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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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• 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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• 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++: call original definition of operator equals

  - by Luis Daniel

  I am overloading the operator equals (==) as show bellow: #include <string> #include <algorithm> bool operator == (std::string str1, std::string str2) { std::transform(str1.begin(), str1.end(), str1.begin(), ::tolower); std::transform(str2.begin(), str2.end(), str2.begin(), ::tolower); return (str1 == str2); } but, the problem appear on line return (str1 == str2), because operator == is called recursively. So, how can I call the original definition for operator equals (not the overloaded) ? Best regards

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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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• 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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• "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 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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• c program for this quesion

  - by sashi

  suppose that a disk drive has 5000 cylinders, numbered 0 to 4999. the drive is currently serving a request at cylinder 143 and the previous request was at cylinder 125. the ueue of pending requests in the given order is 86,1470,913,17774,948,1509,1022,1750,130. write a 'c' program for finding the total distance in cylinders that the disk arm moves to satisfy all the pending reuests from the current heads position, using SSTF scheduling algorith. seek time is the time for the disk arm to move the head to the cylider containing the desired sector. sstf algorithm selects the minimum seek time from the current head position.

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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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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