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• For a primary key of an integral type, why is it important to avoid gaps ?

  - by Jacques René Mesrine

  I am generating a surrogate key for a table & due to my hi/lo algorithm, everytime you reboot/restart the machine, gaps may appear. T1: current hi = 10000000 (sequence being dished out .. 1 to 100) Assume that current sequence is 10000050 T2: restart system. T3: System gives out the next_hi as 10000100 (sequence being dished out now ranges from 101 to 200) T4: Next request for a key returns 100001001 From a primary key or indexing internals perspective, why is it important that there be no gaps in the sequences ? I'm asking this for a deeper understanding of mysql specifically. Thanks

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• Java - sorted stack

  - by msr

  Hello, I need a sorted stack. I mean, the element removed from the stack must be the one with great priority. Stack dimension varies a lot (becomes bigger very fast). I need also to search elements in that stack. Does Java give some good implementation for this? What class or algorithm do you suggest for this? I'm using a PriorityQueue right now which I consider reasonable except for searching, so Im wondering if I can use something better. Thanks in advance!

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• Distance by sea calculator, intermediate coordinates?

  - by Lucian2k

  How do I calculate distance between 2 coordinates by sea? I also want to be able to draw a route between the two coordinates. Only solution I found so far is to split a map into pixels, identify each pixel as LAND or SEA and then try to find the path using A* algorithm. Then transform pixels to relative coordinates. There are some software packages I could buy but none have online extensions. A service that calculates distances between sea ports and plots the path on a map is searates.com

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• Using a priority queue in Java

  - by Bharat

  Forgive me if this is a tried question, but I'm having a little difficulty figuring it out. I currently have a class Node, and each 'node' is a square in a maze. I'm trying to implement the A* algorithm, so each of these nodes will have an f-cost (int) data member inside of it. I was wondering if there's a way that I can create a priority queue of these nodes, and set up the f-cost variable as the comparator? I've looked at examples online, but all I can find are String priority queues. Can I implement Comparator for the Node class? Would this allow me to access the data member stored inside it? Many Thanks!

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• Java Generics Type Safety warning with recursive Hashmap

  - by GC

  Hi, I'm using a recursive tree of hashmaps, specifically Hashmap map where Object is a reference to another Hashmap and so on. This will be passed around a recursive algorithm: foo(String filename, Hashmap<String, Object> map) { //some stuff here for (Entry<String, Object> entry : map.entrySet()) { //type warning that must be suppressed foo(entry.getKey(), (HashMap<String, Object>)entry.getValue()); } } I know for sure Object is of type Hashmap<String, Object> but am irritated that I have to suppress the warning using @SuppressWarnings("unchecked"). I'll be satisfied with a solution that does either a assert(/*entry.getValue() is of type HashMap<String, Object>*/) or throws an exception when it isn't. I went down the Generics route for compile type safety and if I suppress the warning then it defeats the purpose. Thank you for your comments, ksb

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• Extracting pure content / text from HTML Pages by excluding navigation and chrome content

  - by Ankur Gupta

  Hi, I am crawling news websites and want to extract News Title, News Abstract (First Paragraph), etc I plugged into the webkit parser code to easily navigate webpage as a tree. To eliminate navigation and other non news content I take the text version of the article (minus the html tags, webkit provides api for the same). Then I run the diff algorithm comparing various article's text from same website this results in similar text being eliminated. This gives me content minus the common navigation content etc. Despite the above approach I am still getting quite some junk in my final text. This results in incorrect News Abstract being extracted. The error rate is 5 in 10 article i.e. 50%. Error as in Can you Suggest an alternative strategy for extraction of pure content, Would/Can learning Natural Language rocessing help in extracting correct abstract from these articles ? How would you approach the above problem ?. Are these any research papers on the same ?. Regards Ankur Gupta

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• Flash to PHP base64 encode/decode

  - by Gus

  I'm using AS3 to base64 encode a JPG and pass it to Javascript. I'm attempting to use AJAX to pass that base64 encoded string to PHP and have PHP decode it. (I know I could send it back to Flash and Flash could decode it and send it to PHP, but I'm trying to eliminate the need for Flash on the decoding end). It appears that AS3's encodeToBase64String() function and and PHP's base64_decode() function do not use the same algorithm, as PHP evaluates it as a base64 encoded object, but does not seem to output it properly. Is there a way to rectify this problem? Note: Please no posts about not needing Javascript. Javascript is a necessary step for reasons not detailed here.

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• Compute average distance from point to line segment and line segment to line segment

  - by Fred

  Hi everyone, I'm searching for an algorithm to calculate the average distance between a point and a line segment in 3D. So given two points A(x1, y1, z1) and B(x2, y2, z2) that represent line segment AB, and a third point C(x3, y3, z3), what is the average distance between each point on AB to point C? I'm also interested in the average distance between two line segments. So given segment AB and CD, what is the average distance from each point on AB to the closest point on CD? I haven't had any luck with the web searches I've tried, so any suggestions would be appreciated. Thanks.

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• Limit a program's execution time in C (Monte Carlo technique)

  - by rrs90

  I am working on a project which has no determined algorithm to solve using C language. I am Using Monte Carlo technique for solving that problem. And the number of random guesses I want to limit to the execution time specified by the user. This means I want to make full use of the execution time limit defined by the user (as a command line argument) to make as many random iterations as possible. Can I check the execution time elapsed so far for a loop condition. Eg: for(trials=0;execution_time P.S. I am using code blocks 10.05 for coding and GNU compiler.

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• using Excel VBA, given the daily price of 50 stocks, choose 10 stocks such that they have the minumu

  - by correl

  The high-level goal is to choose 10 stocks that have the lowest correlation among one another, out of a pool of 50, so that I can have a well-diversified portfolio. I have managed to write some VBA macro to download the past 3 years of daily price data from Yahoo finance, and then compute the 50x50 correlation matrix (using the Correl function), using the daily close as the data. What I have tried so far is just some local-maximum heuristic: - For the two stocks that have the highest correlation with each other, remove one of them. Between the two, remove the one that has the higher average correlation with all the other stocks. - When I remove a stock from the pool, I just delete the correponding row and column, to give a smaller matrix. - Repeat until I have just 10 stocks remaining (a 10x10 matrix). I was wondering if there is some algorithm that already solves such a problem and gives the optimum solution?

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• Polynomial division overloading operator

  - by Vlad

  Ok. here's the operations i successfully code so far thank's to your help: Adittion: polinom operator+(const polinom& P) const { polinom Result; constIter i = poly.begin(), j = P.poly.begin(); while (i != poly.end() && j != P.poly.end()) { //logic while both iterators are valid if (i->pow > j->pow) { //if the current term's degree of the first polynomial is bigger Result.insert(i->coef, i->pow); i++; } else if (j->pow > i->pow) { // if the other polynomial's term degree is bigger Result.insert(j->coef, j->pow); j++; } else { // if both are equal Result.insert(i->coef + j->coef, i->pow); i++; j++; } } //handle the remaining items in each list //note: at least one will be equal to end(), but that loop will simply be skipped while (i != poly.end()) { Result.insert(i->coef, i->pow); ++i; } while (j != P.poly.end()) { Result.insert(j->coef, j->pow); ++j; } return Result; } Subtraction: polinom operator-(const polinom& P) const //fixed prototype re. const-correctness { polinom Result; constIter i = poly.begin(), j = P.poly.begin(); while (i != poly.end() && j != P.poly.end()) { //logic while both iterators are valid if (i->pow > j->pow) { //if the current term's degree of the first polynomial is bigger Result.insert(-(i->coef), i->pow); i++; } else if (j->pow > i->pow) { // if the other polynomial's term degree is bigger Result.insert(-(j->coef), j->pow); j++; } else { // if both are equal Result.insert(i->coef - j->coef, i->pow); i++; j++; } } //handle the remaining items in each list //note: at least one will be equal to end(), but that loop will simply be skipped while (i != poly.end()) { Result.insert(i->coef, i->pow); ++i; } while (j != P.poly.end()) { Result.insert(j->coef, j->pow); ++j; } return Result; } Multiplication: polinom operator*(const polinom& P) const { polinom Result; constIter i, j, lastItem = Result.poly.end(); Iter it1, it2, first, last; int nr_matches; for (i = poly.begin() ; i != poly.end(); i++) { for (j = P.poly.begin(); j != P.poly.end(); j++) Result.insert(i->coef * j->coef, i->pow + j->pow); } Result.poly.sort(SortDescending()); lastItem--; while (true) { nr_matches = 0; for (it1 = Result.poly.begin(); it1 != lastItem; it1++) { first = it1; last = it1; first++; for (it2 = first; it2 != Result.poly.end(); it2++) { if (it2->pow == it1->pow) { it1->coef += it2->coef; nr_matches++; } } nr_matches++; do { last++; nr_matches--; } while (nr_matches != 0); Result.poly.erase(first, last); } if (nr_matches == 0) break; } return Result; } Division(Edited): polinom operator/(const polinom& P) { polinom Result, temp; Iter i = poly.begin(); constIter j = P.poly.begin(); if (poly.size() < 2) { if (i->pow >= j->pow) { Result.insert(i->coef, i->pow - j->pow); *this = *this - Result; } } else { while (true) { if (i->pow >= j->pow) { Result.insert(i->coef, i->pow - j->pow); temp = Result * P; *this = *this - temp; } else break; } } return Result; } The first three are working correctly but division doesn't as it seems the program is in a infinite loop. Update Because no one seems to understand how i thought the algorithm, i'll explain: If the dividend contains only one term, we simply insert the quotient in Result, then we multiply it with the divisor ans subtract it from the first polynomial which stores the remainder. If the polynomial we do this until the second polynomial( P in this case) becomes bigger. I think this algorithm is called long division, isn't it? So based on these, can anyone help me with overloading the / operator correctly for my class? Thanks!

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• what is the best way to generate fake data for classification problem ?

  - by Berkay

  i'm working on a project and i have a subset of user's key-stroke time data.This means that the user makes n attempts and i will use these recorded attempt time data in various kinds of classification algorithms for future user attempts to verify that the login process is done by the user or some another person. (Simply i can say that this is biometrics) I have 3 different times of the user login attempt process, ofcourse this is subset of the infinite data. until now it is an easy classification problem, i decided to use WEKA but as far as i understand i have to create some fake data to feed the classification algorithm. can i use some optimization algorithms ? or is there any way to create this fake data to get min false positives ? Thanks

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• How are .NET 4 GUIDs generated?

  - by mafutrct

  I am aware of the multitude of questions here as well as Raymond's excellent (as usual) post. However, since the algorithm to create GUIDs was changed apparently, I found it hard to get my hands on any up-to-date information. The MSDN seems to try and provide as few information as possible. What is known about how GUIDs are generated in .NET 4? What was changed, and how does it affect the security ("randomness") and integrity ("uniqueness")? One specific aspect I'm interested in: In v1, it seems to be about impossible to generate the same GUID on a single machine again since there was a timestamp and counter involved. In v4, this is no longer the case (I was told), so the chance to get the same GUID on a single machine ... increased?

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• exe files and Python

  - by Sorush Rabiee

  i have some questions about python: 1- How to build .exe files from .py files? 2- How to run a program with arguments and receive the result by python code? 3- How to load .NET library in python code (or write python in VS.NET IDE [!?])? 4- is built-in integer of python 3.1 something like a string? it calculates 200! in less than one second and calculates 2^1 to 2^7036 (by a simple recursive algorithm & writing them to a text file) with a 1.75GHz cpu in 4 minuets, so if it is a string, how it can be so fast like this? is there a great difference between memory type and logical calculation of python with c++? 5- what is the best python practice? how can i be an expert?

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• Java simple encryption

  - by Ran

  Hello, I would like to encrypt a textual (configuration) file stored on disk. Trying to use DES encryption I've had fatal error on client machines, I later found out caused because the algorithm could not handle accented characters (!) I suspect that was because I was using old packages (sun.misc.BASE64Decoder) - but I'm not sure that is the reason. However, I'm looking for a simpler solution - I need a really simple encryption (I know some people would not agree on that) - not RSA of 128 bit keys or so, just obscuring the text from curious eyes. It is really weird that I could not find on the web a simple trivial solution. Any idea, anyone ? Thanks, Ran

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• C++ find method is not const?

  - by Rachel

  I've written a method that I'd like to declare as const, but the compiler complains. I traced through and found that this part of the method was causing the difficulty: bool ClassA::MethodA(int x) { bool y = false; if(find(myList.begin(), myList.end(), x) != myList.end()) { y = true; } return y; } There is more happening in the method than that, but with everything else stripped away, this was the part that didn't allow the method to be const. Why does the stl find algorithm prevent the method from being const? Does it change the list in any way?

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• Java Spam Filter

  - by JackSparrow

  I'm trying to create a spam filter in Java using the Bayesian algorithm. I use a text file that contains email messages and split the tokens using regex, storing these values into a hashmap. My problem is, with regex, the email addresses are split so instead of: [email protected] regex causes the token to be: john smith example The same holds true for ip addresses, so for example, instead of: 192.55.34.322 regex splits the tokens to be: 192 55 34 322 So does anybody know of a way that I could read the email messages and store their contents as is?

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• Managed language for scientific computing software

  - by heisen

  Scientific computing is algorithm intensive and can also be data intensive. It often needs to use a lot of memory to run analysis and release it before continuing with the next. Sometime it also uses memory pool to recycle memory for each analysis. Managed language is interesting here because it can allow the developer to concentrate on the application logic. Since it might need to deal with huge dataset, performance is important too. But how can we control memory and performance with managed language?

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• Sorting a file with 55K rows and varying Columns

  - by Prasad

  Hi I want to find a programmatic solution using C++. I have a 900 files each of 27MB size. (just to inform about the enormity ). Each file has 55K rows and Varying columns. But the header indicates the columns I want to sort the rows in an order w.r.t to a Column Value. I wrote the sorting algorithm for this (definitely my newbie attempts, you may say). This algorithm is working for few numbers, but fails for larger numbers. Here is the code for the same: basic functions I defined to use inside the main code: int getNumberOfColumns(const string& aline) { int ncols=0; istringstream ss(aline); string s1; while(ss>>s1) ncols++; return ncols; } vector<string> getWordsFromSentence(const string& aline) { vector<string>words; istringstream ss(aline); string tstr; while(ss>>tstr) words.push_back(tstr); return words; } bool findColumnName(vector<string> vs, const string& colName) { vector<string>::iterator it = find(vs.begin(), vs.end(), colName); if ( it != vs.end()) return true; else return false; } int getIndexForColumnName(vector<string> vs, const string& colName) { if ( !findColumnName(vs,colName) ) return -1; else { vector<string>::iterator it = find(vs.begin(), vs.end(), colName); return it - vs.begin(); } } ////////// I like the Recurssive functions - I tried to create a recursive function ///here. This worked for small values , say 20 rows. But for 55K - core dumps void sort2D(vector<string>vn, vector<string> &srt, int columnIndex) { vector<double> pVals; for ( int i = 0; i < vn.size(); i++) { vector<string>meancols = getWordsFromSentence(vn[i]); pVals.push_back(stringToDouble(meancols[columnIndex])); } srt.push_back(vn[max_element(pVals.begin(), pVals.end())-pVals.begin()]); if (vn.size() > 1 ) { vn.erase(vn.begin()+(max_element(pVals.begin(), pVals.end())-pVals.begin()) ); vector<string> vn2 = vn; //cout<<srt[srt.size() -1 ]<<endl; sort2D(vn2 , srt, columnIndex); } } Now the main code: for ( int i = 0; i < TissueNames.size() -1; i++) { for ( int j = i+1; j < TissueNames.size(); j++) { //string fname = path+"/gse7307_Female_rma"+TissueNames[i]+"_"+TissueNames[j]+".txt"; //string fname2 = sortpath2+"/gse7307_Female_rma"+TissueNames[i]+"_"+TissueNames[j]+"Sorted.txt"; string fname = path+"/gse7307_Male_rma"+TissueNames[i]+"_"+TissueNames[j]+".txt"; string fname2 = sortpath2+"/gse7307_Male_rma"+TissueNames[i]+"_"+TissueNames[j]+"4Columns.txt"; //vector<string>AllLinesInFile; BioInputStream fin(fname); string aline; getline(fin,aline); replace (aline.begin(), aline.end(), '"',' '); string headerline = aline; vector<string> header = getWordsFromSentence(aline); int pindex = getIndexForColumnName(header,"p-raw"); int xcindex = getIndexForColumnName(header,"xC"); int xeindex = getIndexForColumnName(header,"xE"); int prbindex = getIndexForColumnName(header,"X"); string newheaderline = "X\txC\txE\tp-raw"; BioOutputStream fsrt(fname2); fsrt<<newheaderline<<endl; int newpindex=3; while ( getline(fin, aline) ){ replace (aline.begin(), aline.end(), '"',' '); istringstream ss2(aline); string tstr; ss2>>tstr; tstr = ss2.str().substr(tstr.length()+1); vector<string> words = getWordsFromSentence(tstr); string values = words[prbindex]+"\t"+words[xcindex]+"\t"+words[xeindex]+"\t"+words[pindex]; AllLinesInFile.push_back(values); } vector<string>SortedLines; sort2D(AllLinesInFile, SortedLines,newpindex); for ( int si = 0; si < SortedLines.size(); si++) fsrt<<SortedLines[si]<<endl; cout<<"["<<i<<","<<j<<"] = "<<SortedLines.size()<<endl; } } can some one suggest me a better way of doing this? why it is failing for larger values. ? The primary function of interest for this query is Sort2D function. thanks for the time and patience. prasad.

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• Combinatorics grouping problem

  - by Harry Pap

  I'm looking for an algorithm in c# that solves a combinatorics problem: Assume i have the objects 1,2,3,4 I want to get all possible ways to group these object in multiple groups, that each time contain all objects. Order is not important. Example: <1,2,3,4 <1,2 / 3,4 <1,3 / 2,4 <1,4 / 3,2 <1,2,3 / 4 <1,2,4 / 3 <1,3,4 / 2 <2,3,4 / 1 <1 / 2 / 3 / 4 In the first case there is one group that contain all 4 objects. Next are cases with 2 groups that contain all objects in many different ways. The last case is 4 groups, that each one contains only one object.

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• How to transform phrases and words into MD5 hash?

  - by brilliant

  Can anyone, please, explain to me how to transform a phrase like "I want to buy some milk" into MD5? I read Wikipedia article on MD5, but the explanation given there is beyond my comprehension: "MD5 processes a variable-length message into a fixed-length output of 128 bits. The input message is broken up into chunks of 512-bit blocks (sixteen 32-bit little endian integers)" "sixteen 32-bit little endian integers" is already hard for me. I checked the article on little endians and didn't understand a bit. However, the examples of some phrases and their MD5 hashes are very nice: MD5("The quick brown fox jumps over the lazy dog") = 9e107d9d372bb6826bd81d3542a419d6 MD5("The quick brown fox jumps over the lazy dog.") = e4d909c290d0fb1ca068ffaddf22cbd0 Can anyone, please, explain to me how this MD5 algorithm works on some very simple example? And also, perhaps you know some software or a code that would transform phrases into their MD5. If yes, please, let me know.

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• Simplex noise vs Perlin noise

  - by raRaRa

  I would like to know why Perlin noise is still so popular today after Simplex came out. Simplex noise was made by Ken Perlin himself and it was suppose to take over his old algorithm which was slow for higher dimensions and with better quality (no visible artifacts). Simplex noise came out in 2001 and over those 10 years I've only seen people talk of Perlin noise when it comes to generating heightmaps for terrains, creating procedural textures, et cetera. Could anyone help me out, is there some downside of Simplex noise? I heard rumors that Perlin noise is faster when it comes to 1D and 2D noise, but I don't know if it's true or not. Thanks!

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• Implementing a linear, binary SVM (support vector machine)

  - by static_rtti

  I want to implement a simple SVM classifier, in the case of high-dimensional binary data (text), for which I think a simple linear SVM is best. The reason for implementing it myself is basically that I want to learn how it works, so using a library is not what I want. The problem is that most tutorials go up to an equation that can be solved as a "quadratic problem", but they never show an actual algorithm! So could you point me either to a very simple implementation I could study, or (better) to a tutorial that goes all the way to the implementation details? Thanks a lot!

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• Sudoku solver evaluation function

  - by Rich

  Hi, So I'm trying to write a simple genetic algorithm for solving a sudoku (not the most efficient way, I know, but it's just to practice evolutionary algorithms). I'm having some problems coming up with an efficient evaluation function to test if the puzzle is solved or not and how many errors there are. My first instinct would be to check if each row and column of the matrix (doing it in octave, which is similar to matlab) have unique elements by ordering them, checking for duplicates and then putting them back the way they were, which seems long winded. Any thoughts? Sorry if this has been asked before...

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• Recursion and Iteration

  - by Doug

  What is the difference? Are these the same? If not, can someone please give me an example? MW: Iteration - 1 : the action or a process of iterating or repeating: as a : a procedure in which repetition of a sequence of operations yields results successively closer to a desired result b : the repetition of a sequence of computer instructions a specified number of times or until a condition is met Recusion - 3 : a computer programming technique involving the use of a procedure, subroutine, function, or algorithm that calls itself one or more times until a specified condition is met at which time the rest of each repetition is processed from the last one called to the first

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