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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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  • 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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  • 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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  • 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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  • 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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  • JQuery - Sticky sidebar not working in Firefox

    - by user1473358
    I'm working on a site with a Sticky sidebar (fixed position under certain conditions, etc) that is working fine in Chrome & Safari, but breaks in Firefox. I'm not sure what the issue is since I didn't write the script: $(document).ready(function() { /* var defaults = { containerID: 'toTop', // fading element id containerHoverID: 'toTopHover', // fading element hover id scrollSpeed: 1200, easingType: 'linear' }; */ $().UItoTop({ easingType: 'easeOutQuart' }); if (!!$('.sticky').offset()) { // make sure ".sticky" element exists var stickyTop = $('.sticky').offset().top; // returns number var newsTop = $('#news_single').offset().top; // returns number $(window).scroll(function(){ // scroll event var windowTop = $(window).scrollTop(); // returns number var width = $(window).width(); var height = $(window).height(); if (stickyTop < windowTop && width > 960 && height > 450){ $('.sticky').css({ position: 'fixed', top: 40 }); $('#news_single').css({ left: 230 }); } else { $('.sticky').css('position','static'); $('#news_single').css({ left: 0 }); } }); } }); Here's the site (the sidebar in question is the one with the red header, to the left): http://www.parisgaa.org/parisgaels/this-is-a-heading-too-a-longer-one I'd appreciate any help with this.

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  • Classification: Dealing with Abstain/Rejected Class

    - by abner.ayala
    I am asking for your input and/help on a classification problem. If anyone have any references that I can read to help me solve my problem even better. I have a classification problem of four discrete and very well separated classes. However my input is continuous and has a high frequency (50Hz), since its a real-time problem. The circles represent the clusters of the classes, the blue line the decision boundary and Class 5 equals the (neutral/resting do nothing class). This class is the rejected class. However the problem is that when I move from one class to the other I activate a lot of false positives in the transition movements, since the movement is clearly non-linear. For example, every time I move from class 5 (neutral class) to 1 I first see a lot of 3's before getting to the 1 class. Ideally, I will want my decision boundary to look like the one in the picture below where the rejected class is Class =5. Has a higher decision boundary than the others classes to avoid misclassification during transition. I am currently implementing my algorithm in Matlab using naive bayes, kNN, and SVMs optimized algorithms using Matlab. Question: What is the best/common way to handle abstain/rejected classes classes? Should I use (fuzzy logic, loss function, should I include resting cluster in the training)?

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  • How to make UISlider output nice rounded numbers exponentially?

    - by RickiG
    Hi I am implementing a UISlider a user can manipulate to set a distance. I have never used the CocoaTouch UISlider, but have used other frameworks sliders, usually there is a variable for setting the "step" and other "helper" properties. The documentation for the UISlider deals only with a max and min value, and the output is always a 6 decimal float with a linear relation to the position of the "slider nob". I guess I will have to implement the desired functionality step by step. To the user, the min/max values range from 10 m to 999 Km, I am trying to implement this in an exponential way, that will feel natural to the user. I.e. the user experiences a feeling of control over the values, big or small. Also that the "output" has reasonable values. Values like 10m 200m 2.5km 150 km etc. instead of 1.2342356 m or 108.93837756 km. I would like for the step size to increase by 10m for the first 200m, then maybe by 50m up to 500m, then when passing the 1000 m value, it starts to deal with Kilometers, so then it is step size = 1 km up until 50 km, then maybe 25 km steps etc. Any way I go about this I end up doing a lot of rounding and a lot of calculations wrapped in a forrest of if statements and NSString/Number conversions, each time the user moves the slider just a little. I was hoping someone could lend me a bit of inspiration/math help or make me aware of a more lean approach to solving this problem. My last idea is to populate and array with a 100 string values, then have the slider int value correspond to a string, this is not very flexible, but doable. Thank you in advance for any help given:)

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  • Save PyML.classifiers.multi.OneAgainstRest(SVM()) object?

    - by Michael Aaron Safyan
    I'm using PYML to construct a multiclass linear support vector machine (SVM). After training the SVM, I would like to be able to save the classifier, so that on subsequent runs I can use the classifier right away without retraining. Unfortunately, the .save() function is not implemented for that classifier, and attempting to pickle it (both with standard pickle and cPickle) yield the following error message: pickle.PicklingError: Can't pickle : it's not found as __builtin__.PySwigObject Does anyone know of a way around this or of an alternative library without this problem? Thanks. Edit/Update I am now training and attempting to save the classifier with the following code: mc = multi.OneAgainstRest(SVM()); mc.train(dataset_pyml,saveSpace=False); for i, classifier in enumerate(mc.classifiers): filename=os.path.join(prefix,labels[i]+".svm"); classifier.save(filename); Notice that I am now saving with the PyML save mechanism rather than with pickling, and that I have passed "saveSpace=False" to the training function. However, I am still gettting an error: ValueError: in order to save a dataset you need to train as: s.train(data, saveSpace = False) However, I am passing saveSpace=False... so, how do I save the classifier(s)? P.S. The project I am using this in is pyimgattr, in case you would like a complete testable example... the program is run with "./pyimgattr.py train"... that will get you this error. Also, a note on version information: [michaelsafyan@codemage /Volumes/Storage/classes/cse559/pyimgattr]$ python Python 2.6.1 (r261:67515, Feb 11 2010, 00:51:29) [GCC 4.2.1 (Apple Inc. build 5646)] on darwin Type "help", "copyright", "credits" or "license" for more information. import PyML print PyML.__version__ 0.7.0

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  • Do you like Twisted?

    - by Luca
    I use Python Twisted for web development, and I don't like it? I know async programming is a great idea, I know there are may async web servers now, I know it's the only way to solve some problems you'd have with threads but I don't like. The problem is that, you're forced to program in a twisted way. So, the architecture you have in mind, very often have to be modified to fit the way twisted works. The architecture have to follow the technology, I don't think this is good. When we use callback in javascript, we don't have too many difficulties: things are usually simpler, we use a callback in response to an Ajax call. But in a server web app things are, very often, a bit more complex. Writing chain of callbacks don't seem to me a wonderful way of programming. The code is not simple, and so it is difficult to understand and to maintain. Writing twisted code we very often lost the linear intuitive idea of the algorithm we wanted to implement, especially when things grow in complexity. What's your point of view?

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  • Why do my CouchDB databases grow so fast?

    - by konrad
    I was wondering why my CouchDB database was growing to fast so I wrote a little test script. This script changes an attributed of a CouchDB document 1200 times and takes the size of the database after each change. After performing these 1200 writing steps the database is doing a compaction step and the db size is measured again. In the end the script plots the databases size against the revision numbers. The benchmarking is run twice: The first time the default number of document revision (=1000) is used (_revs_limit). The second time the number of document revisions is set to 1. The first run produces the following plot The second run produces this plot For me this is quite an unexpected behavior. In the first run I would have expected a linear growth as every change produces a new revision. When the 1000 revisions are reached the size value should be constant as the older revisions are discarded. After the compaction the size should fall significantly. In the second run the first revision should result in certain database size that is then keeps during the following writing steps as every new revision leads to the deletion of the previous one. I could understand if there is a little bit of overhead needed to manage the changes but this growth behavior seems weird to me. Can anybody explain this phenomenon or correct my assumptions that lead to the wrong expectations?

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  • CMYK + CMYK = ? CMYK / 2 = ?

    - by Pete
    Suppose there are two colors defined in CMYK: color1 = 30, 40, 50, 60 color2 = 50, 60, 70, 80 If they were to be printed what values would the resulting color have? color_new = min(cyan1 + cyan2, 100), min(magenta1 + magenta2, 100), min(yellow1 + yellow2, 100), min(black1 + black2, 100)? Suppose there is a color defined in CMYK: color = 40, 30, 30, 100 It is possible to print a color at partial intensity, i.e. as a tint. What values would have a 50% tint of that color? color_new = cyan / 2, magenta / 2, yellow / 2, black / 2? I'm asking this to better understand the "tintTransform" function in PDF Reference 1.7, 4.5.5 Special Color Spaces, DeviceN Color Spaces Update: To better clarify: I'm not entirely concerned with human perception or how the CMYK dyies react to the paper. If someone specifies 90% tint which, when printed, looks like full intensity colorant, that's ok. In other words, if I asking how to compute 50% of cmyk(40, 30, 30, 100) I'm asking how to compute the new values, regardless of whether the result looks half-dark or not. Update 2: I'm confused now. I checked this in InDesign and Acrobat. For example Pantone 3005 has CMYK 100, 34, 0, 2, and its 25% tint has CMYK 25, 8.5, 0, 0.5. Does it mean I can "monkey around in a linear way"?

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  • Should I write more SQL to be more efficient, or less SQL to be less buggy?

    - by RenderIn
    I've been writing a lot of one-off SQL queries to return exactly what a certain page needs and no more. I could reuse existing queries and issue a number of SQL requests linear to the number of records on the page. As an example, I have a query to return People and a query to return Job Details for a person. To return a list of people with their job details I could query once for people and then once for each person to retrieve their job details. I've found that in most cases that solution returns things in a reasonable amount of time, but I don't know how well it will scale in my environment. Instead I've been writing queries to join people + job details, or people + salary history, etc. I'm looking at my models and I see how I could shave off maybe 30% of my code if I were to re-use existing queries. This is a big temptation. Is it a bad thing to go for reuse over efficiency in general or does it all come down to the specific situation? Should I first do it the easy way and then optimize later, or is it best to get the code knocked out while everything is fresh in my mind? Thoughts, experiences?

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  • pylab.savefig() and pylab.show() image difference

    - by Jack1990
    I'm making an script to automatically create plots from .xvg files, but there's a problem when I'm trying to use pylab's savefig() method. Using pylab.show() and saving from there, everything's fine. Using pylab.show() Using pylab.savefig() def producePlot(timestep, energy_values,type_line = 'r', jump = 1,finish = 100): fc = sp.interp1d(timestep[::jump], energy_values[::jump],kind='cubic') xnew = numpy.linspace(0, finish, finish*2) pylab.plot(xnew, fc(xnew),type_line) pylab.xlabel('Time in ps ') pylab.ylabel('kJ/mol') pylab.xlim(xmin=0, xmax=finish) def produceSimplePlot(timestep, energy_values,type_line = 'r', jump = 1,finish = 100): pylab.plot(timestep, energy_values,type_line) pylab.xlabel('Time in ps ') pylab.ylabel('kJ/mol') pylab.xlim(xmin=0, xmax=finish) def linearRegression(timestep, energy_values, type_line = 'g'): #, jump = 1,finish = 100): from scipy import stats import numpy #print 'fuck' timestep = numpy.asarray(timestep) slope, intercept, r_value, p_value, std_err = stats.linregress(timestep,energy_values) line = slope*timestep+intercept pylab.plot(timestep, line, type_line) def plottingTime(Title,file_name, timestep, energy_values ,loc, jump , finish): pylab.title(Title) producePlot(timestep,energy_values, 'b',jump, finish) linearRegression(timestep,energy_values) import numpy Average = numpy.average(energy_values) #print Average pylab.legend(("Average = %.2f" %(Average),'Linear Reg'),loc) #pylab.show() pylab.savefig('%s.jpg' %file_name[:-4], bbox_inches= None, pad_inches=0) #if __name__ == '__main__': #plottingTime(Title,timestep1, energy_values, jump =10, finish = 4800) def specialCase(Title,file_name, timestep, energy_values,loc, jump, finish): #print 'Working here ...?' pylab.title(Title) producePlot(timestep,energy_values, 'b',jump, finish) import numpy from pylab import * Average = numpy.average(energy_values) #print Average pylab.legend(("Average = %.2g" %(Average), Title),loc) locs,labels = yticks() yticks(locs, map(lambda x: "%.3g" % x, locs)) #pylab.show() pylab.savefig('%s.jpg' %file_name[:-4] , bbox_inches= None, pad_inches=0) Thanks in advance, John

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  • JMF microphone volume controller

    - by TacB0sS
    How to obtain the Microphone volume controller in JMF? this is what I have: I tried this implementation concept of yours, but I keep getting a null from the first volume processor when I try to get the stream, here is how I do it: // the device is the media device specifically audio Processor processorForVolume = Manager.createProcessor(device.getLocator()); // wait until configured ProcessorStates newState = new ProcessorStateListener(Processor.Configured).waitForProcessorState(processorForVolume); System.out.println("volumeProcessorState: "+newState); // setting the content descriptor to null - read in another thread this allows to get the gain control processorForVolume.setContentDescriptor(null); // set the track control format to one supported by the device and the track control. // I didn't match it to an RTP allowed format, but I don't think this has anything to do with it... TrackControl[] trackControls = processorForVolume.getTrackControls(); if (trackControls.length == 0) throw new MC_Exception("No track controls where found for this device:", new Object[]{device}); for (TrackControl control : trackControls) trackManipulator.manipulateTrackControls(control); // wait until the processor is realized newState = new ProcessorStateListener(Controller.Realized).waitForProcessorState(processorForVolume); System.out.println("volumeProcessorState: "+newState); // receives the gain control micVolumeController = processorForVolume.getGainControl(); // cannot get the output stream to process further... any suggestions? processor = Manager.createProcessor(processorForVolume.getDataOutput()); new ProcessorStateListener(Processor.Configured).waitForProcessorState(processor); processor.setContentDescriptor(DeviceCapturingManager.RAW_RTP); new ProcessorStateListener(Controller.Realized).waitForProcessorState(processor); this is the output It generates: volumeProcessorState: Configured format set to track control - com.sun.media.ProcessEngine$ProcTControl@1627c16: LINEAR, 48000.0 Hz, 16-bit, Stereo, LittleEndian, Signed volumeProcessorState: Realized and the data output from the processor is Null. I should make clear that when the content descriptor != null I do get an output stream but not the volume controller, and the when it is null I get the controller, but no stream. I try to connect to an audio microphone device Adam.

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  • How much detail should be in a project plan or spec?

    - by DeanMc
    I have an issue that I feel many programmers can relate to... I have worked on many small scale projects. After my initial paper brain storm I tend to start coding. What I come up with is usually a rough working model of the actual application. I design in a disconnected fashion so I am talking about underlying code libraries, user interfaces are the last thing as the library usually dictates what is needed in the UI. As my projects get bigger I worry that so should my "spec" or design document. The above paragraph, from my investigations, is echoed all across the internet in one fashion or another. When a UI is concerned there is a bit more information but it is UI specific and does not relate to code libraries. What I am beginning to realise is that maybe code is code is code. It seems from my extensive research that there is no 1:1 mapping between a design document and the code. When I need to research a topic I dump information into OneNote and from there I prioritise features into versions and then into related chunks so that development runs in a fairly linear fashion, my tasks tend to look like so: Implement Binary File Reader Implement Binary File Writer Create Object to encapsulate Data for expression to the caller Now any programmer worth his salt is aware that between those three to do items could be a potential wall of code that could expand out to multiple files. I have tried to map the complete code process for each task but I simply don't think it can be done effectively. By the time one mangles pseudo code it is essentially code anyway so the time investment is negated. So my question is this: Am I right in assuming that the best documentation is the code itself. We are all in agreement that a high level overview is needed. How high should this be? Do you design to statement, class or concept level? What works for you?

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  • Simulating 3D 'cards' with just orthographic rendering

    - by meds
    I am rendering textured quads from an orthographic perspective and would like to simulate 'depth' by modifying UVs and the vertex positions of the quads four points (top left, top right, bottom left, bottom right). I've found if I make the top left and bottom right corners y position be the same I don't get a linear 'skew' but rather a warped one where the texture covering the top triangle (which makes up the quad) seems to get squashed while the bottom triangles texture looks normal. I can change UVs, any of the four points on the quad (but only in 2D space, it's orthographic projection anyway so 3D space won't matter much). So basically I'm trying to simulate perspective on a two dimensional quad in orthographic projection, any ideas? Is it even mathematically possible/feasible? ideally what I'd like is a situation where I can set an x/y rotation as well as a virtual z 'position' (which simulates z depth) through a function and see it internally calclate the positions/uvs to create the 3D effect. It seems like this should all be mathematical where a set of 2D transforms can be applied to each corner of the quad to simulate depth, I just don't know how to make it happen. I'd guess it requires trigonometry or something, I'm trying to crunch the math but not making much progress. here's what I mean: Top left is just the card, center is the card with a y rotation of X degrees and right most is a card with an x and y rotation of different degrees.

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  • Thoughts about alternatives to barplot-with-error-bars

    - by gd047
    I was thinking of an alternative to the barplot-with-error-bars plot. To get an idea by example, I roughly 'sketched' what I mean using the following code library(plotrix) plot(0:12,type="n",axes=FALSE) gradient.rect(1,0,3,8,col=smoothColors("red",38,"red"),border=NA,gradient="y") gradient.rect(4,0,6,6,col=smoothColors("blue",38,"blue"),border=NA,gradient="y") lines(c(2,2),c(5.5,10.5)) lines(c(2-.5,2+.5),c(10.5,10.5)) lines(c(2-.5,2+.5),c(5.5,5.5)) lines(c(5,5),c(4.5,7.5)) lines(c(5-.5,5+.5),c(7.5,7.5)) lines(c(5-.5,5+.5),c(4.5,4.5)) gradient.rect(7,8,9,10.5,col=smoothColors("red",100,"white"),border=NA,gradient="y") gradient.rect(7,5.5,9,8,col=smoothColors("white",100,"red"),border=NA,gradient="y") lines(c(7,9),c(8,8),lwd=3) gradient.rect(10,6,12,7.5,col=smoothColors("blue",100,"white"),border=NA,gradient="y") gradient.rect(10,4.5,12,6,col=smoothColors("white",100,"blue"),border=NA,gradient="y") lines(c(10,12),c(6,6),lwd=3) The idea was to use bars like the ones in the second pair, instead of those in the first. However, there is something that I would like to change in the colors. Instead of a linear gradient fill, I would like to adjust the color intensity in accordance with the values of the pdf of the mean estimator. Do you think it is possible? A slightly different idea (where gradient fill isn't an issue) was to use one (or 2 back-to-back) bell curve(s) filled with (solid) color, instead of a rectangle. See for example the shape that corresponds to the letter F here. In that case the bell-curve(s) should (ideally) be drawn using something like plot(x, dnorm(x, mean = my.mean, sd = std.error.of.the.mean)) I have no idea though, of a way to draw rotated (and filled with color) bell curves. Of course, all of the above may be freely judged as midnight springtime dreams :-)

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  • How to Implement Overlay blend method using opengles 1.1

    - by Cylon
    Blow is the algorithm of overlay. and i want using it on iphone, but iphone 3g only support opengles 1.1, can not using glsl. can i using blend function or texture combine to implement it. thank you /////////Reference from OpenGL Shading® Language Third Edition /////////// 19.6.12 Overlay OVERLAY first computes the luminance of the base value. If the luminance value is less than 0.5, the blend and base values are multiplied together. If the luminance value is greater than 0.5, a screen operation is performed. The effect is that the base value is mixed with the blend value, rather than being replaced. This allows patterns and colors to overlay the base image, but shadows and highlights in the base image are preserved. A discontinuity occurs where luminance = 0.5. To provide a smooth transition, we actually do a linear blend of the two equations for luminance in the range [0.45,0.55]. float luminance = dot(base, lumCoeff); if (luminance < 0.45) result = 2.0 * blend * base; else if (luminance 0.55) result = white - 2.0 * (white - blend) * (white - base); else { vec4 result1 = 2.0 * blend * base; vec4 result2 = white - 2.0 * (white - blend) * (white - base); result = mix(result1, result2, (luminance - 0.45) * 10.0); }

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  • CIE XYZ colorspace: do I have 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. I have seen the three points being referred to as X, Y and Z (upper case) somewhere, but I cannot find the page anymore (I marked them to the picture myself). 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. 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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  • Designing small comparable objects

    - by Thomas Ahle
    Intro Consider you have a list of key/value pairs: (0,a) (1,b) (2,c) You have a function, that inserts a new value between two current pairs, and you need to give it a key that keeps the order: (0,a) (0.5,z) (1,b) (2,c) Here the new key was chosen as the average between the average of keys of the bounding pairs. The problem is, that you list may have milions of inserts. If these inserts are all put close to each other, you may end up with keys such to 2^(-1000000), which are not easily storagable in any standard nor special number class. The problem How can you design a system for generating keys that: Gives the correct result (larger/smaller than) when compared to all the rest of the keys. Takes up only O(logn) memory (where n is the number of items in the list). My tries First I tried different number classes. Like fractions and even polynomium, but I could always find examples where the key size would grow linear with the number of inserts. Then I thought about saving pointers to a number of other keys, and saving the lower/greater than relationship, but that would always require at least O(sqrt) memory and time for comparison. Extra info: Ideally the algorithm shouldn't break when pairs are deleted from the list.

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  • Remove redundant SQL code

    - by Dave Jarvis
    Code The following code calculates the slope and intercept for a linear regression against a slathering of data. It then applies the equation y = mx + b against the same result set to calculate the value of the regression line for each row. Can the two separate sub-selects be joined so that the data and its slope/intercept are calculated without executing the data gathering part of the query twice? SELECT AVG(D.AMOUNT) as AMOUNT, Y.YEAR * ymxb.SLOPE + ymxb.INTERCEPT as REGRESSION_LINE, Y.YEAR as YEAR, MAKEDATE(Y.YEAR,1) as AMOUNT_DATE FROM CITY C, STATION S, YEAR_REF Y, MONTH_REF M, DAILY D, (SELECT ((avg(t.AMOUNT * t.YEAR)) - avg(t.AMOUNT) * avg(t.YEAR)) / (stddev( t.AMOUNT ) * stddev( t.YEAR )) as CORRELATION, ((sum(t.YEAR) * sum(t.AMOUNT)) - (count(1) * sum(t.YEAR * t.AMOUNT))) / (power(sum(t.YEAR), 2) - count(1) * sum(power(t.YEAR, 2))) as SLOPE, ((sum( t.YEAR ) * sum( t.YEAR * t.AMOUNT )) - (sum( t.AMOUNT ) * sum(power(t.YEAR, 2)))) / (power(sum(t.YEAR), 2) - count(1) * sum(power(t.YEAR, 2))) as INTERCEPT FROM ( SELECT AVG(D.AMOUNT) as AMOUNT, Y.YEAR as YEAR, MAKEDATE(Y.YEAR,1) as AMOUNT_DATE FROM CITY C, STATION S, YEAR_REF Y, MONTH_REF M, DAILY D WHERE $X{ IN, C.ID, CityCode } AND SQRT( POW( C.LATITUDE - S.LATITUDE, 2 ) + POW( C.LONGITUDE - S.LONGITUDE, 2 ) ) < $P{Radius} AND S.STATION_DISTRICT_ID = Y.STATION_DISTRICT_ID AND Y.YEAR BETWEEN 1900 AND 2009 AND M.YEAR_REF_ID = Y.ID AND M.CATEGORY_ID = $P{CategoryCode} AND M.ID = D.MONTH_REF_ID AND D.DAILY_FLAG_ID <> 'M' GROUP BY Y.YEAR ) t ) ymxb WHERE $X{ IN, C.ID, CityCode } AND SQRT( POW( C.LATITUDE - S.LATITUDE, 2 ) + POW( C.LONGITUDE - S.LONGITUDE, 2 ) ) < $P{Radius} AND S.STATION_DISTRICT_ID = Y.STATION_DISTRICT_ID AND Y.YEAR BETWEEN 1900 AND 2009 AND M.YEAR_REF_ID = Y.ID AND M.CATEGORY_ID = $P{CategoryCode} AND M.ID = D.MONTH_REF_ID AND D.DAILY_FLAG_ID <> 'M' GROUP BY Y.YEAR Question How do I execute the duplicate bits only once per query, instead of twice? The duplicate bit is the WHERE clause: $X{ IN, C.ID, CityCode } AND SQRT( POW( C.LATITUDE - S.LATITUDE, 2 ) + POW( C.LONGITUDE - S.LONGITUDE, 2 ) ) < $P{Radius} AND S.STATION_DISTRICT_ID = Y.STATION_DISTRICT_ID AND Y.YEAR BETWEEN 1900 AND 2009 AND M.YEAR_REF_ID = Y.ID AND M.CATEGORY_ID = $P{CategoryCode} AND M.ID = D.MONTH_REF_ID AND D.DAILY_FLAG_ID <> 'M' Related http://stackoverflow.com/questions/1595659/how-to-eliminate-duplicate-calculation-in-sql Thank you!

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  • Pseudo-quicksort time complexity

    - by Ord
    I know that quicksort has O(n log n) average time complexity. A pseudo-quicksort (which is only a quicksort when you look at it from far enough away, with a suitably high level of abstraction) that is often used to demonstrate the conciseness of functional languages is as follows (given in Haskell): quicksort :: Ord a => [a] -> [a] quicksort [] = [] quicksort (p:xs) = quicksort [y | y<-xs, y<p] ++ [p] ++ quicksort [y | y<-xs, y>=p] Okay, so I know this thing has problems. The biggest problem with this is that it does not sort in place, which is normally a big advantage of quicksort. Even if that didn't matter, it would still take longer than a typical quicksort because it has to do two passes of the list when it partitions it, and it does costly append operations to splice it back together afterwards. Further, the choice of the first element as the pivot is not the best choice. But even considering all of that, isn't the average time complexity of this quicksort the same as the standard quicksort? Namely, O(n log n)? Because the appends and the partition still have linear time complexity, even if they are inefficient.

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  • Good data structure for efficient insert/querying on arbitrary properties

    - by Juliet
    I'm working on a project where Arrays are the default data structure for everything, and every query is a linear search in the form of: Need a customer with a particular name? customer.Find(x => x.Name == name) Need a customer with a particular unique id? customer.Find(x => x.Id == id) Need a customer of a particular type and age? customer.Find(x => x is PreferredCustomer && x.Age >= age) Need a customer of a particular name and age? customer.Find(x => x.Name == name && x.Age == age) In almost all instances, the criteria for lookups is well-defined. For example, we only search for customers by one or more of the properties Id, Type, Name, or Age. We rarely search by anything else. Is a good data structure to support arbitrary queries of these types with lookup better than O(n)? Any out-of-the-box implementations for .NET?

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  • Intro Bar like stack overflow

    - by Dasa
    I have a simple top bar using jquery like the one on stackoverflow, but i want it to only appear on the first time a person visits the website. below is the HTML followed by the "bxSlider.js" file <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html> <head> <script src="http://ajax.googleapis.com/ajax/libs/jquery/1.3.2/jquery.min.js"></script> <script type="text/javascript" src="bxSlider.js"></script> <title>topbar</title> <style type="text/css" media="screen"> #message { font-family:Arial,Helvetica,sans-serif; position:fixed; top:0px; left:0px; width:100%; z-index:105; text-align:center; color:white; padding:2px 0px 2px 0px; background-color:#8E1609; } #example1 { text-align: center; width: 80%; } .close-notify { white-space: nowrap; float:right; margin-right:10px; color:#fff; text-decoration:none; padding-left:3px; padding-right:3px } .close-notify a { color: #fff; } h4, p { margin:0px; padding:0px; } </style> </head> <body> <DIV ID='message' style="display: none;"> <DIV ID="example1"> <DIV CLASS="item"> <h4>Head 1</h4> <p>Text 1</p> </div><!-- end item --> <DIV CLASS="item"> <h4>Head 2</h4> <p>Text 2</p> </div><!-- end item --> </div><!-- end example1 --> <a href="#" CLASS="close-notify" onclick="closeNotice()">X</a> </div> <script type="text/javascript"> $(document).ready(function() { $("#message").fadeIn("slow"); $('#example1').bxSlider({ mode: 'slide', speed: 250, wrapper_CLASS: 'example1_container' }); }); function closeNotice() { $("#message").fadeOut("slow"); } </script> </body> </html> /** * * * bxSlider: Content slider / fade / ticker using the jQuery javascript library. * * Author: Steven Wanderski * Email: [email protected] * URL: http://bxslider.com * * **/ jQuery.fn.bxSlider = function(options){ ///////////////////////////////////////////////////////////////////////////////////////////////////////////// // Declare variables and functions ///////////////////////////////////////////////////////////////////////////////////////////////////////////// var defaults = { mode: 'slide', speed: 500, auto: false, auto_direction: 'left', pause: 2500, controls: true, prev_text: 'prev', next_text: 'next', width: $(this).children().width(), prev_img: '', next_img: '', ticker_direction: 'left', wrapper_class: 'container' }; options = $.extend(defaults, options); if(options.mode == 'ticker'){ options.auto = true; } var $this = $(this); var $parent_width = options.width; var current = 0; var is_working = false; var child_count = $this.children().size(); var i = 0; var j = 0; var k = 0; function animate_next(){ is_working = true; $this.animate({'left':'-' + $parent_width * 2 + 'px'}, options.speed, function(){ $this.css({'left':'-' + $parent_width + 'px'}).children(':first').appendTo($this); is_working = false; }); } function animate_prev(){ is_working = true; $this.animate({'left': 0}, options.speed, function(){ $this.css({'left':'-' + $parent_width + 'px'}).children(':last').insertBefore($this.children(':first')); is_working = false; }); } function fade(direction){ if(direction == 'next'){ var last_before_switch = child_count - 1; var start_over = 0; var incr = k + 1; }else if(direction == 'prev'){ var last_before_switch = 0; var start_over = child_count -1; var incr = k - 1; } is_working = true; if(k == last_before_switch){ $this.children().eq(k).fadeTo(options.speed, 0); $this.children().eq(start_over).fadeTo(options.speed, 1, function(){ is_working = false; k = start_over; }); }else{ $this.children().eq(k).fadeTo(options.speed, 0); $this.children().eq(incr).fadeTo(options.speed, 1, function(){ is_working = false; k = incr; }); } } function add_controls(){ ///////////////////////////////////////////////////////////////////////////////////////////////////////////// // Check if user selected images to use for next / prev ///////////////////////////////////////////////////////////////////////////////////////////////////////////// if(options.prev_img != '' || options.next_img != ''){ $this.parent().append('<a class="slider_prev" href=""><img src="' + options.prev_img + '" alt=""/></a><a class="slider_next" href=""><img src="' + options.next_img + '" alt="" /></a>'); }else{ $this.parent().append('<a class="slider_prev" href="">' + options.prev_text + '</a><a class="slider_next" href="">' + options.next_text + '</a>'); } $this.parent().find('.slider_prev').css({'float':'left', 'outline':'0', 'color':'yellow'}); $this.parent().find('.slider_next').css({'float':'right', 'outline':'0', 'color':'yellow'}); ///////////////////////////////////////////////////////////////////////////////////////////////////////////// // Accomodate padding-top for controls when elements are absolutely positioned (only in fade mode) ///////////////////////////////////////////////////////////////////////////////////////////////////////////// if(options.mode == 'fade'){ $this.parent().find('.slider_prev').css({'paddingTop' : $this.children().height()}) $this.parent().find('.slider_next').css({'paddingTop' : $this.children().height()}) } ///////////////////////////////////////////////////////////////////////////////////////////////////////////// // Actions when user clicks next / prev buttons ///////////////////////////////////////////////////////////////////////////////////////////////////////////// $this.parent().find('.slider_next').click(function(){ if(!is_working){ if(options.mode == 'slide'){ animate_next(); if(options.auto){ clearInterval($.t); $.t = setInterval(function(){animate_next();}, options.pause); } }else if(options.mode == 'fade'){ fade('next'); if(options.auto){ clearInterval($.t); $.t = setInterval(function(){fade('next');}, options.pause); } } } return false; }); $this.parent().find('.slider_prev').click(function(){ if(!is_working){ if(options.mode == 'slide'){ animate_prev(); if(options.auto){ clearInterval($.t); $.t = setInterval(function(){animate_prev();}, options.pause); } }else if(options.mode == 'fade'){ fade('prev'); if(options.auto){ clearInterval($.t); $.t = setInterval(function(){fade('prev');}, options.pause); } } } return false; }); } function ticker() { if(options.ticker_direction == 'left'){ $this.animate({'left':'-' + $parent_width * 2 + 'px'}, options.speed, 'linear', function(){ $this.css({'left':'-' + $parent_width + 'px'}).children(':first').appendTo($this); ticker(); }); }else if(options.ticker_direction == 'right'){ $this.animate({'left': 0}, options.speed, 'linear', function(){ $this.css({'left':'-' + $parent_width + 'px'}).children(':last').insertBefore($this.children(':first')); ticker(); }); } } ///////////////////////////////////////////////////////////////////////////////////////////////////////////// // Create content wrapper and set CSS ///////////////////////////////////////////////////////////////////////////////////////////////////////////// $this.wrap('<div class="' + options.wrapper_class + '"></div>'); //console.log($this.parent().css('paddingTop')); if(options.mode == 'slide' || options.mode == 'ticker'){ $this.parent().css({ 'overflow' : 'hidden', 'position' : 'relative', 'margin' : '0 auto', 'width' : options.width + 'px' }); $this.css({ 'width' : '999999px', 'position' : 'relative', 'left' : '-' + $parent_width + 'px' }); $this.children().css({ 'float' : 'left', 'width' : $parent_width }); $this.children(':last').insertBefore($this.children(':first')); }else if(options.mode == 'fade'){ $this.parent().css({ 'overflow' : 'hidden', 'position' : 'relative', 'width' : options.width + 'px' //'height' : $this.children().height() }); if(!options.controls){ $this.parent().css({'height' : $this.children().height()}); } $this.children().css({ 'position' : 'absolute', 'width' : $parent_width, 'listStyle' : 'none', 'opacity' : 0 }); $this.children(':first').css({ 'opacity' : 1 }); } ///////////////////////////////////////////////////////////////////////////////////////////////////////////// // Check if user selected "auto" ///////////////////////////////////////////////////////////////////////////////////////////////////////////// if(!options.auto){ add_controls(); }else{ if(options.mode == 'ticker'){ ticker(); }else{ ///////////////////////////////////////////////////////////////////////////////////////////////////////////// // Set a timed interval ///////////////////////////////////////////////////////////////////////////////////////////////////////////// if(options.mode == 'slide'){ if(options.auto_direction == 'left'){ $.t = setInterval(function(){animate_next();}, options.pause); }else if(options.auto_direction == 'right'){ $.t = setInterval(function(){animate_prev();}, options.pause); } }else if(options.mode == 'fade'){ if(options.auto_direction == 'left'){ $.t = setInterval(function(){fade('next');}, options.pause); }else if(options.auto_direction == 'right'){ $.t = setInterval(function(){fade('prev');}, options.pause); } } if(options.controls){ add_controls(); } } } }

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