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  • Combine Arbitrary number of polygons together

    - by Jakobud
    I have an arbitrary number of polygons (hexes in this case) that are arranged randomly, but they are all touching another hex. Each individual hex has 6 x,y vertices. The vertex's are known for all the hexes. Can anyone point me in the direction of an algorithm that will combine all the hexes into a single polygon? Essentially I'm just looking for a function that spits out an array of vertex locations that are ordered in a way that when drawing lines from one to the next, it forms the polygon. This is my method so far: Create array of all the vertices for all the hexes. Determine the number of times a vertex occurs in the array If vertex is in the array 3+ times, delete the vertices from the array. If vertex is in the array 2 times, delete one of them. The next step is tricky though. I'm using canvas to draw out these polygons, which essentially involves drawing a line from one vertex to the next. So the order of the vertices in the final array is important. It can't be sorted arbitrarily. Also, I'm not looking for a "convex hull" algorithm, as that would not draw the polygon correctly. Are there any functions out there that do something like this? Am I on the right track or is there a better more efficient way?

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  • What is the n in O(n) when comparing sorting algorithms?

    - by Mumfi
    The question is rather simple, but I just can't find a good enough answer. I've taken a look at the most upvoted question regarding the Big-Oh notation, namely this: Plain English explanation of Big O It says there that: For example, sorting algorithms are typically compared based on comparison operations (comparing two nodes to determine their relative ordering). Now let's consider the simple bubble sort algorithm: for (int i = arr.length - 1; i > 0 ; i--) { for (int j = 0; j<i; j++) { if (arr[j] > arr[j+1]) { switchPlaces(...) } } } I know that worst case is O(n^2) and best case is O(n), but what is n exactly? If we attempt to sort an already sorted algorithm (best case), we would end up doing nothing, so why is it still O(n)? We are looping through 2 for-loops still, so if anything it should be O(n^2). n can't be the number of comparison operations, because we still compare all the elements, right? This confuses me, and I appreciate if someone could help me.

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  • Making more recent items more likely to be drawn

    - by bobo
    There are a few hundred of book records in the database and each record has a publish time. In the homepage of the website, I am required to write some codes to randomly pick 10 books and put them there. The requirement is that newer books need to have higher chances of getting displayed. Since the time is an integer, I am thinking like this to calculate the probability for each book: Probability of a book to be drawn = (current time - publish time of the book) / ((current time - publish time of the book1) + (current time - publish time of the book1) + ... (current time - publish time of the bookn)) After a book is drawn, the next round of the loop will minus the (current time - publish time of the book) from the denominator and recalculate the probability for each of the remaining books, the loop continues until 10 books have been drawn. Is this algorithm a correct one? By the way, the website is written in PHP. Feel free to suggest some PHP codes if you have a better algorithm in your mind. Many thanks to you all.

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  • Best CPUs for speeding up compiling times of C++ w/ DistGCC

    - by Jay
    I'm putting together a distributed build farm with DistGCC to speed up our teams compile times and just looking for thoughts on which processors to use in the hosts. Are we going to get a noticeable decrease in time using 8 cores vs. 4-hyperthreaded cores? Big difference in time between i7 and Xeon? etc, etc. Just need advice from people who've put together kick-a build clusters. We've got a majority of the normal things to speed up builds in place (pre-compiled headers, ccache, local gigabit connections between them, tons of ram, etc) so please just give advice on the best processor to use. And money is a factor, but anythings doable if the performance increase is noticeable. Thanks. Jay EDIT: Although any advice IS welcome, please refrain from "Do this first" posts as we're not planning on skimping on things like SSD, maxed out RAM, etc. My personal system is a iMac Quad-core i5 with 8GB of RAM. When I build our project locally, my processor floats around 99-100% a majority of the time, which makes me assume it is a bottleneck, even if you made everything else faster. My ram on the other hand doesn't even get close to maxing out. It's also worth noting that I did research this, however every discussion I could find was primarily for gaming machines, which is obviously a different beast in usage. These machines won't even have monitors or anything but integrated graphics since they have one purpose: Build freakin fast. (hopefully)

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  • Best CPUs for speeding up compiling times of C++ w/ DistGCC

    - by Jay
    I'm putting together a distributed build farm with DistGCC to speed up our teams compile times and just looking for thoughts on which processors to use in the hosts. Are we going to get a noticeable decrease in time using 8 cores vs. 4-hyperthreaded cores? Big difference in time between i7 and Xeon? etc, etc. Just need advice from people who've put together kick-a build clusters. We've got a majority of the normal things to speed up builds in place (pre-compiled headers, ccache, local gigabit connections between them, tons of ram, etc) so please just give advice on the best processor to use. And money is a factor, but anythings doable if the performance increase is noticeable. Thanks. Jay EDIT: Although any advice IS welcome, please refrain from "Do this first" posts as we're not planning on skimping on things like SSD, maxed out RAM, etc. My personal system is a iMac Quad-core i5 with 8GB of RAM. When I build our project locally, my processor floats around 99-100% a majority of the time, which makes me assume it is a bottleneck, even if you made everything else faster. My ram on the other hand doesn't even get close to maxing out. It's also worth noting that I did research this, however every discussion I could find was primarily for gaming machines, which is obviously a different beast in usage. These machines won't even have monitors or anything but integrated graphics since they have one purpose: Build freakin fast. (hopefully)

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  • Best CPUs for speeding up compiling times of C++ w/ DistGCC

    - by Jay
    I'm putting together a distributed build farm with DistGCC to speed up our teams compile times and just looking for thoughts on which processors to use in the hosts. Are we going to get a noticeable decrease in time using 8 cores vs. 4-hyperthreaded cores? Big difference in time between i7 and Xeon? etc, etc. Just need advice from people who've put together kick-a build clusters. We've got a majority of the normal things to speed up builds in place (pre-compiled headers, ccache, local gigabit connections between them, tons of ram, etc) so please just give advice on the best processor to use. And money is a factor, but anythings doable if the performance increase is noticeable. Thanks. Jay EDIT: Although any advice IS welcome, please refrain from "Do this first" posts as we're not planning on skimping on things like SSD, maxed out RAM, etc. My personal system is a iMac Quad-core i5 with 8GB of RAM. When I build our project locally, my processor floats around 99-100% a majority of the time, which makes me assume it is a bottleneck, even if you made everything else faster. My ram on the other hand doesn't even get close to maxing out. It's also worth noting that I did research this, however every discussion I could find was primarily for gaming machines, which is obviously a different beast in usage. These machines won't even have monitors or anything but integrated graphics since they have one purpose: Build freakin fast. (hopefully)

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  • Distributing processing for an application that wasn't designed with that in mind

    - by Tim
    We've got the application at work that just sits and does a whole bunch of iterative processing on some data files to perform some simulations. This is done by an "old" Win32 application that isn't multi-processor aware, so new(ish) computers and workstations are mostly sitting idle running this application. However, since it's installed by a typical Windows Install Shield installer, I can't seem to install and run multiple copies of the application. The work can be split up manually before processing, enabling the work to be distributed across multiple machines, but we still can't take advantage of multiple core CPUs. The results can be joined back together after processing to make a complete simulation. Is there a product out there that would let me "compartmentalize" an installation (or 4) so I can take advantage of a multi-core CPU? I had thought of using MS Softgrid, but I believe that still depends on a remote server to do the heavy lifting (though please correct me if I'm wrong). Furthermore, is there a way I can distribute the workload off the one machine? So an input could be split into 50 chunks, handed out to 50 machines, and worked on? All without really changing the initial application? In a perfect world, I'd get the application to take advantage of a DesktopGrid (BOINC), but like most "mission critical corporate applications", the need is there, but the money is not. Thank you in advance (and sorry if this isn't appropriate for serverfault).

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  • Clustering filesystem for small files

    - by viraptor
    Hi, I'm looking for a distributed filesystem which I could use for storing lots of small files (<1MB usually). What I want to get is: 2 servers which have the fs mounted themselves and mirror the data locking support (among reachable nodes) some kind of best-effort automatic resynchronisation after one node goes down and comes back again What I mean by the resync is that, I'm ok with both servers doing read/write operations even if they split-brain. I'm also ok if a local process obtains a lock if the other host is not reachable. From the resync I expect only a file-level consistent view after a while - that is - if file x is modified on both nodes during a split-brain, I don't really care which one is available after they join again, as long as it's full file, not one block coming from node1 and another block from node2. Is there a solution like that out there? I see that gluster has some problems with file locks (even in 3.1). I also noticed that OCFS2 will panic if both nodes split-brain. What other filesystem would allow me to do what I want?

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  • Nagios DNX plugins

    - by danneh3826
    I'm toying with the idea of multiple Nagios instances setup to monitor our infrastructure. I've looked at all the various methods of distributed Nagios checks, and I think DNX comes out the closest. DNX handles failure of worker nodes, that's fine. What happens if the main DNX server fails though? Is there a way to replicate the server too? I'm using AWS EC2 primarily, so I can utilise Elastic Load Balancing for the web UI, but I need to be able to handle the AZ where the monitoring server is to fail over, and essentially for a second to pick up the checking load (active/passive, active/active, so long as it doesn't fail completely) The other thing I'm trying to solve is an issue with routing. What I'd like is to have multiple nodes report a fault before Nagios confirms it as critical. Not the NRPE checks, as they're pretty self explanitory, but things more like check_ping. I often have routing issues out of AWS to certain datacenters, so Nagios can often report bad/no ping/timeout as a critical issue, even though the machine in question is working fine. Would it be possible to have a setup where a worker complains a service check is critical, and have a second worker node (positioned in another datacenter/AZ) also report the service as critical before the Nagios central server issues a critical alert? I realise I might be asking a bit much (how far down the line do you go setting up failover systems before it starts to get ridiculous), however surely someone must have thought of this scenario when developing DNX?

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  • How to distribute multiple executions of an app across many machines

    - by Salec
    I've got a simulation app (64-bit windows) that runs without any user interaction. This app gathers information and pushes it to a remote MS SQL Server. What I'd like to do is execute this simulation as many times as I can on multiple machines after our nightly build has finished and it has passed the test suite. If possible I'd love to have the ability to configure it to stop after x total runs or if the entire batch has taken over y hours. I've tried using Visual Studio's built in test framework since we already have a test lab set up with multiple agents. I created a single unit test that simply runs the simulation then I created an ordered test and added that single test multiple times (from what I gather, this is the only way to execute the same unit test more than once). I found that ordered tests are only run on a single agent and not distributed which is very limiting. We use TeamCity to perform our nightly builds and I suspect it's possible to implement this on top of that, but I'm fairly new to TeamCity. We also have Jenkins and Bamboo available and I'm open to any other software that would get the job done presuming it runs on a 64-bit Windows OS. Any suggestions?

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  • What are the real-world applications of huffman coding?

    - by jcyang
    I am told that Huffman coding is used as loseless data compression algorithm but also am told that real data compress software do not employ huffman coding,cause if the keys are not distributed decentralized enough,the compressed file could be even larger than the orignal file. This leave me wondering are there any real-world application of huffman coding? thanks.

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  • parallel sorting methods

    - by davit-datuashvili
    in book algorithm in c++ by robert sedgewick there is such kind of problem how many parallel steps would be required to sort n records that are distributed on some k disks(let say k=1000 or any value ) and using some m processors the same m can be 100 or arbitrary number i have questions what we should do in such case? what are methods to solve such kind of problems? and what is answer in this case?

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  • How are PID's generated?

    - by Helltone
    On *nix, PIDs are unique identifiers for running processes. How are PID's generated? Is it just an integer which gets incremented or a more complex structure such as a list? How do they get recycled? By recycling I mean that, when a process terminates, it's PID will eventually be reused by another process.

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  • A star vs internet routing pathfinding

    - by alan2here
    In many respects pathfinding algorythms like A star for finding the shortest route though graphs are similar to the pathfinding on the internet when routing trafic. However the pathfinding routers perform seem to have remarkable properties. As I understand it: It's very perfromant. New nodes can be added at any time that use a free address from a finite (not tree like) address space. It's real routing, like A*, theres never any doubling back for example. IP addresses don't have to be geographicly nearby. The network reacts quickly to changes to the networks shape, for example if a line is down. Routers share information and it takes time for new IP's to be registered everywhere, but presumably every router dosn't have to store a list of all the addresses each of it's directions leads most directly to. I can't find this information elsewhere however I don't know where to look or what search tearms to use. I'm looking for a basic, general, high level description to the algorithms workings, from the point of view of an individual router.

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  • Utility to optimally distribute files onto multiple DVDs?

    - by Alex R
    I have a bunch of media files which I want to record to DVD, but since each DVD only fits 4.5GB, I have to find the optimal way to organize the files to use the minimum number of DVDs (otherwise the empty space left in each DVD can easily add up). Are there any tools to help with this? Many years ago there was a DOS utility to do this with floppy disks.

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  • No recent books on MPI: is it dying?

    - by Jono
    I've never used Message Passing Interface (MPI), but I've heard its name thrown about, most recently with Windows HPC Server. I had a quick look on amazon to see if there were any books on it, but they're all dated around 7 or more years ago. Is MPI still a valid technology choice for new applications, or has it been largely superceded by other distributed programming alternatives (e.g. DataSynapse GridServer)? As it's not really an implementation, but rather a standard, what is the likelihood (assuming it's not dead) that learning it will result in better design of distributed programming systems? Is there something else I should be looking at instead?

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  • Distributing cpu-bound compression jobs to multiple computers?

    - by barnaby
    The other day I needed to archive a lot of data on our network and I was frustrated I had no immediate way to harness the power of multiple machines to speed-up the process. I understand that creating a distributed job management system is a leap from a command-line archiving tool. I'm now wondering what the simplest solution to this type of distributed performance scenario could be. Would a custom tool always be a requirement or are there ways to use standard utilities and somehow distribute their load transparently at a higher level? Thanks for any suggestions.

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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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  • Solved: Chrome v18, self signed certs and &ldquo;signed using a weak signature algorithm&rdquo;

    - by David Christiansen
    So chrome has just updated itself automatically and you are now running v18 – great. Or is it… If like me, you are someone that are running sites using a self-signed SSL Certificate (i.e. when running a site on a developer machine) you may come across the following lovely message; Fear not, this is likely as a result of you following instructions you found on the apache openssl site which results in a self signed cert using the MD5 signature hashing algorithm. Using OpenSSL The simple fix is to generate a new certificate specifying to use the SHA512 signature hashing algorithm, like so; openssl req -new -x509 -sha512 -nodes -out server.crt -keyout server.key Simples! Now, you should be able to confirm the signature algorithm used is sha512 by looking at the details tab of certificate Notes If you change your certificate, be sure to reapply any private key permissions you require – such as allowing access to the application pool user.

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  • Who owns the code, who owns the algorithm, who owns the idea?

    - by Vorac
    This question got me thinking what products of the programming effort belong to the employer, and what don't. The two extremes are (0) the code - it apparently belongs to the employer and (1) the learned personal and technical skills. But what is in between? Who owns the pseudocode/algorithm? Who owns the general idea of the algorithm? Who owns the know-how that such an algorithm may serve some useful purpose (e.g. on this site questions are values, as well as answers)? Also: Who owns an idea on the web?

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  • What is the difference between these two nloglog(n) sorting algorithms? (Andersson et al., 1995 vs.

    - by Yktula
    Swanepoel's comment here lead me to this paper. Then, searching for an implementation in C, I came across this, which referenced another paper on an algorithm described here. Both papers describe integer sorting algorithms that run in O(nloglog(n)) time. What is the difference between the two? Have there been any more recent findings about this topic? Andersson et al., 1995 Han, 2004

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