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• Why might different computers calculate different arithmetic results in VB.NET?

  - by Eyal

  I have some software written in VB.NET that performs a lot of calculations, mostly extracting jpegs to bitmaps and computing calculations on the pixels like convolutions and matrix multiplication. Different computers are giving me different results despite having identical inputs. What might be the reason? Edit: I can't provide the algorithm because it's proprietary but I can provide all the relevant operations: ULong \ ULong (Turuncating division) Bitmap.Load("filename.bmp') (Load a bitmap into memory) Bitmap.GetPixel(Integer, Integer) (Get a pixel's brightness) Double + Double Double * Double Math.Sqrt(Double) Math.PI Math.Cos(Double) ULong - ULong ULong * ULong ULong << ULong List.OrderBy(Of Double)(Func) Hmm... Is it possible that OrderBy is using a non-stable QuickSort and that QuickSort is using a random pivot? Edit: Just tested, nope. The sort is stable.

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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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• is it possible to dynamically set the level of for loop nesting

  - by galaxy

  I'm working out an algorithm to get permutations like 123 132 213 231 312 321 I'm doing it using nested foreach loops. for (..) { for(..) { for(..) { echo $i . $j . $k . "<br />"; } } } Problem is those # of nested loops are optimized for 3-spot permutations. How can I could I dynamically set the number of nested for loops to generate 4-letter or 5-letter permutations?

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• How do I visualize a complex graph in .Net?

  - by Ivan

  I need to visualize a graph (technically being a set of Entity Framework objects, but I can translate it to another representation if needed) of this kind. I don't know how to name it (by the way, if you know - I'll appreciate if you tell me). It would be ideal for graph elements to be clickable (so that when user clicks on a block, I can handle an event with the element id specified) but I can survive even without any interactivity. Are there any components available good for this task? If no, what should I look for to help me to develop an algorithm for drawing such a graph with visually-comfortable layout?

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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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• Portable Programming IDE

  - by Click Ok

  Frequently I'm brainstormed with programming ideas that I would like to directly code. More or less like "Wow, that algorithm will rock! I need to write it now!". For this kind of "impulse" to write, I use http://www.jarte.com/ that is a cool portable text editor. If I'm near a cybecafe or a friend computer, I just plug the usb pen drive and start to write... So, I would like: 1) a portable minimalist IDE 2) with minimal OS requirement (ie.: I want run from XP, Vista, etc...) 3) any modern language (I can learn a new language if needed. I just want write/test the algoritm) 4) Syntax Highlight/intellisense is good, but not required 5) Free Is there something like this?

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• set / line intersection solution

  - by Xavier

  I have two lists in python and I want to know if they intersect at the same index. Is there a mathematical way of solving this? For example if I have [9,8,7,6,5] and [3,4,5,6,7] I'd like a simple and efficient formula/algorithm that finds that at index 3 they intersect. I know I could do a search just wondering if there is a better way. I know there is a formula to solve two lines in y = mx + b form by subtracting them from each other but my "line" isn't truly a line because its limited to the items in the list and it may have curves. Any help is appreciated.

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• What is better for a student programming in C++ to learn for writing GUI: C# vs QT?

  - by flashnik

  I'm a teacher(instructor) of CS in the university. The course is based on Cormen and Knuth and students program algorithms in C++. But sometimes it is good to show how an algorithm works or just a result of task through GUI. Also in my opinion it's very imporant to be able to write full programs. They will have courses concerning GUI but a three years, later, in fact, before graduatuion. I think that they should be able to write simple GUI applications earlier. So I want to teach them it. How do you think, what is more useful for them to learn: programming GUI with QT or writing GUI in C# and calling unmanaged C++ library?

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• C#: Efficiently search a large string for occurences of other strings

  - by Jon

  Hi, I'm using C# to continuously search for multiple string "keywords" within large strings, which are = 4kb. This code is constantly looping, and sleeps aren't cutting down CPU usage enough while maintaining a reasonable speed. The bog-down is the keyword matching method. I've found a few possibilities, and all of them give similar efficiency. 1) http://tomasp.net/articles/ahocorasick.aspx -I do not have enough keywords for this to be the most efficient algorithm. 2) Regex. Using an instance level, compiled regex. -Provides more functionality than I require, and not quite enough efficiency. 3) String.IndexOf. -I would need to do a "smart" version of this for it provide enough efficiency. Looping through each keyword and calling IndexOf doesn't cut it. Does anyone know of any algorithms or methods that I can use to attain my goal?

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• Gradients and memory

  - by user146780

  I'm creating a drawing application with OpenGL. I'v created an algorithm that generates gradient textures. I then map these to my polygons and this works quite well. What I realized is how much memory this requires. Creating 1000 gradients takes about 800MB and that's way too much. Is there an alternative to textures, or a way to compress them, or another way to map gradients to polygons that doesn't use up as much memory? Thanks My polygons are concave, I use GLUTesselator, and they are multicolored and point to point

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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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• deleting and reusing a temp table in a stored precedure

  - by Sheagorath

  Hi I need to SELECT INTO a temp table multiple times with a loop but I just can't do it, because after the table created by SELECT INTO you can't simply drop the table at the end of the loop, because you can't delete a table and create it again in the same batch. so how can I delete a table in a stored procedure and create it again? is it possible to this without using a temp table? here is a snippet of where I am actualy using the temp table which is supposed to be a pivoting algorithm: WHILE @offset<@NumDays BEGIN SELECT bg.*, j.ID, j.time, j.Status INTO #TEMP1 FROM #TEMP2 AS bg left outer join PersonSchedule j on bg.PersonID = j.PersonID and bg.TimeSlotDateTime = j.TimeSlotDateTime and j.TimeSlotDateTime = @StartDate + @offset DROP TABLE #TEMP2; SELECT * INTO #TEMP2 FROM #TEMP1 DROP TABLE #TEMP1 SET @offset = @offset + 1 END

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• Color space - RGB and YCbCr question

  - by HardCoder1986

  Hello! I am now trying to understand how JPEG encoding works and everything seems fine except the color transformation part. Before attempting to do a DCT in JPEG algorithm, the image is transformed into YCbCr color space. To me this essentially means that we just (comparing to initial RGB image) take a chunk of color information and dispose it while applying the RGB -> YCbCr transformation. So, our encoding steps look generally like RGB -> YCbCr -> DCT -> Huffman. The decoding means inversing this process. And my question is - why does the image (for example, created and exported to JPEG) remain the same in terms of color, although we have to make inverse YCbCr -> RGB transform. Where does the disposed part of color information comes from or how is it handled?

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• How secure are GUIDs in terms of predictability?

  - by ssg

  We're using .NET's Guid.NewGuid() to generate activation codes and API keys currently. I wonder if that poses a security problem since their algorithm is open. .NET Guid uses Win32 CoCreateGuid and I don't know it's internals (possibly MAC address + timestamp?). Can someone derive a second GUID out of the first one, or can he hit it with some smart guesses or is the randomness good enough so search space becomes too big? Generating random keys have the problem of collision, they need a double check before adding to a database. That's why we stuck with GUIDs but I'm unsure about their security for these purposes. Here are the 4 consecutive UUIDGEN outputs: c44dc549-5d92-4330-b451-b29a87848993 d56d4c8d-bfba-4b95-8332-e86d7f204c1c 63cdf958-9d5a-4b63-ae65-74e4237888ea 6fd09369-0fbd-456d-9c06-27fef4c8eca5 Here are 4 of them by Guid.NewGuid(): 0652b193-64c6-4c5e-ad06-9990e1ee3791 374b6313-34a0-4c28-b336-bb2ecd879d0f 3c5a345f-3865-4420-a62c-1cdfd2defed9 5b09d7dc-8546-4ccf-9c85-de0bf4f43bf0

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• For Qt 4.6.x, how to auto-size text to fit in a specified width?

  - by darenchow

  Inside of my QGraphicsRectItem::paint(), I am trying to draw the name of the item within its rect(). However, for each of the different items, they can be of variable width and similarly names can be of variable length. Currently I am starting with a maximum font size, checking if it fits and decrementing it until I find a font size that fits. So far, I haven't been able to find a quick and easy way to do this. Is there a better, or more efficient way to do this? Thanks! void checkFontSize(QPainter *painter, const QString& name) { // check the font size - need a better algorithm... this could take awhile while (painter->fontMetrics().width(name) > rect().width()) { int newsize = painter->font().pointSize() - 1; painter->setFont(QFont(painter->font().family(), newsize)); } }

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• JavaScript - checking for any lowercase letters in a string

  - by pcampbell

  Consider a JavaScript method that needs to check whether a given string is in all uppercase letters. The input strings are people's names. The current algorithm is to check for any lowercase letters. var check1 = "Jack Spratt"; var check2 = "BARBARA FOO-BAR"; var check3 = "JASON D'WIDGET"; var isUpper1 = HasLowercaseCharacters(check1); var isUpper2 = HasLowercaseCharacters(check2); var isUpper3 = HasLowercaseCharacters(check3); function HasLowercaseCharacters(string input) { //pattern for finding whether any lowercase alpha characters exist var allLowercase; return allLowercase.test(input); } Is a regex the best way to go here? What pattern would you use to determine whether a string has any lower case alpha characters?

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• "painting" one array onto another using python / numpy

  - by Nate

  I'm writing a library to process gaze tracking in Python, and I'm rather new to the whole numpy / scipy world. Essentially, I'm looking to take an array of (x,y) values in time and "paint" some shape onto a canvas at those coordinates. For example, the shape might be a blurred circle. The operation I have in mind is more or less identical to using the paintbrush tool in Photoshop. I've got an interative algorithm that trims my "paintbrush" to be within the bounds of my image and adds each point to an accumulator image, but it's slow(!), and it seems like there's probably a fundamentally easier way to do this. Any pointers as to where to start looking?

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• Reverse Bredth First Search in C#

  - by Ngu Soon Hui

  Anyone has a ready implementation of the Reverse Bredth First Search algorithm in C#? By Reverse Bredth First Search, I mean instead of searching a tree starting from a common node, I want to search the tree from the bottom and gradually converged to a common node. Let's see the below figure, this is the output of a Bredth First Search: In my reverse bredth first search, 9,10,11 and 12 will be the first few nodes found ( the order of them are not important as they are all first order). 5, 6, 7 and 8 are the second few nodes found, and so on. 1 would be the last node found. Any ideas or pointers?

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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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• 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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• RSA implementations for Java, alternative to BC

  - by Tom Brito

  The RSA implementation that ships with Bouncy Castle only allows the encrypting of a single block of data. The RSA algorithm is not suited to streaming data and should not be used that way. In a situation like this you should encrypt the data using a randomly generated key and a symmetric cipher, after that you should encrypt the randomly generated key using RSA, and then send the encrypted data and the encrypted random key to the other end where they can reverse the process (ie. decrypt the random key using their RSA private key and then decrypt the data). I can't use the workarond of using symmetric key. So, are there other implementations of RSA than Bouncy Castle?

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• Why does my program occasionally segfault when out of memory rather than throwing std::bad_alloc?

  - by Bradford Larsen

  I have a program that implements several heuristic search algorithms and several domains, designed to experimentally evaluate the various algorithms. The program is written in C++, built using the GNU toolchain, and run on a 64-bit Ubuntu system. When I run my experiments, I use bash's ulimit command to limit the amount of virtual memory the process can use, so that my test system does not start swapping. Certain algorithm/test instance combinations hit the memory limit I have defined. Most of the time, the program throws an std::bad_alloc exception, which is printed by the default handler, at which point the program terminates. Occasionally, rather than this happening, the program simply segfaults. Why does my program occasionally segfault when out of memory, rather than reporting an unhandled std::bad_alloc and terminating?

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• Google Maps API v3 - Directions/Paths breaking KML Overlay Infowindows

  - by Douglas

  I'm in the end stages before content filling and then production on the Google Maps project I've been working on. A number of bugs and such have been thwarted, but this latest one has me relatively stumped. The demo map can be viewed here: http://dougglover.com/samples/finalProduct/ Everything works fine until you create a path using the Directions section(not to be confused with Get Directions). To reproduce the problem, play around with the map, click on a building or two, just to see the functionality. After ensuring that clicking on a building works(brings up an infowindow), choose two buildings to get directions to in the Directions area. It works great with the routing algorithm I've implemented, and the paths show up nicely, and intelligently. The problem being that you can't click buildings anymore to see their info. I'm assuming it has something to do with the z-index error popping up in the console, but I'm not sure how to handle that if it is the problem. Any guidance is greatly appreciated. :)

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• How do I measure distances in an image?

  - by Ram Bhat

  Let's say we have an image like so Let's say we've already used filters and an edge detection algorithm in this pic. Now my goal is to measure distances (NOT actual distances, distance can be in any arbitrary unit) . eg: How do I find the length of the hall? (until the window) Or the height of the bookshelves? How exactly do you place the "scale" and measure. I'm looking for ideas. However it would help if the answers were in terms of OpenCV.

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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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