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  • Why is it still so hard to write software?

    - by nornagon
    Writing software, I find, is composed of two parts: the Idea, and the Implementation. The Idea is about thinking: "I have this problem; how do I solve it?" and further, "how do I solve it elegantly?" The answers to these questions are obtainable by thinking about algorithms and architecture. The ideas come partially through analysis and partially through insight and intuition. The Idea is usually the easy part. You talk to your friends and co-workers and you nut it out in a meeting or over coffee. It takes an hour or two, plus revisions as you implement and find new problems. The Implementation phase of software development is so difficult that we joke about it. "Oh," we say, "the rest is a Simple Matter of Code." Because it should be simple, but it never is. We used to write our code on punch cards, and that was hard: mistakes were very difficult to spot, so we had to spend extra effort making sure every line was perfect. Then we had serial terminals: we could see all our code at once, search through it, organise it hierarchically and create things abstracted from raw machine code. First we had assemblers, one level up from machine code. Mnemonics freed us from remembering the machine code. Then we had compilers, which freed us from remembering the instructions. We had virtual machines, which let us step away from machine-specific details. And now we have advanced tools like Eclipse and Xcode that perform analysis on our code to help us write code faster and avoid common pitfalls. But writing code is still hard. Writing code is about understanding large, complex systems, and tools we have today simply don't go very far to help us with that. When I click "find all references" in Eclipse, I get a list of them at the bottom of the window. I click on one, and I'm torn away from what I was looking at, forced to context switch. Java architecture is usually several levels deep, so I have to switch and switch and switch until I find what I'm really looking for -- by which time I've forgotten where I came from. And I do that all day until I've understood a system. It's taxing mentally, and Eclipse doesn't do much that couldn't be done in 1985 with grep, except eat hundreds of megs of RAM. Writing code has barely changed since we were staring at amber on black. We have the theoretical groundwork for much more advanced tools, tools that actually work to help us comprehend and extend the complex systems we work with every day. So why is writing code still so hard?

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  • How to interpret weka classification?

    - by gargi2010
    How can we interpret the classification result in weka using naive bayes? How is mean, std deviation, weight sum and precision calculated? How is kappa statistic, mean absolute error, root mean squared error etc calculated? What is the interpretation of the confusion matrix?

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  • Performance Optimization for Matrix Rotation

    - by Summer_More_More_Tea
    Hello everyone: I'm now trapped by a performance optimization lab in the book "Computer System from a Programmer's Perspective" described as following: In a N*N matrix M, where N is multiple of 32, the rotate operation can be represented as: Transpose: interchange elements M(i,j) and M(j,i) Exchange rows: Row i is exchanged with row N-1-i A example for matrix rotation(N is 3 instead of 32 for simplicity): ------- ------- |1|2|3| |3|6|9| ------- ------- |4|5|6| after rotate is |2|5|8| ------- ------- |7|8|9| |1|4|7| ------- ------- A naive implementation is: #define RIDX(i,j,n) ((i)*(n)+(j)) void naive_rotate(int dim, pixel *src, pixel *dst) { int i, j; for (i = 0; i < dim; i++) for (j = 0; j < dim; j++) dst[RIDX(dim-1-j, i, dim)] = src[RIDX(i, j, dim)]; } I come up with an idea by inner-loop-unroll. The result is: Code Version Speed Up original 1x unrolled by 2 1.33x unrolled by 4 1.33x unrolled by 8 1.55x unrolled by 16 1.67x unrolled by 32 1.61x I also get a code snippet from pastebin.com that seems can solve this problem: void rotate(int dim, pixel *src, pixel *dst) { int stride = 32; int count = dim >> 5; src += dim - 1; int a1 = count; do { int a2 = dim; do { int a3 = stride; do { *dst++ = *src; src += dim; } while(--a3); src -= dim * stride + 1; dst += dim - stride; } while(--a2); src += dim * (stride + 1); dst -= dim * dim - stride; } while(--a1); } After carefully read the code, I think main idea of this solution is treat 32 rows as a data zone, and perform the rotating operation respectively. Speed up of this version is 1.85x, overwhelming all the loop-unroll version. Here are the questions: In the inner-loop-unroll version, why does increment slow down if the unrolling factor increase, especially change the unrolling factor from 8 to 16, which does not effect the same when switch from 4 to 8? Does the result have some relationship with depth of the CPU pipeline? If the answer is yes, could the degrade of increment reflect pipeline length? What is the probable reason for the optimization of data-zone version? It seems that there is no too much essential difference from the original naive version. EDIT: My test environment is Intel Centrino Duo processor and the verion of gcc is 4.4 Any advice will be highly appreciated! Kind regards!

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  • installing mysql on mac os x 10.4 powerpc

    - by Slinky
    Hi, I have an old Mac G4 PowerPc, running OSX 10.4.11 MySQL no longer has DMG installation package for PowerPC. I would like to install MySQL on this machine - What's the best way to go about it? This machine currently does not have an install of mysql. Thanks

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  • DirectShow Filter Graph Editor doesn't show remote graphs

    - by vucetica
    I have a problem with connecting to remote graph from DirectShow Filter Graph Editor. When I run application that creates a direct show graph, on my Windows XP machine graph is shown in the list of remote graphs, but on the Windows 7 (x64) machine list of remote graphs is empty. I have registered proppage.dll and also registered directshowspy.dll ... but still no results. Any ideas?

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  • How can one extract rdf:about or rdf:ID properties from triples using SPARQL?

    - by lennyks
    It seemed a trivial matter at the beginning but so far I have not managed to get the unique identifier for a given resource using SPARQL. What I mean is given, e.g., rdf:Description rdf:about="http://..." and then some properties identifying this resource, what I want to do is to first find this very resource and then retrieve all the triples given some URI. I have tried naïve approaches by writing statements in a WHERE clause such as: ?x rdf:about ?y and ?x rdfs:about ?y I hope I am being precise.

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  • Why a different SHA-1 for the same file under windows or linux?

    - by Fabio Vitale
    Why on the same machine computing the SHA-1 hash of the same file produces two completely different SHA-1 hashes in windows and inside a msysgit Git bash? Doesn't the SHA-1 algorithm was intended to produce the same hash for the same file in all OSes? On windows (with HashCheck): File hello.txt 22596363b3de40b06f981fb85d82312e8c0ed511 Inside a msysgit's Git bash windows (same machine, same file): $ git hash-object hello.txt 3b18e512dba79e4c8300dd08aeb37f8e728b8dad

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  • Connection Multiplexing

    - by whoi
    Hi; Supposing we have opened a connection of type either TCP or UDP to another remote machine. Having this connection, can we allow multiple connections virtually over this connection like VPN(but not VPN)? I mean multiple applications run on remote machine and you try to access to these applications, is there any multiplexing mechanism or concept supporting such feature?

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  • How do I send email over SMTP with SSL using Java client?

    - by Ido
    I need to send email over smtp with ssl using java client. I'm not sure how to do that. If I have my server certificate installed on my Windows machine, how do I use it? If I want it to work on a non-Windows machine, do I need to get the certificates in a different way? BTW: If the SMTP server that I use is using SSL, can I be sure that it will send the mail to the recipient using SSL?

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  • Crash Reporting Utility for Windows 7, MFC Application

    - by nimo
    hi, I'm having a MFC application (VS 2008) which is going to be deployed on Windows 7 machine. I need to distribute my application with debugging information, so that a debugable core will be generated in case of application crash event. Can somebody please let me know how can I achieve this purpose ? I have read about minidump utility, just would like to whether there is a better way of generating coredump on windows 7 machine Thank you

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  • How to catch 'exceptions' for out of order execution in Workflow Foundation 4?

    - by Alex Key
    Hi, I am attempting to model a worklfow using a "WCF Workflow Service" in .net / vs 2010 that needs to handle out of order execution gracefully (but not allow it - if thath makes sense!?) For example I have 2 receive activities one called Initialize and the other called GetValue inside a FlowChart. In most cases Initialize should be called first and GetValue after (as modled in the flow chart). However if GetValue is executed before Initialize I do not want to return an "out of order" exception (although when I look at the WCF test client, I can't actually see an exception). But instead a custom exception saying something like "you must initialize first". In theory I could model this with lots of parallel activities and conditions to check if Initialized / Running / Terminated etc. But the business process I am modelling if very very similar to a state machine... except it must handle people executing things in the wrong order. Ideally I would like to catch the "out of order" exception (thought I don't think it's really an exception as such), check the 'exception' to see which function was attempted to run and then handle it. I have done some research around enabling AllowBufferedReceive. However I don't want to be able to execute out of order (I don't think), but instead give a detailed response if it does happen. I've looked at the new beta state machine template for WF 4 - but i'm not sure if it does what i'm after? I'm not sure if I have the wrong end of the stick, so any help would be greatly appreciated. [EDIT] To help clarify... Sorry it's a tricky one to explain. The standard I am trying to implement (the e-learning standard SCORM RTE) is structured like a state machine i.e. certain functions can only be executed in certain states. However the standard specifies that if the calling clients tries to execute a function that it is not meant to, then a warning should be issued... for example "you cannot use GetValue(), because you have not yet Initialized". Ideally I'd like to structure the workflow as the theoretical state machine and not need to have to use multiple if/else's to handle all the scenarios where something could be executed out-of-order. I'd like to catch a out-of-order exception (but I don't think there is such an exception - as it's not in the debugger) and rethrow it.

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  • Proxy setings for web service(client or service hosted server)

    - by tc
    I am trying to add the a web service through Web reference, i am able to find the service while trying to add it, not able to add, the option is disabled. I suspect this is because of the proxy settings, What do you suggest? While mentioning he proxy in the the client application which proxy should i mention,the proxy of my machine in which client application is hosted which is consuming the web service or the proxy of the machine in which the web service is hosted?

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  • Escaping Code for Different Shells

    - by Jon Purdy
    Question: What characters do I need to escape in a user-entered string to securely pass it into shells on Windows and Unix? What shell differences and version differences should be taken into account? Can I use printf "%q" somehow, and is that reliable across shells? Backstory (a.k.a. Shameless Self-Promotion): I made a little DSL, the Vision Web Template Language, which allows the user to create templates for X(HT)ML documents and fragments, then automatically fill them in with content. It's designed to separate template logic from dynamic content generation, in the same way that CSS is used to separate markup from presentation. In order to generate dynamic content, a Vision script must defer to a program written in a language that can handle the generation logic, such as Perl or Python. (Aside: using PHP is also possible, but Vision is intended to solve some of the very problems that PHP perpetuates.) In order to do this, the script makes use of the @system directive, which executes a shell command and expands to its output. (Platform-specific generation can be handled using @unix or @windows, which only expand on the proper platform.) The problem is obvious, I should think: test.htm: <!-- ... --> <form action="login.vis" method="POST"> <input type="text" name="USERNAME"/> <input type="password" name="PASSWORD"/> </form> <!-- ... --> login.vis: #!/usr/bin/vision # Think USERNAME = ";rm -f;" @system './login.pl' { USERNAME; PASSWORD } One way to safeguard against this kind of attack is to set proper permissions on scripts and directories, but Web developers may not always set things up correctly, and the naive developer should get just as much security as the experienced one. The solution, logically, is to include a @quote directive that produces a properly escaped string for the current platform. @system './login.pl' { @quote : USERNAME; @quote : PASSWORD } But what should @quote actually do? It needs to be both cross-platform and secure, and I don't want to create terrible problems with a naive implementation. Any thoughts?

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  • Seam on Linux Problems

    - by Anand
    Hi, When a seam application on JBOSS using java 1,5 is deployed in Unix platform, I am getting this error. errorjava.lang.NoClassDefFoundError at java.lang.Class.forName0(Native Method) at java.lang.Class.forName(Class.java:141) at java.awt.GraphicsEnvironment.getLocalGraphicsEnvironment(GraphicsEnvi ronment.java:62) It runs fine on windows platform. On my local linux machine it runs fine. but on another linux machine it works some times and sometimes it throws up the above error

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  • How can one extra rdf:about or rdf:ID properties from triples using SPARKQL?

    - by lennyks
    It seemed a trivial matter at the beginning but so far I had not managed to get unique identifier for a given resource using SPARKQL. What I mean is given and then some properties identifiying this resource in perfect world I want to first know how to retrieve an individual triple given some uri. I have tried naive approaches by writing statements in a WHERE clause such as ?x rdf:about ?y and ?x rdfs:about ?y. I hope I am being precise.

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  • Receiving UDP broadcasts on multihomed systems

    - by theller
    I have a Windows XP machine with more than one network adapter. When I receive a UDP broadcast package from another machine that does not yet have a valid IP address, howcan I determine which network adapter received this package? I need to implement a kind on custom DHCP server...

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  • SharePoint Transferring pages to Production

    - by bmw0128
    I am building an internet site, using my local machine as the development box (I have MOSS 2007 installed). I have a custom master page, packaged in a WSP, so I may use STSADM on the production server to install it. I have made some pages via SPD (on my local machine) and put them in the "Pages" gallery. What is the recommended way to get these pages to production. Also, is the process the same when I make edits to current pages?

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  • Building two different versions a given war with maven profiles and filtering from eclipse

    - by balteo
    I am trying to use maven profiles and filtering in order to produce two different versions of a given web archive (war): A first one for local deployment to my local machine on localhost A second one for remote deployment to cloudfoundry There are a number of properties that differ according to whether the app is deployed to my local machine or to cloudfoundry. Of course the difficult bit is that I am trying to do all this from STS/Eclipse and deploy from Eclipse to my local tomcat and to cloudfoundry... Can anyone please provide advice, tips or suggestions?

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  • Running Java CORBA Client on Unix

    - by Benny
    I'm trying to run a Java application I wrote to subscribe to a CORBA event service. It runs OK on my Windows machine, but as soon as I deploy it to the UNIX server, it gives me an org.omg.CORBA.NO_IMPLEMENT exception. Any ideas as to why this might be happening? I'm using JacORB on my Windows machine and passing VM arguments to initialize the client ORB, but I'm not sure how to do that on UNIX and if it's even necessary. Thanks in advance!

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  • State server in webfarm scenario?

    - by Curtis White
    This is a fairly basic question about state server but assume there are 2 servers behind a load balancer. How do I configure the session state server? So, I have machine1 and machine2. I would assume that I would need to install the state server on 1 machine only and then use the internal IP to refer to that machine. Is this correct? As oppose too, I would not install state server on both machines.

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