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• Is Python appropriate for algorithms focused on scientific computing?

  - by gmatt

  My interests in programming lie mainly in algorithms, and lately I have seen many reputable researchers write a lot of their code in python. How easy and convenient is python for scientific computing? Does it have a library of algorithms that compares to matlab's? Is Python a scripting language or does it compile? Is it a great language for prototyping an algorithm? How long would it take me to learn enough of it to be productive provided I know C well and OO programming somewhat? Is it OO based? Sorry for the condensed format of questions, but I'm very curious and was hoping a more experienced programmer could help me out.

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• SOLR and Natural Language Parsing - Can I use it?

  - by andy

  hey guys, my requirements are pretty similar to this: Requirements http://stackoverflow.com/questions/90580/word-frequency-algorithm-for-natural-language-processing Using Solr While the answer for that question is excellent, I was wondering if I could make use of all the time I spent getting to know SOLR for my NLP. I thought of SOLR because: It's got a bunch of tokenizers and performs a lot of NLP. It's pretty use to use out of the box. It's restful distributed app, so it's easy to hook up I've spent some time with it, so using could save me time. Can I use Solr? Although the above reasons are good, I don't know SOLR THAT well, so I need to know if it would be appropriate for my requirements. Ideal Usage Ideally, I'd like to configure SOLR, and then be able to send SOLR some text, and retrieve the indexed tonkenized content. Context So you guys know, I'm working on a small component of a bigger recommendation engine.

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• Aes key length significance/implications

  - by cppdev

  Hi, I am using a AES algorithm in my application for encrypting plain text. I am trying to use a key which is a six digit number. But as per the AES spec, the key should be minimum sixteen bytes in length. I am planning to append leading zeros to my six digit number to make it a 16 byte and then use this as a key. Would it have any security implications ? I mean will it make my ciphertext more prone to attacks. Please help.

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• How to estimate the quality of a web page?

  - by roddik

  Hello, I'm doing a university project, that must gather and combine data on a user provided topic. The problem I've encountered is that Google search results for many terms are polluted with low quality autogenerated pages and if I use them, I can end up with wrong facts. How is it possible to estimate the quality/trustworthiness of a page? You may think "nah, Google engineers are working on the problem for 10 years and he's asking for a solution", but if you think about it, SE must provide up-to-date content and if it marks a good page as a bad one, users will be dissatisfied. I don't have such limitations, so if the algorithm accidentally marks as bad some good pages, that wouldn't be a problem.

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• What are some useful SQL statements that should be known by all developers who may touch the Back en

  - by Jian Lin

  What are some useful SQL statements that should be known by all developers who may touch the Back end side of the project? (Update: just like in algorithm, we know there are sorting problems, shuffling problems, and we know some solutions to them. This question is aiming at the same thing). For example, ones I can think of are: Get a list of Employees and their boss. Or one with the employee's salary greater than the boss. (Self-join) Get a list of the most popular Classes registered by students, from the greatest number to the smallest. (Count, group by, order by) Get a list of Classes that are not registered by any students. (Outer join and check whether the match is NULL, or by Get from Classes table, all ClassIDs which are NOT IN (a subquery to get all ClassIDs from the Registrations table)) Are there some SQL statements that should be under the sleeve of all developers that might touch back end data?

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• Subtracting Delphi Time Ranges from a Date Range, Calculate Remaining Time

  - by Anagoge

  I'm looking for an algorithm that will help calculate a workday working time length. It would have an input date range and then allow subtracting partially or completely intersecting time range slices from that date range and the result would be the number of minutes (or the fraction/multiple of a day) left in the original date range, after subtracting out the various non-working time slices. For Example: Input date range: 1/4/2010 11:21 am - 1/5/2010 3:00 pm Subtract out any partially or completely intersecting slices like this: Remove all day Sunday Non-Sundays remove 11:00 - 12:00 Non-Sundays remove time after 5:00 pm Non-Sundays remove time before 8:00 am Non-Sundays remove time 9:15 - 9:30 am Output: # of minutes left in the input date range I don't need anything overly-general. I could hardcode the rules to simplify the code. If anyone knows of sample code or a library/function somewhere, or has some pseudo-code ideas, I'd love something to start with. I didn't see anything in DateUtils, for example. Even a basic function that calculates the number of minutes of overlap in two date ranges to subtract out would be a good start.

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• Strange problem when converting RGB to HSV

  - by zaplec

  Hi, I made a small RGB to HSV converter algorithm with C. It seems to work pretty well, but there is one strange problem: If I first convert i.e. a 800x600 picture into HSV map and then back to RGB map without doing any changes in the values, I get some pixels that are convertet incorrectly. Then if I try to convert those misbehaving single pixels alone to and back, they're converted correctly. Any idea what could be the problem? I'm using Daniel Karlings PNGLite to open that PNG file. Here are the source code of my main.c, rgbtohsv.c and rgbtohsv.h rgbToHsv.h rgbToHsv.c pngmain.c I linked pngmain only that if somebody wants to test and run this on his own system. -zaplec

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• How to detect identical part(s) inside string?

  - by Horace Ho

  I try to break down the http://stackoverflow.com/questions/2711961/decoding-algorithm-wanted question into smaller questions. This is Part I. Question: two strings: s1 and s2 part of s1 is identical to part of s2 space is separator how to extract the identical part(s)? example 1: s1 = "12 November 2010 - 1 visitor" s2 = "6 July 2010 - 100 visitors" the identical parts are "2010", "-", "1" and "visitor" example 2: s1 = "Welcome, John!" s2 = "Welcome, Peter!" the identical parts are "Welcome," and "!" Python and Ruby preferred. Thanks

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• Finding if a path between 2 sides of a game board exists

  - by Meny

  Hi, i'm currently working on a game as an assignment for school in java. the game cuurently is designed for Console. the game is for 2 players, one attacking from north to south, and the other from west to east. the purpose of the game is to build a "bridge"/"path" between the 2 of your sides before your opponent does. for example: A B C D E F 1 _ _ X _ _ _ 1 2 O X X _ _ _ 2 3 O X O O O O 3 4 O X O _ _ _ 4 5 X X _ _ _ _ 5 6 X O _ _ _ _ 6 A B C D E F player that attacks from north to south won (path/bridge from C to A) my problem is, what algorithm would be good to check if the user have managed to create a path (will be checked at the end of each turn). you're help would be very appreciated.

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• tomcat multithreading problem

  - by jutky

  Hi all I'm writing a java application that runs in Tomcat, on a multi-core hardware. The application executes an algorithm and returns the answer to the user. The problem is that even when I run two requests simultaneously, the tomcat process uses at most one CPU core. As far as I understand each request in Tomcat is executed in separate thread, and JVM should run each thread on separate CPU core. What could be the problem that bounds the JVM or Tomcat to use no more than one core? Thanks in advance.

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• Breadth first search all paths

  - by Amndeep7

  First of all, thank you for looking at this question. For a school assignment we're supposed to create a BFS algorithm and use it to do various things. One of these things is that we're supposed to find all of the paths between the root and the goal nodes of a graph. I have no idea how to do this as I can't find a way to keep track of all of the alternate routes without also including copies/cycles. Here is my BFS code: def makePath(predecessors, last): return makePath(predecessors, predecessors[last]) + [last] if last else [] def BFS1b(node, goal): Q = [node] predecessor = {node:None} while Q: current = Q.pop(0) if current[0] == goal: return makePath(predecessor, goal) for subnode in graph[current[0]][2:]: if subnode[0] not in predecessor: predecessor[subnode[0]] = current[0] Q.append(subnode[0]) A conceptual push in the right direction would be greatly appreciated. tl;dr How do I use BFS to find all of the paths between two nodes?

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• Convert VB6 Randomize to C#

  - by Thomas G. Mayfield

  I'm writing a C# frontend to a legacy database that uses VB6 Rnd() and Randomize() methods for user password encryption. The encryption function is very simplistic and really not all that secure, but it's what all current passwords are stored with. What I'd like to be able to do is authenticate legacy users from a C# application. I can write new encryption (or preferably hashing) code for VB6 so that all future users have a more secure password, and that can be duplicated in C#. But I don't want to require current users to have had their password reset before they can use the new frontend. Is there any way I can reimplement that algorithm in C# so that it produces identical results to the legacy VB6 code?

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• MATLAB: draw centroids

  - by Myx

  Hello - my main question is given a feature centroid, how can I draw it in MATLAB? In more detail, I have an NxNx3 image (an rgb image) of which I take 4x4 blocks and compute a 6-dimensional feature vector for each block. I store these feature vectors in an Mx6 matrix on which I run kmeans function and obtain the centroids in a kx6 matrix, where k is the number of clusters and 6 is the number of features for each block. How can I draw these center clusters in my image in order to visualize if the algorithm is performing the way I wish it to perform? Or if anyone has any other way/suggestions on how I can visualize the centroids on my image, I'd greatly appreciate it. Thank you.

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• Sorting a list of variable length integers delimited by decimal points...

  - by brewerdc

  Hey guys, I'm in need of some help. I have a list of delimited integer values that I need to sort. An example: Typical (alpha?) sort: 1.1.32.22 11.2.4 2.1.3.4 2.11.23.1.2 2.3.7 3.12.3.5 Correct (numerical) sort: 1.1.32.22 2.1.3.4 2.3.7 2.11.23.1.2 3.12.3.5 11.2.4 I'm having trouble figuring out how to setup the algorithm to do such a sort with n number of decimal delimiters and m number of integer fields. Any ideas? This has to have been done before. Let me know if you need more information. Thanks a bunch! -Daniel

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• extract data from an array without using loop in R

  - by Manolo

  I have a vector v with row positions: v<-c(10,3,100,50,...) with those positions I want to extract elements of a matrix, having a column fixed, for example lets suppose my column number is 2, so I am doing: data<-c() data<-c(matrix[[v]][[2]]) matrix has the data in the following format: [[34]] [1] "200_s_at" "4853" "1910" "3554" "2658" So for example, I want to extract from the row 342 the value 1910 only, column 2, and do the same with the next rows but I got an error when I want to do that, is it possible to do it directly? or should I have a loop that read one by one the positions in v and fill the data vector like: #algorithm for i<-1 to length(v) pos<-v[i] data[[i]]<-c(matriz[[pos]][[2]]) next i Thanks

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• Speed up multiple JDBC SQL querys?

  - by paddydub

  I'm working on a shortest path a* algorithm in java with a mysql db. I'm executing the following SQL Query approx 300 times in the program to find route connections from a database of 10,000 bus connections. It takes approx 6-7 seconds to execute the query 300 times. Any suggestions on how I can speed this up or any ideas on a different method i can use ? Thanks ResultSet rs = stmt.executeQuery("select * from connections" + " where Connections.From_Station_stopID ="+StopID+";"); while (rs.next()) { int id = rs.getInt("To_Station_id"); String routeID = rs.getString("To_Station_routeID"); Double lat = rs.getDouble("To_Station_lat"); Double lng = rs.getDouble("To_Station_lng"); int time = rs.getInt("Time"); }

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• head detection from video

  - by Aman Kaushal

  I have to detect heads of people in crowd in real time.For that I detected edge from video using matlab but from edge detected video , how to identify heads that i am unable to do. I used edge detection of video because it is easy to find circle from edged video and detection of head would be easy can anyone help me or suggest me any method for head- detection in real time. I have used VGG head detector and viola jones algorithm but it is only detecting face for small size video not detecting heads for large crowd. Suggestions?

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• Embarrassingly parallel workflow creates too many output files

  - by Hooked

  On a Linux cluster I run many (N > 10^6) independent computations. Each computation takes only a few minutes and the output is a handful of lines. When N was small I was able to store each result in a separate file to be parsed later. With large N however, I find that I am wasting storage space (for the file creation) and simple commands like ls require extra care due to internal limits of bash: -bash: /bin/ls: Argument list too long. Each computation is required to run through a qsub scheduling algorithm so I am unable to create a master program which simply aggregates the output data to a single file. The simple solution of appending to a single fails when two programs finish at the same time and interleave their output. I have no admin access to the cluster, so installing a system-wide database is not an option. How can I collate the output data from embarrassingly parallel computation before it gets unmanageable?

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• Tracing\profiling instructions

  - by LeChuck2k

  Hi Y'all. I'd like to statistically profile my C code at the instruction level. I need to know how many additions, multiplications, devides, etc,... I'm performing. This is not your usual run of the mill code profiling requirement. I'm an algorithm developer and I want to estimate the cost of converting my code to hardware implementations. For this, I'm being asked the instruction call breakdown during run-time (parsing the compiled assembly isn't sufficient as it doesn't consider loops in the code). After looking around, It seems VMWare may offer a possible solution, but I still couldn't find the specific feature that will allow me to trace the instruction call stream of my process. Are you aware of any profiling tools which enable this?

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• I'm having a problem identifying a floating point exception.

  - by Peter Stewart

  I'm using c++ in visual studio express to generate random expression trees for use in a genetic algorithm type of program. Because they are random, the trees often generate (I'll call them exceptions, I'm not sure what they are) Thanks to a suggestion by George, I turned the mask _MCW_EM on so that hardware interrupts are turned off. (the default) So, the program runs uninterrupted, but some of the values returned are: -1.#INF, -1.#NAN, -1.#INV. I don't know how to identify these so that I can throw an exeption: if ( variable == -1.#INF) ?? DigitalRoss in this post seemed to have the solution, but as I understood it I couldn't make it work. I've been looking all over the place for this simple bit of code, that I assumed would be used all the time, but have had no luck. thanks

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• What are some useful SQL statements / usage patterns that should be known by all developers who may

  - by Jian Lin

  What are some useful SQL statements that should be known by all developers who may touch the Back end side of the project? (Update: just like in algorithm, we know there are sorting problems, shuffling problems, and we know some solutions to them. This question is aiming at the same thing). For example, ones I can think of are: Get a list of Employees and their boss. Or one with the employee's salary greater than the boss. (Self-join) Get a list of the most popular Classes registered by students, from the greatest number to the smallest. (Count, group by, order by) Get a list of Classes that are not registered by any students. (Outer join and check whether the match is NULL, or by Get from Classes table, all ClassIDs which are NOT IN (a subquery to get all ClassIDs from the Registrations table)) Are there some SQL statements that should be under the sleeve of all developers that might touch back end data?

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• Encryption-Decryption in Rails

  - by Salil

  Hi All, I am using require 'digest/sha1' to encrypt my password and save into database. During login I authenticate by matching the encrypted password saved in database and again encrypted the one use enter in password field. As of now everything works fine but now I want to do 'Forgot Password' functionality. To do this I need to decrypt the password which is saved in database to find original one. How to decrypt using digest/sha1? Or does anyone know any algorithm which supports encryption & decryption as well? I am using ruby on rails so I need Ruby way to accomplish it.

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• Matching a rotated bitmap to a collage image

  - by Dmi

  Hi, My problem is that I have an image of a detailed street map. On this map, there can be a certain small image of a sign (such as a traffic light icon) rotated at any angle, maybe resized. I have this small image in a bitmap. Is there any algorithm or technique by which I can locate this bitmap if a copy of it exists, rotated and maybe resized, in the large collage image? This is similar to the problem with Augmented Reality and locating the marker image, but mine is only 2D with no perspective distortion.

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• How can I tell if a closed path contains a given point?

  - by Tom Seago

  In Android, I have a Path object which I happen to know defines a closed path, and I need to figure out if a given point is contained within the path. What I was hoping for was something along the lines of path.contains(int x, int y) but that doesn't seem to exist. The specific reason I'm looking for this is because I have a collection of shapes on screen defined as paths, and I want to figure out which one the user clicked on. If there is a better way to be approaching this such as using different UI elements rather than doing it "the hard way" myself, I'm open to suggestions. I'm open to writing an algorithm myself if I have to, but that means different research I guess.

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• [PHP] - Lowering script memory usage in a "big" file creation

  - by Riccardo

  Hi there people, it looks like I'm facing a typical memory outage problem when using a PHP script. The script, originally developed by another person, serves as an XML sitemap creator, and on large websites uses quite a lot of memory. I thought that the problem was related due to an algorithm holding data in memory until the job was done, but digging into the code I have discovered that the script works in this way: open file in output (will contain XML sitemap entries) in the loop: ---- for each entry to be added in sitemap, do fwrite close file end Although there are no huge arrays or variables being kept in memory, this technique uses a lot of memory. I thought that maybe PHP was buffering under the hood the fwrites and "flushing" data at the end of the script, so I have modified the code to close and open the file every Nth record, but the memory usage is still the same.... I'm debugging the script on my computer and watching memory usage: while script execution runs, memory allocation grows. Is there a particular technique to instruct PHP to free unsed memory, to force flushing buffers if any? Thanks

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