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• Complex behavior generated by simple computation

  - by Yuval A

  Stephen Wolfram gave a fascinating talk at TED about his work with Mathematica and Wolfram Alpha. Amongst other things, he pointed out how very simple computations can yield extremely complex behaviors. (He goes on to discuss his ambition for computing the entire physical universe. Say what you will, you gotta give the guy some credit for his wild ideas...) As an example he showed several cellular automata. What other examples of simple computations do you know of that yield fascinating results?

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• Entry Level Programming Jobs with Applied Math Degree

  - by Mark

  I am about to finish my B.Sc. in Applied Math. I started out in CS a few years back had a bit of a change of heart and decided to go the math route. Now that I am looking for career options finishing up and I'm just wonder how my Applied Math degree will look when applying for programming jobs. I have taken CS courses in C++/Java/C and done 2 semester of Scientific Computing with MATLAB/Mathematica and the like, so I feel like i at least know how to program. Of course I am lacking some of the theoretical courses on the CS. I'd very much like to know how I stack up for a programming job as a math major. Thanks.

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• Best language to learn complementing java

  - by danielrutledge

  Hi all, I'm a somewhat experienced java ee developer, and I wish to complement my background by learning a newish language. I'm recently out of school where I did a ton of scientific computing and some functional programming, so I'm pretty comfortable with those families of languages. If at all possible, I'd like to pick a language with some market value, though I know this is tough to gauge. After snooping around a bit, the consensus seems to be one of Python/Ruby/Perl; how would each of these work with java in a web application environment, and in your opinion which complements it best? Any other suggestions for languages would also be welcome.

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• NFS Server in Java

  - by dmeister

  I search an implementation of a network (or distributed) file system like NFS in Java. The goal is to extend it and do some research stuff with it. On the web I found some implementation e.g. DJ NFS, but the open question is how mature and fast they are. Can anyone purpose a good starting point, has anyone experience with such things? P.S. I know Hadoop DFS and I used it for some projects, but Hadoop is not a good fit for the things I want to do here. --EDIT-- Hadoop is really focused on highly scalable, high throughput computing without the possibilities to overwrite parts of a file and so an. The goal is you could use the filesystem e.g. for user home directories. --EDIT-- More Details: The idea is to modify such a implementation so that the files are not stored directly on a local filesystem, but to apply data de-duplication.

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• How do people prove the correctness of Computer Vision methods?

  - by solvingPuzzles

  I'd like to pose a few abstract questions about computer vision research. I haven't quite been able to answer these questions by searching the web and reading papers. How does someone know whether a computer vision algorithm is correct? How do we define "correct" in the context of computer vision? Do formal proofs play a role in understanding the correctness of computer vision algorithms? A bit of background: I'm about to start my PhD in Computer Science. I enjoy designing fast parallel algorithms and proving the correctness of these algorithms. I've also used OpenCV from some class projects, though I don't have much formal training in computer vision. I've been approached by a potential thesis advisor who works on designing faster and more scalable algorithms for computer vision (e.g. fast image segmentation). I'm trying to understand the common practices in solving computer vision problems.

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• Why aren't unsigned OpenMP index variables allowed?

  - by Moe

  I have a loop in my C++/OpenMP code that looks like this: #pragma omp parallel for for(unsigned int i=0; i<count; i++) { // do stuff } When I compile it (with Visual Studio 2005) I get the following error: error C3016: 'i' : index variable in OpenMP 'for' statement must have signed integral type I understand that the error occurs because i is unsigned instead of signed, and changing i to be signed removed this error. What I want to know is why is this an error? Why aren't unsigned index variables allowed? Looking at the MSDN page for this error gives me no clues.

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• Precompile Lambda Expression Tree conversions as constants?

  - by Nathan

  It is fairly common to take an Expression tree, and convert it to some other form, such as a string representation (for example this question and this question, and I suspect Linq2Sql does something similar). In many cases, perhaps even most cases, the Expression tree conversion will always be the same, i.e. if I have a function public string GenerateSomeSql(Expression<Func<TResult, TProperty>> expression) then any call with the same argument will always return the same result for example: GenerateSomeSql(x => x.Age) //suppose this will always return "select Age from Person" GenerateSomeSql(x => x.Ssn) //suppose this will always return "select Ssn from Person" So, in essence, the function call with a particular argument is really just a constant, except time is wasted at runtime re-computing it continuously. Assuming, for the sake of argument, that the conversion was sufficiently complex to cause a noticeable performance hit, is there any way to pre-compile the function call into an actual constant?

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• How do I give MacPorts privileges?

  - by cojadate

  I tried to install PostgreSQL server development libraries using MacPorts and got the following: Warning: MacPorts running without privileges. You may be unable to complete certain actions (e.g. install). ---> Computing dependencies for postgresql-server-devel ---> Dependencies to be installed: postgresql-devel ---> Building postgresql-devel Error: Target org.macports.build returned: shell command failed Error: The following dependencies failed to build: postgresql-devel Error: Status 1 encountered during processing. To report a bug, see <http://guide.macports.org/#project.tickets> So I guess that means I need to running MacPorts with privileges and try again. Unfortunately I've no idea how to give MacPorts privileges. I'm running OS X 10.6.3

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• Formatting a barcode with hyphens in between - Assignment question

  - by capex

  Hi, The assignment at my first year uni computing course says my program should read a barcode number, and then display the same 13 digit barcode number separated by hyphens. For example, 9300675016902 should look like 930-067501-690-1. The restrictions say I can't use the following: No arrays No strings No functions. Any directions on this? (So far I have done this: part1 = barcode/10000000000; which gives me the first three digits, and this: part4 = barcode%10; which gives me the last digit. Thanks in advance!

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• JavaScript multithreading

  - by Krzysztof Hasinski

  I'm working on comparison for several different methods of implementing (real or fake) multithreading in JavaScript. As far as I know only webworkers and Google Gears WorkerPool can give you real threads (ie. spread across multiple processors with real parallel execution). I've found the following methods: switch between tasks using yield() use setInterval() (or other non-blocking function) with threads waiting one for another use Google Gears WorkerPool threads (with plugin) use html5 web workers I read related questions and found several variations of the above methods, but most of those questions are old, so there might be a few new ideas. I'm wondering - how else can you achieve multithreading in JavaScript? Any other important methods? UPDATE: As pointed out in comments what I really meant was concurrency. UPDATE 2: I found information that Silverlight + JScript supports multithreading, but I'm unable to verify this. UPDATE 3: Google deprecated Gears: http://code.google.com/apis/gears/api_workerpool.html

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• Mixed alignment with Java Swing's GroupLayout

  - by zigdon

  I'm trying to build a GUI window in my application. What I'm trying to do is have a window, with a few buttons at the top, and a large text area. Something like this: +--------------------------------------------------+ | [button1] [button2] [button3] | | +----------------------------------------------+ | | | text area | | | | | | | | | | | | | | | +----------------------------------------------+ | +--------------------------------------------------+ I'm almost there, using GroupLayout: layout.setHorizontalGroup( layout.createParallelGroup() .addGroup(layout.createSequentialGroup() .addComponent(button1) .addComponent(button2)) .addComponent(closeWindow)) .addComponent(textarea1) ); layout.setVerticalGroup( layout.createSequentialGroup() .addGroup(layout.createParallelGroup() .addComponent(button1) .addComponent(button2) .addComponent(button3)) .addComponent(textarea) ); The problem is that this ends up with button3 aligned to the left, with the other two. I can't seem to figure out how I can specify the alignment on just that one button. I can do GroupLayout.Alignment.TRAILING on the entire button bar, but that hits all 3 buttons, which is also not quite right. So what's the correct approach? Since the alignment only applies for Parallel Groups, I don't think having a HorizontalGroup with two Sequential Groups in it will help? What am I missing?

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• Sum of path products in DAG

  - by Jules

  Suppose we have a DAG with edges labeled with numbers. Define the value of a path as the product of the labels. For each (source,sink)-pair I want to find the sum of the values of all the paths from source to sink. You can do this in polynomial time with dynamic programming, but there are still some choices that can be made in how you decompose the problem. In my case I have one DAG that has to be evaluated repeatedly with different labelings. My question is: for a given DAG, how can we pre-compute a good strategy for computing these values for different labelings repeatedly. It would be nice if there was an algorithm that finds an optimal way, for example a way that minimizes the number of multiplications. But perhaps this is too much to ask, I would be very happy with an algorithm that just gives a good decomposition.

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• Help using Horner's rule and Hash Functions in JAVA?

  - by Matt

  I am trying to use Horner's rule to convert words to integers. I understand how it works and how if the word is long, it may cause an overflow. My ultimate goal is to use the converted integer in a hash function h(x)=x mod tableSize. My book suggests, because of the overflow, you could "apply the mod operator after computing each parenthesized expression in Horner's rule." I don't exactly understand what they mean by this. Say the expression looks like this: ((14*32+15)*32+20)*32+5 Do I take the mod tableSize after each parenthesized expression and add them together? What would it look like with this hash function and this example of Horner's rule?

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• Machine learning in OCaml or Haskell?

  - by griffin

  I'm hoping to use either Haskell or OCaml on a new project because R is too slow. I need to be able to use support vectory machines, ideally separating out each execution to run in parallel. I want to use a functional language and I have the feeling that these two are the best so far as performance and elegance are concerned (I like Clojure, but it wasn't as fast in a short test). I am leaning towards OCaml because there appears to be more support for integration with other languages so it could be a better fit in the long run (e.g. OCaml-R). Does anyone know of a good tutorial for this kind of analysis, or a code example, in either Haskell or OCaml?

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• How to correctly pop a modeless dialog from console using MFC

  - by Vertilka

  I need to create a console application that has a main() function and pop a modeless dialog, so the console can still work in parallel to the modeless dialog (do other work, like communicating with the modeless dialog). Whatever i tried, i could only pop a modal dialog. (where the console is in hold till the modal dialog close itself). When switching to modeless dialog using Create() and ShowWindow() the dialog is displayed without its controls and it freeze / block (you can see the hourglass cursor). 1) i tried to pop the modeless dialog from the main() function 2) i tried to pop the modeless dialog from the InitInstance() of a CWinApp derived class In all cases the modeless dialog freeze / block. I believe this is a one line solution. TNX,Vertilka

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• http/html/ajax: show result before site is completely processed

  - by chris

  hi! I am looking for a way to show in a webapp in front of a task a wait-message and after it hide the message. The task is running a longer time. I dont know if it is possible at all. The problem is, so far I can see, that the site will be returned to the users browser AFTER the task is completed because the task is part of the site as a inline code replaces by the webserver interpreter (no matter if php, perl or whatever). The only solution I can imagine is to parallel the task with threads or processes and requery the state with ajax in the website. Any idea to do it less complex? Thanks for help! regards chris

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• Need details about applications that are running on Windows Azure

  - by veda

  I have an application which requires large amount of data storage (say some PB) and computing resources. Instead of going for clusters, I am planning to propose to use Windows Azure Cloud for this application. I have gone through white papers of Windows Azure and have collected some details about Azure. But I feel that is not substantial. I need to do some case study about applications that are running on the azure and that uses azure storage efficiently. I looked for several research paper in related to performance of the applications in Windows Azure. But as Azure was quite new, I wasn't able to find any. Now, I am looking for some white papers/details regarding application that uses azure storage to substantiate my proposal. I also need to understand the windows azure storage architecture and virtual machine architecture. Do anyone know some research papers or details or blogs or something related to these topics.

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• Sharing view logic in Django

  - by Jeremy B.

  I've begun diving into Django again and I'm having trouble finding the parallel to some common concepts from my life in C#. While using .NET MVC I very often find myself creating a base controller which will provide a base action implementation to take care of the type of stuff I want to do on every request, like retrieving user information, getting localization values. Where I'm finding myself confused is how to do this in Django. I am getting more familiar with the MVT concept but I can't seem to find how to solve this scenario. I've looked at class based views and the generic views yet they didn't seem to work how I expected. What am I missing? How can i create default logic that each view will be instructed to run but not have to write it in each view method?

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• Binomial test in Python

  - by Morlock

  I need to do a binomial test in Python that allows calculation for 'n' numbers of the order of 10000. I have implemented a quick binomial_test function using scipy.misc.comb, however, it is pretty much limited around n = 1000, I guess because it reaches the biggest representable number while computing factorials or the combinatorial itself. Here is my function: from scipy.misc import comb def binomial_test(n, k): """Calculate binomial probability """ p = comb(n, k) * 0.5**k * 0.5**(n-k) return p How could I use a native python (or numpy, scipy...) function in order to calculate that binomial probability? If possible, I need scipy 0.7.2 compatible code. Many thanks!

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• In C#, can I hide/modify accessors in subclasses?

  - by Diego

  I'm not even sure what this principle is called or how to search for it, so I sincerely apologize if it has been brought up before, but the best way to do it is with an example. class Properties { public string Name { get; set; } } class MyClass { class SubProperties: Properties { public override Name { get { return GetActualName(); } set { _value = SetActualName(value); } } } public SubProperties ClassProperties; private GetActualName() { ClassProperties.Name = "name"; } private SetActualName(string s) { ClassProperties.Name = SomeOtherFunction(s); } } The idea is to have any object that instantiates MyClass have a fully accessible property ClassProperties. To that object, it would look exactly like a Properties object, but behind the scenes, MyClass is actually computing and modifying the results of the fields. This method of declaration is obviously wrong since I can't access GetActualName() and SetActualName() from within the SubProperties definition. How would I achieve something like this?

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• How to move an element in a sorted list and keep the CouchDb write "atomic"

  - by karlthorwald

  I have elements of a list in couchdb documents. Let's say these are 3 elements in 3 documents: { "id" : "783587346", "type" : "aList", "content" : "joey", "sort" : 100.0 } { "id" : "358734ff6", "type" : "aList", "content" : "jill", "sort" : 110.0 } { "id" : "abf587346", "type" : "aList", "content" : "jack", "sort" : 120.0 } A view retrieves all "aList" documents and displays them sorted by "sort". Now I want to move the elements, when I want to move "jack" to the middle, I could do this atomic in one write and change it's sort key to 105.0. The view now returns the documents in the new sort order. After a lot of sorting I could end up with sort keys like 50.99999 and 50.99998 after some years and in extreme situations run out of digits? What can you recommend, is there a better way to do this? I'd rather keep the elements in seperate documents. Different users might edit different elements in parallel (which also can get tricky). Maybe there is a much better way?

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• Pipeline For Downloading and Processing Files In Unix/Linux Environment With Perl

  - by neversaint

  I have a list of files URLS where I want to download them: http://somedomain.com/foo1.gz http://somedomain.com/foo2.gz http://somedomain.com/foo3.gz What I want to do is the following for each file: Download foo1,2.. in parallel with wget and nohup. Every time it complete download process them with myscript.sh What I have is this: #! /usr/bin/perl @files = glob("foo*.gz"); foreach $file (@files) { my $downurls = "http://somedomain.com/".$file; system("nohup wget $file &"); system("./myscript.sh $file >> output.txt"); } The problem is that I can't tell the above pipeline when does the file finish downloading. So now it myscript.sh doesn't get executed properly. What's the right way to achieve this?

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• Scripting window positioning in OS X

  - by Matt Trent

  My primary computing setup is a macbook pro with a large external monitor. I'm looking for a convenient way of moving a number of the windows of open programs from the laptop screen to the external monitor when I plug it in. I've seen a few partial scripts for accomplishing this, but nothing comprehensive. Ideally I'd like to specify the laptop screen location and external monitor location for each window and be able to toggle between them. Is anyone aware of any existing utility or Applscripts that can perform this?

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• C or Ada for engineering computations?

  - by yCalleecharan

  Hi,as an engineer I currently use C to write programs dealing with numerical methods. I like C as it's very fast. I don't want to move to C++ and I have been reading a bit about Ada which has some very good sides. I believe that much of the software in big industries have been or more correctly were written in Ada. I would like to know how C compares with Ada. Is Ada fast as C? I understand that no language is perfect but I would like to know if Ada was designed for scientific computing. Thanks a lot...

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• Showing edittext obliquely in android

  - by Chandra Sekhar

  I have an EditText, which generally shows parallel to the screen X-axis. I want to show it obliquely (around 45 degree to horizontal axis). Is it possible to do this in Android. Please guide me in a direction so that I can try for it. After getting the two links in the answer by pawelzeiba, I proceed a little bit in solving this, but stuck again so I put another question on this. here is the link. So please help me to solve this.

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