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  • How can you predict the time it will take for two processes in two different machines in a cluster to communicate?

    - by Dokkat
    I am trying to develop a computing application which needs a lot of memory (500gb). Buying a single machine for that is overly expensive. I can, though, buy ~100 small instances on Digital Ocean or similar, divide the memory in blocks and use TCP to emulate shared memory between the instances. Now, my question is: how can I measure/predict the time it will take for two processes in two different machines like that to share information, in comparison to IPC and shared memory? Are there rules of thumb? I don't want exact values, but knowing more or less how much faster one is would be very helpful in visualising the feasibility of this approach.

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  • Strange behavior of flash in Google Chrome

    - by Bakhtiyor
    I have the last version of Chrome 5.0.xx. and my Ubuntu is also of the last version 10.04. What I usually do is to open two instances of Chrome and divide the screen into two parts. In one part my son watches cartoons in Youtube and in the other part I just read some news. So, sometimes, when I close some pages of the news I have being read the video which was being played in youtube crashes and immediately stops. I need to refresh youtube page and see the video again. What is the problem? How to solve it

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  • Consistency vs. Usability?

    - by dsimcha
    When designing an API, consistency often aids usability. However, sometimes they conflict where an extra API feature can be added to streamline a common case. It seems like there's somewhat of a divide over what to do here. Some designs (the Java standard library come to mind) favor consistency even if it makes common cases more verbose. Others (the Python standard library comes to mind) favor usability even if it means treating the common case as "special" to make it easier. What is your opinion on how consistency and usability should be balanced?

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  • Efficient way of detecting a touched object in a game?

    - by Pin
    Imagine a Sims-like 2D game for a touch based mobile phone where one can interact with virtually any object in the scene. How can I efficiently detect which object is being touched by the player? In my short experience, looping through all the visible objects in the scene and checking if they're touched has so far done the job, but when there may be many many moving objects in the screen that sounds kind of inefficient isn't it? Keeping the visible moving objects list can consume time in itself as one may have to loop through all of them each frame. Other solutions I've thought are: Spatial hashing. Divide the screen as a grid and place the visible objects in the corresponding bucket. Detection of the clicked object is fast but there's additional overhead for placing the objects in the correct bucket each frame. Maintaining a quad-tree. Moving objects have to be rearranged all the time, the previous solution looks better. What is usually done in this case?

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  • Alternatives to voxel-based terrain

    - by Neomex
    Are there any alternatives to voxel based terrains? Such terrain should be fully destructable, allow for arches, overhangs, preserve sharp features where needed and keep consistent topology. Maybe you can explain the problem that makes you ask this question? Voxel based terrain is basically just using a 3D grid of data to store data. There are lots of ways to render that data, but it doesn't get much simpler for storing it. – Byte56 Current isosurface extraction methods aren't most effective/bug-free. Cubical Marching Squares seem to solve most of the issues, however it is a relatively new method and there aren't too many resources about it. (I've found single university paper) Even if we stick to CMS, when we want to add multi-material support, we can either divide surface into multiple meshes, or pass a texture array or texture atlas to shaders, then we are limited to set amount of textures and additionally increase memory-usage alot.

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  • In 3D camera math, calculate what Z depth is pixel unity for a given FOV

    - by badweasel
    I am working in iOS and OpenGL ES 2.0. Through trial and error I've figured out a frustum to where at a specific z depth pixels drawn are 1 to 1 with my source textures. So 1 pixel in my texture is 1 pixel on the screen. For 2d games this is good. Of course it means that I also factor in things like the size of the quad and the size of the texture. For example if my sprite is a quad 32x32 pixels. The quad size is 3.2 units wide and tall. And the texcoords are 32 / the size of the texture wide and tall. Then the frustum is: matrixFrustum(-(float)backingWidth/frustumScale,(float)backingWidth/frustumScale, -(float)backingHeight/frustumScale, (float)backingHeight/frustumScale, 40, 1000, mProjection); Where frustumScale is 800 for a retina screen. Then at a distance of 800 from camera the sprite is pixel for pixel the same as photoshop. For 3d games sometimes I still want to be able to do this. But depending on the scene I sometimes need the FOV to be different things. I'm looking for a way to figure out what Z depth will achieve this same pixel unity for a given FOV. For this my mProjection is set using: matrixPerspective(cameraFOV, near, far, (float)backingWidth / (float)backingHeight, mProjection); With testing I found that at an FOV of 45.0 a Z of 38.5 is very close to pixel unity. And at an FOV of 30.0 a Z of 59.5 is about right. But how can I calculate a value that is spot on? Here's my matrixPerspecitve code: void matrixPerspective(float angle, float near, float far, float aspect, mat4 m) { //float size = near * tanf(angle / 360.0 * M_PI); float size = near * tanf(degreesToRadians(angle) / 2.0); float left = -size, right = size, bottom = -size / aspect, top = size / aspect; // Unused values in perspective formula. m[1] = m[2] = m[3] = m[4] = 0; m[6] = m[7] = m[12] = m[13] = m[15] = 0; // Perspective formula. m[0] = 2 * near / (right - left); m[5] = 2 * near / (top - bottom); m[8] = (right + left) / (right - left); m[9] = (top + bottom) / (top - bottom); m[10] = -(far + near) / (far - near); m[11] = -1; m[14] = -(2 * far * near) / (far - near); } And my mView is set using: lookAtMatrix(cameraPos, camLookAt, camUpVector, mView); * UPDATE * I'm going to leave this here in case anyone has a different solution, can explain how they do it, or why this works. This is what I figured out. In my system I use a 10th scale unit to pixels on non-retina displays and a 20th scale on retina displays. The iPhone is 640 pixels wide on retina and 320 pixels wide on non-retina (obsolete). So if I want something to be the full screen width I divide by 20 to get the OpenGL unit width. Then divide that by 2 to get the left and right unit position. Something 32 units wide centered on the screen goes from -16 to +16. Believe it or not I have an excel spreadsheet do all this math for me and output all the vertex data for my sprite sheet. It's an arbitrary thing I made up to do .1 units = 1 non-retina pixel or 2 retina pixels. I could have made it .01 units = 2 pixels and someday I might switch to that. But for now it's the other. So the width of the screen in units is 32.0, and that means the left most pixel is at -16.0 and the right most is at 16.0. After messing a bit I figured out that if I take the [0] value of an identity modelViewProjection matrix and multiply it by 16 I get the depth required to get 1:1 pixels. I don't know why. I don't know if the 16 is related to the screen size or just a lucky guess. But I did a test where I placed a sprite at that calculated depth and varied the FOV through all the valid values and the object stays steady on screen with 1:1 pixels. So now I'm just calculating the unityDepth that way. If someone gives me a better answer I'll checkmark it.

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  • How can I compute the Big-O notation for a given piece of code?

    - by TheNew Rob Mullins
    So I just took a data structure midterm today and I was asked to determine the run time, in Big O notation, of the following nested loop: for (int i = 0; i < n-1; i++) { for(int j = 0; j < i; j++2) { //1 Statement } } I'm having trouble understanding the formula behind determining the run time. I thought that since the inner loop has 1 statement, and using the series equation of: (n * (n - 1)) / 2, I figured it to be: 1n * (n-1) / 2. Thus equaling (n^2 - 1) / 2. And so I generalized the runtime to be O(n^2 / 2). I'm not sure this is right though haha, was I supposed to divide my answer again by 2 since j is being upped in intervals of 2? Or is my answer completely off?

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  • "Testing Plan Lite" for web project

    - by Emmmmm
    How do you draft a quick & easy "Testing Plan Lite" for a medium-sized web project (70k lines, 2 developers)? I've seen many tutorials/articles on methods of testing, but all seem cumbersome. For us, the goal is to be able to be able to divide up and delegate testing instructions to our friends for different project segments, browsers, etc. What's the quick & easy way to write test plans for web apps? (the 20 of the 20/80 rule) Thanks!

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  • Issues with time slicing

    - by user12331
    I was trying to see the effect of time slicing. And how it can consume significant amount of time. Actually, I was trying to divide a certain work into number of threads and see the effect. I have a two core processor. So two threads can run in parallel. I was trying to see if I have a work w that is done by 2 threads, and if I have the same work done by t threads with each thread doing w/t of the work. How much does time slicing play a role in it As time slicing is time consuming process, I was expecting that when I do the same work using a two thread process or by a t thread process, the amount of time taken by the t thread process will be more Any suggestions?

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  • Vector normalization gives very imprecise results

    - by Kipras
    When I normalize vectors I receive very strange results. The lengths of the normalized vectors range from 1.0 to almost 1.5. The functions are all written by me, but I just can't find a mistake in my algorithm. When I normalize I just divide all components of the vector by the vector's length. public double length(){ return Math.sqrt(x*x + y*y); } public void normalize(){ if(length() > 0){ x /= length(); y /= length(); } } Is this supposed to happen? I mean I can see the length ranging from 0.9 to 1.1 at worst, but this is just overwhelming. Cheers

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  • Architecture driven by users, or by actions/content?

    - by hugerth
    I have a question about designing MVC app architecture. Let's say our application has three main categories of views (items of type 1, items of type 2...). And we have three (or more in future) types of users - Admins, let's say Moderators and typical Users. And in the future there might be more of them. Admins have full access to app, Moderators can visit only 2/3 type of items, and Users can visit only basic type of items. Should I divide my controllers/views/whatever like this: Items "A", Items "B", Items "C", then make them 100% finished and at the end add access privileges? Pros: DRY option Cons Conditional expressions in views Or another options: Items "A" / Admin, Items "A" / Moderator / Items "B" Admin ...? Pros: Divided parts of application for specific user (is that pros?) Cons: A lot of repeated code I don't have great experience in planning such things so it would nice if you can give me some tips or links to learn something about it.

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  • Is there a library or other way to do 128-bit math operations?

    - by samoz
    I am writing a cryptography application and need to work with 128 bit numbers. In addition to standard add, subtract, multiply, divide, and comparisons, I also need a power and modulo function as well. Does anyone know of a library or other implementation that can do this? If not 128-bit, is there a 64-bit option available?

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  • How do I use try...catch to catch floating point errors?

    - by Peter Stewart
    I'm using c++ in visual studio express to generate random expression trees for use in a genetic algorithm type of program. Because they are random, the trees often generate: divide by zero, overflow, underflow as well as returning "inf" and other strings. I can write handlers for the strings, but the literature left me baffled about the others. If I understand it correctly, I have to set some flags first? Advice and/or a pointer to some literature would be appreciated.

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  • Compute data between record of SQL database within Visual Studio

    - by Carl
    Hello, I am attempting to calculate the miles per gallon for logged fuel full-ups. My table consists of the flowing: FillUp(CarID, Date, ODReading, Gallons, StopGo, Highway, FillupID, MPG) I want to subtract the ODReading from the previous record and divide gallons by this computed value. How do I work between records to achieve this within Visual Studio 2008's column properties (formula) section? Thanks much, Carl

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  • Frequently Asked Riddles in Job Interviews

    - by Faruz
    Were you asked any logic riddles in job interviews? Are you usually asking riddles in job interviews? What are they, and what are the answers? I was asked once how can you divide evenly 5 apples to 6 people without dividing any apple to 1/6 (or 1/12 or 1/18 etc.). (Would love to hear answers in the comments, I'm not sure my answer was the best)

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  • Algorithm for dividing very large numbers

    - by pocoa
    I need to write an algorithm(I cannot use any 3rd party library, because this is an assignment) to divide(integer division, floating parts are not important) very large numbers like 100 - 1000 digits. I found http://en.wikipedia.org/wiki/Fourier_division algorithm but I don't know if it's the right way to go. Do you have any suggestions?

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  • masm division overflow

    - by Help I'm in college
    I'm trying divide two numbers in assembly. I'm working out of the Irvine assembly for intel computers book and I can't make division work for the life of me. Here's my code .code main PROC call division exit main ENDP division PROC mov eax, 4 mov ebx, 2 div ebx call WriteDec ret divison ENDP END main Where WriteDec should write whatever number is in the eax register (should be set to the quotient after the division call). Instead everytime I run it visual studio crashes (the program does compile however).

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  • python simple function error ?

    - by abhilashm86
    Here's a simple function to do simple math operations, when i call this from other program using import, output i get is none. When i remove def function, everything is working fine. What's the problem with defining this function? I'm new to python. def calci(a, op, b): if op == '+': c = a + b elif op == '-': c = a-b elif op == '*': c= a*b elif op =='/': if(b == 0): print('can\'t divide') c = a/b print('value is',c) return c result = calci(12,'+', 12) print(result) nter code here

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  • XSL - Unknown Error in FF media:content/@url

    - by danit
    I keep getting "Unknow Error occurred" when i try this in my XSLT: <table class="TEDtalks"> <xsl:for-each select="/rss/channel/item"> <tr> <td><xsl:value-of select="title"/></td> <td> <xsl:value-of select="media:content/@url" /> </td> </tr> </xsl:for-each> </table> The XML <rss> <channel> <item> <title>TEDTalks : Karen Armstrong: Let's revive the Golden Rule - Karen Armstrong (2009)</title> <itunes:author>Karen Armstrong</itunes:author> <description>Weeks from the Charter for Compassion launch, Karen Armstrong looks at religion's role in the 21st century: Will its dogmas divide us? Or will it unite us for common good? She reviews the catalysts that can drive the world's faiths to rediscover the Golden Rule.&lt;img src="http://feeds.feedburner.com/~r/TEDTalks_video/~4/th6FBgvV22o" height="1" width="1"/&gt;</description> <itunes:subtitle>Karen Armstrong: Let's revive the Golden Rule</itunes:subtitle> <itunes:summary><![CDATA[Weeks from the Charter for Compassion launch, Karen Armstrong looks at religion's role in the 21st century: Will its dogmas divide us? Or will it unite us for common good? She reviews the catalysts that can drive the world's faiths to rediscover the Golden Rule.]]></itunes:summary> <link>http://feedproxy.google.com/~r/TEDTalks_video/~3/th6FBgvV22o/647</link> <guid isPermaLink="false">http://video.ted.com/talks/podcast/KarenArmstrong_2009G.mp4</guid> <pubDate>Tue, 29 Sep 2009 12:46:00 -0500</pubDate> <category>Higher Education</category> <itunes:explicit>no</itunes:explicit> <itunes:duration>00:09:54</itunes:duration> <itunes:keywords>TED</itunes:keywords> <media:content url="http://feedproxy.google.com/~r/TEDTalks_video/~5/XT8k_DqlzGc/KarenArmstrong_2009G.mp4" fileSize="33726021" type="video/mp4" />

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  • Firefox extension file structure best practice

    - by user353969
    Is it a good practice to put js files of the "content" folders in inner folders representing their logical module? For example have a "datalayer" and "view" folders? I looked into some well known extensions, such as Firebug, and saw no such devision. I'm a Java developer so its seems much more natural to divide the files logically.

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