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• Give a session on C++ AMP – here is how

  - by Daniel Moth

  Ever since presenting on C++ AMP at the AMD Fusion conference in June, then the Gamefest conference in August, and the BUILD conference in September, I've had numerous requests about my material from folks that want to re-deliver the same session. The C++ AMP session I put together has evolved over the 3 presentations to its final form that I used at BUILD, so that is the one I recommend you base yours on. Please get the slides and the recording from channel9 (I'll refer to slide numbers below). This is how I've been presenting the C++ AMP session: Context (slide 3, 04:18-08:18) Start with a demo, on my dual-GPU machine. I've been using the N-Body sample (for VS 11 Developer Preview). (slide 4) Use an nvidia slide that has additional examples of performance improvements that customers enjoy with heterogeneous computing. (slide 5) Talk a bit about the differences today between CPU and GPU hardware, leading to the fact that these will continue to co-exist and that GPUs are great for data parallel algorithms, but not much else today. One is a jack of all trades and the other is a number cruncher. (slide 6) Use the APU example from amd, as one indication that the hardware space is still in motion, emphasizing that the C++ AMP solution is a data parallel API, not a GPU API. It has a future proof design for hardware we have yet to see. (slide 7) Provide more meta-data, as blogged about when I first introduced C++ AMP. Code (slide 9-11) Introduce C++ AMP coding with a simplistic array-addition algorithm – the slides speak for themselves. (slide 12-13) index<N>, extent<N>, and grid<N>. (Slide 14-16) array<T,N>, array_view<T,N> and comparison between them. (Slide 17) parallel_for_each. (slide 18, 21) restrict. (slide 19-20) actual restrictions of restrict(direct3d) – the slides speak for themselves. (slide 22) bring it altogether with a matrix multiplication example. (slide 23-24) accelerator, and accelerator_view. (slide 26-29) Introduce tiling incl. tiled matrix multiplication [tiling probably deserves a whole session instead of 6 minutes!]. IDE (slide 34,37) Briefly touch on the concurrency visualizer. It supports GPU profiling, but enhancements specific to C++ AMP we hope will come at the Beta timeframe, which is when I'll be spending more time talking about it. (slide 35-36, 51:54-59:16) Demonstrate the GPU debugging experience in VS 11. Summary (slide 39) Re-iterate some of the points of slide 7, and add the point that the C++ AMP spec will be open for other compiler vendors to implement, even on other platforms (in fact, Microsoft is actively working on that). (slide 40) Links to content – see slide – including where all your questions should go: http://social.msdn.microsoft.com/Forums/en/parallelcppnative/threads.   "But I don't have time for a full blown session, I only need 2 (or just 1, or 3) C++ AMP slides to use in my session on related topic X" If all you want is a small number of slides, you can take some from the session above and customize them. But because I am so nice, I have created some slides for you, including talking points in the notes section. Download them here. Comments about this post by Daniel Moth welcome at the original blog.

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• Oh no! My padding's invalid!

  - by Simon Cooper

  Recently, I've been doing some work involving cryptography, and encountered the standard .NET CryptographicException: 'Padding is invalid and cannot be removed.' Searching on StackOverflow produces 57 questions concerning this exception; it's a very common problem encountered. So I decided to have a closer look. To test this, I created a simple project that decrypts and encrypts a byte array: // create some random data byte[] data = new byte[100]; new Random().NextBytes(data); // use the Rijndael symmetric algorithm RijndaelManaged rij = new RijndaelManaged(); byte[] encrypted; // encrypt the data using a CryptoStream using (var encryptor = rij.CreateEncryptor()) using (MemoryStream encryptedStream = new MemoryStream()) using (CryptoStream crypto = new CryptoStream( encryptedStream, encryptor, CryptoStreamMode.Write)) { crypto.Write(data, 0, data.Length); encrypted = encryptedStream.ToArray(); } byte[] decrypted; // and decrypt it again using (var decryptor = rij.CreateDecryptor()) using (CryptoStream crypto = new CryptoStream( new MemoryStream(encrypted), decryptor, CryptoStreamMode.Read)) { byte[] decrypted = new byte[data.Length]; crypto.Read(decrypted, 0, decrypted.Length); } Sure enough, I got exactly the same CryptographicException when trying to decrypt the data even in this simple example. Well, I'm obviously missing something, if I can't even get this single method right! What does the exception message actually mean? What am I missing? Well, after playing around a bit, I discovered the problem was fixed by changing the encryption step to this: // encrypt the data using a CryptoStream using (var encryptor = rij.CreateEncryptor()) using (MemoryStream encryptedStream = new MemoryStream()) { using (CryptoStream crypto = new CryptoStream( encryptedStream, encryptor, CryptoStreamMode.Write)) { crypto.Write(data, 0, data.Length); } encrypted = encryptedStream.ToArray(); } Aaaah, so that's what the problem was. The CryptoStream wasn't flushing all it's data to the MemoryStream before it was being read, and closing the stream causes it to flush everything to the backing stream. But why does this cause an error in padding? Cryptographic padding All symmetric encryption algorithms (of which Rijndael is one) operates on fixed block sizes. For Rijndael, the default block size is 16 bytes. This means the input needs to be a multiple of 16 bytes long. If it isn't, then the input is padded to 16 bytes using one of the padding modes. This is only done to the final block of data to be encrypted. CryptoStream has a special method to flush this final block of data - FlushFinalBlock. Calling Stream.Flush() does not flush the final block, as you might expect. Only by closing the stream or explicitly calling FlushFinalBlock is the final block, with any padding, encrypted and written to the backing stream. Without this call, the encrypted data is 16 bytes shorter than it should be. If this final block wasn't written, then the decryption gets to the final 16 bytes of the encrypted data and tries to decrypt it as the final block with padding. The end bytes don't match the padding scheme it's been told to use, therefore it throws an exception stating what is wrong - what the decryptor expects to be padding actually isn't, and so can't be removed from the stream. So, as well as closing the stream before reading the result, an alternative fix to my encryption code is the following: // encrypt the data using a CryptoStream using (var encryptor = rij.CreateEncryptor()) using (MemoryStream encryptedStream = new MemoryStream()) using (CryptoStream crypto = new CryptoStream( encryptedStream, encryptor, CryptoStreamMode.Write)) { crypto.Write(data, 0, data.Length); // explicitly flush the final block of data crypto.FlushFinalBlock(); encrypted = encryptedStream.ToArray(); } Conclusion So, if your padding is invalid, make sure that you close or call FlushFinalBlock on any CryptoStream performing encryption before you access the encrypted data. Flush isn't enough. Only then will the final block be present in the encrypted data, allowing it to be decrypted successfully.

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• What Color is your Jetpack ?

  - by JoshReuben

  I’m a programmer, Im approaching 40, and I’m fairly decent at my job – I’ll keep doing what I’m doing for as long as they let me!   So what are your career options if you know how to code? A Programmer could be ..   An Algorithm developer Pros Interesting High barriers of entry, potential for startup competitive factor Cons Do you have the skill, qualifications? What are working conditions n this mystery niche ? micro-focus An Academic Pros Low pressure Job security – or is this an illusion ? Cons Low Pay Need a PhD A Software Architect Pros: strategic, rather than tactical Setting technology platform and high level vision You say how it should work, others have to figure out why its not working the way its supposed to ! broad view – you are paid to learn (how do you con people into paying for you to learn ??) Cons: Glorified developer – more often than not! competitive – everyone wants to do it ! loose touch with underlying tech in tough times, first guy to get the axe ! A Software Engineer Pros: interesting, always more to learn fun I can do it Fallback Cons: Nothing new under the sun – been there, done that Dealing with poor requirements, deadlines, other peoples code, overtime C#, XAML, Web - Low barriers of entry –> à race to the bottom A Team leader Pros: Setting code standards and proposing technology choices Cons: Glorified developer – more often than not! Inspecting other peoples code and debugging the problems they cannot fix Dealing with mugbies and prima donas Responsible for QA of others A Project Manager Pros No need for debugging other peoples code Cons Low barrier of entry High pressure Responsible for QA of others Loosing touch with technology A lot of bullshit meetings Have to be an asshole A Product Manager Pros No need for debugging other peoples code Learning new skillset of sales and marketing Cons Travel (I'm a family man) May need to know the bs details of an uninteresting product things I want to work with: AI, algorithms, Numerical Computing, Mathematica, C++ AMP – unfortunately, the work here is few & far between. VS & TFS Extensibility, DSLs (Workflow , Lightswitch), Code Generation – one day, code will write code ! Unity3D, WebGL – fun, fun, fun ! Modern Web – Knockout, SignalR, MVC, Node.Js ??? (tentative – I'll wait until things stabilize as this area is undergoing a pre-Cambrian explosion) Things I don’t want to work with: (but will if I'm asked to !) C# – same old, same old – not learning anything new here Old code – blech ! Environment with code & fix mentality , ad hoc requirements, excessive overtime Pc support, System administration – even after 20 years, people still ask you to do this sometimes ! debugging – my skills are just not there yet Oracle Old tech: VB 6, XSLT, WinForms, Net 3.51 or less Old style Web dev Information Systems: ASP.NET webforms, Reporting services / crystal reports, SQL Server CRUD with manual data layer, XAML MVVM – variations of the same concept, ad nauseaum. Low barriers of entry –> race to the bottom.  Metro – an elegant API coupled to a horrendous UX – I'll wait for market penetration viability before investing further in this.   Conclusion So if you are in a slump, take heart: Programming is a great career choice compared to every other job !

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• How to deal with overly aggressive "Link Take Down Demands"?

  - by Eoin

  I've been receiving a large number of emails recently requesting I clean from link spam from my forum. Initially the emails were very polite and professional, and I was happy to remove the links. Recently the email have gotten very abrasive, here is a particularly rude example: From: [email protected] To: [email protected] Hi, This is the second time we are reaching out to you regarding your link to our site hxxp://www.company-two.com from hxxp://www.my-forum.com/some-topic-id. We really do need to remove this link. We have to report to Google any link we were unable to remove, and I wouldn't want to have to include your site in the list. Could you please remove our link from this page and any other page on your site? Thank You, Name Changed Behind the superficial pleasantries I feel there is some very real maliciousness. Note the email address, DMCA Violations, I don't see how the DMCA is involved here, except as a word which tends to strike fear in many people. Also relating to the email address, it doesn't match the company being linked to at all. How am I to trust they are truely operating on behalf of company-two when they don't even use one of it's email addresses. My email is hidden by privacypost. While a service with legitimate uses, I feel it's highly unprofessional for communications between to companies. The claim "This is the second time..." Every email I've received has started like this, but a check of my spam filters has never revealed a 1st mail. Initially I gave them the benefit of the doubt, by now though it's clear this is a cheap ploy to start me off on the defensive. And finally worst of all- the threats of reporting me to Google if I don't do everything they ask. I sent a polite reply asking for more information. I have no idea if the email address was even valid but I never received any response. Much later I got this followup mail From: [email protected] To: [email protected] Hi, This is the final time we are reaching out to you regarding your link to our site hxxp://www.company-two.com from hxxp://www.my-forum.com/some-topic-id. We will soon be reporting to Google any link we were unable to remove, and currently your site will have to be on the list. Could you please remove our link from this page and any other page on your site? I appreciate your urgent attention to this matter. Thank You, Name Changed This time the from address was more personal, though still not obviously connected to the spammed company. Lets be honest, I don't for one second believe that the companies were the victim of a 3rd party spammer as they claim. The links in questions were generated well over a year ago, and I firmly believe the companies were directly responsible for the spam links in question, a type of spam that has plagued my forum. Now they have the audacity to demand I spend my time cleaning up their mess, using threats to ensure they get their way. Have recent changes in Googles algorithms meant all the cash they spent spamming the web has now turned into a liability? If so I can see why these companies are all of a sudden running scared. Frankly, cleaning up my forum is a good things, but the threats they are using sickens me. So my question here is specifically about the threats: Are they vaild, and would such reports to Google destroy my page rankings? Is there a way I can report this abusive behaviour to Google?

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• Experimenting with other search engines

  - by Bill Graziano

  I’ve been a Google user so long I can hardly remember what I used before it.  Alta Vista maybe?  Or Yahoo.  I’ve tried Bing off and on but it never really stuck.  I probably care more about search engines than your average user because of their impact on SQLTeam.com.  Lately I’ve been trying two other search engines and actually switched to one of them. I’ve played with Blekko a little in the past.  They have some interesting ways to “slice up” your results.  For example, searching on “SQL Server /blogs /date” should just search all the recently updated blogs.  Those two extra words on the search are slashtags.  The full list of slashtags runs from /forums to just see forums to /twitter to /nikon to /reviews and on and on and on.  I laughed when I saw they had slashtags for both liberal and conservative.  I’d hate to find any search results that don’t match my existing worldview :)  You can also create your own slashtags.  I created a mini-search engine for the SQL Server blogs that I read.  You can search it for “backup” at http://blekko.com/ws/backup+/billgraziano/sql-sites.  I uploaded my OPML and it limited the search to just those sites.  It seems like the site is focusing more on curating results and less on algorithms.  This is an interesting site for those power searchers.  There are some great ways to curate results using slashtags.  For 99% of my searches (type words, click on one of the first few links) slashtags are overkill.  They do have some good information on page and site ranking though so I’ll probably send some time looking through that. Blekko recently got my attention again when they said they were banning “content farms” - and that includes eHow and experts-exchange.  I always feel used when I click on a link to EE and find myself scrolling all the way to the bottom to see if I can find the answer.  Sometimes it’s there but sometimes it tells me I need to pay first.  I’ve longed for a way to always exclude certain sites.  Blekko might be taking a hammer to a problem that needs a scalpel but it’s an interesting choice.  (And some of the comments in the TechCrunch link are interesting if you’re a search nerd.) DuckDuckGo is an odd name for a search engine.  Their big hook is that they don’t have search history.  If you wade through your Google account you can probably find the page where it stores your search history.  It was pretty enlightening to find mine.  It was easy to disable but that got me started looking at other search engines.  DDG (or DukGo) just feels like Google used to in the old days.  The results are good enough and the site is fast. Searches will return a snippet from WikiPedia or other site (like StackOverflow) at the top.  I think the idea is to answer the question without needing to visit the site.  I’m not sure that’s a good thing for SQLTeam.com. The only thing I really miss is image search.  You can add a “!i” at the end of any search and it will search the images on Bing.  Bing doesn’t have a great image search but it works for most of what I need.  They call these exclamation marks “!bangs” and they are kinda, sorta like slashtags.  I’ve been using DuckDuckGo now for a few weeks and I’m pretty happy with it.  I use Chrome for my browser and it was an easy switch to make.  It’s still a little surprising seeing my search results come up in a different format.  I’m starting to get used to it though.

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• Questions to ask to ensure someone understands programming? (and iOS)

  - by Stephen J

  So, I've been tutoring my friend for 2 years. Most people learn programming on their own in 3-6 months, (sans algorithms). It's confusing 'cause he'll run anywhere I tell him to, understands how to read C and C++ honestly better than the average college student, and he'll modify and repeat anything I do... but for the love of god he doesn't move on to new things and he still has test anxiety. I've recently realized he's copied and toyed with existing, but not once gained an understanding of why. I was under the impression he was learning fast because he could write it, but when you say "Make a function that takes an NSString" and he says "How?" and I say "The same way you make ANY function that takes any parameter, NSString is just a type like int" and all I hear is "No, it's an NSString, it's a special thing." and we get into an arguing match 'cause I'm like "It's just a class like any other class, you've used them for months now" and blah... I've subconsciously avoided comprehension questions because of this. Anyway, if you have him copy a program and say "Just initialize it" "Where?" "I don't care, didLoad or initWithCoder or Awake from nib, anywhere it gets initialized" and "No, it has to be exactly where you had it!" "No it doesn't!" I'm sick of this, but he won't give up. So I'm done avoiding these yelling matches and becoming a sadist from now on. I would like some help in finding questions to ask him that force him to understand what he's doing. I'd like some help and any resources I can find. CQuestions looked like a good site, but now I need some iPhone stuff. For example: *What do properties do? How are they changed? How do you change the name of the getter? *Why are Booleans inefficent? What advantage does int have over a boolean and how does the bit-shift operator help? *What does Copy do to a string? *What's the difference between a view controller and a uiview? *Write a program from memory that displays blah on screen, and flashes each view one by one. From beginner up to intermediate, hobbyist with some algebra at most. I'm just looking for resources to work with. I left in backstory so you know to "twist" the questions so he doesn't know he's supposed to init a variable here or there, but has to figure it out, and learn why it goes "here" or that "anywhere is fine as long as it's". Sample programs, anything. I'm relatively open about this because, being a programmer, I seriously doubt he's the only one who has this issue. I'd like to know how others have overcome similar. What made things "click"? for you? Did you have a hard time finding answers on Google, and how did you learn a better way to find what you were looking for? (He's so exact, he'll search for how to write a checkers program with color X and Y inside a uiview, as his search string, instead of breaking it up into components, I need help with that too, and believe it is related). This type of problem has to remind one of us of someone they know. So, Exercises to force them to think? Ways we overcame this thing in the past? I greatly appreciate any help.

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• HERMES Medical Solutions Helps Save Lives with MySQL

  - by Bertrand Matthelié

  Normal 0 false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Cambria","serif"; mso-ascii-font-family:Cambria; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Cambria; mso-hansi-theme-font:minor-latin;} HERMES Medical Solutions was established in 1976 in Stockholm, Sweden, and is a leading innovator in medical imaging hardware/software products for health care facilities worldwide. HERMES delivers a plethora of different medical imaging solutions to optimize hospital workflow. Normal 0 false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Cambria","serif"; mso-ascii-font-family:Cambria; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Cambria; mso-hansi-theme-font:minor-latin;} HERMES advanced algorithms make it possible to detect the smallest changes under therapies important and necessary to optimize different therapeutic methods and doses. Challenges Fighting illness & disease requires state-of-the-art imaging modalities and software in order to diagnose accurately, stage disease appropriately and select the best treatment available. Selecting and implementing a new database platform that would deliver the needed performance, reliability, security and flexibility required by the high-end medical solutions offered by HERMES. Solution Decision to migrate from in-house database to an embedded SQL database powering the HERMES products, delivered either as software, integrated hardware and software solutions, or via the cloud in a software-as-a-service configuration. Evaluation of several databases and selection of MySQL based on its high performance, ease of use and integration, and low Total Cost of Ownership. On average, between 4 and 12 Terabytes of data are stored in MySQL databases underpinning the HERMES solutions. The data generated by each medical study is indeed stored during 10 years or more after the treatment was performed. MySQL-based HERMES systems also allow doctors worldwide to conduct new drug research projects leveraging the large amount of medical data collected. Hospitals and other HERMES customers worldwide highly value the “zero administration” capabilities and reliability of MySQL, enabling them to perform medical analysis without any downtime. Relying on MySQL as their embedded database, the HERMES team has been able to increase their focus on further developing their clinical applications. HERMES Medical Solutions could leverage the Oracle Financing payment plan to spread its investment over time and make the MySQL choice even more valuable. “MySQL has proven to be an excellent database choice for us. We offer high-end medical solutions, and MySQL delivers the reliability, security and performance such solutions require.” Jan Bertling, CEO.

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• Auto-organized / smart inventory system?

  - by VeXe

  for the past week I've been working on an inventory system with Unity3D. At first I got help from the guys at Design3 but it wasn't too long till we split path, because I really didn't like the way they did their code, it didn't have any smell of OOP whatsoever. I took it further steps ahead - items take more than one slot, advanced placement system (items tries their best to find the best close fit), local mouse system (mouse gets trapped in active bag area), etc. Here's a demo of my work. What we would like to have in our game, is an auto-organizing feature - not auto-sort. We want this feature because our inventory's going to be in 'real-time' - not like in Resident Evil 1,2,3 etc where you would pause the game and do things in your inventory. Now imagine your self in a sticky situation surrounded by zombies, and you don't have bullets, you look around, you see that there are bullets nearby on the ground, so you go for them and try to pick them up, but they don't fit! you look at your inventory and find out that if you reorganize some of the items, it will fit! - now the player - in that situation doesn't have time to reorganize because he's surrounded with zombies and will die if he stops and organizes the inventory to make space (remember inventory in real-time, no pausing) - wouldn't it be nice for that to happen automatically? - Yes! (I believe this has been implemented in some games like Dungeon siege or something, so sure it's doable) take a look at this picture for example: Yes, so if you auto-sort the issue you will get your spaces but it's bad because: 1- Expensive: it doesn't need a whole sort operation to free those spaces, in the first picture, just slide the red item at the bottom to the very left, and you get the same spaces that you got from the auto-sort. 2- It's annoying to the player: "Who the F told you to re-order my stuff?" I'm not asking for "How to write the code" for this, I'm just asking for some guidance, where to look, what algorithms are involved? Is this something related to graphs and shortest path stuff? I hope not cuz I didn't manage to continue my college studies :/ But even if it is, just tell me and I will learn the stuff related. Notice there could be more than just one solution. So I guess the first thing I have to do is figure out if the situation is 'solvable' - if I know how to determine if a situation is solvable or not, then I can 'solve' it. I just need to know the conditions that makes it 'solvable'. And I believe there must be some algorithm/data structure for this. Here's a pic for more than one solution of trying to fit a 1x3 item: The arrows show just one of the solutions, but if you look you will find more than one. This is what I ultimately not auto-sorting but find a solution and applying it. Note that if I spend time on it I will come up with a way to solve it, but it wouldn't be the best way, it's like, holding a car wheel with your feet instead of your hands! XD Or just like trying to solve an issue that requires arrays, but you're not yet aware of their existence! So what is the right approach to this? Hope somebody helps, thanks a lot in advance :)

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• How do you go from a so so programmer to a great one? [closed]

  - by Cervo

  How do you go from being an okay programmer to being able to write maintainable clean code? For example David Hansson was writing Basecamp when in the process he created Rails as part of writing Basecamp in a clean/maintainable way. But how do you know when there is value in a side project like that? I have a bachelors in computer science, and I am about to get a masters and I will say that colleges teach you to write code to solve problems, not neatly or anything. Basically you think of a problem, come up with a solution, and write it down...not necessarily the most maintainable way in the world. Also my first job was in a startup, and now my third is in a small team in a large company where the attitude was/is get it done yesterday (also most of my jobs are mainly database development with SQL with a few ASP.NET web pages/.NET apps on the side). So of course cut/paste is more favored than making things more cleanly. And they would rather have something yesterday even if you have to rewrite it next month rather than to have something in a week that lasts for a year. Also spaghetti code turns up all over the place, and it takes very smart people to write/understand/maintain spaghetti code...However it would be better to do things so simple/clean that even a caveman/woman could do maintenance. Also I get very bored/unmotivated having to go modify the same things cut/pasted in a few locations. Is this the type of skill that you need to learn by working with a serious software organization that has an emphasis on maintenance and maybe even an architect who designs a system architecture and reviews code? Could you really learn it by volunteering on an open source project (it seems to me that a full time programmer job is way more practice than a few hours a week on an open source project)? Is there some course where you can learn this? I can attest that graduate school and undergraduate school do not really emphasize clean software at all. They just teach the structures/algorithms and then send you off into the world to solve problems. Overall I think the first thing is learning to write clean/maintainable code within the bounds of the project in order to become a good programmer. Then the next thing is learning when you need to do a side project (like a framework) to make things more maintainable/clean even while you still deliver things for the deadline in order to become a great programmer. For example, you are making an SQL report and someone gives you 100 calculations for individual columns. At what point does it make sense to construct a domain specific language to encode the rules in simply and then generate all the SQL as opposed to cut/pasting the query from the table a bunch of times and then adjusting each query to do the appropriate calculations. This is the type of thing I would say a great programmer would know. He/she would maybe even know ways to avoid the domain specific language and to still do all the calculations without creating an unmaintainable mess or a ton of repetitive code to cut/paste everywhere.

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• Reading graph inputs for a programming puzzle and then solving it

  - by Vrashabh

  I just took a programming competition question and I absolutely bombed it. I had trouble right at the beginning itself from reading the input set. The question was basically a variant of this puzzle http://codercharts.com/puzzle/evacuation-plan but also had an hour component in the first line(say 3 hours after start of evacuation). It reads like this This puzzle is a tribute to all the people who suffered from the earthquake in Japan. The goal of this puzzle is, given a network of road and locations, to determine the maximum number of people that can be evacuated. The people must be evacuated from evacuation points to rescue points. The list of road and the number of people they can carry per hour is provided. Input Specifications Your program must accept one and only one command line argument: the input file. The input file is formatted as follows: the first line contains 4 integers n r s t n is the number of locations (each location is given by a number from 0 to n-1) r is the number of roads s is the number of locations to be evacuated from (evacuation points) t is the number of locations where people must be evacuated to (rescue points) the second line contains s integers giving the locations of the evacuation points the third line contains t integers giving the locations of the rescue points the r following lines contain to the road definitions. Each road is defined by 3 integers l1 l2 width where l1 and l2 are the locations connected by the road (roads are one-way) and width is the number of people per hour that can fit on the road Now look at the sample input set 5 5 1 2 3 0 3 4 0 1 10 0 2 5 1 2 4 1 3 5 2 4 10 The 3 in the first line is the additional component and is defined as the number of hours since the resuce has started which is 3 in this case. Now my solution was to use Dijisktras algorithm to find the shortest path between each of the rescue and evac nodes. Now my problem started with how to read the input set. I read the first line in python and stored the values in variables. But then I did not know how to store the values of the distance between the nodes and what DS to use and how to input it to say a standard implementation of dijikstras algorithm. So my question is two fold 1.) How do I take the input of such problems? - I have faced this problem in quite a few competitions recently and I hope I can get a simple code snippet or an explanation in java or python to read the data input set in such a way that I can input it as a graph to graph algorithms like dijikstra and floyd/warshall. Also a solution to the above problem would also help. 2.) How to solve this puzzle? My algorithm was: Find shortest path between evac points (in the above example it is 14 from 0 to 3) Multiply it by number of hours to get maximal number of saves Also the answer given for the variant for the input set was 24 which I dont understand. Can someone explain that also. UPDATE: I get how the answer is 14 in the given problem link - it seems to be just the shortest path between node 0 and 3. But with the 3 hour component how is the answer 24 UPDATE I get how it is 24 - its a complete graph traversal at every hour and this is how I solve it Hour 1 Node 0 to Node 1 - 10 people Node 0 to Node 2- 5 people TotalRescueCount=0 Node 1=10 Node 2= 5 Hour 2 Node 1 to Node 3 = 5(Rescued) Node 2 to Node 4 = 5(Rescued) Node 0 to Node 1 = 10 Node 0 to Node 2 = 5 Node 1 to Node 2 = 4 TotalRescueCount = 10 Node 1 = 10 Node 2= 5+4 = 9 Hour 3 Node 1 to Node 3 = 5(Rescued) Node 2 to Node 4 = 5+4 = 9(Rescued) TotalRescueCount = 9+5+10 = 24 It hard enough for this case , for multiple evac and rescue points how in the world would I write a pgm for this ?

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• Hopcroft–Karp algorithm in Python

  - by Simon

  I am trying to implement the Hopcroft Karp algorithm in Python using networkx as graph representation. Currently I am as far as this: #Algorithms for bipartite graphs import networkx as nx import collections class HopcroftKarp(object): INFINITY = -1 def __init__(self, G): self.G = G def match(self): self.N1, self.N2 = self.partition() self.pair = {} self.dist = {} self.q = collections.deque() #init for v in self.G: self.pair[v] = None self.dist[v] = HopcroftKarp.INFINITY matching = 0 while self.bfs(): for v in self.N1: if self.pair[v] and self.dfs(v): matching = matching + 1 return matching def dfs(self, v): if v != None: for u in self.G.neighbors_iter(v): if self.dist[ self.pair[u] ] == self.dist[v] + 1 and self.dfs(self.pair[u]): self.pair[u] = v self.pair[v] = u return True self.dist[v] = HopcroftKarp.INFINITY return False return True def bfs(self): for v in self.N1: if self.pair[v] == None: self.dist[v] = 0 self.q.append(v) else: self.dist[v] = HopcroftKarp.INFINITY self.dist[None] = HopcroftKarp.INFINITY while len(self.q) > 0: v = self.q.pop() if v != None: for u in self.G.neighbors_iter(v): if self.dist[ self.pair[u] ] == HopcroftKarp.INFINITY: self.dist[ self.pair[u] ] = self.dist[v] + 1 self.q.append(self.pair[u]) return self.dist[None] != HopcroftKarp.INFINITY def partition(self): return nx.bipartite_sets(self.G) The algorithm is taken from http://en.wikipedia.org/wiki/Hopcroft%E2%80%93Karp_algorithm However it does not work. I use the following test code G = nx.Graph([ (1,"a"), (1,"c"), (2,"a"), (2,"b"), (3,"a"), (3,"c"), (4,"d"), (4,"e"),(4,"f"),(4,"g"), (5,"b"), (5,"c"), (6,"c"), (6,"d") ]) matching = HopcroftKarp(G).match() print matching Unfortunately this does not work, I end up in an endless loop :(. Can someone spot the error, I am out of ideas and I must admit that I have not yet fully understand the algorithm, so it is mostly an implementation of the pseudo code on wikipedia

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• Do SEO-friendly URLs really affect a page's ranking?

  - by Lee Harold

  SEO-friendly URLs are all the rage these days. But do they actually have a meaningful impact on a page's ranking in Google and other search engines? If so, why? If not, why not? (Note that I would absolutely agree that SEO-friendly URLs are nicer to use for human beings. My question is whether they actually make a difference to the ranking algorithms.) Update: As it turns out, the Google post that endorphine points to here has caused tremendous confusion in the SEO community. For a sampling of the discussion, see here, here, and here. Part of the problem is that the Google post is addressing the worst case where URL rewriting is done poorly and so you'd be better off sticking with a dynamic URL rather than a mangled static "SEO-friendly" URL. There's no question dynamic URLs can be crawled by Google and can achieve high rankings. Maybe it would be easier to reframe the question more concretely: given 2 otherwise equivalent pages, which will rank higher for the search "do seo friendly urls really affect page ranking"? A) http://stackoverflow.com/questions/505793/do-seo-friendly-urls-really-affect-a-pages-ranking or B) http://stackoverflow.com?question=505793 (a fake URL for comparison only)

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• Algorithm design, "randomising" timetable schedule in Python although open to other languages.

  - by S1syphus

  Before I start I should add I am a musician and not a native programmer, this was undertook to make my life easier. Here is the situation, at work I'm given a new csv file each which contains a list of sound files, their length, and the minimum total amount of time they must be played. I create a playlist of exactly 60 minutes, from this excel file. Each sample played the by the minimum number of instances, but spread out from each other; so there will never be a period where for where one sound is played twice in a row or in close proximity to itself. Secondly, if the minimum instances of each song has been used, and there is still time with in the 60 min, it needs to fill the remaining time using sounds till 60 minutes is reached, while adhering to above. The smallest duration possible is 15 seconds, and then multiples of 15 seconds. Here is what I came up with in python and the problems I'm having with it, and as one user said its buggy due to the random library used in it. So I'm guessing a total rethink is on the table, here is where I need your help. Whats is the best way to solve the issue, I have had a brief look at things like knapsack and bin packing algorithms, while both are relevant neither are appropriate and maybe a bit beyond me.

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• Most useful free .NET libraries?

  - by Binoj Antony

  I have used a lot of free .NET libraries, some from Microsoft itself! Which ones have you found the most useful? Dependency Injection/Inversion of Control Unity Framework - Microsoft StructureMap - Jeremy Miller Castle Windsor NInject Spring Framework Autofac Managed Extensibility Framework Logging Logging Application Block - Microsoft Log4Net - Apache Error Logging Modules and Handlers(ELMAH) NLog Compression SharpZipLib DotNetZip YUI Compressor (CSS and JS compression/minification) AjaxMinifier (in other downloads) (JS compression. Also includes MSBuild task) Ajax Ajax Control Toolkit - Microsoft AJAXNet Pro Data Mapper XmlDataMapper AutoMapper ORM NHibernate Castle ActiveRecord Subsonic XmlDataMapper Charting/Graphics Microsoft Chart Controls for ASP.NET 3.5 SP1 Microsoft Chart Controls for Winforms ZedGraph Charting NPlot - Charting for ASP.NET and WinForms PDF Creators/Generators PDFsharp iTextSharp Unit Testing/Mocking NUnit Rhino Mocks Moq TypeMock.Net xUnit.net mbUnit Machine.Specifications Automated Web Testing Selenium Watin URL Rewriting url rewriter UrlRewriting.Net Url Rewriter and Reverse Proxy - Managed Fusion Controls Krypton - Free winform controls Source Grid - A Grid control Devexpress - free controls Unclassified CSLA Framework - Business Objects Framework AForge.net - AI, computer vision, genetic algorithms, machine learning Enterprise Library 4.1 - Logging, Exception Management, Validation, Policy Injection File helpers library C5 Collections - Collections for .NET Quartz.NET - Enterprise Job Scheduler for .NET Platform MiscUtil - Utilities by Jon Skeet Lucene.net - Text indexing and searching Json.NET - Linq over JSON Flee - expression evaluator PostSharp - AOP IKVM - brings the extensive world of Java libraries to .NET. Title of the question taken from here. [EDIT] Please provide links to these free libraries as well. Once we have a huge list of this, it can be arranged in categories! Please do not mention .NET Applications/EXEs here.

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• how to tackle this combinatorial algorithm problem

  - by Andrew Bullock

  I have N people who must each take T exams. Each exam takes "some" time, e.g. 30 min (no such thing as finishing early). Exams must be performed in front of an examiner. I need to schedule each person to take each exam in front of an examiner within an overall time period, using the minimum number of examiners for the minimum amount of time (i.e. no examiners idle) There are the following restrictions: No person can be in 2 places at once each person must take each exam once noone should be examined by the same examiner twice I realise that an optimal solution is probably NP-Complete, and that I'm probably best off using a genetic algorithm to obtain a best estimate (similar to this? http://stackoverflow.com/questions/184195/seating-plan-software-recommendations-does-such-a-beast-even-exist). I'm comfortable with how genetic algorithms work, what i'm struggling with is how to model the problem programatically such that i CAN manipulate the parameters genetically.. If each exam took the same amount of time, then i'd divide the time period up into these lengths, and simply create a matrix of time slots vs examiners and drop the candidates in. However because the times of each test are not necessarily the same, i'm a bit lost on how to approach this. currently im doing this: make a list of all "tests" which need to take place, between every candidate and exam start with as many examiners as there are tests repeatedly loop over all examiners, for each one: find an unscheduled test which is eligible for the examiner (based on the restrictions) continue until all tests that can be scheduled, are if there are any unscheduled tests, increment the number of examiners and start again. i'm looking for better suggestions on how to approach this, as it feels rather crude currently.

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• Merge method in MergeSort Algorithm .

  - by Tony

  I've seen many mergeSort implementations .Here is the version in Data Structures and Algorithms in Java (2nd Edition) by Robert Lafore : private void recMergeSort(long[] workSpace, int lowerBound,int upperBound) { if(lowerBound == upperBound) // if range is 1, return; // no use sorting else { // find midpoint int mid = (lowerBound+upperBound) / 2; // sort low half recMergeSort(workSpace, lowerBound, mid); // sort high half recMergeSort(workSpace, mid+1, upperBound); // merge them merge(workSpace, lowerBound, mid+1, upperBound); } // end else } // end recMergeSort() private void merge(long[] workSpace, int lowPtr, int highPtr, int upperBound) { int j = 0; // workspace index int lowerBound = lowPtr; int mid = highPtr-1; int n = upperBound-lowerBound+1; // # of items while(lowPtr <= mid && highPtr <= upperBound) if( theArray[lowPtr] < theArray[highPtr] ) workSpace[j++] = theArray[lowPtr++]; else workSpace[j++] = theArray[highPtr++]; while(lowPtr <= mid) workSpace[j++] = theArray[lowPtr++]; while(highPtr <= upperBound) workSpace[j++] = theArray[highPtr++]; for(j=0; j<n; j++) theArray[lowerBound+j] = workSpace[j]; } // end merge() One interesting thing about merge method is that , almost all the implementations didn't pass the lowerBound parameter to merge method . lowerBound is calculated in the merge . This is strange , since lowerPtr = mid + 1 ; lowerBound = lowerPtr -1 ; that means lowerBound = mid ; Why the author didn't pass mid to merge like merge(workSpace, lowerBound,mid, mid+1, upperBound); ? I think there must be a reason , otherwise I can't understand why an algorithm older than half a center ,and have all coincident in the such little detail.

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• Dealing with huge SQL resultset

  - by Dave McClelland

  I am working with a rather large mysql database (several million rows) with a column storing blob images. The application attempts to grab a subset of the images and runs some processing algorithms on them. The problem I'm running into is that, due to the rather large dataset that I have, the dataset that my query is returning is too large to store in memory. For the time being, I have changed the query to not return the images. While iterating over the resultset, I run another select which grabs the individual image that relates to the current record. This works, but the tens of thousands of extra queries have resulted in a performance decrease that is unacceptable. My next idea is to limit the original query to 10,000 results or so, and then keep querying over spans of 10,000 rows. This seems like the middle of the road compromise between the two approaches. I feel that there is probably a better solution that I am not aware of. Is there another way to only have portions of a gigantic resultset in memory at a time? Cheers, Dave McClelland

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• SHA512 vs. Blowfish and Bcrypt

  - by Chris

  I'm looking at hashing algorithms, but couldn't find an answer. Bcrypt uses Blowfish Blowfish is better than MD5 Q: but is Blowfish better than SHA512? Thanks.. Update: I want to clarify that I understand the difference between hashing and encryption. What prompted me to ask the question this way is this article, where the author refers to bcrypt as "adaptive hashing" http://chargen.matasano.com/chargen/2007/9/7/enough-with-the-rainbow-tables-what-you-need-to-know-about-s.html Since bcrypt is based on Blowfish, I was led to think that Blowfish is a hashing algorithm. If it's encryption as answers have pointed out, then seems to me like it shouldn't have a place in this article. What's worse is that he's concluding that bcrypt is the best. What's also confusing me now is that the phpass class (used for password hashing I believe) uses bcrypt (i.e. blowfish, i.e. encryption). Based on this new info you guys are telling me (blowfish is encryption), this class sounds wrong. Am I missing something?

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• Schliemann's method of programming language learning

  - by DVK

  Background: 19th-century German archeologist Heinrich Schliemann was of course famous for his successful quest to find and excavate the city of Troy (an actual archeological site for the Troy of Homer's Iliad). However, he is just as famous for being an astonishing learner of languages - within the space of two years, he taught himself fluent Dutch, English, French, Spanish, Italian and Portuguese, and later went on to learn seven more, including both modern and ancient Greek. One of the methods he famously used was comparison of a known text, e.g. take a book in a language one is fluent in, take a good translation of a book in a language you wish to learn, and go over them in parallel. (various sources cited the book used by Schliemann to be the Bible, or, as the link above states, a novel). Now, for the actual question. Has anyone used (or heard of) an equivalent of Schliemann's method for learning a new programming language? E.g. instead of basing the leaning on references and tutorials, take a somewhat comprehensive set of programs known to have high-quality code in both languages implementing similar/identical algorithms and learn by comparing them? I'm curious about either personal experiences of applying such an approach, or references to something published, or existance of codebases which could be used for such an approach? What got me thinking about the idea was Project Euler and some code snippets I saw on SO, in C++, Perl and Lisp.

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• Sample uniformly at random from an n-dimensional unit simplex.

  - by dreeves

  Sampling uniformly at random from an n-dimensional unit simplex is the fancy way to say that you want n random numbers such that they are all non-negative, they sum to one, and every possible vector of n non-negative numbers that sum to one are equally likely. In the n=2 case you want to sample uniformly from the segment of the line x+y=1 (ie, y=1-x) that is in the positive quadrant. In the n=3 case you're sampling from the triangle-shaped part of the plane x+y+z=1 that is in the positive octant of R3: (Image from http://en.wikipedia.org/wiki/Simplex.) Note that picking n uniform random numbers and then normalizing them so they sum to one does not work. You end up with a bias towards less extreme numbers. Similarly, picking n-1 uniform random numbers and then taking the nth to be one minus the sum of them also introduces bias. Wikipedia gives two algorithms to do this correctly: http://en.wikipedia.org/wiki/Simplex#Random_sampling (Though the second one currently claims to only be correct in practice, not in theory. I'm hoping to clean that up or clarify it when I understand this better. I initially stuck in a "WARNING: such-and-such paper claims the following is wrong" on that Wikipedia page and someone else turned it into the "works only in practice" caveat.) Finally, the question: What do you consider the best implementation of simplex sampling in Mathematica (preferably with empirical confirmation that it's correct)? Related questions http://stackoverflow.com/questions/2171074/generating-a-probability-distribution http://stackoverflow.com/questions/3007975/java-random-percentages

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• Perf: Viewing thousands of images in Silverlight 3 on a 3D Wall

  - by Bob Holland

  I currently work on a very cool Silverlight app that displays photos in a 3D wall space like the Wall3D demo that is thrown in with Blend 3. The problem I am currently facing is performance. The app works like this: As you scroll right or left the 3d photo wall rotates As each movement is made, the next column of photos are downloaded, decoded into a BitmapImage and thrown into a 3D Wall Node. As you can imagine users (if you let them) will want to flip through the photos really quickly, but the problem I have is I cannot display the photos quick enough. In most cases it's a beautiful app that works really well, but when an album contains over 300 photos, you can imagine the sort of memory taken up by all the BitmapImage classes and how moving the slider can jump from photo 20 to photo 120 in a second. Of course we have algorithms in place to not download every photo in between, but I still can't work out a fast way to get the photos displayed. It may be a case that we need to throw away the 'great for show' 3D wall and go to a flat DeepZoom like wall like the Playboy archive one that Vertigo did. Still not sure, let me know your thoughts. P.S. We are using Kit3D for all the 3D work, it's using PerspectiveCamera, Model3DGroup, ModelVisual3D, RotateTransform3D & TranslateTransform3D. Cheers, Bob.

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• Instantiating a list of parameterized types, making beter use of Generics and Linq

  - by DanO

  I'm hashing a file with one or more hash algorithms. When I tried to parametrize which hash types I want, it got a lot messier than I was hoping. I think I'm missing a chance to make better use of generics or LINQ. I also don't like that I have to use a Type[] as the parameter instead of limiting it to a more specific set of type (HashAlgorithm descendants), I'd like to specify types as the parameter and let this method do the constructing, but maybe this would look better if I had the caller new-up instances of HashAlgorithm to pass in? public List<string> ComputeMultipleHashesOnFile(string filename, Type[] hashClassTypes) { var hashClassInstances = new List<HashAlgorithm>(); var cryptoStreams = new List<CryptoStream>(); FileStream fs = File.OpenRead(filename); Stream cryptoStream = fs; foreach (var hashClassType in hashClassTypes) { object obj = Activator.CreateInstance(hashClassType); var cs = new CryptoStream(cryptoStream, (HashAlgorithm)obj, CryptoStreamMode.Read); hashClassInstances.Add((HashAlgorithm)obj); cryptoStreams.Add(cs); cryptoStream = cs; } CryptoStream cs1 = cryptoStreams.Last(); byte[] scratch = new byte[1 << 16]; int bytesRead; do { bytesRead = cs1.Read(scratch, 0, scratch.Length); } while (bytesRead > 0); foreach (var stream in cryptoStreams) { stream.Close(); } foreach (var hashClassInstance in hashClassInstances) { Console.WriteLine("{0} hash = {1}", hashClassInstance.ToString(), HexStr(hashClassInstance.Hash).ToLower()); } }

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• Reinforcement learning toy project

  - by Betamoo

  My toy project to learn & apply Reinforcement Learning is: - An agent tries to reach a goal state "safely" & "quickly".... - But there are projectiles and rockets that are launched upon the agent in the way. - The agent can determine rockets position -with some noise- only if they are "near" - The agent then must learn to avoid crashing into these rockets.. - The agent has -rechargable with time- fuel which is consumed in agent motion - Continuous Actions: Accelerating forward - Turning with angle I need some hints and names of RL algorithms that suit that case.. - I think it is POMDP , but can I model it as MDP and just ignore noise? - In case POMDP, What is the recommended way for evaluating probability? - Which is better to use in this case: Value functions or Policy Iterations? - Can I use NN to model environment dynamics instead of using explicit equations? - If yes, Is there a specific type/model of NN to be recommended? - I think Actions must be discretized, right? I know it will take time and effort to learn such a topic, but I am eager to.. You may answer some of the questions if you can not answer all... Thanks

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• Is there any open source tool that automatically 'detects' email threading like Gmail?

  - by Chris W.

  For instance, if the original message (message 1) is... Hey Jon, Want to go get some pizza? -Bill And the reply (message 2) is... Bill, Sorry, I can't make lunch today. Jonathon Parks, CTO Acme Systems On Wed, Feb 24, 2010 at 4:43 PM, Bill Waters wrote: Hey John, Want to go get some pizza? -Bill In Gmail, the system (a) detects that message 2 is a reply to message 1 and turns this into a 'thread' of sorts and (b) detects where the replied portion of the message actually is and hides it from the user. (In this case the hidden portion would start at "On Wed, Feb..." and continue to the end of the message.) Obviously, in this simple example it would be easy to detect the "On <Date, <Name wrote:" or the "" character prefixes. But many email systems have many different style of marking replies (not to mention HTML emails). I get the feeling that you would have to have some damn smart string parsing algorithms to get anywhere near how good GMail's is. Does this technology already exist in an open source project somewhere? Either in some library devoted to this exclusively or perhaps in some open source email client that does similar message threading? Thanks.

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• Optimized graph drawing for the web

  - by Andreas Petersson

  Having seen some suggestions for graphs, I wonder what's the optimum for my problem. I want to render a directed graph to a servlet/picture that is displayed in the browser. There should be some kind of optimization of position. No dependency to Swing would be preferred. Algorithms are not important, since the structure of the graph is determined by business logic. It would be desired to be able add labels to edges as well. it would be optimal if i can serve this as png/svg. Which library/service would you recommend? clarifications: 1) The question is all about Graphs - like Directed Acyclic Graph - NOT - Charts. 2) flot, Google Charts - cannot plot graphs, only charts, or have i missed something? 3) no i do not need interactivity 4) graphviz would be nice, but the grappa java library is quite outdated and is built upon swing/awt. while it may be theoretically possible to render swing to images, it would not be my favorite way to to so in a server-app. 5) it would be fine to use an online service where the images are not hosted locally. edit: added links to Wikipedia to clarify graph/chart term

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