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  • How meaningful is the Big-O time complexity of an algorithm?

    - by james creasy
    Programmers often talk about the time complexity of an algorithm, e.g. O(log n) or O(n^2). Time complexity classifications are made as the input size goes to infinity, but ironically infinite input size in computation is not used. Put another way, the classification of an algorithm is based on a situation that algorithm will never be in: where n = infinity. Also, consider that a polynomial time algorithm where the exponent is huge is just as useless as an exponential time algorithm with tiny base (e.g., 1.00000001^n) is useful. Given this, how much can I rely on the Big-O time complexity to advise choice of an algorithm?

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  • Which useful alternative control structures do you know?

    - by bigown
    Similar question was closed on SO. Sometimes when we're programming, we find that some particular control structure would be very useful to us, but is not directly available in our programming language. What alternative control structures do you think are a useful way of organizing computation? The goal here is to get new ways of thinking about structuring code, in order to improve chunking and reasoning. You can create a wishful syntax/semantic not available now or cite a less known control structure on an existent programming language. Answers should give ideas for a new programming language or enhancing an actual language. Think of this as brainstorming, so post something you think is a crazy idea but it can be viable in some scenario. It's about imperative programming.

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  • How/where to run the algorithm on large dataset?

    - by niko
    I would like to run the PageRank algorithm on graph with 4 000 000 nodes and around 45 000 000 edges. Currently I use neo4j graph databse and classic relational database (postgres) and for software projects I mostly use C# and Java. Does anyone know what would be the best way to perform a PageRank computation on such graph? Is there any way to modify the PageRank algorithm in order to run it at home computer or server (48GB RAM) or is there any useful cloud service to push the data along the algorithm and retrieve the results? At this stage the project is at the research stage so in case of using cloud service if possible, would like to use such provider that doesn't require much administration and service setup, but instead focus just on running the algorith once and get the results without much overhead administration work.

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  • No OpenCL devices (13.10 Core I5 4430 Intel Graphics HD)

    - by Itai Bar-Haim
    I've been looking quite a lot for this but couldn't find anything that worked. I have an Intel Core I5-4430 based system with no extra graphics adapter (so it's using the on-board, integrated Intel Graphics HD that is part of the CPU), running Ubuntu 13.10. When running BOINC World Community Grid it says "No usable GPUs". When running a bitcoin mining program it says "No OpenCL devices". I searched the web, found two possible solutions - one was to use the Intel OpenCL driver for Xeon platforms, the other was to use the AMD driver. Tried both. I failed installing the Intel driver as there were too many prerequisites that I just didn't manage to install, and the AMD installation was quite fast to its size (it's 200MB, and took far less than a minute to install), but it didn't solve the problem. Perhaps I'm looking in the wrong direction here, I'm not sure, but is there anyway I can utilize the advance features of my CPU for those distributed computation programs?

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  • CS Concentrations and Career Paths

    - by xbonez
    I'm approaching the end of Sophomore year in college (Studying Computer Science), and very soon I'm going to have to decide on my concentration, but I honestly don't know what each concentration means. I basically have two questions: 1. How much influence does your concentration have on your career path? For example, would a video game development company only look at people with a concentration in Game Development? 2.It would be great if you guys could, in a line or two, tell me what sort of jobs am I looking at for each of the concentrations? I need to pick at least two of the 9 below. - Algorithms and Data Structures - Artificial Intelligence - Computer and Network Society - Computer graphics and vision - Human-Computer Interaction - Game Development and Design - Numeric and Symbolic Computation - Programming languages - Systems

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  • Distinct Count of Customers in a SCD Type 2 in #DAX

    - by Marco Russo (SQLBI)
    If you have a Slowly Changing Dimension (SCD) Type 2 for your customer and you want to calculate the number of distinct customers that bought a product, you cannot use the simple formula: Customers := DISTINCTCOUNT( FactTable[Customer Id] ) ) because it would return the number of distinct versions of customers. What you really want to do is to calculate the number of distinct application keys of the customers, that could be a lower number than the number you’ve got with the previous formula. Assuming that a Customer Code column in the Customers dimension contains the application key, you should use the following DAX formula: Customers := COUNTROWS( SUMMARIZE( FactTable, Customers[Customer Code] ) ) Be careful: only the version above is really fast, because it is solved by xVelocity (formerly known as VertiPaq) engine. Other formulas involving nested calculations might be more complex and move computation to the formula engine, resulting in slower query. This is absolutely an interesting pattern and I have to say it’s a killer feature. Try to do the same in Multidimensional…

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  • Most efficient AABB - Ray intersection algorithm for input/output distance calculation

    - by Tobbey
    Thanks to the following thread : most efficient AABB vs Ray collision algorithms I have seen very fast algorithm for ray/AABB intersection point computation. Unfortunately, most of the recent algorithm are accelerated by omitting the "output" intersection point of the box. In my application, I would interested in getting both the the distance from source ray to input: t0 and source ray to output of bounding box: t1. I have seen for instance Eisemann designed a very fast version regarding plucker, smits, ... , but it does not compare the case when both input/output distance should be computed see: http://www.cg.cs.tu-bs.de/publications/Eisemann07FRA/ Does someone know where I can find more information on algorithm performances for the specific input/output problem ? Thank you in advance

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  • migrating from struts2, looking for a new framework

    - by adhg
    We are supposed to start a relatively big project that will require lots of computation and analysis. Presentation (UI) for the end user is very crucial (graphs, tabels...) So far we've been using struts2. It's ok+. It has some drawbacks (specially if you work with tiles and all that XML) but if you get the lingo - you're ok. One option on the table is to continue using struts2 with jquery and all the other stuff that we've been doing for so long. Alternatively, I think we have an opportunity to learn something new and maybe a bit better then struts2. My question is this: Anyone has migrated from struts2 to something new and can share the experience. Or had some great experience witha particular java framework. Many thanks for any pointers.

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  • Frame timing for GLFW versus GLUT

    - by linello
    I need a library which ensures me that the timing between frames are more constant as possible during an experiment of visual psychophics. This is usually done synchronizing the refresh rate of the screen with the main loop. For example if my monitor runs at 60Hz I would like to specify that frequency to my framework. For example if my gameloop is the following void gameloop() { // do some computation printDeltaT(); Flip buffers } I would like to have printed a constant time interval. Is it possible with GLFW?

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  • My rhythm game runs choppy even with high frame rate

    - by felipedrl
    I'm coding a rhythm game and the game runs smoothly with uncapped fps. But when I try to cap it around 60 the game updates in little chunks, like hiccups, as if it was skipping frames or at a very low frame rate. The reason I need to cap frame rate is because in some computers I tested, the fps varies a lot (from ~80 - ~250 fps) and those drops are noticeable and degrade response time. Since this is a rhythm game this is very important. This issue is driving me crazy. I've spent a few weeks already on it and still can't figure out the problem. I hope someone more experienced than me could shed some light on it. I'll try to put here all the hints I've tried along with two pseudo codes for game loops I tried, so I apologize if this post gets too lengthy. 1st GameLoop: const uint UPDATE_SKIP = 1000 / 60; uint nextGameTick = SDL_GetTicks(); while(isNotDone) { // only false when a QUIT event is generated! if (processEvents()) { if (SDL_GetTicks() > nextGameTick) { update(UPDATE_SKIP); render(); nextGameTick += UPDATE_SKIP; } } } 2nd Game Loop: const uint UPDATE_SKIP = 1000 / 60; while (isNotDone) { LARGE_INTEGER startTime; QueryPerformanceCounter(&startTime); // process events will return false in case of a QUIT event processed if (processEvents()) { update(frameTime); render(); } LARGE_INTEGER endTime; do { QueryPerformanceCounter(&endTime); frameTime = static_cast<uint>((endTime.QuadPart - startTime.QuadPart) * 1000.0 / frequency.QuadPart); } while (frameTime < UPDATE_SKIP); } [1] At first I thought it was a timer resolution problem. I was using SDL_GetTicks, but even when I switched to QueryPerformanceCounter, supposedly less granular, I saw no difference. [2] Then I thought it could be due to a rounding error in my position computation and since game updates are smaller in high FPS that would be less noticeable. Indeed there is an small error, but from my tests I realized that it is not enough to produce the position jumps I'm getting. Also, another intriguing factor is that if I enable vsync I'll get smooth updates @60fps regardless frame cap code. So why not rely on vsync? Because some computers can force a disable on gfx card config. [3] I started printing the maximum and minimum frame time measured in 1sec span, in the hope that every a few frames one would take a long time but still not enough to drop my fps computation. It turns out that, with frame cap code I always get frame times in the range of [16, 18]ms, and still, the game "does not moves like jagger". [4] My process' priority is set to HIGH (Windows doesn't allow me to set REALTIME for some reason). As far as I know there is only one thread running along with the game (a sound callback, which I really don't have access to it). I'm using AudiereLib. I then disabled Audiere by removing it from the project and still got the issue. Maybe there are some others threads running and one of them is taking too long to come back right in between when I measured frame times, I don't know. Is there a way to know which threads are attached to my process? [5] There are some dynamic data being created during game run. But It is a little bit hard to remove it to test. Maybe I'll have to try harder this one. Well, as I told you I really don't know what to try next. Anything, I mean, anything would be of great help. What bugs me more is why at 60fps & vsync enabled I get an smooth update and at 60fps & no vsync I don't. Is there a way to implement software vsync? I mean, query display sync info? Thanks in advance. I appreciate the ones that got this far and yet again I apologize for the long post. Best Regards from a fellow coder.

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  • What makes an application memory bandwidth bound?

    - by TheLQ
    This has been something that's been bothering me for a while: What makes an application memory bandwidth bound? For example, take this monstrosity of a computer that calculated the 5 trillionth digit of pi (and later 10 trillionth digit). I was surprised that they choose the lower but faster 98 GB RAM at 1066 MHz instead of the larger but slower 144 GB at 800 MHz. This is especially surprising considering they are using 22 TB HD array to store the results from computation; more RAM means less need for hard drives. Maybe its because I don't write applications for HPC servers, but how would RAM be the bottleneck? Are there any other non-HPC applications that usually run into this problem?

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  • Challenge 19 – An Explanation of a Query

    - by Dave Ballantyne
    I have received a number of requests for an explanation of my winning query of TSQL Challenge 19. This involved traversing a hierarchy of employees and rolling a count of orders from subordinates up to superiors. The first concept I shall address is the hierarchyId , which is constructed within the CTE called cteTree.   cteTree is a recursive cte that will expand the parent-child hierarchy of the personnel in the table @emp.  One useful feature with a recursive cte is that data can be ‘passed’ from the parent to the child data.  The hierarchyId column is similar to the hierarchyId data type that was introduced in SQL Server 2008 and represents the position of the person within the organisation. Let us start with a simplistic example Albert manages Bob and Eddie.  Bob manages Carl and Dave. The hierarchyId will represent each person’s position in this relationship in a single field.  In this simple example we could append the userID together into a varchar field as detailed below. This will enable us to select a branch of the tree by filtering using Where hierarchyId  ‘1,2%’ to select Bob and all his subordinates.  Naturally, this is not comprehensive enough to provide a full solution, but as opposed to concatenating the Id’s together into a varchar datatyped column, we can apply the same theory to a varbinary.  By CASTing the ID’s into a datatype of varbinary(4) ,4 is used as 4 bytes of data are used to store an integer and building a hierarchyId  from those.  For example: The important point to bear in mind for later in the query is that the binary data generated is 'byte order comparable'. ie We can ORDER a dataset with it and the resulting data, will be in the order required. Now, would probably be a good time to download the example file and, after the cte ‘cteTree’, uncomment the line ‘select * from cteTree’.  Mark this and all prior code and execute.  This will show you how this theory directly relates to the actual challenge data.  The only deviation from the above, is that instead of using the ID of an employee, I have used the row_number() ranking function to order each level by LastName,Firstname.  This enables me to order by the HierarchyId in the final result set so that the result set is in the required order. Your output should be something like the below.  Notice also the ‘Level’ Column that contains the depth that the employee is within the tree.  I would encourage you to ‘play’ with the query, change the order in the row_number() or the length of the cast in the hierarchyId to see how that effects the outcome.  The next cte, ‘cteTreeWithOrderCount’, is a join between cteTree and the @ord table, and COUNT’s the number of orders per employee.  A LEFT JOIN is employed here to account for the occasion where an employee has made no sales.   Executing a ‘Select * from cteTreeWithOrderCount’ will return the result set as below.  The order here is unimportant as this is only a staging point of the data and only the final result set in a cte chain needs an Order by clause, unless TOP is utilised. cteExplode joins the above result set to the tally table (Nums) for Level Occurances.  So, if level is 2 then 2 rows are required.  This is done to expand the dataset, to create a new column (PathInc), which is the (n+1) integers contained within the heirarchyid.  For example, with the data for Robert King as given above, the below 3 rows will be returned. From this you can see that the pathinc column now contains the values for Andrew Fuller and Steven Buchanan who are Robert King’s superiors within the tree.    Finally cteSumUp, sums the orders for each person and their subordinates using the PathInc generated above, and the final select does the final simple mathematics and filters to restrict the result set to only the ‘original’ row per employee.

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  • Skewed: a rotating camera in a simple CPU-based voxel raycaster/raytracer

    - by voxelizr
    TL;DR -- in my first simple software voxel raycaster, I cannot get camera rotations to work, seemingly correct matrices notwithstanding. The result is skewed: like a flat rendering, correctly rotated, however distorted and without depth. (While axis-aligned ie. unrotated, depth and parallax are as expected.) I'm trying to write a simple voxel raycaster as a learning exercise. This is purely CPU based for now until I figure out how things work exactly -- fow now, OpenGL is just (ab)used to blit the generated bitmap to the screen as often as possible. Now I have gotten to the point where a perspective-projection camera can move through the world and I can render (mostly, minus some artifacts that need investigation) perspective-correct 3-dimensional views of the "world", which is basically empty but contains a voxel cube of the Stanford Bunny. So I have a camera that I can move up and down, strafe left and right and "walk forward/backward" -- all axis-aligned so far, no camera rotations. Herein lies my problem. Screenshot #1: correct depth when the camera is still strictly axis-aligned, ie. un-rotated. Now I have for a few days been trying to get rotation to work. The basic logic and theory behind matrices and 3D rotations, in theory, is very clear to me. Yet I have only ever achieved a "2.5 rendering" when the camera rotates... fish-eyey, bit like in Google Streetview: even though I have a volumetric world representation, it seems --no matter what I try-- like I would first create a rendering from the "front view", then rotate that flat rendering according to camera rotation. Needless to say, I'm by now aware that rotating rays is not particularly necessary and error-prone. Still, in my most recent setup, with the most simplified raycast ray-position-and-direction algorithm possible, my rotation still produces the same fish-eyey flat-render-rotated style looks: Screenshot #2: camera "rotated to the right by 39 degrees" -- note how the blue-shaded left-hand side of the cube from screen #2 is not visible in this rotation, yet by now "it really should"! Now of course I'm aware of this: in a simple axis-aligned-no-rotation-setup like I had in the beginning, the ray simply traverses in small steps the positive z-direction, diverging to the left or right and top or bottom only depending on pixel position and projection matrix. As I "rotate the camera to the right or left" -- ie I rotate it around the Y-axis -- those very steps should be simply transformed by the proper rotation matrix, right? So for forward-traversal the Z-step gets a bit smaller the more the cam rotates, offset by an "increase" in the X-step. Yet for the pixel-position-based horizontal+vertical-divergence, increasing fractions of the x-step need to be "added" to the z-step. Somehow, none of my many matrices that I experimented with, nor my experiments with matrix-less hardcoded verbose sin/cos calculations really get this part right. Here's my basic per-ray pre-traversal algorithm -- syntax in Go, but take it as pseudocode: fx and fy: pixel positions x and y rayPos: vec3 for the ray starting position in world-space (calculated as below) rayDir: vec3 for the xyz-steps to be added to rayPos in each step during ray traversal rayStep: a temporary vec3 camPos: vec3 for the camera position in world space camRad: vec3 for camera rotation in radians pmat: typical perspective projection matrix The algorithm / pseudocode: // 1: rayPos is for now "this pixel, as a vector on the view plane in 3d, at The Origin" rayPos.X, rayPos.Y, rayPos.Z = ((fx / width) - 0.5), ((fy / height) - 0.5), 0 // 2: rotate around Y axis depending on cam rotation. No prob since view plane still at Origin 0,0,0 rayPos.MultMat(num.NewDmat4RotationY(camRad.Y)) // 3: a temp vec3. planeDist is -0.15 or some such -- fov-based dist of view plane from eye and also the non-normalized, "in axis-aligned world" traversal step size "forward into the screen" rayStep.X, rayStep.Y, rayStep.Z = 0, 0, planeDist // 4: rotate this too -- 0,zstep should become some meaningful xzstep,xzstep rayStep.MultMat(num.NewDmat4RotationY(CamRad.Y)) // set up direction vector from still-origin-based-ray-position-off-rotated-view-plane plus rotated-zstep-vector rayDir.X, rayDir.Y, rayDir.Z = -rayPos.X - me.rayStep.X, -rayPos.Y, rayPos.Z + rayStep.Z // perspective projection rayDir.Normalize() rayDir.MultMat(pmat) // before traversal, the ray starting position has to be transformed from origin-relative to campos-relative rayPos.Add(camPos) I'm skipping the traversal and sampling parts -- as per screens #1 through #3, those are "basically mostly correct" (though not pretty) -- when axis-aligned / unrotated.

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  • Issues printing through ssh tunnel and port forwarding

    - by simogasp
    I'm having some problems trying to print through a ssh tunnel. I'd like to print from my laptop to a network printer (Toshiba es453, for what matters) which is in a local network. I can reach the local network using a gateway. So far I did the following: ssh -N -L19100:<Printer_IP>:9100 <username>@<ssh_gateway> Basically i just mapped the port 19100 of my laptop directly to the input port of the printer, passing through the gateway. So far, so good. Then, i tried to install on my laptop a new printer with the GUI config tool of ubuntu, so that the new printer is on localhost at port 19100 (as APP Socket/HP Jet Direct) , then I provided the proper driver of the printer. In theory, once the tunnel is open I should be able to print from any program just selecting this printer. Of course, it does not work. :-) The document hangs in the queue with status Processing while in the shell where I set up the tunnel I get these errors on failing opening channels debug1: Local forwarding listening on ::1 port 19100. debug1: channel 0: new [port listener] debug1: Local forwarding listening on 127.0.0.1 port 19100. debug1: channel 1: new [port listener] debug1: Requesting [email protected] debug1: Entering interactive session. debug1: Connection to port 19100 forwarding to 195.220.21.227 port 9100 requested. debug1: channel 2: new [direct-tcpip] debug1: Connection to port 19100 forwarding to 195.220.21.227 port 9100 requested. debug1: channel 3: new [direct-tcpip] channel 2: open failed: connect failed: Connection timed out debug1: channel 2: free: direct-tcpip: listening port 19100 for 195.220.21.227 port 9100, connect from ::1 port 44434, nchannels 4 debug1: Connection to port 19100 forwarding to 195.220.21.227 port 9100 requested. debug1: channel 2: new [direct-tcpip] channel 3: open failed: connect failed: Connection timed out debug1: channel 3: free: direct-tcpip: listening port 19100 for 195.220.21.227 port 9100, connect from ::1 port 44443, nchannels 4 channel 2: open failed: connect failed: Connection timed out debug1: channel 2: free: direct-tcpip: listening port 19100 for 195.220.21.227 port 9100, connect from ::1 port 44493, nchannels 3 debug1: Connection to port 19100 forwarding to 195.220.21.227 port 9100 requested. debug1: channel 2: new [direct-tcpip] As a further debugging test I tried the following. From a machine inside the local network I did a telnet <IP_printer> 9100, got access, wrote some random thing, closed the connection and correctly I got a print of what I had written. So the port and the ip of the printer should be correct. I tried the same from my laptop with the tunnel opened, the telnet succeeded but, again, the printer didn't print anything, getting the usual channel x: open failed: errors. I'm not a great expert on the matter, I just thought that in theory it was possible to do something like that, but maybe there is something that I didn't consider or I did wrong. Any clue? Thanks! Simone [update] As further debugging test, I tried to replicate the procedure from a machine in the local network. From that machine, I did ssh -N -L19100:<IP_printer>:9100 <username>@<ssh_gateway> (note that now the machine, the gateway and the printer are in the same local network) then I tried again the telnet test with telnet localhost 19100, I got access and everything, but I didn't get the print but the usual error channel 2: open failed: connect failed: Connection timed out Maybe I am missing some other connection to be forwarded or maybe this is not allowed by the administrators. Of course, if I connect via ssh tunneling to the local machine from my laptop through the gateway, I can successfully print using the lpr command (from the local machine). But this is what I would like to avoid (yes, I'm lazy...:-), I would like to have a more 'elegant' and transparent way to do that.

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  • Growing Talent

    The subtitle of Daniel Coyles intriguing book The Talent Code is Greatness Isnt Born. Its Grown. Heres How. The Talent Code proceeds to layout a theory of how expertise can be cultivated through specific practices that encourage the growth of myelin in the brain. Myelin is a material that is produced and wraps around heavily used circuits in the brain, making them more efficient. Coyle uses an analogy that geeks will appreciate. When a circuit in the brain is used a lot (i.e. a specific action is repeated), the myelin insulates that circuit, increasing its bandwidth from telephone over copper to high speed broadband. This leads to the funny phenomenon of effortless expertise. Although highly skilled, the best players make it look easy. Coyle provides some biological backing for the long held theory that it takes 10,000 hours of practice to achieve mastery over a given subject. 10,000 hours or 10 years, as in, Teach Yourself Programming in Ten Years and others. However, it is not just that more hours equals more mastery. The other factors that Coyle identifies includes deep practice, practice which crucially involves drills that are challenging without being impossible. Another way to put it is that every day you spend doing only tasks you find monotonous and automatic, you are literally stagnating your brains development! Perhaps Coyles subtitle, needs one more phrase, Greatness Isnt Born. Its Grown. Heres How. And oh yeah, its not easy. Challenging yourself, continuing to persist in the face of repeated failures, practicing every day is not easy. As consultants, we sell our expertise, so it makes sense that we plan projects so that people can play to their strengths. At the same time, an important part of our culture is constant improvement, challenging yourself to be better. And the balancing contest ensues. I just finished working on a proof of concept (POC) we did for a project we are bidding on. Completely time boxed, so our team naturally split responsibilities amongst ourselves according to who was better at what. I must have been pretty bad at the other components, as I found myself working on the user interface, not my usual strength. The POC had a website frontend, and one thing I do know is HTML. After starting out in pure ASP.NET WebForms, I got frustrated as time was ticking, I knew what I wanted in HTML, but I couldnt coax the right output out of the ASP.NET controls. I needed two or three elements on the screen that were identical in layout, with different content. With a backup plan in  of writing the HTML into the response by hand, I decided to challenge myself a bit and see what I could do in an hour or two using the Microsoft submitted jQuery micro-templating JavaScript library. This risk paid off. I was able to quickly get the user interface up and running, responsive to the JSON data we were working with. I felt energized by the double win of getting the POC ready and learning something new. Opportunities  specifically like this POC dont come around often, but the takeaway is that while it wont be easy, there are ways to generate your own opportunities to grow towards greatness.Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • How does heap compaction work quickly?

    - by Mason Wheeler
    They say that compacting garbage collectors are faster than traditional memory management because they only have to collect live objects, and by rearranging them in memory so everything's in one contiguous block, you end up with no heap fragmentation. But how can that be done quickly? It seems to me that that's equivalent to the bin-packing problem, which is NP-hard and can't be completed in a reasonable amount of time on a large dataset within the current limits of our knowledge about computation. What am I missing?

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  • c++ exceptions and program execution logic

    - by Andrew
    Hello everyone, I have been thru a few questions but did not find an answer. I wonder how should the exception handling be implemented in a C++ software so it is centralized and it is tracking the software progress? For example, I want to process exceptions at four stages of the program and know that exception happened at that specific stage: 1. Initialization 2. Script processing 3. Computation 4. Wrap-up. At this point, I tried this: int main (...) { ... // start logging system try { ... } catch (exception &e) { cerr << "Error: " << e.what() << endl; cerr << "Could not start the logging system. Application terminated!\n"; return -1; } catch(...) { cerr << "Unknown error occured.\n"; cerr << "Could not start the logging system. Application terminated!\n"; return -2; } // open script file and acquire data try { ... } catch (exception &e) { cerr << "Error: " << e.what() << endl; cerr << "Could not acquire input parameters. Application terminated!\n"; return -1; } catch(...) { cerr << "Unknown error occured.\n"; cerr << "Could not acquire input parameters. Application terminated!\n"; return -2; } // computation try { ... } ... This is definitely not centralized and seems stupid. Or maybe it is not a good concept at all?

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  • Truncating double without rounding in C

    - by Coder
    Lets consider we have a double R = 99.999999; (which may be obtained by a result of some other computation),now the desired output is 99.99 I tried using printf("%.2lf",R); but it's rounding off the value.How to get the desired output ? (preferably using printf)

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  • How to do the processing and keep GUI refreshed using databinding?

    - by macias
    History of the problem This is continuation of my previous question How to start a thread to keep GUI refreshed? but since Jon shed new light on the problem, I would have to completely rewrite original question, which would make that topic unreadable. So, new, very specific question. The problem Two pieces: CPU hungry heavy-weight processing as a library (back-end) WPF GUI with databinding which serves as monitor for the processing (front-end) Current situation -- library sends so many notifications about data changes that despite it works within its own thread it completely jams WPF data binding mechanism, and in result not only monitoring the data does not work (it is not refreshed) but entire GUI is frozen while processing the data. The aim -- well-designed, polished way to keep GUI up to date -- I am not saying it should display the data immediately (it can skip some changes even), but it cannot freeze while doing computation. Example This is simplified example, but it shows the problem. XAML part: <StackPanel Orientation="Vertical"> <Button Click="Button_Click">Start</Button> <TextBlock Text="{Binding Path=Counter}"/> </StackPanel> C# part (please NOTE this is one piece code, but there are two sections of it): public partial class MainWindow : Window,INotifyPropertyChanged { // GUI part public MainWindow() { InitializeComponent(); DataContext = this; } private void Button_Click(object sender, RoutedEventArgs e) { var thread = new Thread(doProcessing); thread.IsBackground = true; thread.Start(); } // this is non-GUI part -- do not mess with GUI here public event PropertyChangedEventHandler PropertyChanged; public void OnPropertyChanged(string property_name) { if (PropertyChanged != null) PropertyChanged(this, new PropertyChangedEventArgs(property_name)); } long counter; public long Counter { get { return counter; } set { if (counter != value) { counter = value; OnPropertyChanged("Counter"); } } } void doProcessing() { var tmp = 10000.0; for (Counter = 0; Counter < 10000000; ++Counter) { if (Counter % 2 == 0) tmp = Math.Sqrt(tmp); else tmp = Math.Pow(tmp, 2.0); } } } Known workarounds (Please do not repost them as answers) Those two first are based on Jon ideas: pass GUI dispatcher to library and use it for sending notifications -- why it is ugly? because it could be no GUI at all give up with data binding COMPLETELY (one widget with databinding is enough for jamming), and instead check from time to time data and update the GUI manually -- well, I didn't learn WPF just to give up with it now ;-) and this is mine, it is ugly, but simplicity of it kills -- before sending notification freeze a thread -- Thread.Sleep(1) -- to let the potential receiver "breathe" -- it works, it is minimalistic, it is ugly though, and it ALWAYS slows down computation even if no GUI is there So... I am all ears for real solutions, not some tricks.

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  • Is MapReduce one form of Continuation-Passing Style (CPS)?

    - by Jeffrey
    As the title says. I was reading Yet Another Language Geek: Continuation-Passing Style and I was sort of wondering if MapReduce can be categorized as one form of Continuation-Passing Style aka CPS. I am also wondering how can CPS utilise more than one computer to perform complex computation. Maybe CPS makes it easier to work with Actor model.

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  • How can I find the size of a ELF file/image with Header information?

    - by fasil
    I need to find the size of an elf image for some computation. I have tried with the readelf utility on linux which gives the informations about the headers and section. I need to have the exact file size of the elf(on the whole). How do I find the size of the ELF from the header information or Is there any other means to find the size of an elf without reading the full image.

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