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• What is it about Fibonacci numbers?

  - by Ian Bishop

  Fibonacci numbers have become a popular introduction to recursion for Computer Science students and there's a strong argument that they persist within nature. For these reasons, many of us are familiar with them. They also exist within Computer Science elsewhere too; in surprisingly efficient data structures and algorithms based upon the sequence. There are two main examples that come to mind: Fibonacci heaps which have better amortized running time than binomial heaps. Fibonacci search which shares O(log N) running time with binary search on an ordered array. Is there some special property of these numbers that gives them an advantage over other numerical sequences? Is it a density quality? What other possible applications could they have? It seems strange to me as there are many natural number sequences that occur in other recursive problems, but I've never seen a Catalan heap.

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• Efficiently compute the row sums of a 3d array in R

  - by Gavin Simpson

  Consider the array a: > a <- array(c(1:9, 1:9), c(3,3,2)) > a , , 1 [,1] [,2] [,3] [1,] 1 4 7 [2,] 2 5 8 [3,] 3 6 9 , , 2 [,1] [,2] [,3] [1,] 1 4 7 [2,] 2 5 8 [3,] 3 6 9 How do we efficiently compute the row sums of the matrices indexed by the third dimension, such that the result is: [,1] [,2] [1,] 12 12 [2,] 15 15 [3,] 18 18 ?? The column sums are easy via the 'dims' argument of colSums(): > colSums(a, dims = 1) but I cannot find a way to use rowSums() on the array to achieve the desired result, as it has a different interpretation of 'dims' to that of colSums(). It is simple to compute the desired row sums using: > apply(a, 3, rowSums) [,1] [,2] [1,] 12 12 [2,] 15 15 [3,] 18 18 but that is just hiding the loop. Are there other efficient, truly vectorised, ways of computing the required row sums?

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• How to store static content across branches in a single location in version control

  - by Shravan

  [Just a random thought] I have a pdf doc that is downloaded when the user clicks on 'help' on my website. Now, this is a pretty huge document and is saved in version control (SVN) and is thus copied for all branches that exist in SVN. This is static content and something that developers are not working on, and does not change often. Is there a more efficient way to store it (that would not hamper local deployments) that would make SVN checkouts and updates relatively faster. I know the benefit we get is not huge, this is something that came to my head none the less.

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• How to deal with Rounding-off TimeSpan?

  - by infant programmer

  I take the difference between two DateTime fields, and store it in a TimeSpan variable, Now I have to round-off the TimeSpan by the following rules: if the minutes in TimeSpan is less than 30 then Minutes and Seconds must be set to zero, if the minutes in TimeSpan is equal to or greater than 30 then hours must be incremented by 1 and Minutes and Seconds must be set to zero. TimeSpan can also be a negative value, so in that case I need to preserve the sign.. I could be able to achieve the requirement if the TimeSpan wasn't a negative value, though I have written a code I am not happy with its inefficiency as it is more bulky .. Please suggest me a simpler and efficient method. Thanks regards,

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• C# Importing Large Volume of Data from CSV to Database

  - by guazz

  What's the most efficient method to load large volumes of data from CSV (3 million + rows) to a database. The data needs to be formatted(e.g. name column needs to be split into first name and last name, etc.) I need to do this in a efficiently as possible i.e. time constraints I am siding with the option of reading, transforming and loading the data using a C# application row-by-row? Is this ideal, if not, what are my options? Should I use multithreading?

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• Shared library to minimise size of FLA file

  - by Dmitry

  In a project we use large flash FLA file with lots of graphic assets, but the actual data that is changed is just in a few symbols. Sometimes it is not very efficient to transfer the whole FLA file that comes up to 20MB now. I was thinking about using Shared Libraries, but it seems that, even if you import external library, it still copies the whole assets into the destination file, but does not link it from external file. Consequently, size of the FLA file still remains the same. Is there any way to split FLA files into few separate in order to minimise size of the most frequently updated file and keep all unchanged data in another file?

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• How to return arrays with the biggest elements in C#?

  - by theateist

  I have multiple int arrays: 1) [1 , 202,4 ,55] 2) [40, 7] 3) [2 , 48 ,5] 4) [40, 8 ,90] I need to get the array that has the biggest numbers in all positions. In my case that would be array #4. Explanation: arrays #2, #4 have the biggest number in 1st position, so after the first iteration these 2 arrays will be returned ([40, 7] and [40, 8 ,90]) now after comparing 2nd position of the returned array from previous iteration we will get array #4 because 8 7 and so on... Can you suggest an efficient algorithm for this? Doing with Linq will be preferable. UPDATE There is no limitation for the length, but as soon as some number in any position is greater, so this array is the biggest.

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• Best practice -- Content Tracking Remote Data (cURL, file_get_contents, cron, et. al)?

  - by user322787

  I am attempting to build a script that will log data that changes every 1 second. The initial thought was "Just run a php file that does a cURL every second from cron" -- but I have a very strong feeling that this isn't the right way to go about it. Here are my specifications: There are currently 10 sites I need to gather data from and log to a database -- this number will invariably increase over time, so the solution needs to be scalable. Each site has data that it spits out to a URL every second, but only keeps 10 lines on the page, and they can sometimes spit out up to 10 lines each time, so I need to pick up that data every second to ensure I get all the data. As I will also be writing this data to my own DB, there's going to be I/O every second of every day for a considerably long time. Barring magic, what is the most efficient way to achieve this? it might help to know that the data that I am getting every second is very small, under 500bytes.

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• How to properly catch a 404 error in .NET

  - by Luke101

  I would like to know the proper way to catch a 404 error with c# asp.net here is the code I'm using HttpWebRequest request = (HttpWebRequest) WebRequest.Create(String.Format("http://www.gravatar.com/avatar/{0}?d=404", hashe)); // execute the request try { //TODO: test for good connectivity first //So it will not update the whole database with bad avatars HttpWebResponse response = (HttpWebResponse)request.GetResponse(); Response.Write("has avatar"); } catch (Exception ex) { if (ex.ToString().Contains("404")) { Response.Write("No avatar"); } } This code works but I just would like to know if this is the most efficient.

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• Converting mxml Rect & SolidColor to actionscript

  - by touB

  I'm trying to learn how to use actionscript over mxml for flexibility. I have this simple block of mxml that I'm trying to convert to actionscript, but I'm stuck half way though <s:Rect id="theRect" x="0" y="50" width="15%" height="15%"> <s:fill> <s:SolidColor color="black" alpha="0.9" /> </s:fill> </s:Rect> I can convert the Rect no problem to private var theRect:Rect = new Rect(); theRect.x = 0; theRect.y = 50; theRect.width = "15%"; theRect.height = "15%"; then I'm stuck on the fill. What's the most efficient way to add the SolidColor in as few lines of code as possible.

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• Longest substring that appears n times

  - by xcoders

  For a string of length L, I want to find the longest substring that appears n (n<L) or more times in ths string. For example, the longest substring that occurs 2 or more times in "BANANA" is "ANA", once starting from index 1, and once again starting from index 3. The substrings are allowed to overlap. In the string "FFFFFF", the longest string that appears 3 or more times is "FFFF". The brute force algorithm for n=2 would be selecting all pairs of indexes in the string, then running along until the characters are different. The running-along part takes O(L) and the number of pairs is O(L^2) (duplicates are not allowed but I'm ignoring that) so the complexity of this algorithm for n=2 would be O(L^3). For greater values of n, this grows exponentially. Is there a more efficient algorithm for this problem?

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• How to roll my own index in c#?

  - by bill seacham

  I need a faster way to create an index file. The application generates pairs of items to be indexed. I currently add each pair as it is generated to a sorted dictionary and then write it out to a disk file. This works well until the number of items added exceeds one million, at which time it slows to the point that is unacceptable. There can be as many as three million data items to be indexed. I prefer to avoid a database because I do not want to significantly increase the size of the deployment package, which is now less than one-half of one megabyte. I tried Access but it is even slower than the sorted dictionary -if it had an efficient bulk load utility then that might work, but I do not find such a tool for Access. Is there a better way to roll my own index?

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• Return specific HREF attribute using Xpath query

  - by Michael Pasqualone

  Having a major brain freeze, I have the following chunk of code: // Get web address $domQuery = query_HtmlDocument($html, '//a[@class="productLink"]'); foreach($domQuery as $rtn) { $web = $rtn->getAttribute('href'); } Which obviously gets the entire href attribute, however I only want 1 specific attribute within the href. I.e. If the href is: /website/product1234.do?code=1234&version=1.3&somethingelse=blaah I only want to return the variable for "version", so wish to only return "1.3" in my example. What's most efficient way to do this?

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• Opinions regarding C++ programming practice

  - by Sagar

  I have a program that I am writing, not too big. Apart from the main function, it has about 15 other functions that called for various tasks at various times. The code works just fine all in one file, and as it is right now. However, I was wondering if anyone had any advice on whether it is smarter/more efficient/better programming to put those functions in a separate file different from where main is, or whether it even matters at all. If yes, why? If no, why not? I am not new at C++, but definitely not an expert either, so if you think this question is stupid, feel free to tell me so. Thanks for your time!

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• C++ Thread Safe Integer

  - by Paul Ridgway

  Hello everyone, I have currently created a C++ class for a thread safe integer which simply stores an integer privately and has public get a set functions which use a boost::mutex to ensure that only one change at a time can be applied to the integer. Is this the most efficient way to do it, I have been informed that mutexes are quite resource intensive? The class is used a lot, very rapidly so it could well be a bottleneck... Googleing C++ Thread Safe Integer returns unclear views and oppinions on the thread safety of integer operations on different architectures. Some say that a 32bit int on a 32bit arch is safe, but 64 on 32 isn't due to 'alignment' Others say it is compiler/OS specific (which I don't doubt). I am using Ubuntu 9.10 on 32 bit machines, some have dual cores and so threads may be executed simultaneously on different cores in some cases and I am using GCC 4.4's g++ compiler. Thanks in advance...

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• to get columns from Excel files using Apache POI??

  - by posdef

  Hi, In order to do some statistical analysis I need to extract values in a column of an Excel sheet. I have been using the Apache POI package to read from Excel files, and it works fine when one needs to iterate over rows. However I couldn't find anything about getting columns neither in the API (link text) nor through google searching. As I need to get max and min values of different columns and generate random numbers using these values, so without picking up individual columns, the only other option is to iterate over rows and columns to get the values and compare one by one, which doesn't sound all that time-efficient. Any ideas on how to tackle this problem? Thanks,

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• Get value from ajax-loaded form before submitting

  - by ldvldv

  Hi, I have an app that loads an ajax form when a button is clicked. I then want to check a value in that ajax loaded form called "comment_content" so that I don't send an ajax request if the comment_content is empty. I can capture the form submission using the live method, however, I can't capture the form element because it needs an element. I was looking at livequery but was wondering if there is a more efficient way by using live or if that I shouldn't even bother? Your help is very much appreciated. $("#comment_submit").live('click', function(){ var comment = $("#comment_content").html(); if(comment == ""){ $("#notice").html("").stop(true, true); $("#notice").append("<p>Are you going to write something in that comment?</p>"); $('#notice').slideDown().delay(2000).slideUp(); return false; } return true; });

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• LINQ to Entity, joining on NOT IN tables

  - by SlackerCoder

  My brain seems to be mush right now! I am using LINQ to Entity, and I need to get some data from one table that does NOT exist in another table. For example: I need the groupID, groupname and groupnumber from TABLE A where they do not exist in TABLE B. The groupID will exist in TABLE B, along with other relevant information. The tables do not have any relationship. In SQL it would be quite simply (there is a more elegant and efficient solution, but I want to paint a picture of what I need) SELECT GroupID, GroupName, GroupNumber, FROM TableA WHERE GroupID NOT IN (SELECT GroupID FROM TableB) Is there an easy/elegant way to do this? Right now I have a bunch of queries hitting the db, then comparing, etc. It's pretty messy. Thanks.

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• CUDA small kernel 2d convolution - how to do it

  - by paulAl

  I've been experimenting with CUDA kernels for days to perform a fast 2D convolution between a 500x500 image (but I could also vary the dimensions) and a very small 2D kernel (a laplacian 2d kernel, so it's a 3x3 kernel.. too small to take a huge advantage with all the cuda threads). I created a CPU classic implementation (two for loops, as easy as you would think) and then I started creating CUDA kernels. After a few disappointing attempts to perform a faster convolution I ended up with this code: http://www.evl.uic.edu/sjames/cs525/final.html (see the Shared Memory section), it basically lets a 16x16 threads block load all the convolution data he needs in the shared memory and then performs the convolution. Nothing, the CPU is still a lot faster. I didn't try the FFT approach because the CUDA SDK states that it is efficient with large kernel sizes. Whether or not you read everything I wrote, my question is: how can I perform a fast 2D convolution between a relatively large image and a very small kernel (3x3) with CUDA?

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• Programming language for fast calculations with big integers

  - by sub

  I'm doing Project Euler problems at the moment and I can solve most of them using my own programming language which uses direct C++ integers (so they are bound to 2^32 on my machine). However, at times there are problems which require me to work with very high numbers, I can't do that with native integers. So I implemented a BigInt library in my language which unfortunately gets extremely slow at times. Is there a programming language suitable for very efficient handling of big numbers? I mean that I want to do the things I could do in other programming languages with it (variables, loops, etc.), but in a faster way. If you have got tips for workarounds of the 2^32 limit in my language/C++/other languages, please tell me too!

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• How to store images efficiently (memory-wise) while still being able to process them

  - by Sheeo

  I'm working on a silverlight project where users get to create their own Collages. The problem When loading images into memory, I'm using BitmapImage so that they can be displayed directly with the Image control--but they're locked in afterwards. So I've tried storing them seperately aswell, but that just sucks up huge amounts of RAM. So in short, is there a class that'll let me store JPEG images, be able to show them with the image control, and still be able to export it afterwards? All this needs to be efficient--i.e. I'd rather not want any copying to ARGB arrays or use the WriteableBitmap to copy them over. I require to work with large collections of images, up to 300 at most. Any help apreciated!

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• WPF: How to efficiently update an Image 30 times per second

  - by John

  Hello, I'm writing a WPF application that uses a component, and this component returns a pointer (IntPtr) to pixels of a bitmap (stride * height). I know in advance that the bitmap is a 24bits rgb, its width and height. Updating the Image control with these bitmaps makes up a video to the user, but I'm not sure what's the most efficient way to do that, most of the time the CPU usage goes to 75%+ and memory changing from 40mb to 500mb and the nI think GC starts to work and then it drops again to 40mm. The app starts to not be responsive. What shoud I do? thanks!

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• How to store the result of a JSP in a string?

  - by Spines

  I want to store the result of a JSP in a string. For example, I want to be able to call a function like: String result = ProcessJsp("/jspfile.jsp"); Also, this must be rather efficient. Making a url request to the jsp and then storing it would definitely be too slow. How could I do this? Here are my thoughts on how to do this, though I'm not sure if it would work, and I'm hoping there is something simpler: Do RequestDispatcher("/jspfile.jsp").include(hreq, hresp), but instead of putting the real HttpResponse object in there, you put your own where the getWriter() method returns something that writes to your String or a memory buffer, etc.

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• Best way to collect and store data daily?

  - by mktb

  I have a bunch of statistics: # of users, # of families, ratio user/family, etc. I'd like to store these daily so I can view this data historically. However, I'm looking for the most effective way to store this data. Should I run a cron job that writes to the database DATE: today USERS: 123 FAMILIES: 456 RATIO: 7.89 or whatever? (or should I write multiple rows like DATE: today DATATYPE: users VALUE: 123?) Or is there another option I can use that is more efficient or more effective? Thanks!

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• Python: Unpack arbitary length bits for database storage

  - by sberry2A

  I have a binary data format consisting of 18,000+ packed int64s, ints, shorts, bytes and chars. The data is packed to minimize it's size, so they don't always use byte sized chunks. For example, a number whose min and max value are 31, 32 respectively might be stored with a single bit where the actual value is bitvalue + min, so 0 is 31 and 1 is 32. I am looking for the most efficient way to unpack all of these for subsequent processing and database storage. Right now I am able to read any value by using either struct.unpack, or BitBuffer. I use struct.unpack for any data that starts on a bit where (bit-offset % 8 == 0 and data-length % 8 == 0) and I use BitBuffer for anything else. I know the offset and size of every packed piece of data, so what is going to be the fasted way to completely unpack them? Many thanks.

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