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• Efficient Context-Free Grammar parser, preferably Python-friendly

  - by Max Shawabkeh

  I am in need of parsing a small subset of English for one of my project, described as a context-free grammar with (1-level) feature structures (example) and I need to do it efficiently . Right now I'm using NLTK's parser which produces the right output but is very slow. For my grammar of ~450 fairly ambiguous non-lexicon rules and half a million lexical entries, parsing simple sentences can take anywhere from 2 to 30 seconds, depending it seems on the number of resulting trees. Lexical entries have little to no effect on performance. Another problem is that loading the (25MB) grammar+lexicon at the beginning can take up to a minute. From what I can find in literature, the running time of the algorithm used to parse such a grammar (Earley or CKY) should be linear to the size of the grammar and cubic to the size of the input token list. My experience with NLTK indicates that ambiguity is what hurts the performance most, not the absolute size of the grammar. So now I'm looking for a CFG parser to replace NLTK. I've been considering PLY but I can't tell whether it supports feature structures in CFGs, which are required in my case, and the examples I've seen seem to be doing a lot of procedural parsing rather than just specifying a grammar. Can anybody show me an example of PLY both supporting feature structs and using a declarative grammar? I'm also fine with any other parser that can do what I need efficiently. A Python interface is preferable but not absolutely necessary.

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• stock management of assemblys and its sub parts

  - by The Disintegrator

  I have to track the stock of individual parts and kits (assembly) and can't find a satisfactory way of doing this. Sample bogus and hyper simplified database: Table prod: prodID 1 prodName Flux capacitor prodCost 900 prodPrice 1350 (900*1.5) prodStock 3 - prodID 2 prodName Mr Fusion prodCost 300 prodPrice 600 (300*2) prodStock 2 - prodID 3 prodName Time travel kit prodCost 1650 (1350+300) prodPrice 2145 (1650*1.3) prodStock 2 Table rels relID 1 relSrc 1 (Flux capacitor) relType 4 (is a subpart of) relDst 3 (Time travel kit) - relID 2 relSrc 2 (Mr Fusion) relType 4 (is a subpart of) relDst 3 (Time travel kit) prodPrice: it's calculated based on the cost but not in a linear way. In this example for costs of 500 or less, the markup is a 200%. For costs of 500-1000 the markup is 150%. For costs of 1000+ the markup is 130% That's why the time travel kit is much cheaper than the individual parts prodStock: here is my problem. I can sell kits or the individual parts, So the stock of the kits is virtual. The problem when I buy: Some providers sell me the Time Travel kit as a whole (with one barcode) and some sells me the individual parts (with a different barcode) So when I load the stock I don't know how to impute it. The problem when I sell: If I only sell kits, calculate the stock would be easy: "I have 3 Flux capacitors and 2 Mr Fusions, so I have 2 Time travel kits and a Flux Capacitor" But I can sell Kits or individual parts. I have to track the stock of the individual parts and the possible kits at the same time (and I have to compensate for the sell price) Probably this is really simple, but I can't see a simple solution. Resuming: I have to find a way of tracking the stock and the database/program is the one who has to do it (I cant ask the clerk to correct the stock) I'm using php+MySql. But this is more a logical problem than a programing one

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• Finding string in php

  - by Roshan

  I have a content and i want to search a keyword in that content. Content When charting multiple data series, or just to improve the appearance of your charts, you can control the fill for each series in the chart or each item in a series. The fill lets you specify a pattern that defines how Flex draws the chart element. You also use fills to specify the background colors of the chart or bands of background colors defined by the grid lines. Fills can be solid or can use linear and radial gradients. A gradient specifies a gradual color transition in the fill color therefore. NOw, if the keyword we are searching is "When", it is the starting word so should display as "When charting multiple data ..........." If the keyword is "draws" , it lies in middle so should be displayed as ".... how Flex draws....." If the kewyword is "therefore", it is in the last position so should be displayed as ".........transition in the fill color therefore." Can anyone help me out how to do this in php server script?

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• Low Latency Serial Communications In .Net

  - by bvillersjr

  I have been researching various third party libraries and approaches to low latency serial communications in .Net. I've read enough that I have now come full circle and know as little as I did when I started due to the variety of conflicting opinions. For example, the functionality in the Framework was ruled out due to some convincing articles stating: "that the Microsoft provided solution has not been stable across framework versions and is lacking in functionality." I have found articles bashing many of the older COM based libraries. I have found articles bashing the idea of a low latency .Net app as a whole due to garbage collection. I have also read articles demonstrating how P/Invoking Windows API functionality for the purpose of low latency communication is unacceptable. THIS RULES OUT JUST ABOUT ANY APPROACH I CAN THINK OF! I would really appreciate some words from those with been there / done that experience. Ideally, I could locate a solid library / partner and not have to build the communications library myself. I have the following simple objectives: Sustained low latency serial communication in C# / VB.Net 32/64 bit Well documented (if the solution is 3rd party) Relatively unimpacted (communication and latency wise) by garbage collection . Flexible (I have no idea what I will have to interface with in the future!) The only requirement that I have for certain is that I need to be able to interface with many different industrial devices such as RS485 based linear actuators, serial / microcontroller based gauges, and ModBus (also RS485) devices. Any comments, ideas, thoughts or links to articles that may iron out my confusion are much appreciated!

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• how to do introspection in R (stat package)

  - by Lebron James

  Hi all, I am somewhat new to R, and i have this piece of code which generates a variable that i don't know the type for. Are there any introspection facility in R which will tell me which type this variable belongs to? The following illustrates the property of this variable: I am working on linear model selection, and the resource I have is lm result from another model. Now I want to retrieve the lm call by the command summary(model)$call so that I don't need to hardcode the model structure. However, since I have to change the dataset, I need to do a bit of modification on the "string", but apparently it is not a simple string. I wonder if there is any command similar to string.replace so that I can manipulate this variable from the variable $call. Thanks > str<-summary(rdnM)$call > str lm(formula = y ~ x1, data = rdndat) > str[1] lm() > str[2] y ~ x1() > str[3] rdndat() > str[3] <- data Warning message: In str[3] <- data : number of items to replace is not a multiple of replacement length > str lm(formula = y ~ x1, data = c(10, 20, 30, 40)) > str<-summary(rdnM)$call > str lm(formula = y ~ x1, data = rdndat) > str[3] <- 'data' > str lm(formula = y ~ x1, data = "data") > str<-summary(rdnM)$call > type str Error: unexpected symbol in "type str" >

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• How to continuously scroll content within a DIV using jQuery?

  - by Camsoft

  Aim The aim is to a have a container DIV with a fixed height and width and have the HTML content within that DIV automatically scroll vertically continuously. Question Basically I've created the code below using jQuery to scroll (move) the child DIV vertically upwards until its outside the bounding parent box where the animation then completes which triggers an event handler which resets the position of the child DIV and starts the process again. This works fine, so the content scrolls up leaving a blank space and then starts from the bottom again and scrolls up. The problem I have is that the requirements for this is for the content to appear as if it was continuously repeating, see below diagram to better explain this, is there a way to do this? (I don't want to use 3rd party plug ins or libraries other than jQuery): What I have so far The HTML: <div id="scrollingContainer"> <div class="scroller"> <h1>This is a title</h1> <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Suspendisse at orci mi, id gravida tellus. Integer malesuada ante sit amet enim pulvinar congue. Donec pulvinar dolor et arcu posuere feugiat id et felis.</p> <p>More content....</p> </div> </div> The CSS: #scrollingContainer{ height: 300px; width: 300px; overflow: hidden; } #scrollingContainer DIV.scroller{ position: relative; } The JavaScript: /** * Scrolls the content DIV */ function scroll() { if($('DIV.scroller').height() > $('#scrollingContainer').height()) { var t = $('DIV.scroller').position().top + $('DIV.scroller').height(); /* Animate */ $('DIV.scroller').animate( { top: '-=' + t + 'px' } , 4000, 'linear', animationComplete); } } function animationComplete() { $(this).css('top', $('#scrollingContainer').height()); scroll(); }

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• Asymptotic complexity of a compiler

  - by Meinersbur

  What is the maximal acceptable asymptotic runtime of a general-purpose compiler? For clarification: The complexity of compilation process itself, not of the compiled program. Depending on the program size, for instance, the number of source code characters, statements, variables, procedures, basic blocks, intermediate language instructions, assembler instructions, or whatever. This is highly depending on your point of view, so this is a community wiki. See this from the view of someone who writes a compiler. Will the optimisation level -O4 ever be used for larger programs when one of its optimisations takes O(n^6)? Related questions: When is superoptimisation (exponential complexity or even incomputable) acceptable? What is acceptable for JITs? Does it have to be linear? What is the complexity of established compilers? GCC? VC? Intel? Java? C#? Turbo Pascal? LCC? LLVM? (Reference?) If you do not know what asymptotic complexity is: How long are you willing to wait until the compiler compiled your project? (scripting languages excluded)

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• How to keep only duplicates efficiently?

  - by Marc Eaddy

  Given an STL vector, I'd like an algorithm that outputs only the duplicates in sorted order, e.g., INPUT : { 4, 4, 1, 2, 3, 2, 3 } OUTPUT: { 2, 3, 4 } The algorithm is trivial, but the goal is to make it as efficient as std::unique(). My naive implementation modifies the container in-place: My naive implementation: void keep_duplicates(vector<int>* pv) { // Sort (in-place) so we can find duplicates in linear time sort(pv->begin(), pv->end()); vector<int>::iterator it_start = pv->begin(); while (it_start != pv->end()) { size_t nKeep = 0; // Find the next different element vector<int>::iterator it_stop = it_start + 1; while (it_stop != pv->end() && *it_start == *it_stop) { nKeep = 1; // This gets set redundantly ++it_stop; } // If the element is a duplicate, keep only the first one (nKeep=1). // Otherwise, the element is not duplicated so erase it (nKeep=0). it_start = pv->erase(it_start + nKeep, it_stop); } } If you can make this more efficient, elegant, or general, please let me know. For example, a custom sorting algorithm, or copy elements in the 2nd loop to eliminate the erase() call.

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• RadioGroup does not appear ?

  - by Mina Samy

  Hi all I have a linear layout with this form <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent" > <RadioGroup android:id="@+id/group" android:layout_width="wrap_content" android:layout_height="wrap_content"> <RadioButton android:id="@+id/item1" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Item1" android:checked="true" /> <RadioButton android:id="@+id/item2" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Item2" /> <RadioButton android:id="@+id/item3" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Item3" /> </RadioGroup> <TextView android:id="@+id/txt" android:layout_width="fill_parent" android:layout_height="fill_parent" /> </LinearLayout> this works fine but if I put the TextView above the RadioGroup like this <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent" > <TextView android:id="@+id/txt" android:layout_width="fill_parent" android:layout_height="fill_parent" /> <RadioGroup android:id="@+id/group" android:layout_width="wrap_content" android:layout_height="wrap_content" > <RadioButton android:id="@+id/item1" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Item1" android:checked="true" /> <RadioButton android:id="@+id/item2" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Item2" /> <RadioButton android:id="@+id/item3" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Item3" /> </RadioGroup> </LinearLayout> the activity appears blank what can be the reason for this thanks

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• Stock management of assemblies and its sub parts

  - by The Disintegrator

  I have to track the stock of individual parts and kits (assemblies) and can't find a satisfactory way of doing this. Sample bogus and hyper simplified database: Table prod: prodID 1 prodName Flux capacitor prodCost 900 prodPrice 1350 (900*1.5) prodStock 3 - prodID 2 prodName Mr Fusion prodCost 300 prodPrice 600 (300*2) prodStock 2 - prodID 3 prodName Time travel kit prodCost 1650 (1350+300) prodPrice 2145 (1650*1.3) prodStock 2 Table rels relID 1 relSrc 1 (Flux capacitor) relType 4 (is a subpart of) relDst 3 (Time travel kit) - relID 2 relSrc 2 (Mr Fusion) relType 4 (is a subpart of) relDst 3 (Time travel kit) prodPrice: it's calculated based on the cost but not in a linear way. In this example for costs of 500 or less, the markup is a 200%. For costs of 500-1000 the markup is 150%. For costs of 1000+ the markup is 130% That's why the time travel kit is much cheaper than the individual parts prodStock: here is my problem. I can sell kits or the individual parts, So the stock of the kits is virtual. The problem when I buy: Some providers sell me the Time Travel kit as a whole (with one barcode) and some sells me the individual parts (with a different barcode) So when I load the stock I don't know how to impute it. The problem when I sell: If I only sell kits, calculate the stock would be easy: "I have 3 Flux capacitors and 2 Mr Fusions, so I have 2 Time travel kits and a Flux Capacitor" But I can sell Kits or individual parts. So, I have to track the stock of the individual parts and the possible kits at the same time (and I have to compensate for the sell price) Probably this is really simple, but I can't see a simple solution. Resuming: I have to find a way of tracking the stock and the database/program is the one who has to do it (I cant ask the clerk to correct the stock) I'm using php+MySql. But this is more a logical problem than a programing one

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• CIE XYZ colorspace: is it RGBA or XYZA?

  - by Tronic

  I plan to write a painting program based on linear combinations of xy plane points (0,1), (1,0 ) and (0,0). Such system works identically to RGB, except that the primaries are not within the gamut but at the corners of a triangle that encloses the entire gamut, therefore allowing for all colors to be reproduced. I have seen the three points being referred to as X, Y and Z (upper case) somewhere, but I cannot find the page anymore. My pixel format stores the intensity of each of those three components the same way as RGB does, together with alpha value. This allows using pretty much any image manipulation operation designed for RGBA without modifying the code. What is my format called? Is it XYZA, RGBA or something else? Google doesn't seem to know of XYZA and RGBA will get confused with sRGB + alpha (which I also need to use in the same program). Notice that the primaries X, Y and Z and their intensities have little to do with the x, y and z coordinates (lower case) that are more commonly used.

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• Python fit polynomial, power law and exponential from data

  - by Nadir

  I have some data (x and y coordinates) coming from a study and I have to plot them and to find the best curve that fits data. My curves are: polynomial up to 6th degree; power law; and exponential. I am able to find the best fit for polynomial with while(i < 6): coefs, val = poly.polyfit(x, y, i, full=True) and I take the degree that minimizes val. When I have to fit a power law (the most probable in my study), I do not know how to do it correctly. This is what I have done. I have applied the log function to all x and y and I have tried to fit it with a linear polynomial. If the error (val) is lower than the others polynomial tried before, I have chosen the power law function. Am I correct? Now how can I reconstruct my power law starting from the line y = mx + q in order to draw it with the original points? I need also to display the function found. I have tried with: def power_law(x, m, q): return q * (x**m) using x_new = np.linspace(x[0], x[-1], num=len(x)*10) y1 = power_law(x_new, coefs[0], coefs[1]) popt, pcov = curve_fit(power_law, x_new, y1) but it seems not to work well.

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• What is Adobe Flex? Is it just Flash II?

  - by Adam Davis

  Question Alright, I'm confused by all the buzzwords and press release bingo going on. What is the relationship between flash and flex: Replace flash (not really compatible) Enhance flash The next version of flash but still basically compatible Separate technology altogether ??? If I'm starting out in Flash now, should I just skip to Flex? Follow up Ok, so what I'm hearing is that there's three different parts to the puzzle: Flash The graphical editor used to make "Flash Movies", ie it's an IDE that focuses on the visual aspect of "Flash" (Officially Flash CS3?) The official name for the display plugins (ie, "Download Flash Now!") A general reference to the entire technology stack In terms of the editor, it's a linear timeline based editor, best used for animations with complex interactivity. Actionscript The "Flash" programming language Flex An Adobe Flash IDE that focuses on the coding/programming aspect of "Flash" (Flex Builder?) A Flash library that enhances Flash and makes it easier to program for (Flex SDK?) Is not bound to a timeline (as the Flash IDE is) and so "standard" applications are more easily accomplished. Is this correct?

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• Big-O of PHP functions?

  - by Kendall Hopkins

  After using PHP for a while now, I've noticed that not all PHP built in functions as fast as expected. Consider the below two possible implementations of a function that finds if a number is prime using a cached array of primes. //very slow for large $prime_array $prime_array = array( 2, 3, 5, 7, 11, 13, .... 104729, ... ); $result_array = array(); foreach( $array_of_number => $number ) { $result_array[$number] = in_array( $number, $large_prime_array ); } //still decent performance for large $prime_array $prime_array => array( 2 => NULL, 3 => NULL, 5 => NULL, 7 => NULL, 11 => NULL, 13 => NULL, .... 104729 => NULL, ... ); foreach( $array_of_number => $number ) { $result_array[$number] = array_key_exists( $number, $large_prime_array ); } This is because in_array is implemented with a linear search O(n) which will linearly slow down as $prime_array grows. Where the array_key_exists function is implemented with a hash lookup O(1) which will not slow down unless the hash table gets extremely populated (in which case it's only O(logn)). So far I've had to discover the big-O's via trial and error, and occasionally looking at the source code. Now for the question... I was wondering if there was a list of the theoretical (or practical) big O times for all* the PHP built in functions. *or at least the interesting ones For example find it very hard to predict what the big O of functions listed because the possible implementation depends on unknown core data structures of PHP: array_merge, array_merge_recursive, array_reverse, array_intersect, array_combine, str_replace (with array inputs), etc.

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• How to analyze the efficiency of this algorithm Part 2

  - by Leonardo Lopez

  I found an error in the way I explained this question before, so here it goes again: FUNCTION SEEK(A,X) 1. FOUND = FALSE 2. K = 1 3. WHILE (NOT FOUND) AND (K < N) a. IF (A[K] = X THEN 1. FOUND = TRUE b. ELSE 1. K = K + 1 4. RETURN Analyzing this algorithm (pseudocode), I can count the number of steps it takes to finish, and analyze its efficiency in theta notation, T(n), a linear algorithm. OK. This following code depends on the inner formulas inside the loop in order to finish, the deal is that there is no variable N in the code, therefore the efficiency of this algorithm will always be the same since we're assigning the value of 1 to both A & B variables: 1. A = 1 2. B = 1 3. UNTIL (B > 100) a. B = 2A - 2 b. A = A + 3 Now I believe this algorithm performs in constant time, always. But how can I use Algebra in order to find out how many steps it takes to finish?

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• Read line and change the line that not consist of certain words and not end with dot

  - by igo

  I wanna read some text files in a folder line by line. for example of 1 txt : Fast and Effective Text Mining Using Linear-time Document Clustering Bjornar Larsen WORD2 Chinatsu Aone SRA International AK, Inc. 4300 Fair Lakes Cow-l Fairfax, VA 22033 {bjornar-larsen, WORD1 I wanna remove line that does not contain of words = word, word2, word3, and does not end with dot . so. from the example, the result will be : Bjornar Larsen WORD2 Chinatsu Aone SRA International, Inc. {bjornar-larsen, WORD1 I am confused, hw to remove the line? it that possible? or can we replace them with a space? here's the code : $url = glob($savePath.'*.txt'); foreach ($url as $file => $files) { $handle = fopen($files, "r") or die ('can not open file'); $ori_content= file_get_contents($files); foreach(preg_split("/((\r?\n)|(\r\n?))/", $ori_content) as $buffer){ $pos1 = stripos($buffer, $word1); $pos2 = stripos($buffer, $word2); $pos3 = stripos($buffer, $word3); $last = $str[strlen($buffer)-1];//read the las character if (true !== $pos1 OR true !== $pos2 OR true !==$pos3 && $last != '.'){ //how to remove } } } please help me, thank you so much :)

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• Stock management of assemblies and its sub parts (relations)

  - by The Disintegrator

  I have to track the stock of individual parts and kits (assemblies) and can't find a satisfactory way of doing this. Sample bogus and hyper simplified database: Table prod: prodID 1 prodName Flux capacitor prodCost 900 prodPrice 1350 (900*1.5) prodStock 3 - prodID 2 prodName Mr Fusion prodCost 300 prodPrice 600 (300*2) prodStock 2 - prodID 3 prodName Time travel kit prodCost 1650 (1350+300) prodPrice 2145 (1650*1.3) prodStock 2 Table rels relID 1 relSrc 1 (Flux capacitor) relType 4 (is a subpart of) relDst 3 (Time travel kit) - relID 2 relSrc 2 (Mr Fusion) relType 4 (is a subpart of) relDst 3 (Time travel kit) prodPrice: it's calculated based on the cost but not in a linear way. In this example for costs of 500 or less, the markup is a 200%. For costs of 500-1000 the markup is 150%. For costs of 1000+ the markup is 130% That's why the time travel kit is much cheaper than the individual parts prodStock: here is my problem. I can sell kits or the individual parts, So the stock of the kits is virtual. The problem when I buy: Some providers sell me the Time Travel kit as a whole (with one barcode) and some sells me the individual parts (with a different barcode) So when I load the stock I don't know how to impute it. The problem when I sell: If I only sell kits, calculate the stock would be easy: "I have 3 Flux capacitors and 2 Mr Fusions, so I have 2 Time travel kits and a Flux Capacitor" But I can sell Kits or individual parts. So, I have to track the stock of the individual parts and the possible kits at the same time (and I have to compensate for the sell price) Probably this is really simple, but I can't see a simple solution. Resuming: I have to find a way of tracking the stock and the database/program is the one who has to do it (I cant ask the clerk to correct the stock) I'm using php+MySql. But this is more a logical problem than a programing one

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• Updating a Minimum spanning tree when a new edge is inserted

  - by Lynette

  Hello, I've been presented the following problem in University: Let G = (V, E) be an (undirected) graph with costs ce = 0 on the edges e € E. Assume you are given a minimum-cost spanning tree T in G. Now assume that a new edge is added to G, connecting two nodes v, tv € V with cost c. a) Give an efficient algorithm to test if T remains the minimum-cost spanning tree with the new edge added to G (but not to the tree T). Make your algorithm run in time O(|E|). Can you do it in O(|V|) time? Please note any assumptions you make about what data structure is used to represent the tree T and the graph G. b)Suppose T is no longer the minimum-cost spanning tree. Give a linear-time algorithm (time O(|E|)) to update the tree T to the new minimum-cost spanning tree. This is the solution I found: Let e1=(a,b) the new edge added Find in T the shortest path from a to b (BFS) if e1 is the most expensive edge in the cycle then T remains the MST else T is not the MST It seems to work but i can easily make this run in O(|V|) time, while the problem asks O(|E|) time. Am i missing something? By the way we are authorized to ask for help from anyone so I'm not cheating :D Thanks in advance

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• LaTeX printing only first two pages of a document

  - by Peter Flom

  I am working in LaTeX, and when I create a pdf file (using LaTeX button or pdfLaTeX button or using yap) the pdf has only the first two pages. No errors. It just stops. If I make the first page longer by adding text, it still stops at end of 2nd page. Any ideas? OK, responding to first comment, here is the code \documentclass{article} \title{Outline of Book} \author{Peter L. Flom} \begin{document} \maketitle \section*{Preface} \subsection*{Audience} \subsection*{What makes this book different?} \subsection*{Necessary background} \subsection*{How to read this book} \section{Introduction} \subsection{The purpose of logistic regression} \subsection{The need for logistic regression} \subsection{Types of logistic regression} \section{General issues in logistic regression} \subsection{Transforming independent and dependent variables} \subsection{Interactions} \subsection{Model selection} \subsection{Parameter estimates, confidence intervals, p values} \subsection{Summary and further reading} \section{Dichotomous logistic regression} \subsection{Introduction, theory, examples} \subsection{Exploratory plots and analysis} \subsection{Basic model fitting} \subsection{Advanced and special issues in model fitting} \subsection{Diagnostic and descriptive plots and analysis} \subsection{Traps and gotchas} \subsection{Power analysis} \subsection{Summary and further reading} \subsection{Exercises} \section{Ordinal logistic regression} \subsection{Introduction, theory, examples} \subsubsection{Introduction - what are ordinal variables?} \subsubsection{Theory of the model} \subsubsection{Examples for this chapter} \subsection{Exploratory plots and analysis} \subsection{Basic model fitting} \subsection{Advanced and special issues in model fitting} \subsection{Diagnostic and descriptive plots and analysis} \subsection{Traps and gotchas} \subsection{Power analysis} \subsection{Summary and further reading} \subsection{Exercises} \section{Multinomial logistic regression} \subsection{Introduction, theory, examples} \subsection{Exploratory plots and analysis} \subsection{Basic model fitting} \subsection{Advanced and special issues in model fitting} \subsection{Diagnostic and descriptive plots and analysis} \subsection{Traps and gotchas} \subsection{Power analysis} \subsection{Summary and further reading} \subsection{Exercises} \section{Choosing a model} \subsection{NOIR and its problems} \subsection{Linear vs. ordinal} \subsection{Ordinal vs. multinomial} \subsection{Summary and further reading} \subsection{Exercises} \section{Extensions and related models} \subsection{Other logistic models} \subsection{Multilevel models - PROC NLMIXED and GLIMMIX} \subsection{Loglinear models - PROC CATMOD} \section{Summary} \end{document} thanks Peter

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• stack overflow problem in program

  - by Jay

  So I am currently getting a strange stack overflow exception when i try to run this program, which reads numbers from a list in a data/text file and inserts it into a binary search tree. The weird thing is that when the program works when I have a list of 4095 numbers in random order. However when i have a list of 4095 numbers in increasing order (so it makes a linear search tree), it throws a stack overflow message. The problem is not the static count variable because even when i removed it, and put t=new BinaryNode(x,1) it still gave a stack overflow exception. I tried debugging it, and it broke at if (t == NULL){ t = new BinaryNode(x,count); Here is the insert function. BinaryNode *BinarySearchTree::insert(int x, BinaryNode *t) { static long count=0; count++; if (t == NULL){ t = new BinaryNode(x,count); count=0; } else if (x < t->key){ t->left = insert(x, t->left); } else if (x > t->key){ t->right = insert(x, t->right); } else throw DuplicateItem(); return t; }

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• Time complexity with bit cost

  - by Keyser

  I think I might have completely misunderstood bit cost analysis. I'm trying to wrap my head around the concept of studying an algorithm's time complexity with respect to bit cost (instead of unit cost) and it seems to be impossible to find anything on the subject. Is this considered to be so trivial that no one ever needs to have it explained to them? Well I do. (Also, there doesn't even seem to be anything on wikipedia which is very unusual). Here's what I have so far: The bit cost of multiplication and division of two numbers with n bits is O(n^2) (in general?) So, for example: int number = 2; for(int i = 0; i < n; i++ ){ number = i*i; } has a time complexity with respect to bit cost of O(n^3), because it does n multiplications (right?) But in a regular scenario we want the time complexity with respect to the input. So, how does that scenario work? The number of bits in i could be considered a constant. Which would make the time complexity the same as with unit cost except with a bigger constant (and both would be linear). Also, I'm guessing addition and subtraction can be done in constant time, O(1). Couldn't find any info on it but it seems reasonable since it's one assembler operation.

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• Using ARIMA to model and forecast stock prices using user-friendly stats program

  - by Brian

  Hi people, Can anyone please offer some insight into this for me? I'm coming from a functional magnetic resonance imaging research background where I analyzed a lot of time series data, and I'd like to analyze the time series of stock prices (or returns) by: 1) modeling a successful stock in a particular market sector and then cross-correlating the time series of this historically successful stock with that of other newer stocks to look for significant relationships; 2) model a stock's price time series and use forecasting (e.g., exponential smoothing) to predict future values of it. I'd like to use non-linear modeling methods (ARIMA and ARCH) to do this. Several questions: How often do ARIMA and ARCH modeling methods (given that the individual who implements them does so accurately) actually fit the stock time series data they target, and what is the optimal fit I can expect? Is the extent to which this model fits the data commensurate with the extent to which it predicts this stock time series' future values? Rather than randomly selecting stocks to compare or model, if profit is my goal, what is an efficient approach, if any, to selecting the stocks I'm going to analyze? Which stats program is the most user-friendly for this? Any thoughts on this would be great and would go a long way for me. Thanks, Brian

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• How Can I: Generate 40/64 Bit WEP Key In Python?

  - by Aktariel

  So, I've been beating my head against the wall of this issue for several months now, partly because it's a side interest and partly because I suck at programming. I've searched and researched all across the web, but have not had any luck (except one small bit of success; see below), so I thought I might try asking the experts. What I am trying to do is, as the title suggests, generate a 40/64 bit WEP key from a passphrase, according to the "de facto" standard. (A site such as [http://www.powerdog.com/wepkey.cgi] produces the expected outputs.) I have already written portions of the script that take inputs and write them to a file; one of the inputs would be the passphrase, sanitized to lower case. For the longest time I had no idea what the defacto standard was, much less how to even go about implementing it. I finally stumbled across a paper (http://www.lava.net/~newsham/wlan/WEP_password_cracker.pdf) that sheds as much light as I've had yet on the issue (page 18 has the relevant bits). Apparently, the passphrase is "mapped to a 32-bit value with XOR," the result of which is then used as the seed for a "linear congruential PRNG (which one of the several PRNGs Python has would fit this description, I don't know), and then from that result several bits of the result are taken. I have no idea how to go about implementing this, since the description is rather vague. What I need is help in writing the generator in Python, and also in understanding how exactly the key is generated. I'm not much of a programmer, so explanations are appreciated as well. (Yes, I know that WEP isn't secure.)

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• How can I apply a PSSM efficiently?

  - by flies

  I am fitting for position specific scoring matrices (PSSM aka Position Specific Weight Matrices). The fit I'm using is like simulated annealing, where I the perturb the PSSM, compare the prediction to experiment and accept the change if it improves agreement. This means I apply the PSSM millions of times per fit; performance is critical. In my particular problem, I'm applying a PSSM for an object of length L (~8 bp) at every position of a DNA sequence of length M (~30 bp) (so there are M-L+1 valid positions). I need an efficient algorithm to apply a PSSM. Can anyone help improve performance? My best idea is to convert the DNA into some kind of a matrix so that applying the PSSM is matrix multiplication. There are efficient linear algebra libraries out there (e.g. BLAS), but I'm not sure how best to turn an M-length DNA sequence into a matrix M x 4 matrix and then apply the PSSM at each position. The solution needs to work for higher order/dinucleotide terms in the PSSM - presumably this means representing the sequence-matrix for mono-nucleotides and separately for dinucleotides. My current solution iterates over each position m, then over each letter in word from m to m+L-1, adding the corresponding term in the matrix. I'm storing the matrix as a multi-dimensional STL vector, and profiling has revealed that a lot of the computation time is just accessing the elements of the PSSM (with similar performance bottlenecks accessing the DNA sequence). If someone has an idea besides matrix multiplication, I'm all ears.

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• What does O(log n) mean exactly?

  - by Andreas Grech

  I am currently learning about Big O Notation running times and amortized times. I understand the notion of O(n) linear time, meaning that the size of the input affects the growth of the algorithm proportionally...and the same goes for, for example, quadratic time O(n2) etc..even algorithms, such as permutation generators, with O(n!) times, that grow by factorials. For example, the following function is O(n) because the algorithm grows in proportion to its input n: f(int n) { int i; for (i = 0; i < n; ++i) printf("%d", i); } Similarly, if there was a nested loop, the time would be O(n2). But what exactly is O(log n)? For example, what does it mean to say that the height of a complete binary tree is O(log n)? I do know (maybe not in great detail) what Logarithm is, in the sense that: log10 100 = 2, but I cannot understand how to identify a function with a logarithmic time.

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