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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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• Google Web Optimizer -- How long until winning combination?

  - by Django Reinhardt

  I've had an A/B Test running in Google Web Optimizer for six weeks now, and there's still no end in sight. Google is still saying: "We have not gathered enough data yet to show any significant results. When we collect more data we should be able to show you a winning combination." Is there any way of telling how close Google is to making up its mind? (Does anyone know what algorithm does it use to decide if there's been any "high confidence winners"?) According to the Google help documentation: Sometimes we simply need more data to be able to reach a level of high confidence. A tested combination typically needs around 200 conversions for us to judge its performance with certainty. But all of our conversions have over 200 conversations at the moment: 230 / 4061 (Original) 223 / 3937 (Variation 1) 205 / 3984 (Variation 2) 205 / 4007 (Variation 3) How much longer is it going to have to run?? Thanks for any help.

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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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• Security & Authentication: SSL vs SASL

  - by 4herpsand7derpsago

  My understanding is that SSL combines an encryption algorithm (like AES, DES, etc.) with akey exchange method (like Diffier-Hellman) to provide secure encryption and identification services between two endpoints on an un-secure network (like the Internet). My understanding is that SASL is an MD5/Kerberos protocol that pretty much does the same thing. So my question: what are the pros/cons to choosing both and what scenarios make both more preferable? Basically, I'm looking for a guidelines to follow when choosing SSL or to go with SASL instead. Thanks in advance!

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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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• 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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• 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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• How do I draw an ellipse with arbitrary orientation pixel by pixel?

  - by amc

  Hi, I have to draw an ellipse of arbitrary size and orientation pixel by pixel. It seems pretty easy to draw an ellipse whose major and minor axes align with the x and y axes, but rotating the ellipse by an arbitrary angle seems trickier. Initially I though it might work to draw the unrotated ellipse and apply a rotation matrix to each point, but it seems as though that could cause errors do to rounding, and I need rather high precision. Is my suspicion about this method correct? How could I accomplish this task more precisely? I'm programming in C++ (although that shouldn't really matter since this is a more algorithm-oriented question).

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• Straight Line Equation between two points

  - by dafero

  Hi, I need to paint the line witch links two points. I developed my own solution using the straight line equation, but my results are different than using the "professional" programs (such as GIMP or even MS Paint). Here is a example of what I want: But my algorithm does this: *The green point is out of the figure and this is not possible. Any ideas? Anyone know which code is been using for this, in "professional" apps? Thanks! Daniel.

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• Reading PGP key information

  - by calccrypto

  can someone show a description of the information of what a pgp looks like if only the descriptions were there but not the actual information? something like (i dont remember if the values are correct): packet-type[4 bits], total length in bytes[16 bits], packet version type [4 bits], creation-time[32 bits], encryption-algorithm[8 bits], ...,etc,etc ive tried to understand rfc4880, but its tedious and confusing. so far, i am think i have extracted the 4 i wrote above, but i cant seem to get the rest of the information out. can anyone help? i know i can just find some pgp program, but the whole point of this is to allow me to learn how those programs work in the first place

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• Calculating Divergent Paths on Subtending Rings

  - by Russ

  I need to calculate two paths from A to B in the following graph, with the constraint that the paths can't share any edges: hmm, okay, can't post images, here's a link. All edges have positive weights; for this example I think we can assume that they're equal. My naive approach is to use Djikstra's algorithm to calculate the first path, shown in the second graph in the above image. Then I remove the edges from the graph and try to calculate the second path, which fails. Is there a variation of Djikstra, Bellman-Ford (or anything else) that will calculate the paths shown in the third diagram above? (Without special knowledge and removal of the subtending link, is what I mean)

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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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• Python or matplotlib limitation error

  - by Werner

  Hi, I wrote an algorithm using python and matplotlib that generates histograms from some text input data. When the number of data input is approx. greater than 15000, I get in the (append) line of my code: mydata = [] for i in range(len(data)): mydata.append(string.atof(data[i])) the error: Traceback (most recent call last): File "get_histogram_picture.py", line 25, in <module> mydata.append(string.atof(data[i])) File "/usr/lib/python2.6/string.py", line 388, in atof return _float(s) ValueError: invalid literal for float(): -a can it be an error in python ? What is the solution ? Thanks

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• Twitter oauth/request_token failing sometimes

  - by Techpriester

  Hello there. I'm implementing Twitters OAuth for Adobe AIR in Javascript. My problem is, that out of 100 requests to api.twitter.com/oauth/request_token about 30 fail with the usual error message: Failed to validate oauth signature and token The other 70% of requests produce a correct response, so I believe that my algorithm for signing is correct. I've read about invalid timestamps in a lot of forums and mailing lists but that is not the problem. My timestamps are correct. I also checked, if the nonces are unique, so that's not the cause either. Any ideas why this is happening?

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• Reverse Breath First Search in C#

  - by Ngu Soon Hui

  Anyone has a ready implementation of the Reverse Breath First Search algorithm in C#? By Reverse Breath 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 Breath First Search: In my reverse breath 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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• 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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• 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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• How to automatically email customers registration keys?

  - by Danny

  I've written a bit of software that I'd like to share with others (a Mac Dashboard widget, specifically), but I'd also like to be compensated a bit for the time I spent on it. I've devised my own simple registration key algorithm, which takes a customer's email address and creates a 12-character alphanumeric key. The software itself is finished, demo limitations, key validation & all. I just need to get the keys to customers. How do I simply alert a key generation script to automatically email a customer a key, upon notification that they paid my account? Can I use PayPal IPN & JavaScript? The simplest solution will do - this is a five dollar widget. :)

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• File management

  - by user343934

  I am working on python and biopython right now. I have a file upload form and whatever file is uploaded suppose(abc.fasta) then i want to pass same name in execute (abc.fasta) function parameter and display function parameter (abc.aln). Right now i am changing file name manually, but i want to have it automatically. Workflow goes like this. ----If submit is not true then display only header and form part --- if submit is true then call execute() and get file name from form input --- Then display the save file result in the same page. File name is same as input. My raw code is here -- http://pastebin.com/FPUgZSSe Any suggestions, changes and algorithm is appreciated Thanks

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• Loading dictionary for input method suggestion list

  - by jpspringall

  Hi, For various reasons, i'm trying to write my own input keyboard. So far all is going well except that of creating the suggestions. I've found the latinIME algorithm, which is all good. However i'm having major difficulty working out how to load the dictionary in the first place. I've had a good look round the net, and found various suggestions, but no definitive answers, and i cant seem to get any of them to work. If anyone has any suggestions on how best to do it, or even better some sample code, that would be brilliant. Many Thanks James

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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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• 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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