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• <= vs < when proving big-o notation

  - by user600197

  We just started learning big-o in class. I understand the general concept that f(x) is big-o of g(x) if there exists two constants c,k such that for all xk |f(x)|<=c|g(x)|. I had a question whether or not it is required that we include the <= to sign or whether it is just sufficient to put the < sign? For example: suppose f(x)=17x+11 and we are to prove that this is O(x^2). Then if we take c=28 and xk=1 we know that 17x+11<=28x^2. So since we know that x will always be greater than 1 this implies that 28x^2 will always be greater than 17x+11. So, do we really need to include the equal sign (<=) or is it okay if we just write (<)? Thanks in advance.

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• Why do I have to explicitly cast sometimes for varargs?

  - by Daniel Lew

  I've got a Class that uses reflection a lot, so I wrote a method to help out: private <T> T callMethod(String methodName, Class[] parameterTypes, Object[] args) { try { Class c = mVar.getClass(); Method m = c.getMethod(methodName, (Class[]) parameterTypes); return (T) m.invoke(mVar, args); } // Insert exception catching here [...] } This worked well for any method that had parameters, however I had to explicitly cast parameterTypes to Class[] in order for this to work for methods with no parameters (e.g., callMethod('funName', null, null);). I've been trying to figure out why this is the case. It seems to me that if parameterTypes, when null, had no concept of what type it is (Class[]), then I'd need to cast it for getMethod(). But if that's the case, why is getMethod() able to tell the difference between null, and (Class[]) null when the method is invoked?

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• Get access to a lot of iPhone and iPad Quality Source Codes for only $89

  - by Pixmator

  Hi developers and coming developers! We are happy to release this new concept from Pixmator.com, where you can get access to a lot of iPhone and iPad source codes for only $89. Start making a pro-developed application by these great application examples with is followed with a Source Code, so you can get everything out of it! These applications is present with a fully professionally designed graphic. The engine and the code is as well, as the graphic! It looks awesome. It is awesome. Take a look, it doesn't hurt anyone. Hope you guys like it! It will be available for purchase soon! Check out the link below: Check it out here!

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• Full GC real time is much more that user+sys times

  - by Stas

  Hi. We have a Web Java based application running on JBoss with allowed maximum heap size of about 1.2 GB (total machine physical memory is 2 GB). At some point the application stops responding (to clients) for several minutes. After some analysis we found out that the culprit is the Full GC. Here's an excerpt from the verbose GC log: 74477.402: [Full GC [PSYoungGen: 3648K-0K(332160K)] [PSOldGen: 778476K-589497K(819200K)] 782124K-589497K(1151360K) [PSPermGen: 102671K-102671K(171328K)], 646.1546860 secs] [Times: user=3.84 sys=3.72, real=646.17 secs] What I don't understand is how is it possible that the real time spent on Full GC is about 11 minutes (646 seconds), while user+sys times are just 7.5 seconds. 7.5 seconds sound to me much more logical time to spend for cleaning <200 MB from the old generation. Where does all the other time go? Thanks a lot.

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• Force Response to Download File(s) to Desktop with Ruby?

  - by viatropos

  I was thinking about making a little crop/resize batch processor online, and wanted to know if there was a way for me to do the following: upload image and specify dimensions click "process" and remote app resizes image image downloads automatically locally to wherever it was I uploaded it (say from my desktop), but with a new name (based on the time for example). This would make it so I could host a free image processor that never stored any data other than tempfiles. Is that possible? Something like Rails' send_file method, but I'm using Sinatra and am looking for something in pure ruby. What's the basic concept behind this? What if I wanted to do this for multiple files? Åssuming I can get multiple files uploaded no problem, how can I download all of them automatically?

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• How to analyse Dalvik GC behaviour?

  - by HRJ

  I am developing an application on Android. It is a long running application that continuously processes sensor data. While running the application I see a lot of GC messages in the logcat; about one every second. This is most probably because of objects being created and immediately de-referenced in a loop. How do I find which objects are being created and released immediately? All the java heap analysis tools that I have tried(*) are bothered with the counts and sizes of objects on the heap. While they are useful, I am more interested in finding out the site where temporary short-lived objects get created the most. (*) I tried jcat and Eclipse MAT. I couldn't get hat to work on the Android heap-dumps; it complained of an unsupported dump file version.

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• What is the 'noreq' Filter Type an Alias for?

  - by Alan Storm

  I'm looking in to Magento's filtering options (Ecommerce System and PHP Framekwork with an expansive ORM system). Specifically the addFieldToFilter method. In this method, you specify a SQLish filter by passing in a single element array, with the key indicating the type of filter. For example, array('eq'=>'bar') //eq means equal array('neq'=>'bar') //neq means not equal would each give you a where clause that looks like where field = 'bar'; where field != 'bar'; So, deep in the bowels of the source, I found a comparison type named 'moreq' that maps to a = comparison operator array('moreq'=>'27') where field >= 27 The weird thing is, there's already a 'gteq' comparision type array('gteq'=>'27') where field >= 27 So, my question is, what does moreq stand for? Is is some special SQL concept that's supported in other databases that the Magento guys wants to map to MySQL, or is it just "more required" and an example what happens when you're doing rapid agile and trying to maintain backwards compatibility.

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• What are good uses for Python3's "Function Annotations"

  - by agscala

  Function Annotations: PEP-3107 I ran across a snippet of code demonstrating Python3's function annotations. The concept is simple but I can't think of why these were implemented in Python3 or any good uses for them. Perhaps SO can enlighten me? How it works: def foo(a: 'x', b: 5 + 6, c: list) -> max(2, 9): ... function body ... Everything following the colon after an argument is an 'annotation', and the information following the -> is an annotation for the function's return value. foo.func_annotations would return a dictionary: {'a': 'x', 'b': 11, 'c': list, 'return': 9} What's the significance of having this available?

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• What are the differences between MVP, Presentation Model, MVVM and MVC?

  - by Nicholas

  I have a pretty good idea how each of these patterns work some of the minor differences between them, but are they really all that different from each other? It seems to me that the Presenter, Presentation Model, ViewModel and Controller are essentially the same concept. Why couldn't I classify all of these concepts as controllers? I feel like it might simplify the entire idea a great deal. Can anyone give a clear description of their differences? I want to clarify that I do understand how the patterns work, and have implemented most of them in one technology or another. What I am really looking for is someone's experience with one of these patterns, and why they would not consider their ViewModel a controller for instance.

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• How to insert variables in R twitteR updates?

  - by analyticsPierce

  Hello, I am using the twitteR package in R to update my twitter status with results from analysis. The static tweet function works: library(twitteR) sess = initSession('username','password') tweet = tweet('I am a tweet', sess) However, when I add a variable to display some specific results I get an error. library(twitteR) sess = initSession('username','password') res = c(3,5,8) msg = cat('Results are: ', res, ', that is nice right?') tweet = tweet(msg, sess) Results in: Error in twFromJSON(rawToChar(out)) : Error: Client must provide a 'status' parameter with a value. Any suggestions are appreciated.

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• How should I build a simple database package for my python application?

  - by Carson Myers

  I'm building a database library for my application using sqlite3 as the base. I want to structure it like so: db/ __init__.py users.py blah.py etc.py So I would do this in Python: import db db.users.create('username', 'password') I'm suffering analysis paralysis (oh no!) about how to handle the database connection. I don't really want to use classes in these modules, it doesn't really seem appropriate to be able to create a bunch of "users" objects that can all manipulate the same database in the same ways -- so inheriting a connection is a no-go. Should I have one global connection to the database that all the modules use, and then put this in each module: #users.py from db_stuff import connection Or should I create a new connection for each module and keep that alive? Or should I create a new connection for every transaction? How are these database connections supposed to be used? The same goes for cursor objects: Do I create a new cursor for each transaction? Create just one for each database connection?

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• How to start coding the "Dining Philosophers" simulation?

  - by GrizzlyGuru

  I'm not a beginner at C# but I really need to increase my understanding, so I've picked a classic deadlock problem to code to help teach myself some of the more advanced concepts of C#. The Dining Philosophers Problem seems like a good one, but I need a little help to get started. I know I need to approach the "diners" as objects, but to simulate the random delays between eating, should I look to threading with each diner in a separate thread? Do I need some kind of "master" to monitor all the actions? Any general design concept advice is welcome, but I'd like to do the grunt programming as an exercise. Thanks!

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• basic database design table on rails

  - by runcode

  I am confuse on a concept. I am doing this on rails. Is that Entity set equal to a table in the database? Is that Relationship set equal to a table in the database? Let say we have Entity set "USER" and Entity set "POST" and Entity set "COMMENT" User- can post many posts and comments as they want Post- belong to users Comments-belong to posts ,users, so comment is weak entity. SCHEMA ====== USER -id -name POST -id -user_id(FK) -comment_id (FK) COMMENT -id -user_id (FK) -post_id (FK) so USER,POST,COMMENT are tables I think. And what else is a table? And do I need a table for the relationship??

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• SRAM Cell Diagram - Can someone explain this a bit more clearly? ( From COMP1917 @ UNSW: Lecture 2 o

  - by Kristina

  I've begun watching a series of first year lectures from the University of New South Wales (UNSW) in Australia, and I'm a bit perplexed by the instructors explanation of how an SRAM gate works. I realize this isn't exactly "programming-related" but since it comes from a series of lectures relating to computing and programming, I thought StackOverflow may be able to help (reddit failed me entirely). In this lecture beginning at around 32:12, Richard (the lecturer) tries to explain how a "latch gate" works within SRAM. Although his students seem to keep up, I feel I'm missing something crucial which is preventing the concept from really "clicking" in my brain. For convenience, I've added the image from the video below: Thanks in advance for any help you can provide, but if this question doesn't fit your view of "programming-related" could you please provide an alternate forum for this in a comment when you cast your close vote? Thanks!

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• Handling null values with PowerShell dates

  - by Tim Ferrill

  I'm working on a module to pull data from Oracle into a PowerShell data table, so I can automate some analysis and perform various actions based on the results. Everything seems to be working, and I'm casting columns into specific types based on the column type in Oracle. The problem I'm having has to do with null dates. I can't seem to find a good way to capture that a date column in Oracle has a null value. Is there any way to cast a [datetime] as null or empty?

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• Where's the definitive resource online about how to carry out Agile development?

  - by jdk

  I want to start Agile practices in a team. I'm assuming the information is available for free online about how to specifically carry it out. Online I can locate the manifesto, the alliances and corporations involved but where is the actual central guide or root instruction set about how to do it? (Maybe the practices themselves are more ethereal or subjective than I expect and it's found in multiple places?) Edit to summarize solutions: Agile is a concept so that's what's to be found online about it. However specific processes or methods of Agile development have been created like Scrum and Extreme programming to provide concrete solutions to teams who want to adopt Agile and reap its proposed benefits. Find the shoe (or method) that fits best. Maybe create it. If looking for solutions online to implement Agile development in your organization or for your project, seek out the specific methods too and decide among them.

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• using helper methods in a view in rails 3

  - by Frida777

  Hello everyone, there is something that is disturbing me a bit about rails 3. i am trying to upgrade my application from rails 2 to rails 3. i followed all the steps necessary to do and things were working well for me till now except one thing: i have a helper method that is defined differently in different helpers, for example it is defined in the application_helper in one way and the same method defined in a different way in the homepage_helper, and defined differently in another helper, let's say video_helper, in addition to that, it is used in a shared view that is used throughout the application, now if i am in the homepage, i want this function to get called from the homepage_helper and if i am in the video page, the function must be called from the video_helper, based on the concept of convention in rails, this worked perfectly in rails 2 but in rails 3, the function is always called from the last helper, alphabetically ordered, that is in the example, video_helper. How can i fix this? Kindly advice. Appreciate all the help.

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• Capturing system command output as a string

  - by dreeves

  Perl and PHP do this with backticks. For example: $output = `ls`; This code returns a directory listing into the variable $output. A similar function, system("ls"), returns the operating system return code for the given command. I'm talking about a variant that returns whatever the command prints to stdout. (There are better ways to get the list of files in a directory; the example code is an example of this concept.) How do other languages do this? Is there a canonical name for this function? (I'm going with "backtick"; though maybe I could coin "syslurp".)

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• How should I capture clickstream data?

  - by editor

  I'd like to start using clickstream analysis to improve a dynamic site's user experience. I'd like to rule out two options: parameterizing URLs (index.php?src=http://www.example.com) and immediate database logging. The former makes pretty ugly URLs and isn't great for SEO and the latter might slow down page render when there are lots of concurrent users. Assuming these aren't viable options, I think I'm left with doing an asynchronous POST to a server side script that runs a database query and returns a 204 (no data) response. Is this the best option for capturing clickstream data?

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• Inconsistent Routing Results in MVC

  - by HapiDjus

  Seems I'm still missing something to the MVC routing concept. I have a route that follows nearly the same pattern as another route in an area but for what ever reason I get a 404 every time I attempt to run it. I've tried to use Phil Haack's Route Tester DLL and according to that it hits the correct route (matched route comes out to common/itemhistory/{contentid}). When I try to run it for real, it blows up. I'm trying to map a call to a JsonResult by passing a Guid. I've had success with other routes working fine (common is an area in my site). What could I be doing wrong? context.MapRoute( "ItemHistory", "common/itemhistory/{contentid}", new { controller = "common", action = "GetItemHistory" }, new { contentid = @"^(\{){0,1}[0-9a-fA-F]{8}\-[0-9a-fA-F]{4}\-[0-9a-fA-F]{4}\-[0-9a-fA-F]{4}\-[0-9a-fA-F]{12}(\}){0,1}$" } ); context.MapRoute( "Common_default", "common/{action}", new { controller="common", action = "Index" } );

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• Significance of date 02/31/2157?

  - by dpatchery

  I work in a large scale IT support environment. Twice now we have seen an invalid date of 02/31/2157 being inserted in an Oracle DATE column. So far I have not been able to reproduce this problem, but it appears to be happening occasionally when a user attempts to save '00/00/0000' into the column. I believe the value is originating from a PowerBuilder DataWindow update. The application uses myriad libraries for all sorts of technologies, so this question may be a bit vague, but... Has anyone seen the date 02/31/2157 in some established library that Oracle could be defaulting to when some other invalid date is entered? Perhaps an end-of-time concept analogous to the beginning-of-time date of 1/1/1970?

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• How to organise a many to many relationship in MongoDB

  - by Gareth Elms

  I have two tables/collections; Users and Groups. A user can be a member of any number of groups and a user can also be an owner of any number of groups. In a relational database I'd probably have a third table called UserGroups with a UserID column, a GroupID column and an IsOwner column. I'm using MongoDB and I'm sure there is a different approach for this kind of relationship in a document database. Should I embed the list of groups and groups-as-owner inside the Users table as two arrays of ObjectIDs? Should I also store the list of members and owners in the Groups table as two arrays, effectively mirroring the relationship causing a duplication of relationship information? Or is a bridging UserGroups table a legitimate concept in document databases for many to many relationships? Thanks

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• Asterisk: Originate API - Which card to use to detect busy/ringing/answer event for FXO

  - by spkhaira

  I want to use Originate API of Asterisk to place an outbound call on a FXO channel, for testing purpose I am using X100P card and, as expected, card is not able to detect if the number is busy/ringing or when it is answered. I want to know which card should I use so that I can get such basic events ... I am not really interested in detailed call progress analysis for answering machine or live voice. I just need basic busy/ringing and answer events and maybe a dis-connect event. Thanks.

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• If I take a large datatype. Will it affect performance in sql server

  - by Shantanu Gupta

  If i takes larger datatype where i know i should have taken datatype that was sufficient for possible values that i will insert into a table will affect any performance in sql server in terms of speed or any other way. eg. IsActive (0,1,2,3) not more than 3 in any case. I know i must take tinyint but due to some reasons consider it as compulsion, i am taking every numeric field as bigint and every character field as nVarchar(Max) Please give statistics if possible, to let me try to overcoming that compulsion. I need some solid analysis that can really make someone rethink before taking any datatype.

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• How can I compute the average cost for this solution of the element uniqueness problem?

  - by Alceu Costa

  In the book Introduction to the Design & Analysis of Algorithms, the following solution is proposed to the element uniqueness problem: ALGORITHM UniqueElements(A[0 .. n-1]) // Determines whether all the elements in a given array are distinct // Input: An array A[0 .. n-1] // Output: Returns "true" if all the elements in A are distinct // and false otherwise. for i := 0 to n - 2 do for j := i + 1 to n - 1 do if A[i] = A[j] return false return true How can I compute the average cost (i.e. number of comparisons for a given n) for this algorithm? What is a reasonable assumption about the input?

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