the instance space consisting of integer points in the x, y plane, where 0 = x, y = 10, and the set of hypotheses consisting of rectangles (i.e. being of the form (a = x = b, c = y = d), where 0 = a, b, c, d = 10). What is the smallest number of training examples one needs to provide so that the Find-S algorithm perfectly learns a particular target concept (e.g. (2 = x = 4, 6 = y = 9))? When can we say that the target concept is exactly learned in the case of the Find-S algorithm, and what is the optimal query strategy? I'd also like to know the answer w.r.t Candidate Elimination. Thanks in advance.

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• Help in formulating sql query

  - by AJ

  Here is my scenario Table 1: GID || Info1 Table 2: GID || Tb1GID (refers to GID of Table1) || Info2 Table 3: GID || Info3 Table 4: GID || Tb2GID (refers to GID of Table2 || Tb3GID (refers to Table3 GID || Value Now I have to build an sql query to get the value, given a particular Info1, Info2, Info3. Essentially, I have to get the GID, of table 1 using info1, GID of table to , by mapping info2 and GID of table 1. And then get the GID of table 3 using info 3. And combine these to GIDs to get the value in table 4. What is the most optimal way of constructing an sql query for this one?

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• Optimality of Binary Search

  - by templatetypedef

  Hello all- This may be a silly question, but does anyone know of a proof that binary search is asymptotically optimal? That is, if we are given a sorted list of elements where the only permitted operation on those objects is a comparison, how do you prove that the search can't be done in o(lg n)? (That's little-o of lg n, by the way.) Note that I'm restricting this to elements where the only operation permitted operation is a comparison, since there are well-known algorithms that can beat O(lg n) on expectation if you're allowed to do more complex operations on the data (see, for example, interpolation search). Thanks so much! This has really been bugging me since it seems like it should be simple but has managed to resist all my best efforts. :-)

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