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• How do I draw an ellipse with arbitrary orientation pixel by pixel?

  - by amc

  Hi, I have to draw an ellipse of arbitrary size and orientation pixel by pixel. It seems pretty easy to draw an ellipse whose major and minor axes align with the x and y axes, but rotating the ellipse by an arbitrary angle seems trickier. Initially I though it might work to draw the unrotated ellipse and apply a rotation matrix to each point, but it seems as though that could cause errors do to rounding, and I need rather high precision. Is my suspicion about this method correct? How could I accomplish this task more precisely? I'm programming in C++ (although that shouldn't really matter since this is a more algorithm-oriented question).

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• Scale GraphicsPaths

  - by serhio

  In a form I draw a graph. This graph has some distinct paths that should have differently drawn. Say AxesPath, SalesPath, CostsPath etc... When I resize the form need I to scale every of components Paths? Take an example: Imports System.Drawing.Drawing2D Public Class Form1 Dim lineOne As GraphicsPath Dim lineTwo As GraphicsPath Dim allPaths As GraphicsPath Dim initSize As Size Public Sub New() ' This call is required by the designer. ' InitializeComponent() initSize = Me.Size lineOne = New GraphicsPath() lineTwo = New GraphicsPath() lineOne.AddLine(20.0F, 20.0F, Me.initSize.Width - 20.0F, 20.0F) lineTwo.AddLine(0.1F, 10.0F, Me.initSize.Width - 20.0F, _ Me.initSize.Height - 0.5F) allPaths = New GraphicsPath() allPaths.AddPath(lineOne, False) allPaths.AddPath(lineTwo, False) Me.ResizeRedraw = True End Sub Protected Overrides Sub OnResize(ByVal e As System.EventArgs) MyBase.OnResize(e) Dim m As New Matrix m.Scale(Me.Width / initSize.Width, Me.Height / initSize.Height) allPaths.Transform(m) initSize = Me.Size End Sub Protected Overrides Sub OnPaint(ByVal e As PaintEventArgs) MyBase.OnPaint(e) ' WORKS ' ' e.Graphics.DrawPath(Pens.GreenYellow, allPaths) ' ' DOES NOT WORK! ' e.Graphics.DrawPath(Pens.DarkGoldenrod, lineOne) e.Graphics.DrawPath(Pens.DarkMagenta, lineTwo) End Sub End Class

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• best method of turning millions of x,y,z positions of particles into visualisation

  - by Griff

  I'm interested in different algorithms people use to visualise millions of particles in a box. I know you can use Cloud-In-Cell, adaptive mesh, Kernel smoothing, nearest grid point methods etc to reduce the load in memory but there is very little documentation on how to do these things online. i.e. I have array with: x,y,z 1,2,3 4,5,6 6,7,8 xi,yi,zi for i = 100 million for example. I don't want a package like Mayavi/Paraview to do it, I want to code this myself then load the decomposed matrix into Mayavi (rather than on-the-fly rendering) My poor 8Gb Macbook explodes if I try and use the particle positions. Any tutorials would be appreciated.

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• Python - Using "Google AJAX Search" API's Local Search Objects

  - by user330739

  Hi! I've just started using Google's search API to find addresses and the distances between those addresses. I used geopy for this, but, I often had the problem of not getting the correct addresses for my queries. I decided to experiment, therefore, with Google's "Local Search" (http://code.google.com/apis/ajaxsearch/local.html). Anyway, I wanted to ask if I could use the "Local Search" objects provided by the API within python. Something tells me that I can't and that I have to use json. Does anyone know if there is a work around? PS: Im trying to make something like this: http://www.google.com/uds/samples/random/lead.html ... except a matrix type deal where the insides will be filled with distances between the addresses. Thanks for reading!

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• C++ MTL Library dimension.h bug?

  - by avanwieringen

  I've installed MTL on my Fedora Core 12 x64 system, but when building an application I get the following error: In file included from /usr/local/include/mtl/matrix.h:41, from /usr/local/include/mtl/mtl.h:40, from ltiSystem.hxx:4, from strTools.hxx:4, from ff.cxx:3: /usr/local/include/mtl/envelope2D.h:72: error: declaration of ‘typedef struct mtl::twod_tag mtl::envelope2D<T>::dimension’ /usr/local/include/mtl/dimension.h:19: error: changes meaning of ‘dimension’ from ‘class mtl::dimension<typename mtl::dense1D<T, 0>::size_type, 0, 0>’ make[1]: *** [ff.o] Error 1 Which would imply an error in MTL. I have changed to different MTL versions and the problem persists, but on Google there is no proper answer. I use the g++ compiler. Does anyone have a clye?

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• invalid conversion from 'char' to 'int* in C

  - by majdal

  Hi, I have the following arrays: int A[] = {0,1,1,1,1, 1,0,1,0,0, 0,1,1,1,1}; int B[] = {1,1,1,1,1, 1,0,1,0,1, 0,1,0,1,0}; int C[] = {0,1,1,1,0, 1,0,0,0,1, 1,0,0,0,1}; //etc... for all letters of the alphabet And a function that prints the letters on a 5x3 LED matrix: void printLetter(int letter[]) I have a string of letters: char word[] = "STACKOVERFLOW"; and I want to pass each character of the string to the printLetter function. I tried: int n = sizeof(word); for (int i = 0; i < n-1; i++) { printLetter(word[i]); } But I get the following error: invalid conversion from 'char' to 'int*' What should i be doing? Thanks!!

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• App crashes every second time a tableview row is selected in navigation controller setup

  - by Thaurin

  Disclaimer first: I'm pretty new to Objective-C and the retain model. I've been developing in a garbage collected .NET environment for the last five years, so I've been spoiled. I'm still learning. I'm having my iPhone app crash with EXC_BAD_ACCESS. It happens in a navigtation controller/tableview setup. When I select a row the first time, no problems. It switches in the child controller without problems. I go back and select the same row again. Program then proceeds to crash. Every other row works fine, but every second time a row is accessed, it's a crash. I've pinpointed the location where this happens. The child controller (which is a class that I reuse for every row of the same type) that's being switched into has an array of NSString's representing the rows that will be displayed. I set it before pushing the child viewcontroller. It's there where this apparently happens. I'm having a hard time debugging this problem, still wrestling with xcode and all. I fear there may be some vital information missing here, but maybe there is something you recognize here.

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• Having some fun - what is a good way to include a secret key functionality and fire the KeyDown event?

  - by Sisyphus

  To keep myself interested, I try to put little Easter Eggs in my projects (mostly to amuse myself). I've seen some websites where you can type a series of letters "aswzaswz" and you get a "secret function" - how would I achieve this in C#? I've assigned a "secret function" in the past by using modifier keys bool showFunThing = (Control.ModifierKeys & Keys.Control) == Keys.Control; but wanted to get a bit more secretive (without the modifier keys) I just wanted the form to detect a certain word typed without any input ... I've built a method that I think should do it: private StringBuilder _pressedKeys = new StringBuilder(); protected override void OnKeyDown(KeyEventArgs e) { const string kWord = "fun"; char letter = (char)e.KeyValue; if (!char.IsLetterOrDigit(letter)) { return; } _pressedKeys.Append(letter); if (_pressedKeys.Length == kWord.Length) { if (_pressedKeys.ToString().ToLower() == kWord) { MessageBox.Show("Fun"); _pressedKeys.Clear(); } } base.OnKeyDown(e); } Now I need to wire it up but I can't figure out how I'm supposed to raise the event in the form designer ... I've tried this: this.KeyDown +=new System.Windows.Forms.KeyEventHandler(OnKeyDown); and a couple of variations on this but I'm missing something because it won't fire (or compile). It tells me that the OnKeyDown method is expecting a certain signature but I've got other methods like this where I haven't specified arguments. I fear that I may have got myself confused so I am turning to SO for help ... anyone?

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• Is there an equivalent for ActiveRecord#find_by equivalent for C#?

  - by Benjamin Manns

  I'm originally a C# developer (as a hobby), but as of late I have been digging into Ruby on Rails and I am really enjoying it. Right now I am building an application in C# and I was wondering if there is any collection implementation for C# that could match (or "semi-match") the find_by method of ActiveRecord. What I am essentially looking for is a list that would hold Rectangles: class Rectangle { public int Width { get; set; } public int Height { get; set; } public String Name { get; set; } } Where I could query this list and find all entries with Height = 10, Width = 20, or name = "Block". This was done with ActiveRecord by doing a call similar to Rectangle.find_by_name('Block'). The only way I can think of doing this in C# is to create my own list implementation and iterate through each item manually checking each item against the criteria. I fear I would be reinventing the wheel (and one of poorer quality). Any input or suggestions is much appreciated.

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• Finding many local max in an image (using MatLab)

  - by wenh42

  How do you go about figuring our multiple max in a 2D image where the max aren't necessarily all the same height? I have found that the imregionalmax(), imextendedmax(), and findpeaks() functions aren't necessarily that helpful because they give many local max that are really just maxes within the background noise. I tried bw=arrayimdilate(array,[1 1 1; 1 0 1; 1 1 1]) but that also is kind of limited for the same reasons (same thing with expanding the matrix that it uses). I'd definitely appreciate some help..

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• Testing for the existence of a field in a class

  - by Brett

  Hi, i have a quick question. I have a 2D array that stores an instance of a class. The elements of the array are assigned a particular class based on a text file that is read earlier in the program. Since i do not know without looking in the file what class is stored at a particular element i could refer to a field that doesn't exist at that index (referring to appearance when an instance of temp is stored in that index). i have come up with a method of testing this, but it is long winded and requires a second matrix. Is there a function to test for the existence of a field in a class? class temp(): name = "default" class temp1(): appearance = "@"

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• iphone: repeating a transformation

  - by gonso

  Hi I'm trying to represent a view that rotates on the iphone screen. I have a button and when you press it, the view rotates 180 degrees. My problem is that this only works the first time. Here is the code: -(IBAction) flip:(id)sender{ CGAffineTransform transform; //the transform matrix to be used below //BEGIN ANIMATIONS [UIView beginAnimations:nil context:NULL]; [UIView setAnimationDuration:2.0]; //animate if (flag){ transform = CGAffineTransformMakeRotation( RADIANS(180) ); } else { transform = CGAffineTransformMakeRotation( RADIANS(-180) ); } flag = !flag; transform = CGAffineTransformTranslate(transform, 0, 0); self.mySuview.transform = transform; //COMMIT ANIMATIONS [UIView commitAnimations]; } The first time you click, the view spins alright, but when you click again NOTHING happens. No errors, no changes on the view. What am I missing? Thanks Gonso

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• Recursion Interview Questions [closed]

  - by halivingston

  Given a string, "ABC", print all permutations Given a dollar bill, fill out possible ways it can summed up using .25, .10, .5, etc. Given a phone number (123-456), print out all it's word counter parters like (ADG-XYZ) A B C D E F G H I J K L M N O P In the above 2D matrix, print all possible words (just literally all words, and sure we could check if it's exists in a dictionary). The base case is I think here is that reaching the same i, j positions. Any others you can think of?

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• Integrate OpenId into an existing site

  - by Andrea

  I have a working web application which already has a login and registration system. I'm looking for some advice on how to do it. Until now, users have a username, an email, a password and some optional fields. The registrartion is the usual process with email confirmation. Now I'd like to allow users to use OpenId. So I have added an openid field to the table. There are two different login forms, and users which are already registered can add their openid info and use either login form. The problem is with new users who come on the site for the first time and try to login with OpenId. I create a new user for them, and I don't need a password, but still I need at least a username, which is used on the site (I'm not sure if the email is needed). So my problems are: 1) How do I manage validation? Some fields are required for some users, (e.g. a password) but not for some others. I mean, I can do this, but it immediately gets messy. 2) Should I ask for a username and email on the first OpenId login? On the one hand I'd say yes, but I fear this vanishes the advantages of using OpenId, that is, not having to provide details. 3) I could get the details via SReg or AttributeExchange, but most providers have a bad support for those. For instance my Gmail OpenId account does not tell the email (!). Is there some place to learn more about the current support for these extensions?

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• Python: Does one of these examples waste more memory?

  - by orokusaki

  In a Django view function which uses manual transaction committing, I have: context = RequestContext(request, data) transaction.commit() return render_to_response('basic.html', data, context) # Returns a Django ``HttpResponse`` object which is similar to a dictionary. I think it is a better idea to do this: context = RequestContext(request, data) response = render_to_response('basic.html', data, context) transaction.commit() return response If the page isn't rendered correctly in the second version, the transaction is rolled back. This seems like the logical way of doing it albeit there won't likely be many exceptions at that point in the function when the application is in production. But... I fear that this might cost more and this will be replete through a number of functions since the application is heavy with custom transaction handling, so now is the time to figure out. If the HttpResponse instance is in memory already (at the point of render_to_response()), then what does another reference cost? When the function ends, doesn't the reference (response variable) go away so that when Django is done converting the HttpResponse into a string for output Python can immediately garbage collect it? Is there any reason I would want to use the first version (other than "It's 1 less line of code.")?

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• Preallocate memory for a program in Linux before it gets started

  - by Fyg

  Hi, folks, I have a program that repeatedly solves large systems of linear equations using cholesky decomposition. Characterising is that I sometimes need to store the complete factorisation which can exceed about 20 GB of memory. The factorisation happens inside a library that I call. Furthermore, this matrix and the resulting factorisation changes quite frequently and as such the memory requirements as well. I am not the only person to use this compute-node. Therefore, is there a way to start the program under Linux and preallocate free memory for the process? Something like: $: prealloc -m 25G ./program

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• Expert system for writing programs?

  - by aaa

  I am brainstorming an idea of developing a high level software to manipulate matrix algebra equations, tensor manipulations to be exact, to produce optimized C++ code using several criteria such as sizes of dimensions, available memory on the system, etc. Something which is similar in spirit to tensor contraction engine, TCE, but specifically oriented towards producing optimized rather than general code. The end result desired is software which is expert in producing parallel program in my domain. Does this sort of development fall on the category of expert systems? What other projects out there work in the same area of producing code given the constraints?

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• How to create a "dependency graph" for IT assets

  - by p.marino

  One of my customers is trying to create an interactive "matrix" of interdependencies for the various applications used in their company (it's a travel&leisure company with around 2500 employees). The idea (still at the prototype stage) is to create a sort of Map, based on Visio or similar tool, which traces the communication and interdependencies between all the IT assets in the company, so that when someone asks for a change they can get an overview of the impacts. This was mentioned in a casual setting and it will not be my responsability to directly work on this, but I did contribute the little I know already in terms of vaguely related methodologies (Zachman Framework). I'd like to hear from the people in here if they know of methodologies, or tools, that may help this kind of effort, and if they have any specific experience to contribute. I'll digest the answers and send the result back to my customer, hoping this may be of some help with their task (which I consider a bit visionary and prone to all the pitfalls of any documentation project, but still well worth pursuing).

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• Being pressured to GOTO the dark-side

  - by Dan McG

  We have a situation at work where developers working on a legacy (core) system are being pressured into using GOTO statements when adding new features into existing code that is already infected with spagetti code. Now, I understand there may be arguments for using 'just one little GOTO' instead of spending the time on refactoring to a more maintainable solution. The issue is, this isolated 'just one little GOTO' isn't so isolated. At least once every week or so there is a new 'one little GOTO' to add. This codebase is already a horror to work with due to code dating back to or before 1984 being riddled with GOTOs that would make many Pastafarians believe it was inspired by the Flying Spagetti Monster itself. Unfortunately the language this is written in doesn't have any ready made refactoring tools, so it makes it harder to push the 'Refactor to increase productivity later' because short-term wins are the only wins paid attention to here... Has anyone else experienced this issue whereby everybody agrees that we cannot be adding new GOTOs to jump 2000 lines to a random section, but continually have Anaylsts insist on doing it just this one time and having management approve it? tldr; How can one go about addressing the issue of developers being pressured (forced) to continually add GOTO statements (by add, I mean add to jump to random sections many lines away) because it 'gets that feature in quicker'? I'm beginning to fear we may loses valuable developers to the raptors over this...

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• Distributing a function over a single dimension of an array in MATLAB?

  - by Alex Feinman

  I often find myself wanting to collapse an n-dimensional matrix across one dimension, and can't figure out if there is a concise incantation I can use to do this. For example, when parsing an image, I often want to do something like this. (Note! Illustrative example only. I know about rgb2gray for this specific case.) img = imread('whatever.jpg'); s = size(img); for i=1:s(1) for j=1:s(2) bw_img = mean(img(i,j,:)); end end I would love to express this as something like: bw = on(color, 3, @mean); or bw(:,:,1) = mean(color); Is there a short way to do this?

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• Why do MSTests Assert.AreEqual(1.0, double.NaN, 0.0) pass?

  - by Egil Hansen

  Short question, why do Assert.AreEqual(1.0, double.NaN, 0.0) pass when Assert.AreEqual(1.0, double.NaN) do not? Is it an error in MSTest or am I missing something here? Best regards, Egil. Update: Should probably add, that the reason behind my question is, that I have a bunch of unit tests that unfortunately passed due to the result of some linear algebraic matrix operation being NaN or (+/-)Infinity. The unit tests are fine, but since Assert.AreEqual on doubles with a delta will pass when actual or/and expected are NaN or Infinity, I was left to believe that the code I was testing was correct.

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• OpenGL Performance Questions

  - by Daniel

  This subject, as with any optimisation problem, gets hit on a lot, but I just couldn't find what I (think) I want. A lot of tutorials, and even SO questions have similar tips; generally covering: Use GL face culling (the OpenGL function, not the scene logic) Only send 1 matrix to the GPU (projectionModelView combination), therefore decreasing the MVP calculations from per vertex to once per model (as it should be). Use interleaved Vertices Minimize as many GL calls as possible, batch where appropriate And possibly a few/many others. I am (for curiosity reasons) rendering 28 million triangles in my application using several vertex buffers. I have tried all the above techniques (to the best of my knowledge), and received almost no performance change. Whilst I am receiving around 40FPS in my implementation, which is by no means problematic, I am still curious as to where these optimisation 'tips' actually come into use? My CPU is idling around 20-50% during rendering, therefore I assume I am GPU bound for increasing performance. Note: I am looking into gDEBugger at the moment Cross posted at Game Development

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• C++ domain specific embedded language operators

  - by aaa

  hi. In numerical oriented languages (Matlab, Fortran) range operator and semantics is very handy when working with multidimensional data. For example: A(i:j,k,:n) // represents two-dimensional slice B(i:j,0:n) of A at index k unfortunately C++ does not have range operator (:). of course it can be emulated using range/slice functor, but semantics is less clean than Matlab. I am prototyping matrix/tensor domain language in C++ and am wondering if there any options to reproduce range operator. I still would like to rely on C++/prprocessor framework exclusively. So far I have looked through boost wave which might be an suitable option. is there any other means to introduce new operators to C++ DSL?

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• Optimizing this "Boundarize" method for Numerics in Ruby

  - by mstksg

  I'm extending Numerics with a method I call "Boundarize" for lack of better name; I'm sure there are actually real names for this. But its basic purpose is to reset a given point to be within a boundary. That is, "wrapping" a point around the boundary; if the area is betweeon 0 and 100, if the point goes to -1, -1.boundarize(0,100) = 99 (going one too far to the negative "wraps" the point around to one from the max). 102.boundarize(0,100) = 2 It's a very simple function to implement; when the number is below the minimum, simply add (max-min) until it's in the boundary. If the number is above the maximum, simply subtract (max-min) until it's in the boundary. One thing I also need to account for is that, there are cases where I don't want to include the minimum in the range, and cases where I don't want to include the maximum in the range. This is specified as an argument. However, I fear that my current implementation is horribly, terribly, grossly inefficient. And because every time something moves on the screen, it has to re-run this, this is one of the bottlenecks of my application. Anyone have any ideas? module Boundarizer def boundarize min=0,max=1,allow_min=true,allow_max=false raise "Improper boundaries #{min}/#{max}" if min >= max new_num = self if allow_min while new_num < min new_num += (max-min) end else while new_num <= min new_num += (max-min) end end if allow_max while new_num > max new_num -= (max-min) end else while new_num >= max new_num -= (max-min) end end return new_num end end class Numeric include Boundarizer end

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• Android SDK: Create image on touch

  - by dagonal

  Hello, I'm a bit stumped here, I'm trying to make it so an image (already in the drawable folder) gets created everytime you touch the screen and removed when the finger is lifted. I have the touch part coded already, overriding the onTouch method with a couple switch cases that handle each type of action (down, up, move, etc). But I can't for the life of me figure out how to make the image appear and then disappear with the coordinates (matrix?) of where the finger is. Any help would be greatly appreciated!

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