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  • Text mining on large database (data mining)

    - by yox
    Hello, I have a large database of resumes (CV), and a certain table skills grouping all users skills. inside that table there's a field skill_text that describes the skill in full text. I'm looking for an algorithm/software/method to extract significant terms/phrases from that table in order to build a new table with standarized skills.. Here are some examples skills extracted from the DB : Sectoral and competitive analysis Business Development (incl. in international settings) Specific structure and road design software - Microstation, Macao, AutoCAD (basic knowledge) Creative work (Photoshop, In-Design, Illustrator) checking and reporting back on campaign progress organising and attending events and exhibitions Development : Aptana Studio, PHP, HTML, CSS, JavaScript, SQL, AJAX Discipline: One to one marketing, E-marketing (SEO & SEA, display, emailing, affiliate program) Mix marketing, Viral Marketing, Social network marketing. The output shoud be something like : Sectoral and competitive analysis Business Development Specific structure and road design software - Macao AutoCAD Photoshop In-Design Illustrator organising events Development Aptana Studio PHP HTML CSS JavaScript SQL AJAX Mix marketing Viral Marketing Social network marketing emailing SEO One to one marketing As you see only skills remains no other representation text. I know this is possible using text mining technics but how to do it ? the database is realy large.. it's a good thing because we can calculate text frequency and decide if it's a real skill or just meaningless text... The big problem is .. how to determin that "blablabla" is a skill ? thanks

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  • I can't compile android projetc wiht JNI code

    - by lobi
    I'm trying to build simple android app with some JNI code. When I press build project in eclipse I get this error: Description Resource Path Location Type fatal error: algorithm: No such file or directory Tracker line 56, external location: /home/slani/code/OpenCV-2.4.6-android-sdk/sdk/native/jni/include/opencv2/core/core.hpp C/C++ Problem make: *** [obj/local/armeabi/objs/detect_jni/detect_jni.o] Error 1 Tracker C/C++ Problem Line 56 in core.hpp contains the relevant include. This is my Android.mk file jni folder: LOCAL_PATH := $(call my-dir) include $(CLEAR_VARS) include /home/slani/code/OpenCV-2.4.6-android-sdk/sdk/native/jni/OpenCV.mk LOCAL_MODULE := detect_jni LOCAL_SRC_FILES := detect_jni.cpp include $(BUILD_SHARED_LIBRARY) This is my Aplication.mk file in jni folder: APP_STL := gnustl_static APP_CPPFLAGS := -frtti -fexceptions APP_ABI := armeabi-v7a APP_PLATFORM := all This is my .cpp file: #include <jni.h> #include <opencv/cv.h> #include <opencv2/imgproc/imgproc.hpp> #include <opencv2/features2d/features2d.hpp> using namespace cv; extern "C"{ JNIEXPORT void JNICALL Java_com_slani_tracker_OpenCamera_findObject((JNIEnv *env, jlong addRgba, jlong addHsv); JNIEXPORT void JNICALL Java_com_slani_tracker_OpenCamera_findObject((JNIEnv *env, jlong addRgba, jlong addHsv) { Mat& rgba = *(Mat*)addRgba; Mat& hsv = *(Mat*)addHsv; cvtColor(rgba, hsv,CV_RGBA2HSV); } } Can someone please help me? What could be causing this problem? Thanks

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  • Lisp Style question label local functions or not?

    - by Andrew Myers
    I was wondering if there is a standard practice regarding the use of labels in Lisp. I've been messing around with a Lisp implementation of the algorithm described in the first answer here http://stackoverflow.com/questions/352203/generating-permutations-lazily My current version uses labels to break out portions of functionality. (defun next-permutation (pmute) (declare (vector pmute)) (let ((len (length pmute))) (if (> len 2) (labels ((get-pivot () (do ((pivot (1- len) (1- pivot))) ((or (= pivot 0) (< (aref pmute (1- pivot)) (aref pmute pivot))) pivot))) (get-swap (pivot) (let ((swp (1- len))) (loop for i from (1- len) downto pivot do (if (or (and (> (aref pmute i) (aref pmute (1- pivot))) (< (aref pmute i) (aref pmute swp))) (< (aref pmute swp) (aref pmute (1- pivot)))) (setf swp i))) swp)) (next (swp pivot) (rotatef (aref pmute (1- pivot)) (aref pmute swp)) (reverse-vector pmute pivot (1- len)))) (let ((piv (get-pivot))) (if (> piv 0) (next (get-swap piv) piv) nil)))))) Since each label is only called once I was wondering if this is considered bad practice since the only reason to do it in this case is for aesthetic reasons. I would argue that the current version with labels is clearer but that may go against common wisdom that I'm not aware of, being new to Lisp.

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  • Using Taylor Series to Avoid Loss of Precision

    - by Zachary
    I'm trying to use Taylor series to develop a numerically sound algorithm for solving a function. I've been at it for quite a while, but haven't had any luck yet. I'm not sure what I'm doing wrong. The function is f(x)=1 + x - sin(x)/ln(1+x) x~0 Also: why does loss of precision even occur in this function? when x is close to zero, sin(x)/ln(1+x) isn't even close to being the same number as x. I don't see where significance is even being lost. In order to solve this, I believe that I will need to use the Taylor expansions for sin(x) and ln(1+x), which are x - x^3/3! + x^5/5! - x^7/7! + ... and x - x^2/2 + x^3/3 - x^4/4 + ... respectfully. I have attempted to use like denominators to combine the x and sin(x)/ln(1+x) components, and even to combine all three, but nothing seems to work out correctly in the end. Any help is appreciated.

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  • Bit reversal of an integer, ignoring integer size and endianness

    - by ??O?????
    Given an integer typedef: typedef unsigned int TYPE; or typedef unsigned long TYPE; I have the following code to reverse the bits of an integer: TYPE max_bit= (TYPE)-1; void reverse_int_setup() { TYPE bits= (TYPE)max_bit; while (bits <<= 1) max_bit= bits; } TYPE reverse_int(TYPE arg) { TYPE bit_setter= 1, bit_tester= max_bit, result= 0; for (result= 0; bit_tester; bit_tester>>= 1, bit_setter<<= 1) if (arg & bit_tester) result|= bit_setter; return result; } One just needs first to run reverse_int_setup(), which stores an integer with the highest bit turned on, then any call to reverse_int(arg) returns arg with its bits reversed (to be used as a key to a binary tree, taken from an increasing counter, but that's more or less irrelevant). Is there a platform-agnostic way to have in compile-time the correct value for max_int after the call to reverse_int_setup(); Otherwise, is there an algorithm you consider better/leaner than the one I have for reverse_int()? Thanks.

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  • Are endless loops in bad form?

    - by rlbond
    So I have some C++ code for back-tracking nodes in a BFS algorithm. It looks a little like this: typedef std::map<int> MapType; bool IsValuePresent(const MapType& myMap, int beginVal, int searchVal) { int current_val = beginVal; while (true) { if (current_val == searchVal) return true; MapType::iterator it = myMap.find(current_val); assert(current_val != myMap.end()); if (current_val == it->second) // end of the line return false; current_val = it->second; } } However, the while (true) seems... suspicious to me. I know this code works, and logically I know it should work. However, I can't shake the feeling that there should be some condition in the while, but really the only possible one is to use a bool variable just to say if it's done. Should I stop worrying? Or is this really bad form. EDIT: Thanks to all for noticing that there is a way to get around this. However, I would still like to know if there are other valid cases.

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  • maintaining a large list in python

    - by Oren
    I need to maintain a large list of python pickleable objects that will quickly execute the following algorithm: The list will have 4 pointers and can: Read\Write each of the 4 pointed nodes Insert new nodes before the pointed nodes Increase a pointer by 1 Pop nodes from the beginning of the list (without overlapping the pointers) Add nodes at the end of the list The list can be very large (300-400 MB), so it shouldnt be contained in the RAM. The nodes are small (100-200 bytes) but can contain various types of data. The most efficient way it can be done, in my opinion, is to implement some paging-mechanism. On the harddrive there will be some database of a linked-list of pages where in every moment up to 5 of them are loaded in the memory. On insertion, if some max-page-size was reached, the page will be splitted to 2 small pages, and on pointer increment, if a pointer is increased beyond its loaded page, the following page will be loaded instead. This is a good solution, but I don't have the time to write it, especially if I want to make it generic and implement all the python-list features. Using a SQL tables is not good either, since I'll need to implement a complex index-key mechanism. I tried ZODB and zc.blist, which implement a BTree based list that can be stored in a ZODB database file, but I don't know how to configure it so the above features will run in reasonable time. I don't need all the multi-threading\transactioning features. No one else will touch the database-file except for my single-thread program. Can anyone explain me how to configure the ZODB\zc.blist so the above features will run fast, or show me a different large-list implementation?

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  • MS SQL Database with clustered GUID PKs - switch clustered index or switch to sequential (comb) GUID

    - by Eyvind
    We have a database in which all the PKs are GUIDs, and most of the PKs are also the clustered index for the table. We know that this is bad (due to the random nature of GUIDs). So, it seems there are basically two options here (short of throwing out GUIDs as PKs altogether, which we cannot do (at least not at this time)). We could change the GUID generation algorithm to e.g. the one that NHibernate uses, as detailed in this post, or we could, for the tables that are under the heaviest use, change to a different clustered index, e.g. an IDENTITY column, and keep the "random" GUIDs as PKs. Is it possible to give any general recommendations in such a scenario? The application in question has 500+ tables, the largest one presently at about 1,5 million rows, a few tables around 500 000 rows, and the rest significantly lower (most of them well below 10K). Furthermore, the application is installed at several customer sites already, so we have to take any possible negative effects for existing customer into consideration. Thanks!

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  • A Question about .net Rfc2898DeriveBytes class?

    - by IbrarMumtaz
    What is the difference in this class? as posed to just using Encoding.ASCII.GetBytes(string object); I have had relative success with either approach, the former is a more long winded approach where as the latter is simple and to the point. Both seem to allow you to do the same thing eventually but I am struggling to the see the point in using the former over the latter. The basic concept I have been able to grasp is that you can convert string passwords into byte arrays to be used for e.g a symmetric encryption class, AesManaged. Via the RFC class but you get to use SaltValues and password when creating your rfc object. I assume its more secure but still thats an uneducated guess at best ! Also that it allows you to return byte arrays of a certain size, well something like that. heres a few examples to show you where I am coming from? byte[] myPassinBytes = Encoding.ASCII.GetBytes("some password"); or string password = "P@%5w0r]>"; byte[] saltArray = Encoding.ASCII.GetBytes("this is my salt"); Rfc2898DeriveBytes rfcKey = new Rfc2898DeriveBytes(password, saltArray); The 'rfcKey' object can now be used towards setting up the the .Key or .IV properties on a Symmetric Encryption Algorithm class. ie. RijndaelManaged rj = new RijndaelManaged (); rj.Key = rfcKey.Getbytes(rj.KeySize / 8); rj.IV = rfcKey.Getbytes(rj.Blocksize / 8); 'rj' should be ready to go ! The confusing part ... so rather than using the 'rfcKey' object can I not just use my 'myPassInBytes' array to help set-up my 'rj' object???? I have tried doing this in VS2008 and the immediate answer is NO ! but have you guys got a better educated answer as to why the RFC class is used over the other alternative I have mentioned above and why????

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  • nested iterator errors

    - by Sean
    //arrayList.h #include<iostream> #include<sstream> #include<string> #include<algorithm> #include<iterator> using namespace std; template<class T> class arrayList{ public: // constructor, copy constructor and destructor arrayList(int initialCapacity = 10); arrayList(const arrayList<T>&); ~arrayList() { delete[] element; } // ADT methods bool empty() const { return listSize == 0; } int size() const { return listSize; } T& get(int theIndex) const; int indexOf(const T& theElement) const; void erase(int theIndex); void insert(int theIndex, const T& theElement); void output(ostream& out) const; // additional method int capacity() const { return arrayLength; } void reverse(); // new defined // iterators to start and end of list class iterator; class seamlessPointer; seamlessPointer begin() { return seamlessPointer(element); } seamlessPointer end() { return seamlessPointer(element + listSize); } // iterator for arrayList class iterator { public: // typedefs required by C++ for a bidirectional iterator typedef bidirectional_iterator_tag iterator_category; typedef T value_type; typedef ptrdiff_t difference_type; typedef T* pointer; typedef T& reference; // constructor iterator(T* thePosition = 0) { position = thePosition; } // dereferencing operators T& operator*() const { return *position; } T* operator->() const { return position; } // increment iterator& operator++() // preincrement { ++position; return *this; } iterator operator++(int) // postincrement { iterator old = *this; ++position; return old; } // decrement iterator& operator--() // predecrement { --position; return *this; } iterator operator--(int) // postdecrement { iterator old = *this; --position; return old; } // equality testing bool operator!=(const iterator right) const { return position != right.position; } bool operator==(const iterator right) const { return position == right.position; } protected: T* position; }; // end of iterator class class seamlessPointer: public arrayList<T>::iterator { // constructor seamlessPointer(T *thePosition) { iterator::position = thePosition; } //arithmetic operators seamlessPointer & operator+(int n) { arrayList<T>::iterator::position += n; return *this; } seamlessPointer & operator+=(int n) { arrayList<T>::iterator::position += n; return *this; } seamlessPointer & operator-(int n) { arrayList<T>::iterator::position -= n; return *this; } seamlessPointer & operator-=(int n) { arrayList<T>::iterator::position -= n; return *this; } T& operator[](int n) { return arrayList<T>::iterator::position[n]; } bool operator<(seamlessPointer &rhs) { if(int(arrayList<T>::iterator::position - rhs.position) < 0) return true; return false; } bool operator<=(seamlessPointer & rhs) { if (int(arrayList<T>::iterator::position - rhs.position) <= 0) return true; return false; } bool operator >(seamlessPointer & rhs) { if (int(arrayList<T>::iterator::position - rhs.position) > 0) return true; return false; } bool operator >=(seamlessPointer &rhs) { if (int(arrayList<T>::iterator::position - rhs.position) >= 0) return true; return false; } }; protected: // additional members of arrayList void checkIndex(int theIndex) const; // throw illegalIndex if theIndex invalid T* element; // 1D array to hold list elements int arrayLength; // capacity of the 1D array int listSize; // number of elements in list }; #endif //main.cpp #include<iostream> #include"arrayList.h" #include<fstream> #include<algorithm> #include<string> using namespace std; bool compare_nocase (string first, string second) { unsigned int i=0; while ( (i<first.length()) && (i<second.length()) ) { if (tolower(first[i])<tolower(second[i])) return true; else if (tolower(first[i])>tolower(second[i])) return false; ++i; } if (first.length()<second.length()) return true; else return false; } int main() { ifstream fin; ofstream fout; string str; arrayList<string> dict; fin.open("dictionary"); if (!fin.good()) { cout << "Unable to open file" << endl; return 1; } int k=0; while(getline(fin,str)) { dict.insert(k,str); // cout<<dict.get(k)<<endl; k++; } //sort the array sort(dict.begin, dict.end(),compare_nocase); fout.open("sortedDictionary"); if (!fout.good()) { cout << "Cannot create file" << endl; return 1; } dict.output(fout); fin.close(); return 0; } Two errors are: ..\src\test.cpp: In function 'int main()': ..\src\test.cpp:50:44: error: no matching function for call to 'sort(<unresolved overloaded function type>, arrayList<std::basic_string<char> >::seamlessPointer, bool (&)(std::string, std::string))' ..\src\/arrayList.h: In member function 'arrayList<T>::seamlessPointer arrayList<T>::end() [with T = std::basic_string<char>]': ..\src\test.cpp:50:28: instantiated from here ..\src\/arrayList.h:114:3: error: 'arrayList<T>::seamlessPointer::seamlessPointer(T*) [with T = std::basic_string<char>]' is private ..\src\/arrayList.h:49:44: error: within this context Why do I get these errors? Update I add public: in the seamlessPointer class and change begin to begin() Then I got the following errors: ..\hw3prob2.cpp:50:46: instantiated from here c:\wascana\mingw\bin\../lib/gcc/mingw32/4.5.0/include/c++/bits/stl_algo.h:5250:4: error: no match for 'operator-' in '__last - __first' ..\/arrayList.h:129:21: note: candidate is: arrayList<T>::seamlessPointer& arrayList<T>::seamlessPointer::operator-(int) [with T = std::basic_string<char>, arrayList<T>::seamlessPointer = arrayList<std::basic_string<char> >::seamlessPointer] c:\wascana\mingw\bin\../lib/gcc/mingw32/4.5.0/include/c++/bits/stl_algo.h:5252:4: instantiated from 'void std::sort(_RAIter, _RAIter, _Compare) [with _RAIter = arrayList<std::basic_string<char> >::seamlessPointer, _Compare = bool (*)(std::basic_string<char>, std::basic_string<char>)]' ..\hw3prob2.cpp:50:46: instantiated from here c:\wascana\mingw\bin\../lib/gcc/mingw32/4.5.0/include/c++/bits/stl_algo.h:2190:7: error: no match for 'operator-' in '__last - __first' ..\/arrayList.h:129:21: note: candidate is: arrayList<T>::seamlessPointer& arrayList<T>::seamlessPointer::operator-(int) [with T = std::basic_string<char>, arrayList<T>::seamlessPointer = arrayList<std::basic_string<char> >::seamlessPointer] Then I add operator -() in the seamlessPointer class ptrdiff_t operator -(seamlessPointer &rhs) { return (arrayList<T>::iterator::position - rhs.position); } Then I compile successfully. But when I run it, I found memeory can not read error. I debug and step into and found the error happens in stl function template<typename _RandomAccessIterator, typename _Distance, typename _Tp, typename _Compare> void __adjust_heap(_RandomAccessIterator __first, _Distance __holeIndex, _Distance __len, _Tp __value, _Compare __comp) { const _Distance __topIndex = __holeIndex; _Distance __secondChild = __holeIndex; while (__secondChild < (__len - 1) / 2) { __secondChild = 2 * (__secondChild + 1); if (__comp(*(__first + __secondChild), *(__first + (__secondChild - 1)))) __secondChild--; *(__first + __holeIndex) = _GLIBCXX_MOVE(*(__first + __secondChild)); ////// stop here __holeIndex = __secondChild; } Of course, there must be something wrong with the customized operators of iterator. Does anyone know the possible reason? Thank you.

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  • How to sort linq result by most similarity/equality

    - by aNui
    I want to do a search for Music instruments which has its informations Name, Category and Origin as I asked in my post. But now I want to sort/group the result by similarity/equality to the keyword such as. If I have the list { Drum, Grand Piano, Guitar, Guitarrón, Harp, Piano} << sorted by name and if I queried "p" the result should be { Piano, Grand Piano, Harp } but it shows Harp first because of the source list's sequence and if I add {Grand Piano} to the list and query "piano" the result shoud be like { Piano, Grand Piano } or query "guitar" it should be { Guitar, Guitarrón } here's my code static IEnumerable<MInstrument> InstrumentsSearch(IEnumerable<MInstrument> InstrumentsList, string query, MInstrument.Category[] SelectedCategories, MInstrument.Origin[] SelectedOrigins) { var result = InstrumentsList .Where(item => SelectedCategories.Contains(item.category)) .Where(item => SelectedOrigins.Contains(item.origin)) .Where(item => { if ( (" " + item.Name.ToLower()).Contains(" " + query.ToLower()) || item.Name.IndexOf(query) != -1 ) { return true; } return false; } ) .Take(30); return result.ToList<MInstrument>(); } Or the result may be like my old self-invented algorithm that I called "by order of occurence", that is just OK to me. And the further things to do is I need to search the Name, Category or Origin such as. If i type "Italy" it should found Piano or something from Italy. Or if I type "string" it should found Guitar. Is there any way to do those things, please tell me. Thanks in advance.

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  • Can't get any speedup from parallelizing Quicksort using Pthreads

    - by Murat Ayfer
    I'm using Pthreads to create a new tread for each partition after the list is split into the right and left halves (less than and greater than the pivot). I do this recursively until I reach the maximum number of allowed threads. When I use printfs to follow what goes on in the program, I clearly see that each thread is doing its delegated work in parallel. However using a single process is always the fastest. As soon as I try to use more threads, the time it takes to finish almost doubles, and keeps increasing with number of threads. I am allowed to use up to 16 processors on the server I am running it on. The algorithm goes like this: Split array into right and left by comparing the elements to the pivot. Start a new thread for the right and left, and wait until the threads join back. If there are more available threads, they can create more recursively. Each thread waits for its children to join. Everything makes sense to me, and sorting works perfectly well, but more threads makes it slow down immensely. I tried setting a minimum number of elements per partition for a thread to be started (e.g. 50000). I tried an approach where when a thread is done, it allows another thread to be started, which leads to hundreds of threads starting and finishing throughout. I think the overhead was way too much. So I got rid of that, and if a thread was done executing, no new thread was created. I got a little more speedup but still a lot slower than a single process. The code I used is below. http://pastebin.com/UaGsjcq2 Does anybody have any clue as to what I could be doing wrong?

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  • Proggraming a VPN, Authontication stage - RFC not clear enough

    - by John
    I have a custom build of a unix OS. My task: Adding an IPSec to the OS. I am working on Phase I, done sending the first 2 packets. what I am trying to do now is making the Identefication Payload. I've been reading RFC 2409 (Apendix B) which discuss the keying materials (SKEYID, SKEYID_d, SKEYID_a, SKEYID_e and the IV making). Now, I use SHA1 for authontication and thus I use HMAC-SHA1 & my encryption algorithem is AES 256bit. The real problem is that the RFC is not clear enough of what should I do regarding the PRF. It says: "Use of negotiated PRFs may require the PRF output to be expanded due to the PRF feedback mechanism employed by this document." I use SHA1, does it mean I do not negotiate a PRF? In my opinion, AES is the only algorithm that needs expention (a fixed length of 256bit), so, do i need to expand only the SKEYID_e? If you happen to know a clearer, though relible, source then the RFC please post a link. Thanks in advance!

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  • Getting started with character and text processing (encoding, regular expressions)

    - by TK
    I'd like to learn foundations of encodings, characters and text. Understanding these is important for dealing with a large set of text whether that are log files or text source for building algorithms for collective intelligence. My current knowledge is pretty basic: something like "As long as I use UTF-8, I'm okay." I don't say I need to learn about advanced topics right away. But I need to know: Bit and bytes level knowledge of encodings. Characters and alphabets not used in English. Multi-byte encodings. (I understand some Chinese and Japanese. And parsing them is important.) Regular expressions. Algorithm for text processing. Parsing natural languages. I also need an understanding of mathematics and corpus linguistics. The current and future web (semantic, intelligent, real-time web) needs processing, parsing and analyzing large text. I'm looking for some resources (maybe books?) that get me started with some of the bullets. (I find many helpful discussion on regular expressions here on Stack Overflow. So, you don't need to suggest resources on that topic.)

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  • LaTeX limitation?

    - by Jayen
    Hi, I've hit an annoying problem in LaTeX. I've got a tex file of about 1000 lines. I've already got a few figures, but when I try to add another figure, It barfs with: ! Undefined control sequence. <argument> ... \sf@size \z@ \selectfont \@currbox l.937 \begin{figure}[t] If I move the figure to other parts of the file, I can get similar errors on different lines: ! Undefined control sequence. <argument> ... \sf@size \z@ \selectfont \@currbox l.657 \paragraph {A Centering Algorithm} If I comment out the figure, all is ok. %\begin{figure}[t] % \caption{Example decision tree, from Reiter and Dale [2000]} % \label{fig:relation-decision-tree} % \centering % \includegraphics[keepaspectratio=true]{./relation-decision-tree.eps} %\end{figure} If I keep just the begin and end like: \begin{figure}%[t] % \caption{Example decision tree, from Reiter and Dale [2000]} % \label{fig:relation-decision-tree} % \centering % \includegraphics[keepaspectratio=true]{./relation-decision-tree.eps} \end{figure} I get: ! Undefined control sequence. <argument> ... \sf@size \z@ \selectfont \@currbox l.942 \end {figure} At first, I thought maybe LaTeX has hit some limit, and I tried playing with the ulimits, but that didn't help. Any ideas? i've got other figures with graphics already. my preamble looks like: \documentclass[acmcsur,acmnow]{acmtrans2n} \usepackage{array} \usepackage{lastpage} \usepackage{pict2e} \usepackage{amsmath} \usepackage{varioref} \usepackage{epsfig} \usepackage{graphics} \usepackage{qtree} \usepackage{rotating} \usepackage{tree-dvips} \usepackage{mdwlist} \makecompactlist{quote*}{quote} \usepackage{verbatim} \usepackage{ulem}

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  • The subsets-sum problem and the solvability of NP-complete problems

    - by G.E.M.
    I was reading about the subset-sums problem when I came up with what appears to be a general-purpose algorithm for solving it: (defun subset-contains-sum (set sum) (let ((subsets) (new-subset) (new-sum)) (dolist (element set) (dolist (subset-sum subsets) (setf new-subset (cons element (car subset-sum))) (setf new-sum (+ element (cdr subset-sum))) (if (= new-sum sum) (return-from subset-contains-sum new-subset)) (setf subsets (cons (cons new-subset new-sum) subsets))) (setf subsets (cons (cons element element) subsets))))) "set" is a list not containing duplicates and "sum" is the sum to search subsets for. "subsets" is a list of cons cells where the "car" is a subset list and the "cdr" is the sum of that subset. New subsets are created from old ones in O(1) time by just cons'ing the element to the front. I am not sure what the runtime complexity of it is, but appears that with each element "sum" grows by, the size of "subsets" doubles, plus one, so it appears to me to at least be quadratic. I am posting this because my impression before was that NP-complete problems tend to be intractable and that the best one can usually hope for is a heuristic, but this appears to be a general-purpose solution that will, assuming you have the CPU cycles, always give you the correct answer. How many other NP-complete problems can be solved like this one?

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  • Why can a struct defined inside a function not be used as functor to std::for_each?

    - by Oswald
    The following code won't compile. The compiler complains about *no matching function for call to for_each*. Why is this so? #include <map> #include <algorithm> struct Element { void flip() {} }; void flip_all(std::map<Element*, Element*> input) { struct FlipFunctor { void operator() (std::pair<Element* const, Element*>& item) { item.second->flip(); } }; std::for_each(input.begin(), input.end(), FlipFunctor()); } When I move struct FlipFunctor before function flip_all, the code compiles. Full error message: no matching function for call to ‘for_each(std::_Rb_tree_iterator<std::pair<Element* const, Element*> >, std::_Rb_tree_iterator<std::pair<Element* const, Element*> >, flip_all(std::map<Element*, Element*, std::less<Element*>, std::allocator<std::pair<Element* const, Element*> > >)::FlipFunctor)’

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  • Beginner video capture and processing/Camera selection

    - by mattbauch
    I'll soon be undertaking a research project in real-time event recognition but have no experience with the programming aspect of video capture (I'm an upperclassman undergraduate in computer engineering). I want to start off on the right foot so advice from anyone with experience would be great. The ultimate goal is to track events such as a person standing up/sitting down, entering/leaving a room, possibly even shrugging/slumping in posture, etc. from a security camera-like vantage point. First of all, which cameras/companies would you recommend? I'm looking to spend ~$100, more if necessary but not much. Great resolution isn't a must, but is desirable if affordable. What about IP network cameras vs. a USB type webcam? Webcams are less expensive, but IP cameras seem like they'd be much less work to deal with in software. What features should I look for in the camera? Once I've selected a camera, what does converting its output to a series of RGB bitmaps entail? I've never dealt with video encoding/decoding so a starting point or a tutorial that will guide me up to this point would be great if anyone has suggestions. Finally, what is the best (least complicated/most efficient) way to display video from the camera plus my own superimposed images (boxes around events in progress, for instance) in a GUI application? I can work on any operating system in any language. I have some experience with win32 GUIs and Java GUIs. The focus of the project is on the algorithm and so I'm trying to get the video capture/display portion of the app done cleanly and quickly. Thanks for any responses!!

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  • Extra fulltext ordering criteria beyond default relevance

    - by Jeremy Warne
    I'm implementing an ingredient text search, for adding ingredients to a recipe. I've currently got a full text index on the ingredient name, which is stored in a single text field, like so: "Sauce, tomato, lite, Heinz" I've found that because there are a lot of ingredients with very similar names in the database, simply sorting by relevance doesn't work that well a lot of the time. So, I've found myself sorting by a bunch of my own rules of thumb, which probably duplicates a lot of the full-text search algorithm which spits out a numerical relevance. For instance (abridged): ORDER BY [ingredient name is exactly search term], [ingredient name starts with search term], [ingredient name starts with any word from the search and contains all search terms in some order], [ingredient name contains all search terms in some order], ...and so on. Each of these is defined in the SELECT specification as an expression returning either 1 or 0, and so I order by those in sequential order. I would love to hear suggestions for: A better way to define complicated order-by criteria in one place, say perhaps in a view or stored procedure that you can pass just the search term to and get back a set of results without having to worry about how they're ordered? A better tool for this than MySQL's fulltext engine -- perhaps if I was using Sphinx or something [which I've heard of but not used before], would I find some sort of complicated config option designed to solve problems like this? Some google search terms which might turn up discussion on how to order text items within a specific domain like this? I haven't found much that's of use. Thanks for reading!

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  • Multiple sendto() using UDP socket

    - by ereOn
    Hi, I have a network software which uses UDP to communicate with other instances of the same program. For different reasons, I must use UDP here. I recently had problems sending huge ammounts of data over UDP and had to implement a fragmentation system to split my messages into small data chunks. So far, it worked well but I now encounter an issue when I have to send a lot of data chunks. I have the following algorithm: Split message into small data chunks (around 1500 bytes) Iterate over the data chunks list and for each, send it using sendto() However, when I send a lot of data chunks, the receiver only gets the first 6 messages. Sometimes it misses the sixth and receives the seventh. It depends. Anyway, sendto() always indicates success. This always happen when I test my software over a loopback interface (127.0.0.1) but never over my LAN network. If I add something like std::cout << "test" << std::endl; between the sendto() then every frame is received. I am aware that UDP allows packet loss and that my frames might be loss for a lot of reasons and I suppose it has to do with the rate I am sending the data chunks at. What would be the right approach here ? Implementing some acknowledgement mechanism (just like TCP) seems overkill. Adding some arbitrary waiting time between the sendto() is ugly and will probably decrease performance. Increasing (if possible) the receiver UDP internal buffer ? I don't even know if this is possible. Something else ? I really need your advices here. Thank very much.

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  • why is this C++ Code not doing his job

    - by hamza
    i want to create a program that write all the primes in a file ( i know that its a popular algorithm but m trying to make it by my self ) , but it still showing all the numbers instead of just the primes , & i dont know why someone pleas tell me why #include <iostream> #include <stdlib.h> #include <stdio.h> void afficher_sur_un_ficher (FILE* ficher , int nb_bit ); int main() { FILE* p_fich ; char tab[4096] , mask ; int nb_bit = 0 , x ; for (int i = 0 ; i < 4096 ; i++ ) { tab[i] = 0xff ; } for (int i = 0 ; i < 4096 ; i++ ) { mask = 0x01 ; for (int j = 0 ; j < 8 ; j++) { if ((tab[i] & mask) != 0 ) { x = nb_bit ; while (( x > 1 )&&(x < 16384)) { tab[i] = tab[i] ^ mask ; x = x * 2 ; } afficher_sur_un_ficher (p_fich , nb_bit ) ; } mask = mask<<1 ; nb_bit++ ; } } system ("PAUSE"); return 0 ; } void afficher_sur_un_ficher (FILE* ficher , int nb_bit ) { ficher = fopen("res.txt","a+"); fprintf (ficher ,"%d \t" , nb_bit); int static z ; z = z+1 ; if ( z%10 == 0) fprintf (ficher , "\n"); fclose(ficher); }

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  • Recurrence relation solution

    - by Travis
    I'm revising past midterms for a final exam this week and am trying to make sense of a solution my professor posted for one of past exams. (You can see the original pdf here, question #6). I'm given the original recurrence relation T(m)=3T(n/2) + n and am told T(1) = 1. I'm pretty sure the solution I've been given is wrong in a few places. The solution is as follows: Let n=2^m T(2^m) = 3T(2^(m-1)) + 2^m 3T(2^(m-1)) = 3^2*T(2^(m-2)) + 2^(m-1)*3 ... 3^(m-1)T(2) = T(1) + 2*3^(m-1) I'm pretty sure this last line is incorrect and they forgot to multiply T(1) by 3^m. He then (tries to) sum the expressions: T(2^m) = 1 + (2^m + 2^(m-1)*3 + ... + 2*3(m-1)) = 1 + 2^m(1 + (3/2)^1 + (3/2)^2 + ... + (3/2)^(m-1)) = 1 + 2^m((3/2)^m-1)*(1/2) = 1 + 3^m - 2^(m-1) = 1 + n^log 3 - n/2 Thus the algorithm is big Theta of (n^log 3). I'm pretty sure that he also got the summation wrong here. By my calculations this should be as follows: T(2^m) = 2^m + 3 * 2^(m-1) + 3^2 * 2^(m-2) + ... + 3^m (3^m because 3^m*T(1) = 3^m should be added, not 1) = 2^m * ((3/2)^1 + (3/2)^2 + ... + (3/2)^m) = 2^m * sum of (3/2)^i from i=0 to m = 2^m * ((3/2)^(m+1) - 1)/(3/2 - 1) = 2^m * ((3/2)^(m+1) - 1)/(1/2) = 2^(m+1) * 3^(m+1)/2^(m+1) - 2^(m+1) = 3^(m+1) - 2 * 2^m Replacing n = 2^m, and from that m = log n T(n) = 3*3^(log n) - 2*n n is O(3^log n), thus the runtime is big Theta of (3^log n) Does this seem right? Thanks for your help!

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  • Source of parsers for programming languages?

    - by Arkaaito
    I'm dusting off an old project of mine which calculates a number of simple metrics about large software projects. One of the metrics is the length of files/classes/methods. Currently my code "guesses" where class/method boundaries are based on a very crude algorithm (traverse the file, maintaining a "current depth" and adjusting it whenever you encounter unquoted brackets; when you return to the level a class or method began on, consider it exited). However, there are many problems with this procedure, and a "simple" way of detecting when your depth has changed is not always effective. To make this give accurate results, I need to use the canonical way (in each language) of detecting function definitions, class definitions and depth changes. This amounts to writing a simple parser to generate parse trees containing at least these elements for every language I want my project to be applicable to. Obviously parsers have been written for all these languages before, so it seems like I shouldn't have to duplicate that effort (even though writing parsers is fun). Is there some open-source project which collects ready-to-use parser libraries for a bunch of source languages? Or should I just be using ANTLR to make my own from scratch? (Note: I'd be delighted to port the project to another language to make use of a great existing resource, so if you know of one, it doesn't matter what language it's written in.)

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  • 48-bit bitwise operations in Javascript?

    - by randomhelp
    I've been given the task of porting Java's Java.util.Random() to JavaScript, and I've run across a huge performance hit/inaccuracy using bitwise operators in Javascript on sufficiently large numbers. Some cursory research states that "bitwise operators in JavaScript are inherently slow," because internally it appears that JavaScript will cast all of its double values into signed 32-bit integers to do the bitwise operations (see https://developer.mozilla.org/En/Core_JavaScript_1.5_Reference/Operators/Bitwise_Operators for more on this.) Because of this, I can't do a direct port of the Java random number generator, and I need to get the same numeric results as Java.util.Random(). Writing something like this.next = function(bits) { if (!bits) { bits = 48; } this.seed = (this.seed * 25214903917 + 11) & ((1 << 48) - 1); return this.seed >>> (48 - bits); }; (which is an almost-direct port of the Java.util.Random()) code won't work properly, since Javascript can't do bitwise operations on an integer that size.) I've figured out that I can just make a seedable random number generator in 32-bit space using the Lehmer algorithm, but the trick is that I need to get the same values as I would with Java.util.Random(). What should I do to make a faster, functional port?

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  • Editing 8bpp indexed Bitmaps

    - by Pedro Sá
    hi, i'm trying to edit the pixels of a 8bpp. Since this PixelFormat is indexed i'm aware that it uses a Color Table to map the pixel values. Even though I can edit the bitmap by converting it to 24bpp, 8bpp editing is much faster (13ms vs 3ms). But, changing each value when accessing the 8bpp bitmap results in some random rgb colors even though the PixelFormat remains 8bpp. I'm currently developing in c# and the algorithm is as follows: (C#) 1- Load original Bitmap at 8bpp 2- Create Empty temp Bitmap with 8bpp with the same size as the original 3-LockBits of both bitmaps and, using P/Invoke, calling c++ method where I pass the Scan0 of each BitmapData object. (I used a c++ method as it offers better performance when iterating through the Bitmap's pixels) (C++) 4- Create a int[256] palette according to some parameters and edit the temp bitmap bytes by passing the original's pixel values through the palette. (C#) 5- UnlockBits. My question is how can I edit the pixel values without having the strange rgb colors, or even better, edit the 8bpp bitmap's Color Table? Regards, Pedro

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