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  • What algorithms are suitable for this simple machine learning problem?

    - by user213060
    I have a what I think is a simple machine learning question. Here is the basic problem: I am repeatedly given a new object and a list of descriptions about the object. For example: new_object: 'bob' new_object_descriptions: ['tall','old','funny']. I then have to use some kind of machine learning to find previously handled objects that had similar descriptions, for example, past_similar_objects: ['frank','steve','joe']. Next, I have an algorithm that can directly measure whether these objects are indeed similar to bob, for example, correct_objects: ['steve','joe']. The classifier is then given this feedback training of successful matches. Then this loop repeats with a new object. a Here's the pseudo-code: Classifier=new_classifier() while True: new_object,new_object_descriptions = get_new_object_and_descriptions() past_similar_objects = Classifier.classify(new_object,new_object_descriptions) correct_objects = calc_successful_matches(new_object,past_similar_objects) Classifier.train_successful_matches(object,correct_objects) But, there are some stipulations that may limit what classifier can be used: There will be millions of objects put into this classifier so classification and training needs to scale well to millions of object types and still be fast. I believe this disqualifies something like a spam classifier that is optimal for just two types: spam or not spam. (Update: I could probably narrow this to thousands of objects instead of millions, if that is a problem.) Again, I prefer speed when millions of objects are being classified, over accuracy. What are decent, fast machine learning algorithms for this purpose?

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  • I'm having trouble with using std::stack to retrieve the values from a recursive function.

    - by Peter Stewart
    Thanks to the help I received in this post: http://stackoverflow.com/questions/2761918/how-do-i-use-this-in-a-member-function I have a nice, concise recursive function to traverse a tree in postfix order: void Node::postfix() { if (left != __nullptr) { left->postfix(); } if (right != __nullptr) { right->postfix(); } cout<<cargo<<"\n"; return; }; Now I need to evaluate the values and operators as they are returned. My problem is how to retrieve them. I tried the std::stack: #include <stack> stack <char*> s; void Node::postfix() { if (left != __nullptr) { left->postfix(); } if (right != __nullptr) { right->postfix(); } s.push(cargo); return; }; but when I tried to access it in main() while (!s.empty()) { cout<<s.top<<"\n"; s.pop; } I got the error: 'std::stack<_Ty::top': function call missing argument list; use '&std::stack<_Ty::top' to create a pointer to member' I'm stuck. Another question to follow shortly.

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  • Fast JSON serialization (and comparison with Pickle) for cluster computing in Python?

    - by user248237
    I have a set of data points, each described by a dictionary. The processing of each data point is independent and I submit each one as a separate job to a cluster. Each data point has a unique name, and my cluster submission wrapper simply calls a script that takes a data point's name and a file describing all the data points. That script then accesses the data point from the file and performs the computation. Since each job has to load the set of all points only to retrieve the point to be run, I wanted to optimize this step by serializing the file describing the set of points into an easily retrievable format. I tried using JSONpickle, using the following method, to serialize a dictionary describing all the data points to file: def json_serialize(obj, filename, use_jsonpickle=True): f = open(filename, 'w') if use_jsonpickle: import jsonpickle json_obj = jsonpickle.encode(obj) f.write(json_obj) else: simplejson.dump(obj, f, indent=1) f.close() The dictionary contains very simple objects (lists, strings, floats, etc.) and has a total of 54,000 keys. The json file is ~20 Megabytes in size. It takes ~20 seconds to load this file into memory, which seems very slow to me. I switched to using pickle with the same exact object, and found that it generates a file that's about 7.8 megabytes in size, and can be loaded in ~1-2 seconds. This is a significant improvement, but it still seems like loading of a small object (less than 100,000 entries) should be faster. Aside from that, pickle is not human readable, which was the big advantage of JSON for me. Is there a way to use JSON to get similar or better speed ups? If not, do you have other ideas on structuring this? (Is the right solution to simply "slice" the file describing each event into a separate file and pass that on to the script that runs a data point in a cluster job? It seems like that could lead to a proliferation of files). thanks.

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  • Wrapping FUSE from Go

    - by Matt Joiner
    I'm playing around with wrapping FUSE with Go. However I've come stuck with how to deal with struct fuse_operations. I can't seem to expose the operations struct by declaring type Operations C.struct_fuse_operations as the members are lower case, and my pure-Go sources would have to use C-hackery to set the members anyway. My first error in this case is "can't set getattr" in what looks to be the Go equivalent of a default copy constructor. My next attempt is to expose an interface that expects GetAttr, ReadLink etc, and then generate C.struct_fuse_operations and bind the function pointers to closures that call the given interface. This is what I've got (explanation continues after code): package fuse // #include <fuse.h> // #include <stdlib.h> import "C" import ( //"fmt" "os" "unsafe" ) type Operations interface { GetAttr(string, *os.FileInfo) int } func Main(args []string, ops Operations) int { argv := make([]*C.char, len(args) + 1) for i, s := range args { p := C.CString(s) defer C.free(unsafe.Pointer(p)) argv[i] = p } cop := new(C.struct_fuse_operations) cop.getattr = func(*C.char, *C.struct_stat) int {} argc := C.int(len(args)) return int(C.fuse_main_real(argc, &argv[0], cop, C.size_t(unsafe.Sizeof(cop)), nil)) } package main import ( "fmt" "fuse" "os" ) type CpfsOps struct { a int } func (me *CpfsOps) GetAttr(string, *os.FileInfo) int { return -1; } func main() { fmt.Println(os.Args) ops := &CpfsOps{} fmt.Println("fuse main returned", fuse.Main(os.Args, ops)) } This gives the following error: fuse.go:21[fuse.cgo1.go:23]: cannot use func literal (type func(*_Ctype_char, *_Ctype_struct_stat) int) as type *[0]uint8 in assignment I'm not sure what to pass to these members of C.struct_fuse_operations, and I've seen mention in a few places it's not possible to call from C back into Go code. If it is possible, what should I do? How can I provide the "default" values for interface functions that acts as though the corresponding C.struct_fuse_operations member is set to NULL?

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  • Getting parameters values blank and null when using custom wsdl in axis2

    - by Narendra
    Hi All, I am using axis2 for my web services creation. I want to user my own wsdl file instead of using generated wsdl file. When I am placing my own wsdl file in META-INF directory and deploying my web services they are deploying successfully. But the problem is when i try to test these web service using soapui it throwing null pointer exception. For example I am invoking following operations in soap ui. public String testWebService(String a, String b) { LogHelper.info("Value of a is:"+a); LogHelper.info("Value of b is :"+b); String c=a.trim()+b.Trim(); return "suceess" } output in console: value of a is: value of b is:null 19:58:47,781 ERROR [RPCMessageReceiver] Exception occurred while trying to invoke service method testWebService java.lang.reflect.InvocationTargetException at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at org.apache.axis2.rpc.receivers.RPCUtil.invokeServiceClass(RPCUtil.java:194) at org.apache.axis2.rpc.receivers.RPCMessageReceiver.invokeBusinessLogic(RPCMessageReceiver.java:102) at org.apache.axis2.receivers.AbstractInOutMessageReceiver.invokeBusinessLogic(AbstractInOutMessageReceiver.java:40) at org.apache.axis2.receivers.AbstractMessageReceiver.receive(AbstractMessageReceiver.java:114) at org.apache.axis2.engine.AxisEngine.receive(AxisEngine.java:173) at org.apache.axis2.transport.http.HTTPTransportUtils.processHTTPPostRequest(HTTPTransportUtils.java:173) at org.apache.axis2.transport.http.AxisServlet.doPost(AxisServlet.java:142) at javax.servlet.http.HttpServlet.service(HttpServlet.java:637) at javax.servlet.http.HttpServlet.service(HttpServlet.java:717) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:96) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:235) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191) at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:190) at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:92) at o...................................................... SO What i understand is i am getting value for a is black and value of b is null. Can any one give me any suggestions please. Thanks, Narendra

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  • java BufferedReader specific length returns NUL characters

    - by Bastien
    I have a TCP socket client receiving messages (data) from a server. messages are of the type length (2 bytes) + data (length bytes), delimited by STX & ETX characters. I'm using a bufferedReader to retrieve the two first bytes, decode the length, then read again from the same bufferedReader the appropriate length and put the result in a char array. most of the time, I have no problem, but SOMETIMES (1 out of thousands of messages received), when attempting to read (length) bytes from the reader, I get only part of it, the rest of my array being filled with "NUL" characters. I imagine it's because the buffer has not yet been filled. char[] bufLen = new char[2]; _bufferedReader.read(bufLen); int len = decodeLength(bufLen); char[] _rawMsg = new char[len]; _bufferedReader.read(_rawMsg); return _rawMsg; I solved the problem in several iterative ways: first I tested the last char of my array: if it wasn't ETX I would read chars from the bufferedReader one by one until I would reach ETX, then start over my regular routine. the consequence is that I would basically DROP one message. then, in order to still retrieve that message, I would find the first occurence of the NUL char in my "truncated" message, read & store additional characters one at a time until I reached ETX, and append them to my "truncated" messages, confirming length is ok. it works also, but I'm really thinking there's something I could do better, like checking if the total number of characters I need are available in the buffer before reading it, but can't find the right way to do it... any idea / pointer ? thanks !

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  • Unity to dispose of object

    - by Johan Levin
    Is there a way to make Unit dispose property-injected objects as part of the Teardown? The background is that I am working on an application that uses ASP.NET MVC 2, Unity and WCF. We have written our own MVC controller factory that uses unity to instantiate the controller and WCF proxies are injected using the [Dependency] attribute on public properties of the controller. At the end of the page life cycle the ReleaseController method of the controller factory is called and we call IUnityContainer.Teardown(theMvcController). At that point the controller is disposed as expected but I also need to dispose the injected wcf-proxies. (Actually I need to call Close and/or Abort on them and not Dispose but that is a later problem.) I could of course override the controllers' Dispose methods and clean up the proxies there, but I don't want the controllers to have to know about the lifecycles of the injected interfaces or even that they refer to WCF proxies. If I need to write code myself for this - what would be the best extension point? I'd appreciate any pointer.

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  • How to print the address an ada access variable points to?

    - by georg
    I want to print the address of an access variable (pointer) for debugging purposes. type Node is private; type Node_Ptr is access Node; procedure foo(n: in out Node_Ptr) is package Address_Node is new System.Address_To_Access_Conversions(Node); use Address_Node; begin Put_Line("node at address " & System.Address_Image(To_Address(n))); end foo; Address_Image returns the string representation of an address. System.Address_To_Access_Conversions is a generic package to convert between addresses and access types (see ARM 13.7.2), defined as follows: generic type Object(<>) is limited private; package System.Address_To_Access_Conversions is -- [...] type Object_Pointer is access all Object; -- [...] function To_Address(Value : Object_Pointer) return Address; -- [...] end System.Address_To_Access_Conversions; gnat gives me the following errors for procedure foo defined above: expected type "System.Address_To_Access_Conversions.Object_Pointer" from instance at line... found type "Node_Ptr" defined at ... Object_Pointer ist definied as access all Object. From my understanding the type Object is Node, therefore Object_Ptr is access all Node. What is gnat complaining about? I guess my understanding of Ada generics is flawed and I am not using System.Address_To_Access_Conversions correctly. EDIT: I compiled my code with "gnatmake -gnatG" to see the generic instantiation: package address_node is subtype btree__clear__address_node__object__2 is btree__node; type btree__clear__address_node__object_pointer__2 is access all btree__clear__address_node__object__2; function to_address (value : btree__clear__address_node__object_pointer__2) return system__address; end address_node; btree__node is the mangled name of the type Node as defined above, so I really think the parameter type for to_address() is correct, yet gnat is complaining (see above).

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  • How to cast sockaddr_storage and avoid breaking strict-aliasing rules

    - by sinoth
    I'm using Beej's Guide to Networking and came across an aliasing issue. He proposes a function to return either the IPv4 or IPv6 address of a particular struct: 1 void *get_in_addr( struct sockaddr *sa ) 2 { 3 if (sa->sa_family == AF_INET) 4 return &(((struct sockaddr_in*)sa)->sin_addr); 5 else 6 return &(((struct sockaddr_in6*)sa)->sin6_addr); 7 } This causes GCC to spit out a strict-aliasing error for sa on line 3. As I understand it, it is because I call this function like so: struct sockaddr_storage their_addr; ... inet_ntop(their_addr.ss_family, get_in_addr((struct sockaddr *)&their_addr), connection_name, sizeof connection_name); I'm guessing the aliasing has to do with the fact that the their_addr variable is of type sockaddr_storage and another pointer of a differing type points to the same memory. Is the best way to get around this sticking sockaddr_storage, sockaddr_in, and sockaddr_in6 into a union? It seems like this should be well worn territory in networking, I just can't find any good examples with best practices. Also, if anyone can explain exactly where the aliasing issue takes place, I'd much appreciate it.

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  • Increase performance on iphone at pdf rendering

    - by burki
    Hi! I have a UITableView, and in every cell there's displayed a UIImage created from a pdf. But now the performance is very bad. Here's my code I use to generate the UIImage from the PDF. Creating CGPDFDocumentRef and UIImageView (in cellForRowAtIndexPath method): ... CFURLRef pdfURL = CFBundleCopyResourceURL(CFBundleGetMainBundle(), (CFStringRef)formula.icon, NULL, NULL); CGPDFDocumentRef documentRef = CGPDFDocumentCreateWithURL((CFURLRef)pdfURL); CFRelease(pdfURL); UIImageView *imageView = [[UIImageView alloc] initWithImage:[self imageFromPDFWithDocumentRef:documentRef]]; ... Generate UIImage: - (UIImage *)imageFromPDFWithDocumentRef:(CGPDFDocumentRef)documentRef { CGPDFPageRef pageRef = CGPDFDocumentGetPage(documentRef, 1); CGRect pageRect = CGPDFPageGetBoxRect(pageRef, kCGPDFCropBox); UIGraphicsBeginImageContext(pageRect.size); CGContextRef context = UIGraphicsGetCurrentContext(); CGContextTranslateCTM(context, CGRectGetMinX(pageRect),CGRectGetMaxY(pageRect)); CGContextScaleCTM(context, 1, -1); CGContextTranslateCTM(context, -(pageRect.origin.x), -(pageRect.origin.y)); CGContextDrawPDFPage(context, pageRef); UIImage *finalImage = UIGraphicsGetImageFromCurrentImageContext(); UIGraphicsEndImageContext(); return finalImage; } What can I do to increas the speed and keep the memory low?

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  • Linked list recursive reverse

    - by Phoenix
    I was looking at the code below from stanford library: void recursiveReverse(struct node** head_ref) { struct node* first; struct node* rest; /* empty list */ if (*head_ref == NULL) return; /* suppose first = {1, 2, 3}, rest = {2, 3} */ first = *head_ref; rest = first->next; /* List has only one node */ if (rest == NULL) return; /* put the first element on the end of the list */ recursiveReverse(&rest); first->next->next = first; /* tricky step -- see the diagram */ first->next = NULL; /* fix the head pointer */ *head_ref = rest; } What I don't understand is in the last recursive step for e.g if list is 1-2-3-4 Now for the last recursive step first will be 1 and rest will be 2. So if you set *head_ref = rest .. that makes the head of the list 2 ?? Can someone please explain how after reversing the head of the list becomes 4 ??

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  • Advice on improving programming skills, learning capabilities?

    - by anonymous-coward1234
    Hi all, After 2,5 years of professional Java programing, I still have problems that make my job difficult and, more importantly - more times that I would like to admit - not enjoyable. I would like to ask for advice by more experienced people on ways that would help me overcome them. These are the problems I have: I do not absorb new knowledge easily. Even when I understand something, after a couple of days I easily forget even basic stuff. Other co-workers, even with the same working experience, when reading new technologies put things easily into "context", and are able to compare in "real time| similar technologies they already have used. I always try to address all the issues to whatever I am doing at one go, which results in me trying to resolve too many problems at the same time, losing completely control. I find it difficult to make my mind on a single problem that I should address first, and even when I do, and find myself throwing away code that I wrote because I started addressing the wrong issue first. As far as architecture and data modeling is concerned, I have difficulty making decisions on what objects must be created, with what hierarchy, interfaces, abstraction etc. I imagine that - to a certain degree - these things come with experience. But after 2,5 years of Java programming, I would expect myself to have come much farther that I have come, both in terms of absorption and experience. Is there a way to improve my learning speed? Any books, methods, advice is welcome.

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  • web browser become slow or no response after several ajax calls

    - by Patrick
    I'm totally newbie to jquery and ajax, my recently project is to help the representatives (reps) to manage customer quotations online. I have a page which displays all the quotations in a big table. I've managed to use ajax to fetch and display the quotations which associate to a particular rep after i click that rep's name. But the only problem is the speed of response. The first few clicks are ok and very smooth. But after several tries, the response become slow and I cant even scroll down the webpage, and later on the web browser craches.... Please have a look at my ajax code. here it is: <!-- AJAX FETCH QUOTES DATA + Tablesorter + FIXED TABLE HEADER--> <script type="text/javascript"> //<![CDATA[ $(function(){ $("a.repID").click(function(){ $('div#loader').append("<p align='center'><img src='images/loadingbar2.gif' id='loading' /></p>"); var repID = $(this).attr("title"); $.ajax({ type:'POST', url:'quote_info.php', data:'repID=' + repID, cache: false, success:function(data) { $("#container").html('<div id="content">' + data + '</div>'); $("#loading").fadeOut(500, function() {$(this).remove();}); $("#sortme").tablesorter(); $('.tbl').fixedtableheader(); } }); return false; }); }); </script> <!-- AJAX FETCH QUOTES DATA + Tablesorter + FIXED TABLE HEADER-->

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  • How to preload images using jquery for carousel?

    - by Pandiya Chendur
    I used jquery stepcarousel plugin and it works fine... But how to preload images that is used by the plugin... I am using this, <div id="mygallery" class="stepcarousel"> <div class="belt"> <div class="panel"> <img src="Images/img1.jpg" /> </div> <div class="panel"> <img src="Images/img2.jpg" /> </div> </div> </div> <script type="text/javascript"> stepcarousel.setup({ galleryid: 'mygallery', //id of carousel DIV beltclass: 'belt', //class of inner "belt" DIV containing all the panel DIVs panelclass: 'panel', //class of panel DIVs each holding content autostep: { enable: true, moveby: 1, pause: 3000 }, panelbehavior: { speed: 500, wraparound: false, persist: true }, defaultbuttons: { enable: true, moveby: 1, leftnav: ['Images/lft_arrow.jpg', -5, 220], rightnav: ['Images/rit_arrow.jpg', -5, 220] }, statusvars: ['statusA', 'statusB', 'statusC'], //register 3 variables that contain current panel (start), current panel (last), and total panels contenttype: ['inline'] //content setting ['inline'] or ['ajax', 'path_to_external_file'] }) </script> How to preload images used by mygallery div such that i can avoid flickering.....

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  • Embedded Vimeo Video Callbacks

    - by Andrew
    This post is kind of a follow up to a post I made earlier in regards to HTML5 video callbacks. In that thread, I was given a great piece of code that would allow for the browser to be informed of when the video stops playing and then fire off an action (with jQuery). This is the code I'm currently using: $('video.normal').bind('ended', function(){ $(this).fadeOut().queue(function(){ $(this).siblings('.post-video').fadeIn(); $(this).dequeue(); }); }); Which basically fades the video out when it's completed and brings a poster frame of the video (or similar image) back into view. Well, the scope of the project has changed and now the client is asking for true full screen video and different size videos to be delivered based on user connection speed, something that's a little over my head and a lot over budget. So I've been researching and a Vimeo Plus player seems like a great alternative for visitors using a desktop browser (HD embeds, true full screen, and more). Thing is, I need that above code to continue working in some capacity or another, so does the embedded Vimeo player offer a similar callback that I can utilize? Or am I SOL here? Thanks in advance!

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  • PHP readfile() and large downloads

    - by Nirmal
    While setting up an online file management system, and now I have hit a block. I am trying to push the file to the client using this modified version of readfile: function readfile_chunked($filename,$retbytes=true) { $chunksize = 1*(1024*1024); // how many bytes per chunk $buffer = ''; $cnt =0; // $handle = fopen($filename, 'rb'); $handle = fopen($filename, 'rb'); if ($handle === false) { return false; } while (!feof($handle)) { $buffer = fread($handle, $chunksize); echo $buffer; ob_flush(); flush(); if ($retbytes) { $cnt += strlen($buffer); } } $status = fclose($handle); if ($retbytes && $status) { return $cnt; // return num. bytes delivered like readfile() does. } return $status; } But when I try to download a 13 MB file, it's just breaking at 4 MB. What would be the issue here? It's definitely not the time limit of any kind because I am working on a local network and speed is not an issue. The memory limit in PHP is set to 300 MB. Thank you for any help.

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  • Why do people say that Ruby is slow?

    - by stephen murdoch
    I like Ruby on Rails and I use it for all my web development projects. A few years ago there was a lot of talk about Rails being a memory hog and about how it didn't scale very well but these suggestions were put to bed by Gregg Pollack here. Lately though, I've been hearing people saying that Ruby itself is slow. Why is Ruby considered slow? I do not find Ruby to be slow but then again, I'm just using it to make simple CRUD apps and company blogs. What sort of projects would I need to be doing before I find Ruby becoming slow? Or is this slowness just something that affects all programming languages? What are your options as a Ruby programmer if you want to deal with this "slowness"? Which version of Ruby would best suit an application like Stack Overflow where speed is critical and traffic is intense? The questions are subjective, and I realise that architectural setup (EC2 vs standalone servers etc) makes a big difference but I'd like to hear what people think about Ruby being slow. Finally, I can't find much news on Ruby 2.0 - I take it we're a good few years away from that then?

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  • Javascript won't execute in iPhone Safari

    - by Stuart Meyer
    I'm running into this issue only because I recently purchased an iPhone. The javascript for a picture carousel on my website (http://www.stuartmeyerphotography.com) won't execute in Safari for iPhone. I thought it worked on Mac Safari last I checked with a friend who had a Mac (a year ago), but now I need to go back and check that too to make sure it works on the Mac. "View source" on my website would show the entire html page, but I've pulled the code from the body section to show here: carousel({id:'Photos', border:'', size_mode:'image', width:120, height:120, sides:8, steps:75, speed:4, direction:'left', images:['mainthumbs/babiesthumb.jpg','mainthumbs/engagementsthumb.jpg','mainthumbs/dancethumb1.jpg','mainthumbs/artistthumb.jpg','mainthumbs/portraitsthumb1.jpg','mainthumbs/seniorsthumb1.jpg','mainthumbs/wedthumb1.jpg'], links:['babies/babies.html','engagements/engagemainshow/engagementpictures.html','dance/dancepictures.html','artists/artists.html','portraits/portraits.html','seniors/highschoolseniors.html','weddings/weddings.html'], lnk_base:'', lnk_targets:['_iframe1', '_iframe1', '_iframe1', '_iframe1', '_iframe1', '_iframe1', '_iframe1' ], lnk_attr:['width=200,height=300,top=200,menubar=yes', 'width=300,height=200,left=400,scrollbars=yes', 'width=150,height=250,left=200,top=100', ''], titles:['Babies', 'Engagements', 'Dance', 'Artists', 'Portraits', 'HS Seniors', 'Weddings'], image_border_width:1, image_border_color:'#E3F0A1' });   </div> Any thoughts? -Stuart

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  • Can you force a crash if a write occurs to a given memory location with finer than page granularity?

    - by Joseph Garvin
    I'm writing a program that for performance reasons uses shared memory (alternatives have been evaluated, and they are not fast enough for my task, so suggestions to not use it will be downvoted). In the shared memory region I am writing many structs of a fixed size. There is one program responsible for writing the structs into shared memory, and many clients that read from it. However, there is one member of each struct that clients need to write to (a reference count, which they will update atomically). All of the other members should be read only to the clients. Because clients need to change that one member, they can't map the shared memory region as read only. But they shouldn't be tinkering with the other members either, and since these programs are written in C++, memory corruption is possible. Ideally, it should be as difficult as possible for one client to crash another. I'm only worried about buggy clients, not malicious ones, so imperfect solutions are allowed. I can try to stop clients from overwriting by declaring the members in the header they use as const, but that won't prevent memory corruption (buffer overflows, bad casts, etc.) from overwriting. I can insert canaries, but then I have to constantly pay the cost of checking them. Instead of storing the reference count member directly, I could store a pointer to the actual data in a separate mapped write only page, while keeping the structs in read only mapped pages. This will work, the OS will force my application to crash if I try to write to the pointed to data, but indirect storage can be undesirable when trying to write lock free algorithms, because needing to follow another level of indirection can change whether something can be done atomically. Is there any way to mark smaller areas of memory such that writing them will cause your app to blow up? Some platforms have hardware watchpoints, and maybe I could activate one of those with inline assembly, but I'd be limited to only 4 at a time on 32-bit x86 and each one could only cover part of the struct because they're limited to 4 bytes. It'd also make my program painful to debug ;)

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  • (solved) jQuery click and drag/scroll window: jagged movement

    - by Josh
    Edit: derp, using pageX/Y instead of clientX/Y -- apparently scrollBy expects input with that offset rather than the other. Jaggy movement gone. I am getting jagged movement when doing small scroll increments using the following bindings. Can anyone point me in the right direction for how to smooth this out? FYI, its intermittent. It seems like, if I click and hold for a second, then drag at a decent speed there are no problems. Edit: What the hell? I get this output on debug... obvious jog backwards and forwards. This will happen in succession and seems to have no correlation with the mouse, other than the mouse is moving. x 398 : 403 y 374 : 377 x 403 : 399 y 377 : 374 x 399 : 404 y 374 : 377 Josh sococo.client.panMap = function(e){ e.preventDefault(); var movex = sococo.client.currX - e.pageX ; var movey = sococo.client.currY - e.pageY; console.log( sococo.client.currX +" : " + e.pageX ); window.scrollBy(movex,movey); sococo.client.currY = e.pageY; sococo.client.currX = e.pageX; } $(document).mousedown( function(e){ e.preventDefault(); sococo.client.currX = e.pageX; sococo.client.currY = e.pageY; $(document).bind( "mousemove", sococo.client.panMap ); }); $(document).mouseup( function(e){ e.preventDefault(); $(document).unbind( "mousemove", sococo.client.panMap ); });

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  • Algorithm to determine which points should be visible on a map based on zoom

    - by lgratian
    Hi! I'm making a Google Maps-like application for a course at my Uni (not something complex, it should load the map of a city for example, not the whole world). The map can have many layers, including markers (restaurants, hospitals, etc.) The problem is that when you have many points and you zoom out the map it doesn't look right. At this zoom level only some points need to be visible (and at the maximum map size, all points). The question is: how can you determine which points should be visible for a specified zoom level? Because I have implemented a PR Quadtree to speed up rendering I thought that I could define some "high-priority" markers (that are always visible, defined in the map editor) and put them in a queue. At each step a marker is removed from the queue and all it's neighbors that are at least D units away (D depends on the zoom levels) are chosen and inserted in the queue, and so on. Is there any better way than the algorithm I thought of? Thanks in advance!

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  • How does one target all divs of any webpage but differentiate them in javascript?

    - by Chaz
    So I am trying to create an extension in Chrome (a prototype for a project that I am doing) that targets all of the <div> tags of any web page, hides them or rather doesn't display them until the user clicks the mouse (further explained below). So typing a url into the browser yields a white page. The person clicks, and the first <div> appears (probably the mast head or menu). The user clicks again and the second <div> appears. I have gotten to the point where I can hide or show all <div>'s (the obvious easy part) but I am not sure how to go about targeting each since every website has different id's for them while still using the <div> tag. This is what I need the most help with. This is part of a grander operation called the Web Crank. It's just a physical crank that controls the speed by which a web page loads. Each time you make one full rotation of the crank, one section (the first <div>) of the web page loads. The faster you go, the quicker the page loads. I hope this is clear enough. I am a newbie when it comes to this, but I have done some minor coding in the past and it's not such a big deal. Thanks for your help!

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  • What would be the safest way to store objects of classes derived from a common interface in a common

    - by Svenstaro
    I'd like to manage a bunch of objects of classes derived from a shared interface class in a common container. To illustrate the problem, let's say I'm building a game which will contain different actors. Let's call the interface IActor and derive Enemy and Civilian from it. Now, the idea is to have my game main loop be able to do this: // somewhere during init std::vector<IActor> ActorList; Enemy EvilGuy; Civilian CoolGuy; ActorList.push_back(EvilGuy); ActorList.push_back(CoolGuy); and // main loop while(!done) { BOOST_FOREACH(IActor CurrentActor, ActorList) { CurrentActor.Update(); CurrentActor.Draw(); } } ... or something along those lines. This example obviously won't work but that is pretty much the reason I'm asking here. I'd like to know: What would be the best, safest, highest-level way to manage those objects in a common heterogeneous container? I know about a variety of approaches (Boost::Any, void*, handler class with boost::shared_ptr, Boost.Pointer Container, dynamic_cast) but I can't decide which would be the way to go here. Also I'd like to emphasize that I want to stay away as far as possible from manual memory management or nested pointers. Help much appreciated :).

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  • MS Query Analyzer / Management Studio replacement?

    - by kprobst
    I've been using SQL Server since version 6.5 and I've always been a bit amazed at the fact that the tools seem to be targeted to DBAs rather than developers. I liked the simplicity and speed of the Query Analyzer for example, but hated the built-in editor, which was really no better than a syntax coloring-capable Notepad. Now that we have Management Studio the management part seems a bit better but from a developer standpoint the tools is even worse. Visual Studio's excellent text editor... without a way to customize keyboard bindings!? Don't get me started on how unusable is the tree-based management hierarchy. Why can't I re-root the tree on a list of stored procs for example the way the Enterprise Manager used to allow? Now I have a treeview that needs to be scrolled horizontally, which makes it eminently useless. The SQL server support in Visual Studio is fantastic for working with stored procedures and functions, but it's terrible as a general ad hoc data query tool. I've tried various tools over the years but invariably they seem to focus on the management side and shortchange the developer in me. I just want something with basic admin capabilities, good keyboard support and requisite DDL functionality (ideally something like the Query Analyzer). At this point I'm seriously thinking of using vim+sqlcmd and a console... I'm that desperate :) Those of you who work day in and day out with SQL Server and Visual Studio... do you find the tools to be adequate? Have you ever wished they were better and if you have found something better, could you share please? Thanks!

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  • How do you update table row background color in IE using Javascript/CSS ?

    - by giulio
    I have a table that i want to "highlight" during onmouseover/onmouseout. I already know this is required in IE but not in other browsers. I have managed to detect the events triggering and this TR tag effectively works. (Note that the originating class "contentTableRow" doesn't seem to be causing any issues.) class="contentTableRow" onclick="openForm('SomeID');" onmouseover="highlight('someRowID', true);" onmouseout="highlight('someRowID', false);" id="someRowID" All is fine and dandy, the "highlight" function fires and actually sets the appropriate class. It's just that IE won't process the CSS class name change. Here is a snippet of the CSS I am using to make the change. .HighlightOn { cursor:pointer; background-color: #D1DFFF; } .HighlightOff { background-color: #E1EEFE; } I can see that the Class names are getting updated when I debug it, and also check it in Firebug. But it seems that IE doesn't like this usage of classes with a TR tag.. Is it the way I am structuring the class for Tables ? Any advice ?

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