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  • B-Tree Revision

    - by stan
    Hi, If we are looking for line intersections (horizontal and vertical lines only) and we have n lines with half of them vertical and no intersections then Sorting the list of line end points on y value will take N log N using mergesort Each insert delete and search of our data structue (assuming its a b-tree) will be < log n so the total search time will be N log N What am i missing here, if the time to sort using mergesort takes a time of N log N and insert and delete takes a time of < log n are we dropping the constant factor to give an overal time of N log N. If not then how comes < log n goes missing in total ONotation run time? Thanks

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  • using BOSH/similar technique for existing application/system

    - by SnapConfig.com
    We've an existing system which connects to the the back end via http (apache/ssl) and polls the server for new messages, needless to say we have scalability issues. I'm researching on removing this polling and have come across BOSH/XMPP but I'm not sure how we should take the BOSH technique (using long lived http connection). I've seen there are few libraries available but the entire thing seems bloaty since we do not need buddy lists etc and simply want to notify the clients of available messages. The client is written in C/C++ and works across most OS so that is an important factor. The server is in Java. does bosh result in huge number of httpd processes? since it has to keep all the clients connected, what would be the limit on that. we are also planning to move to 64 bit JVM/apache what would be the max limit of clients in that case. any hints?

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  • New to AVL tree implementation.

    - by nn
    I am writing a sliding window compression algorithm (LZ77) that searches for phrases in a "moving" dictionary. So far I have written a BST where each node is stored in an array and it's index in the array is also the value of the starting position in the window itself. I am now looking at transforming the BST to an AVL tree. I am a little confused at the sample implementations I have seen. Some only appear to store the balance factors whereas others store the height of each tree. Are there any performance advantage/disadvantages of storing the height and/or balance factor for each node? Apologies if this is a very simple question, but I'm still not visualizing how I want to restructure my BST to implement height balancing. Thanks.

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  • Changing text size on a ggplot bump plot

    - by Tom Liptrot
    Hi, I'm fairly new to ggplot. I have made a bumpplot using code posted below. I got the code from someones blog - i've lost the link.... I want to be able to increase the size of the lables (here letters which care very small on the left and right of the plot) without affecting the width of the lines (this will only really make sense after you have run the code) I have tried changing the size paramater but that always alter the line width as well. Any suggestion appreciated. Tom require(ggplot2) df<-matrix(rnorm(520), 5, 10) #makes a random example colnames(df) <- letters[1:10] Price.Rank<-t(apply(df, 1, rank)) dfm<-melt(Price.Rank) names(dfm)<-c( "Date","Brand", "value") p <- ggplot(dfm, aes(factor(Date), value, group = Brand, colour = Brand, label = Brand)) p1 <- p + geom_line(aes(size=2.2, alpha=0.7)) + geom_text(data = subset(dfm, Date == 1), aes(x = Date , size =2.2, hjust = 1, vjust=0)) + geom_text(data = subset(dfm, Date == 5), aes(x = Date , size =2.2, hjust = 0, vjust=0))+ theme_bw() + opts(legend.position = "none", panel.border = theme_blank()) p1 + theme_bw() + opts(legend.position = "none", panel.border = theme_blank())

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  • Program contains 2 nested loops which contain 4 if conditionals. How many paths?

    - by Student4Life
    In Roger Pressman's book, there is an example described of a program with 2 nested loops, the inner loop enclosing four if statements. The two loops can execute up to 20 times. He states that this makes about 10^14 paths. To get a number this large, it seems the paths inside the loops are multipllied by 2^40, i.e. 2^20 times 2^20 to account for all the possibilities of going through the two loops. I can't see why this factor is not just 400, i.e. 20 times 20. Can someone shed some light? It will help if you have the ppt slides and can see the program graph. Thanks.

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  • Sorting MySQL results within a resultset

    - by InnateDev
    I have a resultset of lets say 10 results. 3 of them have a type 'Pears', and the next 3 have a type 'Apples' and the next three have a type of 'Bananas'. The last record has a type of 'Squeezing Equipment' - unrelated to the fruits. How do I return this set of results (for pagination too) in a GROUPED order that I specify WITHOUT using any inherent sort factor like ALPHABETA or ID etc? I have the all types at my disposal before running the code so they can be specified. i.e. ID | Bananas ID | Bananas ID | Bananas ID | Apples ID | Apples ID | Apples ID | Pears ID | Pears ID | Pears ID | Squeezing Equipment

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  • whats the diference between train, validation and test set, in neural networks?

    - by Daniel
    Im using this library http://pastebin.com/raw.php?i=aMtVv4RZ to implement a learning agent. I have generated the train cases, but i dont know for sure what are the validation and test sets, the teacher says: 70% should be train cases, 10% will be test cases and the rest 20% should be validation cases. Thanks. edit i have this code, for training.. but i have no ideia when to stop training.. def train(self, train, validation, N=0.3, M=0.1): # N: learning rate # M: momentum factor accuracy = list() while(True): error = 0.0 for p in train: input, target = p self.update(input) error = error + self.backPropagate(target, N, M) print "validation" total = 0 for p in validation: input, target = p output = self.update(input) total += sum([abs(target - output) for target, output in zip(target, output)]) #calculates sum of absolute diference between target and output accuracy.append(total) print min(accuracy) print sum(accuracy[-5:])/5 #if i % 100 == 0: print 'error %-14f' % error if ? < ?: break

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  • Binning a numeric variable in R

    - by McPeterson
    I have a vector X that contains positive numbers that I want to bin/discretize. For this vector, I want the numbers [0, 10) to show up just as they exist in the vector, but numbers [10,∞) to be 10+. I'm using: x <- c(0,1,3,4,2,4,2,5,43,432,34,2,34,2,342,3,4,2) binned.x <- as.factor(ifelse(x > 10,"10+",x)) but this feels klugey to me. Does anyone know a better solution or a different approach? mcpeterson

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  • How to prevent traffic to/from a slow Cassandra node using Python

    - by Sergio Ayestarán
    Intro: I have a Python application using a Cassandra 1.2.4 cluster with a replication factor of 3, all reads and writes are done with a consistency level of 2. To access the cluster I use the CQL library. The Cassandra cluster is running on rackspace's virtual servers. The problem: From time to time one of the nodes can become slower than usual, in this case I want to be able to detect this situation and prevent making requests to the slow node and if possible to stop using it at all (this should theoretically be possible since the RF is 3 and the CL is 2 for every single request). The questions: What's the best way of detecting the slow node from a Python application? Is there a way to stop using one of the Cassandra nodes from Python in this scenario without human intervention? Thanks in advance!

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  • SQL to return dates that fall in period and range

    - by Nate
    Hey stackers, I’ve been grinding my head on this for a while… My goal is to return all dates that fall between a start and end date and have a certain period as a factor, from the start date. (hard to explain) For example… Start Date: Nov 20, 1987; End Date: Jan 01, 1988; Period: 10 days; I want these dates: Nov 20, 1987; Nov 30, 1987; Dec 10, 1987; Dec 20, 1987; Dec 30, 1987; I already have a date table with all dates from 1900 to 2099. The period could be by days, months or years. Any ideas? Let me know if you need more info.

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  • Animation with Initial Velocity

    - by abustin
    I've been trying to solve this problem for a number of days now but I must be missing something. Known Variables: vi = Initial Velocity t = Animation Duration d = Distance The function I'm trying to create: D(t) = the current distance for a given time Using this information I want to be able to create a smooth animation curve with varying velocity (ease-in/ease-out). The animation must be able ease-in from an initial velocity. The animation must be exactly t seconds and must be travel exactly d units. The curve should lean towards the average velocity with acceleration occurring at the beginning and the end portions of the curve. I'm open to extra configuration variables. The best I've been able to come up with is something that doesn't factor in the initial velocity. I'm hoping someone smarter can help me out. ;) Thank you! p.s. I'm working with an ECMAScript variant

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  • General zoom algorithm for drawing program

    - by Steven Sproat
    My GUI toolkit, wxPython provides some methods for implementing a user zoom factor, however the quality isn't too good. I'm looking for ideas on how to create a zooming feature, which I know is complicated. I have a bitmap representing my canvas which is drawn to. This is displayed inside a scrolled window. Problems I forsee: - performance when zoomed in and panning around the canvas - difficulties with "real" coordinates and zoomed in coordinates - image quality not degrading with the zoom Using wxPython's SetUserScale() on its device contexts presents image quality like this - this is with a 1px line, at 30% zoomed in. I'm just wondering the general steps I'll need to take and the challenges I'll encounter. Thanks for any suggestions

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  • What is the best Java numerical method package?

    - by Bob Cross
    I am looking for a Java-based numerical method package that provides functionality including: Solving systems of equations using different numerical analysis algorithms. Matrix methods (e.g., inversion). Spline approximations. Probability distributions and statistical methods. In this case, "best" is defined as a package with a mature and usable API, solid performance and numerical accuracy. Edit: derick van brought up a good point in that cost is a factor. I am heavily biased in favor of free packages but others may have a different emphasis.

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  • Overcoming C limitations for large projects

    - by Francisco Garcia
    One aspect where C shows its age is the encapsulation of code. Many modern languages has classes, namespaces, packages... a much more convenient to organize code than just a simple "include". Since C is still the main language for many huge projects. How do you to overcome its limitations? I suppose that one main factor should be lots of discipline. I would like to know what you do to handle large quantity of C code, which authors or books you can recommend.

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  • Parallel Programming. Boost's MPI, OpenMP, TBB, or something else?

    - by unknownthreat
    Hello, I am totally a novice in parallel programming, but I do know how to program C++. Now, I am looking around for parallel programming library. I just want to give it a try, just for fun, and right now, I found 3 APIs, but I am not sure which one should I stick with. Right now, I see Boost's MPI, OpenMP and TBB. For anyone who have experienced with any of these 3 API (or any other parallelism API), could you please tell me the difference between these? Are there any factor to consider, like AMD or Intel architecture?

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  • What are the reasons to use SQL Server instead of MySQL with a complex .Net project?

    - by cdeszaq
    We currently have a 10 year old nasty, spaghetti-code-style SQL Server database that we are soon looking to pretty much re-write from scratch as part of a re-write to a large web application. (The existing application will serve as the functional requirements for the next incarnation of the app) The new version will be developed in .Net, so a large portion of the application stack will be based on Microsoft technologies (Visual Studio will be used IIS will be the application server). One of the developers on the project has raised the possibility of switching to MySQL instead of SQL Server in order to save on cost for both the licence of the DB server, as well as the tools to design and manipulate the DB (such as the wonderfully free MySQL Workbench). What are the various pros and cons of using SQL Server vs. MySQL as the database for a complex .Net project? Price is one factor we have identified, both in terms of the DB server licence as well as tools to manipulate the DB, but what other factors come into play?

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  • Tabbed javascript widget for a Rails app

    - by neilc
    A user registers on our Rails app and they're given javascript to embed a widget in their website. The widget has a tabbed interface, like the JQuery tabs http://stilbuero.de/jquery/tabs_3/. iFrames have been tested, but the widget form factor and cross-domain policy negates the use of iframes. The widget is very dynamic and will often update the DOM with new content - and because of cross-domain policy, it looks as though JSONP is necessary. I understand that 'widget.js.erb' needs to create the widget layout, reference a stylesheet, render the tabs, etc - but once a tab is clicked, how does the widget request the content from the Rails app and render it in the DOM?

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  • Finding the Formula for a Curve

    - by Mystagogue
    Is there a program that will take "response curve" values from me, and provide a formula that approximates the response curve? It would be cool if such a program would take a numeric "percent correct" (perhaps with a standard deviation) so that it returns simplified formulas when laxity is permissable, and more precise (viz. complex) formulas when the curve needs to be approximated closely. My interest is to play with the response curve values and "laxity" factor, until such a tool spits out a curve-fit formula simple enough that I know it will be high performance during machine computations.

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  • Multi-Core Programming. Boost's MPI, OpenMP, TBB, or something else?

    - by unknownthreat
    Hello, I am totally a novice in Multi-Core Programming, but I do know how to program C++. Now, I am looking around for Multi-Core Programming library. I just want to give it a try, just for fun, and right now, I found 3 APIs, but I am not sure which one should I stick with. Right now, I see Boost's MPI, OpenMP and TBB. For anyone who have experienced with any of these 3 API (or any other API), could you please tell me the difference between these? Are there any factor to consider, like AMD or Intel architecture?

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  • more ruby way of gsub from array

    - by aharon
    My goal is to let there be x so that x("? world. what ? you say...", ['hello', 'do']) returns "hello world. what do you say...". I have something that works, but seems far from the "Ruby way": def x(str, arr, rep='?') i = 0 query.gsub(rep) { i+=1; arr[i-1] } end Is there a more idiomatic way of doing this? (Let me note that speed is the most important factor, of course.)

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  • Creating a new coloumn for date info with specific date format

    - by Ayan
    Dear All I am working with a file which has few years data and I am trying to create an aditional coloumn that reads the year and month info from the date coloumn (e.g. 01/01/1997 12:00) and create a new coloumn with month and year together(e.g. Jan-97). I am not sure how to proceed with this but what I am trying to code is the coloumn with name "new_date" in the following picture: my sample data = > dput(df) structure(list(date = structure(c(1L, 4L, 7L, 2L, 5L, 8L, 3L, 6L, 9L), .Label = c("01/01/1997 12:00", "01/01/1998 15:00", "01/01/1999 18:00", "01/02/1997 13:00", "01/02/1998 16:00", "01/02/1999 19:00", "01/03/1997 14:00", "01/03/1998 17:00", "01/03/1999 19:00"), class = "factor"), value = c(29L, 31L, 42L, 42L, 52L, 61L, 57L, 55L, 56L)), .Names = c("date", "value"), row.names = c(NA, -9L), class = "data.frame") I would really appreciate if you could advise me about how should I proceed with this, Many thanks, Ayan

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  • Compiler error: Variable or field declared void [closed]

    - by ?? ?
    i get some error when i try to run this, could someone please tell me the mistakes, thank you! [error: C:\Users\Ethan\Desktop\Untitled1.cpp In function `int main()': 25 C:\Users\Ethan\Desktop\Untitled1.cpp variable or field `findfactors' declared void 25 C:\Users\Ethan\Desktop\Untitled1.cpp initializer expression list treated as compound expression] #include<iostream> #include<cmath> using namespace std; void prompt(int&, int&, int&); int gcd(int , int , int );//3 input, 3 output void findfactors(int , int , int, int, int&, int&);//3 input, 2 output void display(int, int, int, int, int);//5 inputs int main() { int a, b, c; //The coefficients of the quadratic polynomial int ag, bg, cg;//value of a, b, c after factor out gcd int f1, f2; //The two factors of a*c which add to be b int g; //The gcd of a, b, c prompt(a, b, c);//Call the prompt function g=gcd(a, b, c);//Calculation of g void findfactors(a, b, c, f1, f2);//Call findFactors on factored polynomial display(g, f1, f2, a, c);//Call display function to display the factored polynomial system("PAUSE"); return 0; } void prompt(int& num1, int& num2, int& num3) //gets 3 ints from the user { cout << "This program factors polynomials of the form ax^2+bx+c."<<endl; while(num1==0) { cout << "Enter a value for a: "; cin >> num1; if(num1==0) { cout<< "a must be non-zero."<<endl; } } while(num2==0 && num3==0) { cout << "Enter a value for b: "; cin >> num2; cout << "Enter a value for c: "; cin >> num3; if(num2==0 && num3==0) { cout<< "b and c cannot both be 0."<<endl; } } } int gcd(int num1, int num2, int num3) { int k=2, gcd=1; while (k<=num1 && k<=num2 && k<=num3) { if (num1%k==0 && num2%k==0 && num3%k==0) gcd=k; k++; } return gcd; } void findFactors(int Ag, int Bg, int Cg,int& F1, int& F2) { int y=Ag*Cg; int z=sqrt(abs(y)); for(int i=-z; i<=z; i++) //from -sqrt(|y|) to sqrt(|y|) { if(i==0)i++; //skips 0 if(y%i==0) //if i is a factor of y { if(i+y/i==Bg) //if i and its partner add to be b F1=i, F2=y/i; else F1=0, F2=0; } } } void display(int G, int factor1, int factor2, int A, int C) { int k=2, gcd1=1; while (k<=A && k<=factor1) { if (A%k==0 && factor1%k==0) gcd1=k; k++; } int t=2, gcd2=1; while (t<=factor2 && t<=C) { if (C%t==0 && factor2%t==0) gcd2=t; t++; } cout<<showpos<<G<<"*("<<gcd1<<"x"<<gcd2<<")("<<A/gcd1<<"x"<<C/gcd2<<")"<<endl; }

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  • What application domains are CPU bound and will tend to benefit from multi-core technologies?

    - by Glomek
    I hear a lot of people talking about the revolution that is coming in programming due to multi-core processors and parallelism, but I can't shake the feeling that for most of us, CPU cycles aren't the bottleneck. Pretty much all of my programs have been I/O bound in one way or another (database, filesystem, network, user interaction, etc.) for a very long time. Now I can think of a few areas where CPU cycles are a limiting factor, like code breaking, graphics, sound, some forms of simulation (weather, physics, etc.), and some forms of mathematical research, but they all seem like fairly specialized application domains. My general impression is that most programs are still I/O bound and that for most of our industry CPUs have been plenty fast for quite a while now. Am I off my rocker? What other application domains are CPU bound today? Do any of them include a large portion of the programming population? In essence, I'm wondering whether the multi-core CPUs will impact very many of us, and if so, how?

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  • scaleX scaleY increeasing left, top margin, and line spacing

    - by Mark
    If you have Text with a font that is 72 point for example (and scaleX scaleY = 1) you can achieve the same size with a font size of 12 and scaleX,scaleY = 6. For reasons that would take too long to explain I am applying a large scale factor as in the latter example. The problem is, even though the text is the same size, the line spacing and left and top margins have all been increased but I want them to be the same size as well. As far as the line spacing, I discovered that TextFormat.leading was being automatically increased when scaleX, scaleY was greater than 1, so I just had to reset TextFormat.leading back to 0. That leaves the left and top margins, and I have no idea how those are being increased. I tried TextFormat.blockIndent=0 and TextFormat.leftMargin=0 (and also ingnorePadding=true) and it had no effect. And have no clue how to reset the top margin either to its orginal size, in case anyone has an idea for all these.

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  • R error message about variable lengths

    - by Abraham
    I ran the following code in order to recode the variable. Unfortunately, when I move to run an logit model (using the Zelig package), I get an error message that the variable length differ for this variable. ## Independent Variable - Partisanship (ANES 2004) data04$V043114 part <- data04$V043114 attributes(part) summary(part) partb < part partb[part %in% levels(part)[4]] <- NA partb[part %in% levels(part)[5]] <- NA partb[part %in% levels(part)[6]] <- NA partb[part %in% levels(part)[7]] <- NA partb <- factor(partb) attributes(partb) summary(partb) table(partb) table(part, partb) cbind(part, partb) partisan041 <- partb partisan042 <- as.numeric(partb) summary(partisan041) summary(partisan042) ## Regression Model - ANES 2004 ## anes04one <- zelig(trade041a ~ age042 + education042 + personal042 + economy042 + partisan042 + employment042 + union042 + home042 + market042 + race042 + income042 + gender042, model="logit", data=data04) summary(anes04one) #Error in model.frame.default(formula = trade041a ~ age042 + education042 + : # variable lengths differ (found for 'partisan042')

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