Search Results

Search found 7583 results on 304 pages for 'roger guess'.

Page 250/304 | < Previous Page | 246 247 248 249 250 251 252 253 254 255 256 257  | Next Page >

  • How would you code an efficient Circular Buffer in Java or C#

    - by Cheeso
    I want a simple class that implements a fixed-size circular buffer. It should be efficient, easy on the eyes, generically typed. EDIT: It need not be MT-capable, for now. I can always add a lock later, it won't be high-concurrency in any case. Methods should be: .Add and I guess .List, where I retrieve all the entries. On second thought, Retrieval I think should be done via an indexer. At any moment I will want to be able to retrieve any element in the buffer by index. But keep in mind that from one moment to the next Element[n] may be different, as the Circular buffer fills up and rolls over. This isn't a stack, it's a circular buffer. Regarding "overflow": I would expect internally there would be an array holding the items, and over time the head and tail of the buffer will rotate around that fixed array. But that should be invisible from the user. There should be no externally-detectable "overflow" event or behavior. This is not a school assignment - it is most commonly going to be used for a MRU cache or a fixed-size transaction or event log.

    Read the article

  • Ajax request (from .NET) give me unexpected results

    - by ironnailpiercethesky
    I wanted to learn a little more about web and .NET so i decided to write a program to download binaries, webpages and does a little ajax. The first download site i tried was too easy. So i went against uploading.com. It seemed good, no captcha, some ajax use required, you cant guess all the data, it was perfect. After 2hours of messing around i got frustrated. For the life of me i could not get the ajax response to give me what i was expecting. I decided to use tamper data clear my cookies, click on the entry for the ajax request. Copy the Referer, cookies and postdata and came up with this code. It does not work! I am shocked that copying those fields did not work. I even tried setting the user agent (not in code linked) and it still did not work. Why isnt this POST on the ajax request not giving me the correct file? I notice the JsHttpRequest=12719132559480-xml changes based on time so if you want to run the code you should grab a new snapshot with tamperdata (or at least update that url). I dont see any extra headers in tamper data so does anyone know why i might not be getting the response expected? I know disabling cookies or javascript will make the link 'expired' automatically. I dont think javascript will matter because i got the data from tamperdata at the moment of request so what gives? What am i forgetting or what data am i not submitting properly?

    Read the article

  • What is the merit of the "function" type (not "pointer to function")

    - by anatolyg
    Reading the C++ Standard, i see that there are "function" types and "pointer to function" types: typedef int func(int); // function typedef int (*pfunc)(int); // pointer to function typedef func* pfunc; // same as above I have never seen the function types used outside of examples (or maybe i didn't recognize their usage?). Some examples: func increase, decrease; // declares two functions int increase(int), decrease(int); // same as above int increase(int x) {return x + 1;} // cannot use the typedef when defining functions int decrease(int x) {return x - 1;} // cannot use the typedef when defining functions struct mystruct { func add, subtract, multiply; // declares three member functions int member; }; int mystruct::add(int x) {return x + member;} // cannot use the typedef int mystruct::subtract(int x) {return x - member;} int main() { func k; // the syntax is correct but the variable k is useless! mystruct myobject; myobject.member = 4; cout << increase(5) << ' ' << decrease(5) << '\n'; // outputs 6 and 4 cout << myobject.add(5) << ' ' << myobject.subtract(5) << '\n'; // 9 and 1 } Seeing that the function types support syntax that doesn't appear in C (declaring member functions), i guess they are not just a part of C baggage that C++ has to support for backward compatibility. So is there any use for function types, other than demonstrating some funky syntax?

    Read the article

  • User to kernel mode big picture?

    - by fsdfa
    I've to implement a char device, a LKM. I know some basics about OS, but I feel I don't have the big picture. In a C programm, when I call a syscall what I think it happens is that the CPU is changed to ring0, then goes to the syscall vector and jumps to a kernel memmory space function that handle it. (I think that it does int 0x80 and in eax is the offset of the syscall vector, not sure). Then, I'm in the syscall itself, but I guess that for the kernel is the same process that was before, only that it is in kernel mode, I mean the current PCB is the process that called the syscall. So far... so good?, correct me if something is wrong. Others questions... how can I write/read in process memory?. If in the syscall handler I refer to address, say, 0xbfffffff. What it means that address? physical one? Some virtual kernel one?

    Read the article

  • How to retrieve view of MultiIndex DataFrame

    - by Henry S. Harrison
    This question was inspired by this question. I had the same problem, updating a MultiIndex DataFrame by selection. The drop_level=False solution in Pandas 0.13 will allow me to achieve the same result, but I am still wondering why I cannot get a view from the MultiIndex DataFrame. In other words, why does this not work?: >>> sat = d.xs('sat', level='day', copy=False) Traceback (most recent call last): File "<stdin>", line 1, in <module> File "C:\Python27\lib\site-packages\pandas\core\frame.py", line 2248, in xs raise ValueError('Cannot retrieve view (copy=False)') ValueError: Cannot retrieve view (copy=False) Of course it could be only because it is not implemented, but is there a reason? Is it somehow ambiguous or impossible to implement? Returning a view is more intuitive to me than returning a copy then later updating the original. I looked through the source and it seems this situation is checked explicitly to raise an error. Alternatively, is it possible to get the same sort of view from any of the other indexing methods? I've experimented but have not been successful. [edit] Some potential implementations are discussed here. I guess with the last question above I'm wondering what the current best solution is to index into arbitrary multiindex slices and cross-sections.

    Read the article

  • REST from asp.net 2.0

    - by weslleywang
    Hi, I just built a asp.net 2.0 web site. Now I need add REST web service so I can communicate with another web application. I've worked with 2 SOAP web service project before, but have no experise with REST at all. I guess only a coupleweeks would works fine. after googling, I found it's not that easy. This is what I found: There is NO REST out of box of asp.net. WCF REST Starter Kit Codeplex Preview 2 base on .net 3.5 and still in beta Rest ASP.NET Example REST Web Services in ASP.NET 2.0 (C#) Exyus Handling POST and PUT methods with Lullaby ADO.NET Data Service ... Now my question, a) Is a REST solution for .net 2.0? if yes, which one is best solution? b) if I have to, how hard to migrate my asp.net from 2.0 to 3.5? is it as simple as just compile, or I have to change a lot code? c) WCF REST Starter Kit is good enough to use in production? d) Do I have to learn WCF first, then WCF REST Starter Kit? where is the best place to start? I appreciate any help here. Thanks Wes

    Read the article

  • How to debug an external library (OpenCV) in Visual C++?

    - by neuviemeporte
    I am developing a project in VC++2008. The project uses the OpenCV library (but I guess this applies to any other library). I am working with the Debug configuration, the linker properties include the debug versions of the library .lib's as additional dependencies. In VC++ Directories under Tools|Options i set up the include directory, the .lib directory, the source directories for the library as well. I get an error while calling one of the functions from the library and I'd like to see exactly what that function is doing. The line that produces the error is: double error = cvStereoCalibrate(&calObjPointsM, &img1PointsM, &img2PointsM, &pointCountsM, &cam1M, &dist1M, &cam2M, &dist2M, imgSize, &rotM, &transM, NULL, NULL, cvTermCriteria(CV_TERMCRIT_ITER + CV_TERMCRIT_EPS, 100, 1e-5)); I set up a breakpoint at this line to see how the cvStereoCalibrate() function fails. Unfortunately the debugger won't show the source code for this function when I hit "Step into". It skips immediately to the cvTermCriteria() (which is a simple inline, macro-kinda function) and show its contents. Is there anything else I need to do to be able to enter the external library functions in the debugger? EDIT: I think the cvTermCriteria() function shows in the debugger, because it's defined in a header file, therefore immediately accesible to the project.

    Read the article

  • Fast, Unicode-capable, cross-platform programmer's text editor that shows invisibles like ZWSP?

    - by Roger_S
    Our publishing workflow includes Windows and Linux machines (there are some Macs too, but not in the critical-path workflow). Many texts include both English and Khmer and are marked-up in XML. XML Copy Editor is the best cross-platform open-source XML editor I've discovered. It utilizes the Scintilla editing component, which is generally good with Unicode but which does not enable non-printing or invisible characters like U+200B (zero-width space) and U+200C (zero-width non-joiner) to be displayed. Khmer does not separate words with a space character as Western languages do, so ZWSP is used in electronic texts to enable applications to break lines easily. Ideally I'd edit the markup and the content in a single editor, but XML awareness is less important at times than being able to display invisibles. (OpenOffice.org Writer and Microsoft Word are the only two apps I know that will display ZWSP. They are not suitable for the markup and text manipulations that need to be done to prepare manuscripts for publication, unfortunately, although I guess they're fine for authoring.) I tried out a promising editor last week, but a search-and-replace regex operation that took under a second in TextPad 4.7.3 lasted over twenty seconds. So I want to mention that speed and the ability to handle large (up to 150mb) files is also a concern. Is there a good, fast, free or not too expensive text editor, with versions on Windows and Linux and maybe mac too, Unicode-aware and capable of displaying invisibles like ZWSP? That has syntax highlighting, can handle large files and is customizable enough that I won't tear my hair out in frustration? Thanks, Roger_S

    Read the article

  • PHP OOP: Avoid Singleton/Static Methods in Domain Model Pattern

    - by sunwukung
    I understand the importance of Dependency Injection and its role in Unit testing, which is why the following issue is giving me pause: One area where I struggle not to use the Singleton is the Identity Map/Unit of Work pattern (Which keeps tabs on Domain Object state). //Not actual code, but it should demonstrate the point class Monitor{//singleton construction omitted for brevity static $members = array();//keeps record of all objects static $dirty = array();//keeps record of all modified objects static $clean = array();//keeps record of all clean objects } class Mapper{//queries database, maps values to object fields public function find($id){ if(isset(Monitor::members[$id]){ return Monitor::members[$id]; } $values = $this->selectStmt($id); //field mapping process omitted for brevity $Object = new Object($values); Monitor::new[$id]=$Object return $Object; } $User = $UserMapper->find(1);//domain object is registered in Id Map $User->changePropertyX();//object is marked "dirty" in UoW // at this point, I can save by passing the Domain Object back to the Mapper $UserMapper->save($User);//object is marked clean in UoW //but a nicer API would be something like this $User->save(); //but if I want to do this - it has to make a call to the mapper/db somehow $User->getBlogPosts(); //or else have to generate specific collection/object graphing methods in the mapper $UserPosts = $UserMapper->getBlogPosts(); $User->setPosts($UserPosts); Any advice on how you might handle this situation? I would be loathe to pass/generate instances of the mapper/database access into the Domain Object itself to satisfy DI - At the same time, avoiding that results in lots of calls within the Domain Object to external static methods. Although I guess if I want "save" to be part of its behaviour then a facility to do so is required in its construction. Perhaps it's a problem with responsibility, the Domain Object shouldn't be burdened with saving. It's just quite a neat feature from the Active Record pattern - it would be nice to implement it in some way.

    Read the article

  • Class initialization and synchronized class method

    - by nybon
    Hi there, In my application, there is a class like below: public class Client { public synchronized static print() { System.out.println("hello"); } static { doSomething(); // which will take some time to complete } } This class will be used in a multi thread environment, many threads may call the Client.print() method simultaneously. I wonder if there is any chance that thread-1 triggers the class initialization, and before the class initialization complete, thread-2 enters into print method and print out the "hello" string? I see this behavior in a production system (64 bit JVM + Windows 2008R2), however, I cannot reproduce this behavior with a simple program in any environments. In Java language spec, section 12.4.1 (http://java.sun.com/docs/books/jls/second_edition/html/execution.doc.html), it says: A class or interface type T will be initialized immediately before the first occurrence of any one of the following: T is a class and an instance of T is created. T is a class and a static method declared by T is invoked. A static field declared by T is assigned. A static field declared by T is used and the reference to the field is not a compile-time constant (§15.28). References to compile-time constants must be resolved at compile time to a copy of the compile-time constant value, so uses of such a field never cause initialization. According to this paragraph, the class initialization will take place before the invocation of the static method, however, it is not clear if the class initialization need to be completed before the invocation of the static method. JVM should mandate the completion of class initialization before entering its static method according to my intuition, and some of my experiment supports my guess. However, I did see the opposite behavior in another environment. Can someone shed me some light on this? Any help is appreciated, thanks.

    Read the article

  • [OT a bit] Flex+JEE what is it good for?

    - by Zenzen
    Ok so sorry for being, I guess, a bit off topic but still I think this is the best place to ask. My new semester just started (don't worry I won't ask you to do my homework) and this time we have a rather cool subject about www programming in general where we have to do a web service, web abb - whatever as long as it's "web". Here's the problem though, my team and I want to do it with Flex and JEE but we don't have much experience about what are they actually used for. I mean we know you can do virtually anything with it, but we don't really want to lose time on doing something useless. My first idea was to do a "brainstorming" 3D room/service - a place where people could log in have a video conference, a whiteboard, a place to upload pictures everyone could see, some toolbars for google, youtube etc. plus some other features which would make real-time brainstorming easy when you can't get everyone in one place. But is Flex+JEE really suitable? I mean I'm 99% sure it's doable but is it really worth doing it in Flex+JEE or was the whole purpose of JEE completely different? @EDIT: well this was only one of our ideas obviously. I do know the basics of JSP, Servlets, JPA etc. of course but yeah the main goal of this project is to get some actual experience. The problem is we don't really know is it worth doing something like let's say a social network (something like extended facebook) for gamers (doesn't really matter if it already exists) in JEE or would it only look ridiculous (because PHP or whatever would be a far better choice)? Bottom line is that we are wondering are only large scale applications (for banks etc.) written in JEE or is it good for anything (even the smaller projects)?

    Read the article

  • Can't diagnose my MySQL root user problem

    - by George Crawford
    Hi all, I have a problem with the MySQL root user in My MySQL setup, and I just can't for the life of me work out how to fix it. It seems that I have somehow messed up the root user, and my access to databases is now very erratic. For reference, I'm using MAMP on OS X to provide the MySQL server. I'm not sure how much that matters though - I'd guess that whatever I've done will require a command-line fix to solve it. I can start MySQL using MAMP as usual, and access databases using the 'standard' users I have created for my PHP apps. However, the root user, which I use in my MySQL GUI client, and also in phpMyAdmin, can only access the "information_schema" database, as well as two I have created manually, and presumably (and mistakenly) left permissions wide open for. My 15 or so other databases cannot be accessed my the root user. When I load up phpMyAdmin, the home screen says: "Create new database: No Privileges". I certainly did at some stage change my root user's password using the MAMP dialog. But I don't remember if I did anything else which might have caused this problem. I've tried changing the password again, and there seems to be no change in the issue. I've also tried resetting root password using the command line, including starting mysql manually with --skip-grant-tables then flushing privs, but again, nothing seems to fix the issue. I've come to the end of my ideas, and would very much appreciate some step-by-step advice and diagnosis from one of the experts here! Many thanks for your help.

    Read the article

  • strcmp() but with 0-9 AFTER A-Z? (C/C++)

    - by Aaron
    For reasons I completely disagree with but "The Powers (of Anti-Usability) That Be" continue to decree despite my objections, I have a sorting routine which does basic strcmp() compares to sort by its name. It works great; it's hard to get that one wrong. However, at the 11th hour, it's been decided that entries which begin with a number should come AFTER entries which begin with a letter, contrary to the ASCII ordering. They cite the EBCDIC standard has numbers following letters so the prior assumption isn't a universal truth, and I have no power to win this argument... but I digress. Therein lies my problem. I've replaced all appropriate references to strcmp with a new function call nonstd_strcmp, and now need to implement the modifications to accomplish the sort change. I've used a FreeBSD source as my base: http://freebsd.active-venture.com/FreeBSD-srctree/newsrc/libkern/strncmp.c.html if (n == 0) return (0); do { if (*s1 != *s2++) return (*(const unsigned char *)s1 - *(const unsigned char *)(s2 - 1)); if (*s1++ == 0) break; } while (--n != 0); return (0); I guess I might need to take some time away to really think about how it should be done, but I'm sure I'm not the only one who's experienced the brain-deadness of just-before-release spec changes.

    Read the article

  • Attach an entity that is not new, perhaps having been loaded from another DataContext. LINQ to SQL -

    - by soldieraman
    Alright How I got this error I got one application sitting on a server 2 users accessing this application - doing some bulk data processing . eg. entering values and then the application is working with another system to extract values for them and then saving. I can't recreate the error The error logs show: The error happend at the same time in both the application Both happend on a Attach/Submit (but two different functions) There is no way they are using the same DataContext object as I save the DataContext in the HttpContext.Items My hunch / guess is: One datacontext was not refreshed i.e. the an object was created for the same item twice as it was new in both the forms. eg. Customer Number - a customer was created (as one couldn't be found) by one datacontext - the other one couldn't find it either (i am using compiled queries to find it in the datacontext) so it created another object and on attaching failed. The HttpContext.Items lost its value somehow (i am using a virtual pc as server - maybe something went wrong there) I am going more of the second as I can't recreate the error - but it just might be a timing (for attach/save) thing - also the error makes me think of the 2nd too.

    Read the article

  • Why doesn't the Java Collections API include a Graph implementation?

    - by dvanaria
    I’m currently learning the Java Collections API and feel I have a good understanding of the basics, but I’ve never understood why this standard API doesn’t include a Graph implementation. The three base classes are easily understandable (List, Set, and Map) and all their implementations in the API are mostly straightforward and consistent. Considering how often graphs come up as a potential way to model a given problem, this just doesn’t make sense to me (it’s possible it does exist in the API and I’m not looking in the right place of course). Steve Yegge suggests in one of his blog posts that a programmer should consider graphs first when attacking a problem, and if the problem domain doesn’t fit naturally into this data structure, only then consider the alternative structures. My first guess is that there is no universal way to represent graphs, or that their interfaces may not be generic enough for an API implementation to be useful? But if you strip down a graph to its basic components (vertices and a set of edges that connect some or all of the vertices) and consider the ways that graphs are commonly constructed (methods like addVertex(v) and insertEdge(v1, v2)) it seems that a generic Graph implementation would be possible and useful. Thanks for helping me understand this better.

    Read the article

  • Searching in graphs trees with Depth/Breadth first/A* algorithms

    - by devoured elysium
    I have a couple of questions about searching in graphs/trees: Let's assume I have an empty chess board and I want to move a pawn around from point A to B. A. When using depth first search or breadth first search must we use open and closed lists ? This is, a list that has all the elements to check, and other with all other elements that were already checked? Is it even possible to do it without having those lists? What about A*, does it need it? B. When using lists, after having found a solution, how can you get the sequence of states from A to B? I assume when you have items in the open and closed list, instead of just having the (x, y) states, you have an "extended state" formed with (x, y, parent_of_this_node) ? C. State A has 4 possible moves (right, left, up, down). If I do as first move left, should I let it in the next state come back to the original state? This, is, do the "right" move? If not, must I transverse the search tree every time to check which states I've been to? D. When I see a state in the tree where I've already been, should I just ignore it, as I know it's a dead end? I guess to do this I'd have to always keep the list of visited states, right? E. Is there any difference between search trees and graphs? Are they just different ways to look at the same thing?

    Read the article

  • Haskell Cons Operator (:)

    - by Carson Myers
    I am really new to Haskell (Actually I saw "Real World Haskell" from O'Reilly and thought "hmm, I think I'll learn functional programming" yesterday) and I am wondering: I can use the construct operator to add an item to the beginning of a list: 1 : [2,3] [1,2,3] I tried making an example data type I found in the book and then playing with it: --in a file data BillingInfo = CreditCard Int String String | CashOnDelivery | Invoice Int deriving (Show) --in ghci $ let order_list = [Invoice 2345] $ order_list [Invoice 2345] $ let order_list = CashOnDelivery : order_list $ order_list [CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, ...- etc... it just repeats forever, is this because it uses lazy evaluation? -- EDIT -- okay, so it is being pounded into my head that let order_list = CashOnDelivery:order_list doesn't add CashOnDelivery to the original order_list and then set the result to order_list, but instead is recursive and creates an infinite list, forever adding CashOnDelivery to the beginning of itself. Of course now I remember that Haskell is a functional language and I can't change the value of the original order_list, so what should I do for a simple "tack this on to the end (or beginning, whatever) of this list?" Make a function which takes a list and BillingInfo as arguments, and then return a list? -- EDIT 2 -- well, based on all the answers I'm getting and the lack of being able to pass an object by reference and mutate variables (such as I'm used to)... I think that I have just asked this question prematurely and that I really need to delve further into the functional paradigm before I can expect to really understand the answers to my questions... I guess what i was looking for was how to write a function or something, taking a list and an item, and returning a list under the same name so the function could be called more than once, without changing the name every time (as if it was actually a program which would add actual orders to an order list, and the user wouldn't have to think of a new name for the list each time, but rather append an item to the same list).

    Read the article

  • Developing on a windows machine that interacts with a linux system

    - by Jamie
    Sorry for the bad title (couldn't think of a better way to describe it) I have a windows machine which I do development on. However, I have a new project which needs to interact with a linux system (executing linux commands etc.). So, obviously I can't do development on my windows machine..and I don't wish to code on the dev machine, svn commit and then svn update it on the linux machine. Is there a way where any changes I make on my dev machine will be quickly mirrored to the linux machine? SVN is not a very quick alternative and of course some changes will be very minor. Any ideas? A network share I guess....but that's not very pretty (bit slow too). As fellow developers I would like to know if you've been in a similar situation and how you've resolved it. On a furthernote, I can't just install Ubuntu as my development machine and mirror the commands, applications etc. from the linux machine because it's a cluster 'master' machine and so therefore it has quite a special configuration. Thanks guys! EDIT: I've also thought about having web services on the linux machine and then just calling them from code thus seperating platform development dependency. What do you think about that too? thanks

    Read the article

  • How to define a batching routing service in WCF

    - by mattx
    I have designed a custom silverlight wcf channel that I want to leverage to selectively batch calls from the client to the server and possibly to cache on the client and short circuit calls. So far I'm just using this channel as a transport and sending the generic WCF messages that result to the WCF router service example here http://msdn.microsoft.com/en-us/magazine/cc500646.aspx?pr=blog to prototype this on the server side. So my scenario looks like this: IFooClient-MyTransportChannel-IRouterService-IFooService-Return I now need to be able to send more than one message per call through the router and carve them up and service them on the server side. Since this is just an experiment and I'm taking baby steps I will dispatch and service all the messages right away on the server side and return the batch of results. Immediately I noticed that simply making the router interface take Message[] instead of Message doesn't work due to serialization problems. I guess this makes sense. I'm not sure soap envelopes can contain other soap envelopes etc. Is there a simple way to take a collection of WCF Message objects and send them to a single method on a service where they can be split up and forwarded as appropriate? If not I'd love suggestions on how I should approach this. I want to have minimal work to do on the router service side so the goal should be to get as close to being able to "slice and forward" as possible.

    Read the article

  • JVM to ignore certificate name mismatch

    - by Heavy Bytes
    I know there were a lot of questions/answers about how to ignore SSL error in the code. On our dev region dev.domain.tld we have configured a app server over SSL. The certificate that is displayed is for somedev.domain.tld. There is no way to change the certificate, it will always be a domain mismatch. So when I deploy a web-service to https://dev.domain.tld and try to connect/call my webservice I get an exception: Caused by: java.security.cert.CertificateException: No name matching dev.domain.tld found And I have the somedev.domain.tld CERT in my trust store. Now, I saw a lot of samples how to change that in the code (using a Trust Manager that accepts all domains), but how do I specify to the JVM to ignore the domain mismatch when connecting to the server? Is there a -Djavax.net.ssl argument or something? Thank you! UPDATE: Or, since I am using Spring-WS, is there a way to set some property in Spring for that? (WebServiceTemplate) UPDATE I guess I'll have to do use something from Spring Security: http://static.springsource.org/spring-ws/sites/1.5/reference/html/security.html

    Read the article

  • Choosing design method for ladder-like word game.

    - by owca
    I'm trying to build a simple application, with the finished program looking like this : I will also have to implement two different GUI layouts for this. Now I'm trying to figure out the best method to perform this task. My professor told me to introduce Element class with 4 states : - empty - invisible (used in GridLayout) - first letter - other letter I've thought about following solutions (by List I mean any sort of Collection) : 1. Element is a single letter, and each line is Element[]. Game class will be array of arrays Element[]. I guess that's the dumbest way, and the validation might be troublesome. 2. Like previously but Line is a List of Element. Game is an array of Lines. 3. Like previously but Game is a List of Lines. Which one should I choose ? Or maybe do you have better ideas ? What collection would be best if to use one ?

    Read the article

  • Splitting a set of object into several subsets of 'similar' objects

    - by doublep
    Suppose I have a set of objects, S. There is an algorithm f that, given a set S builds certain data structure D on it: f(S) = D. If S is large and/or contains vastly different objects, D becomes large, to the point of being unusable (i.e. not fitting in allotted memory). To overcome this, I split S into several non-intersecting subsets: S = S1 + S2 + ... + Sn and build Di for each subset. Using n structures is less efficient than using one, but at least this way I can fit into memory constraints. Since size of f(S) grows faster than S itself, combined size of Di is much less than size of D. However, it is still desirable to reduce n, i.e. the number of subsets; or reduce the combined size of Di. For this, I need to split S in such a way that each Si contains "similar" objects, because then f will produce a smaller output structure if input objects are "similar enough" to each other. The problems is that while "similarity" of objects in S and size of f(S) do correlate, there is no way to compute the latter other than just evaluating f(S), and f is not quite fast. Algorithm I have currently is to iteratively add each next object from S into one of Si, so that this results in the least possible (at this stage) increase in combined Di size: for x in S: i = such i that size(f(Si + {x})) - size(f(Si)) is min Si = Si + {x} This gives practically useful results, but certainly pretty far from optimum (i.e. the minimal possible combined size). Also, this is slow. To speed up somewhat, I compute size(f(Si + {x})) - size(f(Si)) only for those i where x is "similar enough" to objects already in Si. Is there any standard approach to such kinds of problems? I know of branch and bounds algorithm family, but it cannot be applied here because it would be prohibitively slow. My guess is that it is simply not possible to compute optimal distribution of S into Si in reasonable time. But is there some common iteratively improving algorithm?

    Read the article

  • Hibernate does not allow an embedded object with an int field to be null?

    - by Jason Novak
    Hibernate does not allow me to persist an object that contains an null embedded object with an integer field. For example, if I have a class called Thing that looks like this @Entity public class Thing { @Id public String id; public Part part; } where Part is an embeddable class that looks like this @Embeddable public class Part { public String a; public int b; } then trying to persist a Thing object with a null Part causes Hibernate to throw an Exception. In particular, this code Thing th = new Thing(); th.id = "thing.1"; th.part = null; session.saveOrUpdate(th); causes Hibernate to throw this Exception org.hibernate.PropertyValueException: not-null property references a null or transient value: com.ace.moab.api.jobs.Thing.part My guess is that this is happening because Part is an embedded class and so Part.a and Part.b are simply columns in the Thing database table. Since the Thing.part is null Hibernate wants to set the Part.a and Part.b column values to null for the row for thing.1. However, Part.b is an integer and Hibernate will not allow integer columns in the database to be null. This is what causes the Exception, right? So I am looking for workarounds for this problem. I noticed making Part.b an Integer instead of an int seems to work, but for reasons I won't bore you with this is not a good option for us. Thanks!

    Read the article

  • What exactly does this PHP code do?

    - by Rob
    Alright, my friend gave me this code for requesting headers and comparing them to what the header should be. It works perfectly, but I'm not sure why. Here is the code: $headers = apache_request_headers(); $customheader = "Header: 7ddb6ffab28bb675215a7d6e31cfc759"; foreach ($headers as $header => $value) { // 1 $custom .= "$header: $value"; // 2 } $mystring = $custom; // 3 $findme = $customheader; // 4 $pos = strpos($mystring, $findme); if ($pos !== false) { // Do something } else{ exit(); } //If it doesn't match, exit. I commented with some numbers relating to the following questions: 1: What exactly is happening here? Is it setting the $headers as $header AND $value? 2: Again, don't have any idea what is going on here. 3: Why set the variable to a different variable? This is the only area where the variable is getting used, so is there a reason to set it to something else? 4: Same question as 3. I'm sorry if this is a terrible question, but its been bothering me, and I really want to know WHY it works. Well, I understand why it works, I guess I just want to know more specifically. Thanks for any insight you can provide.

    Read the article

  • Extremely CPU Intensive Alarm Clock

    - by SoulBeaver
    For some reason my program, a console alarm clock I made for laughs and practice, is extremely CPU intensive. It consumes about 2mB RAM, which is already quite a bit for such a small program, but it devastates my CPU with over 50% resources at times. Most of the time my program is doing nothing except counting down the seconds, so I guess this part of my program is the one that's causing so much strain on my CPU, though I don't know why. If it is so, could you please recommend a way of making it less, or perhaps a library to use instead if the problem can't be easily solved? /* The wait function waits exactly one second before returning to the * * called function. */ void wait( const int &seconds ) { clock_t endwait; // Type needed to compare with clock() endwait = clock() + ( seconds * CLOCKS_PER_SEC ); while( clock() < endwait ) {} // Nothing need be done here. } In case anybody browses CPlusPlus.com, this is a genuine copy/paste of the clock() function they have written as an example for clock(). Much why the comment //Nothing need be done here is so lackluster. I'm not entirely sure what exactly clock() does yet. The rest of the program calls two other functions that only activate every sixty seconds, otherwise returning to the caller and counting down another second, so I don't think that's too CPU intensive- though I wouldn't know, this is my first attempt at optimizing code. The first function is a console clear using system("cls") which, I know, is really, really slow and not a good idea. I will be changing that post-haste, but, since it only activates every 60 seconds and there is a noticeable lag-spike, I know this isn't the problem most of the time. The second function re-writes the content of the screen with the updated remaining time also only every sixty seconds. I will edit in the function that calls wait, clearScreen and display if it's clear that this function is not the problem. I already tried to reference most variables so they are not copied, as well as avoid endl as I heard that it's a little slow compared to \n.

    Read the article

< Previous Page | 246 247 248 249 250 251 252 253 254 255 256 257  | Next Page >