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• Can you find a pattern to sync files knowing only dates and filenames?

  - by Robert MacLean

  Imagine if you will a operating system that had the following methods for files Create File: Creates (writes) a new file to disk. Calling this if a file exists causes a fault. Update File: Updates an existing file. Call this if a file doesn't exist causes a fault. Read File: Reads data from a file. Enumerate files: Gets all files in a folder. Files themselves in this operating system only have the following meta data: Created Time: The original date and time the file was created, by the Create File method. Modified Time: The date and time the file was last modified by the Update File method. If the file has never been modified, this will equal the Create Time. You have been given the task of writing an application which will sync the files between two directories (lets call them bill and ted) on a machine. However it is not that simple, the client has required that The application never faults (see methods above). That while the application is running the users can add and update files and those will be sync'd next time the application runs. Files can be added to either the ted or bill directories. File names cannot be altered. The application will perform one sync per time it is run. The application must be almost entirely in memory, in other words you cannot create a log of filenames and write that to disk and then check that the next time. The exception to point 6 is that you can store date and times between runs. Each date/time is associated with a key labeled A through J (so you have 10 to use) so you can compare keys between runs. There is no way to catch exceptions in the application. Answer will be accepted based on the following conditions: First answer to meet all requirements will be accepted. If there is no way to meet all requirements, the answer which ensures the smallest amount of missed changes per sync will be accepted. A bounty will be created (100 points) as soon as possible for the prize. The winner will be selected one day before the bounty ends. Please ask questions in the comments and I will gladly update and refine the question on those.

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• Rails ActiveResource Associations

  - by brad

  I have some ARes models (see below) that I'm trying to use associations with (which seems to be wholly undocumented and maybe not possible but I thought I'd give it a try) So on my service side, my ActiveRecord object will render something like render :xml => @group.to_xml(:include => :customers) (see generated xml below) The models Group and Customers are HABTM On my ARes side, I'm hoping that it can see the <customers> xml attribute and automatically populate the .customers attribute of that Group object , but the has_many etc methods aren't supported (at least as far as I can tell) So I'm wondering how ARes does it's reflection on the XML to set the attributes of an object. In AR for instance I could create a def customers=(customer_array) and set it myself, but this doesn't seem to work in ARes. One suggestion I found for an "association" is the just have a method def customers Customer.find(:all, :conditions => {:group_id => self.id}) end But this has the disadvantage that it makes a second service call to look up those customers... not cool I'd like my ActiveResource model to see that the customers attribute in the XML and automatically populate my model. Anyone have any experience with this?? # My Services class Customer < ActiveRecord::Base has_and_belongs_to_many :groups end class Group < ActiveRecord::Base has_and_belongs_to_many :customer end # My ActiveResource accessors class Customer < ActiveResource::Base; end class Group < ActiveResource::Base; end # XML from /groups/:id?customers=true <group> <domain>some.domain.com</domain> <id type="integer">266</id> <name>Some Name</name> <customers type="array"> <customer> <active type="boolean">true</active> <id type="integer">1</id> <name>Some Name</name> </customer> <customer> <active type="boolean" nil="true"></active> <id type="integer">306</id> <name>Some Other Name</name> </customer> </customers> </group>

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• Using Jquery.Form Plugin + MultiFile to automatically upload a single file

  - by Alan Neal

  I wanted to find a way to upload a single file*, in the background, have it start automatically after file selection, and not require a flash uploader, so I am trying to use two great mechanisms (jQuery.Form and JQuery MultiFile) together. I haven't succeeded, but I'm pretty sure it's because I'm missing something fundamental. Just using MultiFile, I define the form as follows... <form id="photoForm" action="image.php" method="post" enctype="multipart/form-data"> The file input button is defined as... <input id="photoButton" "name="sourceFile" class="photoButton max-1 accept-jpg" type="file"> And the Javascript is... $('#photoButton').MultiFile({ afterFileSelect: function(){ document.getElementById("photoForm").submit(); } }); This works perfectly. As soon as the user selects a single file, MultiFile submits the form to the server. If instead of using MultiFile, as shown above, let's say I include a Submit button along with the JQuery Form plugin defined as follows... var options = { success: respondToUpload }; $('#photoForm').ajaxForm(options); ... this also works perfectly. When the Submit button is clicked, the form is uploaded in the background. What I don't know how to do is get these two to work together. If I use Javascript to submit the form (as shown in the MultiFile example above), the form is submitted but the JQuery.Form function is not called, so the form does not get submitted in the background. I thought that maybe I needed to change the form registration as follows... $('#photoForm').submit(function() { $('#photoForm').ajaxForm(options); }); ...but that didn't solve the problem. The same is true when I tried .ajaxSubmit instead of .ajaxForm. What am I missing? BTW: I know it might sound strange to use MultiFile for single-file uploads, but the idea is that the number of files will be dynamic based on the user's account. So, I'm starting with one but the number changes depending on conditions.

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• custom view with layout

  - by user270811

  ok, what i am trying to do is to embed a custom view in the default layout main.xml: <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent"> <com.lam.customview.CustomDisplayView android:id="@+id/custom_display_view1" android:layout_width="fill_parent" android:layout_height="fill_parent" /> <LinearLayout android:orientation="horizontal" android:layout_width="fill_parent" android:layout_height="wrap_content"> <Button android:id="@+id/prev" android:layout_width="0dip" android:layout_height="wrap_content" android:layout_weight="50" android:textAppearance="?android:attr/textAppearanceSmall" android:text="@string/prev" /> </LinearLayout> </LinearLayout> as you can see the class is called com.lam.customview.CustomDisplayView, with the id of custom_display_view1. now in the com.lam.customview.CustomDisplayView class, i want to use another layout called custom_display_view.xml because i don't want to programmatically create controls/widgets. custom_display_view.xml is just a button and an image, the content of which i want to change based on certain conditions: <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent" > <TextView android:id="@+id/display_text_view1" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="@string/hello" /> <ImageView android:id="@+id/display_image_view1" android:layout_width="wrap_content" android:layout_height="wrap_content"> </ImageView> </LinearLayout> i tried to do: 1) public CustomDisplayView(Context context, AttributeSet attrs) { super(context, attrs); try { // register our interest in hearing about changes to our surface SurfaceHolder holder = getHolder(); holder.addCallback(this); View.inflate(context, R.layout.custom_display_view, null); ... but got this error, "03-08 20:33:15.711: ERROR/onCreate(10879): Binary XML file line #8: Error inflating class java.lang.reflect.Constructor ". 2) public CustomDisplayView(Context context, AttributeSet attrs) { super(context, attrs); try { // register our interest in hearing about changes to our surface SurfaceHolder holder = getHolder(); holder.addCallback(this); View.inflate(context, R.id.custom_display_view1, null); ... but got this error, "03-08 20:28:47.401: ERROR/CustomDisplayView(10806): Resource ID #0x7f050002 type #0x12 is not valid " also, if i do it this way, as someone has suggested, it's not clear to me how the custom_display_view.xml is associated with the custom view class. thanks.

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• Zend database query result converts column values to null

  - by David Zapata

  Hi again. I am using the next instructions to get some registers from my Database. Create the needed models (from the params module): $obj_paramtype_model = new Params_Model_DbTable_Paramtype(); $obj_param_model = new Params_Model_DbTable_Param(); Getting the available locales from the database // This returns a Zend_Db_Table_Row_Abstract class object $obj_paramtype = $obj_paramtype_model->getParamtypeByValue('available_locales'); // This is a query used to add conditions to the next sentence. This is executed from the Params_Model_DbTable_Param instance class, that depends from Params_Model_DbTable_Paramtype class (reference map and dependentTables arrays are fine in both classes) $obj_select = $this->select()->where('deleted_at IS NULL')->order('name'); // Execute the next query, applying the select restrictions. This returns a Zend_Db_Table_Rowset_Abstract class object. This means "Find Params by Paramtype" $obj_params_rowset = $obj_paramtype->findDependentRowset('Params_Model_DbTable_Param', 'Paramtype', $obj_paramtype); // Here the firebug log displays the queries.... Zend_Registry::get('log')->debug($obj_params_rowset); I have a profiler for all my DB executions from Zend. At this point the log and profiler objects (that includes Firebug writers), shows the executed SQL Queries, and the last line displays the resulting Zend_Db_Table_Rowset_Abstract class object. If I execute the SQL Queries in some MySQL Client, the results are as expected. But the Zend Firebug log writer displays as NULL the column values with latin characters (ñ). In other words, the external SQL client shows es_CO | Español de Colombia and en_US | English of United States but the Query results from Zend displays (and returns) es_CO | null and en_US | English of United States. I've deleted the ñ character from Español de Colombia and the query results are just fine in my Zend Log Firebug screen, and in the final Zend Form element. The MySQL database, tables and columns are in UTF-8 - utf8_unicode_ci collation. All my zend framework pages are in UTF-8 charset. I'm using XAMPP 1.7.1 (PHP 5.2.9, Apache at port 90 and MySQL 5.1.33-community) running on Windows 7 Ultimate; Zend Framework 1.10.1. I'm sorry if there is so much information, but I don't really know why could that happen, so I tryed to provide as much related information as I could to help to find some answer.

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• Hibernate + Spring : cascade deletion ignoring non-nullable constraints

  - by E.Benoît

  Hello, I seem to be having one weird problem with some Hibernate data classes. In a very specific case, deleting an object should fail due to existing, non-nullable relations - however it does not. The strangest part is that a few other classes related to the same definition behave appropriately. I'm using HSQLDB 1.8.0.10, Hibernate 3.5.0 (final) and Spring 3.0.2. The Hibernate properties are set so that batch updates are disabled. The class whose instances are being deleted is: @Entity( name = "users.Credentials" ) @Table( name = "credentials" , schema = "users" ) public class Credentials extends ModelBase { private static final long serialVersionUID = 1L; /* Some basic fields here */ /** Administrator credentials, if any */ @OneToOne( mappedBy = "credentials" , fetch = FetchType.LAZY ) public AdminCredentials adminCredentials; /** Active account data */ @OneToOne( mappedBy = "credentials" , fetch = FetchType.LAZY ) public Account activeAccount; /* Some more reverse relations here */ } (ModelBase is a class that simply declares a Long field named "id" as being automatically generated) The Account class, which is one for which constraints work, looks like this: @Entity( name = "users.Account" ) @Table( name = "accounts" , schema = "users" ) public class Account extends ModelBase { private static final long serialVersionUID = 1L; /** Credentials the account is linked to */ @OneToOne( optional = false ) @JoinColumn( name = "credentials_id" , referencedColumnName = "id" , nullable = false , updatable = false ) public Credentials credentials; /* Some more fields here */ } And here is the AdminCredentials class, for which the constraints are ignored. @Entity( name = "admin.Credentials" ) @Table( name = "admin_credentials" , schema = "admin" ) public class AdminCredentials extends ModelBase { private static final long serialVersionUID = 1L; /** Credentials linked with an administrative account */ @OneToOne( optional = false ) @JoinColumn( name = "credentials_id" , referencedColumnName = "id" , nullable = false , updatable = false ) public Credentials credentials; /* Some more fields here */ } The code that attempts to delete the Credentials instances is: try { if ( account.validationKey != null ) { this.hTemplate.delete( account.validationKey ); } this.hTemplate.delete( account.languageSetting ); this.hTemplate.delete( account ); } catch ( DataIntegrityViolationException e ) { return false; } Where hTemplate is a HibernateTemplate instance provided by Spring, its flush mode having been set to EAGER. In the conditions shown above, the deletion will fail if there is an Account instance that refers to the Credentials instance being deleted, which is the expected behaviour. However, an AdminCredentials instance will be ignored, the deletion will succeed, leaving an invalid AdminCredentials instance behind (trying to refresh that instance causes an error because the Credentials instance no longer exists). I have tried moving the AdminCredentials table from the admin DB schema to the users DB schema. Strangely enough, a deletion-related error is then triggered, but not in the deletion code - it is triggered at the next query involving the table, seemingly ignoring the flush mode setting. I've been trying to understand this for hours and I must admit I'm just as clueless now as I was then.

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• rails named_scope ignores eager loading

  - by Craig

  Two models (Rails 2.3.8): User; username & disabled properties; User has_one :profile Profile; full_name & hidden properties I am trying to create a named_scope that eliminate the disabled=1 and hidden=1 User-Profiles. The User model is usually used in conjunction with the Profile model, so I attempt to eager-load the Profile model (:include = :profile). I created a named_scope on the User model called 'visible': named_scope :visible, { :joins => "INNER JOIN profiles ON users.id=profiles.user_id", :conditions => ["users.disabled = ? AND profiles.hidden = ?", false, false] } I've noticed that when I use the named_scope in a query, the eager-loading instruction is ignored. Variation 1 - User model only: # UserController @users = User.find(:all) # User's Index view <% for user in @users %> <p><%= user.username %></p> <% end %> # generates a single query: SELECT * FROM `users` Variation 2 - use Profile model in view; lazy load Profile model # UserController @users = User.find(:all) # User's Index view <% for user in @users %> <p><%= user.username %></p> <p><%= user.profile.full_name %></p> <% end %> # generates multiple queries: SELECT * FROM `profiles` WHERE (`profiles`.user_id = 1) ORDER BY full_name ASC LIMIT 1 SHOW FIELDS FROM `profiles` SELECT * FROM `profiles` WHERE (`profiles`.user_id = 2) ORDER BY full_name ASC LIMIT 1 SELECT * FROM `profiles` WHERE (`profiles`.user_id = 3) ORDER BY full_name ASC LIMIT 1 SELECT * FROM `profiles` WHERE (`profiles`.user_id = 4) ORDER BY full_name ASC LIMIT 1 SELECT * FROM `profiles` WHERE (`profiles`.user_id = 5) ORDER BY full_name ASC LIMIT 1 SELECT * FROM `profiles` WHERE (`profiles`.user_id = 6) ORDER BY full_name ASC LIMIT 1 Variation 3 - eager load Profile model # UserController @users = User.find(:all, :include => :profile) #view; no changes # two queries SELECT * FROM `users` SELECT `profiles`.* FROM `profiles` WHERE (`profiles`.user_id IN (1,2,3,4,5,6)) Variation 4 - use name_scope, including eager-loading instruction #UserConroller @users = User.visible(:include => :profile) #view; no changes # generates multiple queries SELECT `users`.* FROM `users` INNER JOIN profiles ON users.id=profiles.user_id WHERE (users.disabled = 0 AND profiles.hidden = 0) SELECT * FROM `profiles` WHERE (`profiles`.user_id = 1) ORDER BY full_name ASC LIMIT 1 SELECT * FROM `profiles` WHERE (`profiles`.user_id = 2) ORDER BY full_name ASC LIMIT 1 SELECT * FROM `profiles` WHERE (`profiles`.user_id = 3) ORDER BY full_name ASC LIMIT 1 SELECT * FROM `profiles` WHERE (`profiles`.user_id = 4) ORDER BY full_name ASC LIMIT 1 Variation 4 does return the correct number of records, but also appears to be ignoring the eager-loading instruction. Is this an issue with cross-model named scopes? Perhaps I'm not using it correctly. Is this sort of situation handled better by Rails 3?

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• ArgumentNullException when accessing a FormView instance

  - by David

  Background: I have an ASP.NET page which has a numebr of user controls within it. There are 2 user controls which are of interest. I need to display either one of them or neither of them, depending on the record selected previously. In the user controls I need to set properties of some controls which are in a FormView. So in my user control code-behind I have a number of properties which look something like this: Private ReadOnly Property phSectionReports() As PlaceHolder Get Return fvConfirmationReport.FindControl("phSectionReports") End Get End Property The problem: I am having problems with this Property. Sometimes it is returning Nothing/Null and sometimes it is throwing a NullArgumentException with the message "Value cannot be null. Parameter name: container". The exception is coming from trying to reference the fvConfirmationReport variable. fvConfirmationReport is the ID of my FormView in the page itself. So I am really after things to look for and if any ideas what sort of conditions (e.g stage in page cycle, etc.) might lead to this? An example stack trace is included below. ASP.NET 3.5 SP1, VB.NET Thanks, StackTrace: at System.Web.UI.DataBinder.GetPropertyValue(Object container, String propName) at System.Web.UI.WebControls.GridView.CreateChildControls(IEnumerable dataSource, Boolean dataBinding) at System.Web.UI.WebControls.CompositeDataBoundControl.PerformDataBinding(IEnumerable data) at System.Web.UI.WebControls.GridView.PerformDataBinding(IEnumerable data) at System.Web.UI.WebControls.DataBoundControl.OnDataSourceViewSelectCallback(IEnumerable data) at System.Web.UI.DataSourceView.Select(DataSourceSelectArguments arguments, DataSourceViewSelectCallback callback) at System.Web.UI.WebControls.DataBoundControl.PerformSelect() at System.Web.UI.WebControls.BaseDataBoundControl.DataBind() at System.Web.UI.WebControls.GridView.DataBind() at System.Web.UI.Control.DataBindChildren() at System.Web.UI.Control.DataBind(Boolean raiseOnDataBinding) ...snip... at System.Web.UI.Control.DataBind() at System.Web.UI.Control.DataBindChildren() at System.Web.UI.Control.DataBind(Boolean raiseOnDataBinding) at System.Web.UI.WebControls.FormView.CreateChildControls(IEnumerable dataSource, Boolean dataBinding) at System.Web.UI.WebControls.CompositeDataBoundControl.PerformDataBinding(IEnumerable data) at System.Web.UI.WebControls.FormView.PerformDataBinding(IEnumerable data) at System.Web.UI.WebControls.DataBoundControl.OnDataSourceViewSelectCallback(IEnumerable data) at System.Web.UI.DataSourceView.Select(DataSourceSelectArguments arguments, DataSourceViewSelectCallback callback) at System.Web.UI.WebControls.DataBoundControl.PerformSelect() at System.Web.UI.WebControls.BaseDataBoundControl.DataBind() at System.Web.UI.WebControls.FormView.DataBind() at System.Web.UI.WebControls.BaseDataBoundControl.EnsureDataBound() at System.Web.UI.WebControls.FormView.EnsureDataBound() at System.Web.UI.WebControls.CompositeDataBoundControl.CreateChildControls() at System.Web.UI.Control.EnsureChildControls() at System.Web.UI.Control.FindControl(String id, Int32 pathOffset) at System.Web.UI.Control.FindControl(String id) at App_UserControls_xxx_ucConfirmationForm.get_phSectionReports() in ucConfirmationForm.ascx.vb:line 343 at App_UserControls_xxx_ucConfirmationForm.Page_Load(Object sender, EventArgs e) in ucConfirmationForm.ascx.vb:line 412 at System.Web.UI.Control.OnLoad(EventArgs e) at System.Web.UI.Control.LoadRecursive() ...snip... at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

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• Javascript code inside updatepanel usercontrol.

  - by Ed Woodcock

  Ok: I've got an updatepanel on an aspx page that contains a single Placeholder. Inside this placeholder I'm appending one of a selection of usercontrols depending on certain external conditions (this is a configuration page). In each of these usercontrols there is a bindUcEvents() javascript function that binds the various jQuery and javascript events to buttons and validators inside the usercontrol. The issue I'm having is that the usercontrol's javascript is not being recognised. Normally, javascript inside an updatepanel is executed when the updatepanel posts back, however none of this code can be found by the page (I've tried running the function manually via firebug's console, but it tells me it cannot find the function). Does anyone have any suggestions? Cheers, Ed. EDIT: cut down (but functional) example: Markup: <script src="/js/jquery-1.3.2.min.js"></script> <form id="form1" runat="server"> <div> <asp:ScriptManager ID="Script" runat="server" /> <asp:Button ID="Postback" runat="server" Text="Populate" OnClick="PopulatePlaceholder" /> <asp:UpdatePanel ID="UpdateMe" runat="server"> <Triggers> <asp:AsyncPostBackTrigger ControlID="Postback" EventName="Click" /> </Triggers> <ContentTemplate> <asp:Literal ID="Code" runat="server" /> <asp:PlaceHolder ID="PlaceMe" runat="server" /> </ContentTemplate> </asp:UpdatePanel> </div> </form> C#: protected void PopulatePlaceholder(object sender, EventArgs e) { Button button = new Button(); button.ID = "Push"; button.Text = "push"; button.OnClientClick = "javascript:return false;"; Code.Text = "<script type=\"text/javascript\"> function bindEvents() { $('#" + button.ClientID + "').click(function() { alert('hello'); }); } bindEvents(); </script>"; PlaceMe.Controls.Add(button); }

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• Iterator failure while moving over equal_range in Boost MultiIndex container

  - by Sarah

  I'm making some mistake with my iterators, but I can't see it yet. I have a Boost MultiIndex container, HostContainer hmap, whose elements are boost::shared_ptr to members of class Host. All the indices work on member functions of class Host. The third index is by Host::getHousehold(), where the household member variable is an int. Below, I'm trying to iterate over the range of Hosts matching a particular household (int hhold2) and load the corresponding private member variable Host::id into an array. I'm getting an "Assertion failed: (px != 0), function operator-, file /Applications/boost_1_42_0/boost/smart_ptr/shared_ptr.hpp, line 418" error in runtime when the household size is 2. (I can't yet tell if it happens anytime the household size is 2, or if other conditions must be met.) typedef multi_index_container< boost::shared_ptr< Host >, indexed_by< hashed_unique< const_mem_fun<Host,int,&Host::getID> >, // 0 - ID index ordered_non_unique< const_mem_fun<Host,int,&Host::getAgeInY> >, // 1 - Age index ordered_non_unique< const_mem_fun<Host,int,&Host::getHousehold> > // 2 - Household index > // end indexed_by > HostContainer; typedef HostContainer::nth_index<2>::type HostsByHH; // inside main() int numFamily = hmap.get<2>().count( hhold2 ); int familyIDs[ numFamily ]; for ( int f = 0; f < numFamily; f++ ) { familyIDs[ f ] = 0; } int indID = 0; int f = 0; std::pair< HostsByHH::iterator, HostsByHH::iterator pit = hmap.get<2().equal_range( hhold2 ); cout << "\tNeed to update households of " << numFamily << " family members (including self) of host ID " << hid2 << endl; while ( pit.first != pit.second ) { cout << "Pointing at new family member still in hhold " << ((pit.first))-getHousehold() << "; " ; indID = ((pit.first) )-getID(); familyIDs[ f ] = indID; pit.first++; f++; } What could make this code fail? The above snippet only runs when numFamily 1. (Other suggestions and criticisms are welcome too.) Thank you in advance.

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• Understanding CLR 2.0 Memory Model

  - by Eloff

  Joe Duffy, gives 6 rules that describe the CLR 2.0+ memory model (it's actual implementation, not any ECMA standard) I'm writing down my attempt at figuring this out, mostly as a way of rubber ducking, but if I make a mistake in my logic, at least someone here will be able to catch it before it causes me grief. Rule 1: Data dependence among loads and stores is never violated. Rule 2: All stores have release semantics, i.e. no load or store may move after one. Rule 3: All volatile loads are acquire, i.e. no load or store may move before one. Rule 4: No loads and stores may ever cross a full-barrier (e.g. Thread.MemoryBarrier, lock acquire, Interlocked.Exchange, Interlocked.CompareExchange, etc.). Rule 5: Loads and stores to the heap may never be introduced. Rule 6: Loads and stores may only be deleted when coalescing adjacent loads and stores from/to the same location. I'm attempting to understand these rules. x = y y = 0 // Cannot move before the previous line according to Rule 1. x = y z = 0 // equates to this sequence of loads and stores before possible re-ordering load y store x load 0 store z Looking at this, it appears that the load 0 can be moved up to before load y, but the stores may not be re-ordered at all. Therefore, if a thread sees z == 0, then it also will see x == y. If y was volatile, then load 0 could not move before load y, otherwise it may. Volatile stores don't seem to have any special properties, no stores can be re-ordered with respect to each other (which is a very strong guarantee!) Full barriers are like a line in the sand which loads and stores can not be moved over. No idea what rule 5 means. I guess rule 6 means if you do: x = y x = z Then it is possible for the CLR to delete both the load to y and the first store to x. x = y z = y // equates to this sequence of loads and stores before possible re-ordering load y store x load y store z // could be re-ordered like this load y load y store x store z // rule 6 applied means this is possible? load y store x // but don't pop y from stack (or first duplicate item on top of stack) store z What if y was volatile? I don't see anything in the rules that prohibits the above optimization from being carried out. This does not violate double-checked locking, because the lock() between the two identical conditions prevents the loads from being moved into adjacent positions, and according to rule 6, that's the only time they can be eliminated. So I think I understand all but rule 5, here. Anyone want to enlighten me (or correct me or add something to any of the above?)

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• Opinion on "loop invariants", and are these frequently used in the industry?

  - by Michael Aaron Safyan

  I was thinking back to my freshman year at college (five years ago) when I took an exam to place-out of intro-level computer science. There was a question about loop invariants, and I was wondering if loop invariants are really necessary in this case or if the question was simply a bad example... the question was to write an iterative definition for a factorial function, and then to prove that the function was correct. The code that I provided for the factorial function was as follows: public static int factorial(int x) { if ( x < 0 ){ throw new IllegalArgumentException("Parameter must be = 0"); }else if ( x == 0 ){ return 1; }else{ int result = 1; for ( int i = 1; i <= x; i++ ){ result*=i; } return result; } } My own proof of correctness was a proof by cases, and in each I asserted that it was correct by definition (x! is undefined for negative values, 0! is 1, and x! is 1*2*3...*x for a positive value of x). The professor wanted me to prove the loop using a loop invariant; however, my argument was that it was correct "by definition", because the definition of "x!" for a positive integer x is "the product of the integers from 1... x", and the for-loop in the else clause is simply a literal translation of this definition. Is a loop invariant really needed as a proof of correctness in this case? How complicated must a loop be before a loop invariant (and proper initialization and termination conditions) become necessary for a proof of correctness? Additionally, I was wondering... how often are such formal proofs used in the industry? I have found that about half of my courses are very theoretical and proof-heavy and about half are very implementation and coding-heavy, without any formal or theoretical material. How much do these overlap in practice? If you do use proofs in the industry, when do you apply them (always, only if it's complicated, rarely, never)?

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• stop and split generated sequence at repeats - clojure

  - by fitzsnaggle

  I am trying to make a sequence that will only generate values until it finds the following conditions and return the listed results: case head = 0 - return {:origin [all generated except 0] :pattern 0} 1 - return {:origin nil :pattern [all-generated-values] } repeated-value - {:origin [values-before-repeat] :pattern [values-after-repeat] { ; n = int ; x = int ; hist - all generated values ; Keeps the head below x (defn trim-head [head x] (loop [head head] (if (> head x) (recur (- head x)) head))) ; Generates the next head (defn next-head [head x n] (trim-head (* head n) x)) (defn row [x n] (iterate #(next-head % x n) n)) ; Generates a whole row - ; Rows are a max of x - 1. (take (- x 1) (row 11 3)) Examples of cases to stop before reaching end of row: [9 8 4 5 6 7 4] - '4' is repeated so STOP. Return preceding as origin and rest as pattern. {:origin [9 8] :pattern [4 5 6 7]} [4 5 6 1] - found a '1' so STOP, so return everything as pattern {:origin nil :pattern [4 5 6 1]} [3 0] - found a '0' so STOP {:origin [3] :pattern [0]} :else if the sequences reaches a length of x - 1: {:origin [all values generated] :pattern nil} The Problem I have used partition-by with some success to split the groups at the point where a repeated value is found, but would like to do this lazily. Is there some way I can use take-while, or condp, or the :while clause of the for loop to make a condition that partitions when it finds repeats? Some Attempts (take 2 (partition-by #(= 1 %) (row 11 4))) (for [p (partition-by #(stop-match? %) head) (iterate #(next-head % x n) n) :while (or (not= (last p) (or 1 0 n) (nil? (rest p))] {:origin (first p) :pattern (concat (second p) (last p))})) # Updates What I really want to be able to do is find out if a value has repeated and partition the seq without using the index. Is that possible? Something like this - { (defn row [x n] (loop [hist [n] head (gen-next-head (first hist) x n) steps 1] (if (>= (- x 1) steps) (case head 0 {:origin [hist] :pattern [0]} 1 {:origin nil :pattern (conj hist head)} ; Speculative from here on out (let [p (partition-by #(apply distinct? %) (conj hist head))] (if-not (nil? (next p)) ; One partition if no repeats. {:origin (first p) :pattern (concat (second p) (nth 3 p))} (recur (conj hist head) (gen-next-head head x n) (inc steps))))) {:origin hist :pattern nil}))) }

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• WPF Application Slow Unresponsive when demonstrating using remote sharing software

  - by Kev

  After spending 14 hours on this I think its time to share my woes and see if anyone has experienced this issue before. Ill describe the issue and tests I have done to rule out certain things. Ok so I have a WPF application which loads in data from an SQL database. I am using DevExpress Components for datagrids, ribbons etc.. and FluentNhibernate to provide a session for database operations. I am also using log4net to log events to a textfile. Using the application on my laptop with SQL Express 2008 works fine.. the application starts up, retrieves 1000 records and I can tab through the controls on the ribbon. Now, I decided to demo the application to a third party and used remote login/sharing software online to share my desktop with the other person so as I could load the application on my laptop and they could view me using the application. Now, the application takes approx 45 seconds to load... 30 seconds with a blank database where as, when im not sharing out my screen using the online software the application loads in about 7-10 seconds. As well as that, even using the controls in the application during the demo were very sticky, slow and unresponsive. During the sharing session though however I was able to use other applications without any problems.. everything else worked fine. But I cannot understand how my application works ok under normal conditions , even browsing the net at the same time etc... BUT totally fails to perform correctly when I am sharing a session with another user... the CPU usage shot up to 100% too at times when the application was trying to start up... Please see below a list of 3rd party dlls I am using as references in my project. DevExpress dlls FluidKit PixelLab.WPF PixelLab.Common Galasoft WPF Kit FluentNHibernate NHibernate Nhibernate.ByteCode.Castle Skype4ComLib TXTEXTControl log4net LinqKit All of these DLLs are in the output folder with the application dlls created from the class assemblys in the project. So when installed via an installer on a machine the dlls will be in the same application folder as the application file itself. Many thanks

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• User Mailer Failing

  - by Trevor Nederlof

  I have setup a process in my User model to send a bunch of @users to a mailing script, user_mailer.rb I am using the http://postageapp.com app to send out emails. The users are getting to the User_mailer but I am getting an error from there. Can anyone please point me in the right direction. User Model: class User < ActiveRecord::Base acts_as_authentic def self.mail_out weekday = Date.today.strftime('%A').downcase @users = find(:all, :conditions => {"#{weekday}sub".to_sym => 't'}) UserMailer.deliver_mail_out(@users) end end User_mailer.rb class UserMailer < ActionMailer::Base def mail_out(users) @recipients = { } users.each do |user| @recipients[user.email] = { :zipcode => user.zipcode } end from "[email protected]" subject "Check out the trailer of the day!" body :user => user end end mail_out.html.erb {{zipcode}}, Please check out the trailer of the day at http://www.dailytrailer.net Thank you! -- The DailyTrailer.net Team User db schema create_table "users", :force => true do |t| t.string "email" t.date "birthday" t.string "gender" t.string "zipcode" t.datetime "created_at" t.datetime "updated_at" t.string "crypted_password" t.string "password_salt" t.string "persistence_token" t.string "mondaysub", :default => "f", :null => false t.string "tuesdaysub", :default => "f", :null => false t.string "wednesdaysub", :default => "f", :null => false t.string "thursdaysub", :default => "f", :null => false t.string "fridaysub", :default => "f", :null => false t.string "saturdaysub", :default => "f", :null => false t.string "sundaysub", :default => "f", :null => false end Error: /var/lib/gems/1.8/gems/rails-2.3.5/lib/commands/runner.rb:48: undefined method `name' for #<User:0xb6e8ae48> (NoMethodError) from /home/tnederlof/Dropbox/Ruby/daily_trailer/app/models/user_mailer.rb:5:in `mail_out' from /home/tnederlof/Dropbox/Ruby/daily_trailer/app/models/user_mailer.rb:4:in `each' from /home/tnederlof/Dropbox/Ruby/daily_trailer/app/models/user_mailer.rb:4:in `mail_out' from /home/tnederlof/.gem/ruby/1.8/gems/actionmailer-2.3.5/lib/action_mailer/base.rb:459:in `__send__' from /home/tnederlof/.gem/ruby/1.8/gems/actionmailer-2.3.5/lib/action_mailer/base.rb:459:in `create!' from /home/tnederlof/.gem/ruby/1.8/gems/actionmailer-2.3.5/lib/action_mailer/base.rb:452:in `initialize' from /home/tnederlof/.gem/ruby/1.8/gems/actionmailer-2.3.5/lib/action_mailer/base.rb:395:in `new' from /home/tnederlof/.gem/ruby/1.8/gems/actionmailer-2.3.5/lib/action_mailer/base.rb:395:in `method_missing' from /home/tnederlof/Dropbox/Ruby/daily_trailer/app/models/user.rb:13:in `mail_out' from (eval):1 from /usr/lib/ruby/1.8/rubygems/custom_require.rb:31:in `eval' from /var/lib/gems/1.8/gems/rails-2.3.5/lib/commands/runner.rb:48 from /usr/lib/ruby/1.8/rubygems/custom_require.rb:31:in `gem_original_require' from /usr/lib/ruby/1.8/rubygems/custom_require.rb:31:in `require' from script/runner:3

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• CakePHP HABTM: Editing one item casuses HABTM row to get recreated, destroys extra data

  - by leo-the-manic

  I'm having trouble with my HABTM relationship in CakePHP. I have two models like so: Department HABTM Location. One large company has many buildings, and each building provides a limited number of services. Each building also has its own webpage, so in addition to the HABTM relationship itself, each HABTM row also has a url field where the user can visit to find additional information about the service they're interested and how it operates at the building they're interested in. I've set up the models like so: <?php class Location extends AppModel { var $name = 'Location'; var $hasAndBelongsToMany = array( 'Department' => array( 'with' => 'DepartmentsLocation', 'unique' => true ) ); } ?> <?php class Department extends AppModel { var $name = 'Department'; var $hasAndBelongsToMany = array( 'Location' => array( 'with' => 'DepartmentsLocation', 'unique' => true ) ); } ?> <?php class DepartmentsLocation extends AppModel { var $name = 'DepartmentsLocation'; var $belongsTo = array( 'Department', 'Location' ); // I'm pretty sure this method is unrelated. It's not being called when this error // occurs. Its purpose is to prevent having two HABTM rows with the same location // and department. function beforeSave() { // kill any existing rows with same associations $this->log(__FILE__ . ": killing existing HABTM rows", LOG_DEBUG); $result = $this->find('all', array("conditions" => array("location_id" => $this->data['DepartmentsLocation']['location_id'], "department_id" => $this->data['DepartmentsLocation']['department_id']))); foreach($result as $row) { $this->delete($row['DepartmentsLocation']['id']); } return true; } } ?> The controllers are completely uninteresting. The problem: If I edit the name of a Location, all of the DepartmentsLocations that were linked to that Location are re-created with empty URLs. Since the models specify that unique is true, this also causes all of the newer rows to overwrite the older rows, which essentially destroys all of the URLs. I would like to know two things: Can I stop this? If so, how? And, on a less technical and more whiney note: Why does this even happen? It seems bizarre to me that editing a field through Cake should cause so much trouble, when I can easily go through phpMyAdmin, edit the Location name there, and get exactly the result I would expect. Why does CakePHP touch the HABTM data when I'm just editing a field on a row? It's not even a foreign key!

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• Where can I find information on the Get, Set and Address methods for multidimensional System.Array i

  - by Rob Smallshire

  System.Array serves as the base class for all arrays in the Common Language Runtime (CLR). According to this article, For each concrete array type, [the] runtime adds three special methods: Get/Set/Address. and indeed if I disassemble this C# code, int[,] x = new int[1024,1024]; x[0,0] = 1; x[1,1] = 2; x[2,2] = 3; Console.WriteLine(x[0,0]); Console.WriteLine(x[1,1]); Console.WriteLine(x[2,2]); into CIL I get, IL_0000: ldc.i4 0x400 IL_0005: ldc.i4 0x400 IL_000a: newobj instance void int32[0...,0...]::.ctor(int32, int32) IL_000f: stloc.0 IL_0010: ldloc.0 IL_0011: ldc.i4.0 IL_0012: ldc.i4.0 IL_0013: ldc.i4.1 IL_0014: call instance void int32[0...,0...]::Set(int32, int32, int32) IL_0019: ldloc.0 IL_001a: ldc.i4.1 IL_001b: ldc.i4.1 IL_001c: ldc.i4.2 IL_001d: call instance void int32[0...,0...]::Set(int32, int32, int32) IL_0022: ldloc.0 IL_0023: ldc.i4.2 IL_0024: ldc.i4.2 IL_0025: ldc.i4.3 IL_0026: call instance void int32[0...,0...]::Set(int32, int32, int32) IL_002b: ldloc.0 IL_002c: ldc.i4.0 IL_002d: ldc.i4.0 IL_002e: call instance int32 int32[0...,0...]::Get(int32, int32) IL_0033: call void [mscorlib]System.Console::WriteLine(int32) IL_0038: ldloc.0 IL_0039: ldc.i4.1 IL_003a: ldc.i4.1 IL_003b: call instance int32 int32[0...,0...]::Get(int32, int32) IL_0040: call void [mscorlib]System.Console::WriteLine(int32) IL_0045: ldloc.0 IL_0046: ldc.i4.2 IL_0047: ldc.i4.2 IL_0048: call instance int32 int32[0...,0...]::Get(int32, int32) IL_004d: call void [mscorlib]System.Console::WriteLine(int32) where the calls to the aforementioned Get and Set methods can be clearly seen. It seems the arity of these methods is related to the dimensionality of the array, which is presumably why they are created by the runtime and are not pre-declared. I couldn't locate any information about these methods on MSDN and their simple names makes them resistant to Googling. I'm writing a compiler for a language which supports multidimensional arrays, so I'd like to find some official documentation about these methods, under what conditions I can expect them to exist and what I can expect their signatures to be. In particular, I'd like to know whether its possible to get a MethodInfo object for Get or Set for use with Reflection.Emit without having to create an instance of the array with correct type and dimensionality on which to reflect, as is done in the linked example.

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• Checking if an int is prime more efficiently

  - by SipSop

  I recently was part of a small java programming competition at my school. My partner and I have just finished our first pure oop class and most of the questions were out of our league so we settled on this one (and I am paraphrasing somewhat): "given an input integer n return the next int that is prime and its reverse is also prime for example if n = 18 your program should print 31" because 31 and 13 are both prime. Your .class file would then have a test case of all the possible numbers from 1-2,000,000,000 passed to it and it had to return the correct answer within 10 seconds to be considered valid. We found a solution but with larger test cases it would take longer than 10 seconds. I am fairly certain there is a way to move the range of looping from n,..2,000,000,000 down as the likely hood of needing to loop that far when n is a low number is small, but either way we broke the loop when a number is prime under both conditions is found. At first we were looping from 2,..n no matter how large it was then i remembered the rule about only looping to the square root of n. Any suggestions on how to make my program more efficient? I have had no classes dealing with complexity analysis of algorithms. Here is our attempt. public class P3 { public static void main(String[] args){ long loop = 2000000000; long n = Integer.parseInt(args[0]); for(long i = n; i<loop; i++) { String s = i +""; String r = ""; for(int j = s.length()-1; j>=0; j--) r = r + s.charAt(j); if(prime(i) && prime(Long.parseLong(r))) { System.out.println(i); break; } } System.out.println("#"); } public static boolean prime(long p){ for(int i = 2; i<(int)Math.sqrt(p); i++) { if(p%i==0) return false; } return true; } } ps sorry if i did the formatting for code wrong this is my first time posting here. Also the output had to have a '#' after each line thats what the line after the loop is about Thanks for any help you guys offer!!!

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• Good working habits to observe in project development?

  - by Will Marcouiller

  As my development experience grows, I see fit to stick to best practices from here and there to build somehow my own working practices while observing the conventions, etc. I'm currently working on a project which my goals is to graduate the security access model from an environment's Active Directory to another environment's automatically. I don't know for any of you, but as far as I'm concerned, I meet some real difficulties sticking to only one way, then develop. I mean, I learn something new everyday while visiting SO, and recently wanted to get acquainted with generics. On the other hand, I better know the Façade pattern which proved to be very practical in transactional programming in process systems. This seems to be less practical for desktop application as there are plenty of variables to consider in a desktop application that you don't have to care in transactional programming, as you're playing only with information data. As for my current project, I have: Groups; Organizational Units; Users. Which are all considered an entry in the Active Directory. This points out to be a good candidate for generics, as also approached this way by Bart de Smett's Linq to AD on CodePlex. He has a DirectorySource<T>, and to manage let's say groups, then he instantiate a source with the proper type: var groups = new DirectorySource<Group>(); This seems to be very a good way of doing. Despite, I seem to go from one pattern to another and I don't seem to be able to strictly stick to one. While I'm aware that one must not stay with only one way of doing, since each pattern statisfies certain advantages, while also illustrating disadvantages under some usage conditions, I seem to want to develop with both patterns having a singleton Façade class with the underlying factories which represent the sub systems: GroupsFactory; UsersFactory; OrganizationalUnitsFactory. Each of the factories offers the possible operations for their respective entity (group, user, OU). To make a very long story short, I often have plenty of ideas while developping and this causes me some trouble, as I go from an idea to another feeling completely lost after a while. Yet I understand the advantages and disavantages, I have no trouble choosing from one pattern to another depending on the situation. Nevertheless, when it comes to programming itself, if I'm not part of a team, I feel sometimes like I can't do anything good. That is, because I can't stand not doing something "perfect" the first time. The role I play within the project is both: the project manager and the programmer. I am more comfortable in the project manager role, architectural role, analytical role than the developer's. Has any of you some good habbits to observe in project development? Thanks to you all! =)

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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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• Under what circumstances would a LINQ-to-SQL Entity "lose" a changed field?

  - by John Rudy

  I'm going nuts over what should be a very simple situation. In an ASP.NET MVC 2 app (not that I think this matters), I have an edit action which takes a very small entity and makes a few changes. The key portion (outside of error handling/security) looks like this: Todo t = Repository.GetTodoByID(todoID); UpdateModel(t); Repository.Save(); Todo is the very simple, small entity with the following fields: ID (primary key), FolderID (foreign key), PercentComplete, TodoText, IsDeleted and SaleEffortID (foreign key). Each of these obviously corresponds to a field in the database. When UpdateModel(t) is called, t does get correctly updated for all fields which have changed. When Repository.Save() is called, by the time the SQL is written out, FolderID reverts back to its original value. The complete code to Repository.Save(): public void Save() { myDataContext.SubmitChanges(); } myDataContext is an instance of the DataContext class created by the LINQ-to-SQL designer. Nothing custom has been done to this aside from adding some common interfaces to some of the entities. I've validated that the FolderID is getting lost before the call to Repository.Save() by logging out the generated SQL: UPDATE [Todo].[TD_TODO] SET [TD_PercentComplete] = @p4, [TD_TodoText] = @p5, [TD_IsDeleted] = @p6 WHERE ([TD_ID] = @p0) AND ([TD_TDF_ID] = @p1) AND /* Folder ID */ ([TD_PercentComplete] = @p2) AND ([TD_TodoText] = @p3) AND (NOT ([TD_IsDeleted] = 1)) AND ([TD_SE_ID] IS NULL) /* SaleEffort ID */ -- @p0: Input BigInt (Size = -1; Prec = 0; Scale = 0) [5] -- @p1: Input BigInt (Size = -1; Prec = 0; Scale = 0) [1] /* this SHOULD be 4 and in the update list */ -- @p2: Input TinyInt (Size = -1; Prec = 0; Scale = 0) [90] -- @p3: Input NVarChar (Size = 4000; Prec = 0; Scale = 0) [changing text] -- @p4: Input TinyInt (Size = -1; Prec = 0; Scale = 0) [0] -- @p5: Input NVarChar (Size = 4000; Prec = 0; Scale = 0) [changing text foo] -- @p6: Input Bit (Size = -1; Prec = 0; Scale = 0) [True] -- Context: SqlProvider(Sql2005) Model: AttributedMetaModel Build: 4.0.30319.1 So somewhere between UpdateModel(t) (where I've validated in the debugger that FolderID updated) and the output of this SQL, the FolderID reverts. The other fields all save. (Well, OK, I haven't validated SaleEffortID yet, because that subsystem isn't really ready yet, but everything else saves.) I've exhausted my own means of research on this: Does anyone know of conditions which would cause a partial entity reset (EG, something to do with long foreign keys?), and/or how to work around this?

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• To detect if the user is closing the IE browser apart from onunload event, as it is triggerred when

  - by AndAars

  hi, After being through numerous forums available on the net for last 5 days, I am still not able to completely track down the browser close event. My requirement is to generate a popup message, when user tries to close the browser. I have called my javascript function on body 'onbeforeunload' event. And I have hardcoded the conditions to check the mouse-coordinates for the red 'X' buton of browser, refresh, File-close or Alt-F4. My code works fine when browser window is Maximized, but fails if we shrink it after a limit. Please help me, if some body has already found the solution to a similar problem. Thank you. Aggregated Responses of OP Ok, just tell me if it is possible to detect if a user has clicked on the Refresh button of the browser. Also, Refresh can be triggered by Right-click - Refresh or Ctrl-R. My requirement is to make a variable false on Refresh. I am just able to do it on F5, but all other ways are still out of my reach. The same would be applied to Back buton. Hi ppl, Thanks for all who replied atleast. I have talked to my seniors regarding this and they have now understood and have compromised with the browser menu buttons. So now my task has become easy. Now, I am using a variable and making it true by default. As, I mentioned earlier I just have to catch the onbeforeunload and popup a message when user tries to leave. The message will not popup when user is navigating to other pages, as I have made the variable as false on all the links of my page using following piece of code: document.onclick = function() { //To check if user is navigating from the page by clicking on a hyperlink. if (event.srcElement.tagName == 'A') blnShowMsg = false; //To not popup the warning message else blnShowMsg = true; //To popup the warning message } In my case still the message is shown when user does Refresh, back or goes to any link in Favorites, etc. Thanks buddy, but I have already gone through that and didn't find much help there too. My seniors are not happy with that solution as putting a flag on evry link of my application is a complicated job and they fear of breaking the application. Any other suggestions would be appreciated. Thanks once again. Is there no one who can think of a solution here!!! where are all the experts???

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• Why do some questions get closed for no reason? [closed]

  - by IVlad

  Recently there was a question asking about generating all subsets of a set using a stack and a queue, which was closed (and now deleted it seems) as not a real question for no good reason, since it didn't fit into any of these conditions: It's difficult to tell what is being asked here. No, it was clear what was being asked. This question is ambiguous, vague, incomplete, or rhetorical and cannot be reasonably answered in its current form. Not ambiguous, not vague, not incomplete, definitely not rhetorical and could easily be answered if one knew the solution. Now, the exact same thing has happened with this question: http://stackoverflow.com/questions/2791982/a-shortest-path-problem-with-superheroes-and-intergalactic-journeys/2793746#2793746 I am interested in hearing a logical argument for why that question is either ambiguous, vague, incomplete, rhetorical or cannot reasonably be answered in its current form. It seems that (the same bunch of) people like to close questions that they think are homework questions, especially when they think people want to be served the solution on a platter, which is also not the case: Any suggestions or ideas of how this problem might be solved would be most welcomed. Most of the time the people asking these questions are very reasonable and appreciate even the most vague idea, yet their question is closed. Let's go further and assume that it IS a homework problem. So what? When I registered here I didn't see any rule that said not to post homework problems, nor do I see such a rule now. What is wrong with posting homework problems that makes people hunt them down with a passion to close them without even reading the entire question body? This site is full of questions asked by people who get paid to know the things they are asking, yet their questions are considered fine. How is solving someone's homework problem worse? In some places (like where I live), computer science is a mandatory high school subject, and not everyone is interested in it. How is helping at least those people worse than doing someone's JOB? Not answering homework questions is fine and it's everyone's choice, but I consider closing them to be an act of power abuse, selfishness, and an insult to the fellow community members who are also interested in a solution or want feedback on their proposed solution. So my questions are: - Why do questions like the above get closed for reasons that do not apply? Why do you close them? Why don't you? - Why doesn't a vote to reopen a question reopen it automatically? Needing 5 votes for a reopen takes too long, and it's not fair because one reopen vote basically cancels out a close vote, making it 4 close votes (or 5 to 1, which is the same as only 4 people wanting to close the question), which isn't enough to close the question. I think a question should only be closed when CloseVotes - ReopenVotes >= 5. I'm hoping this will stay up, but I realize it probably won't. In either case, I think this is worth saying and discussing, since it IS community-related.

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• Parsing language for both binary and character files

  - by Thorsten S.

  The problem: You have some data and your program needs specified input. For example strings which are numbers. You are searching for a way to transform the original data in a format you need. And the problem is: The source can be anything. It can be XML, property lists, binary which contains the needed data deeply embedded in binary junk. And your output format may vary also: It can be number strings, float, doubles.... You don't want to program. You want routines which gives you commands capable to transform the data in a form you wish. Surely it contains regular expressions, but it is very good designed and it offers capabilities which are sometimes much more easier and more powerful. Something like a super-grep which you can access (!) as program routines, not only as tool. It allows: joining/grouping/merging of results inserting/deleting/finding/replacing write macros which allows to execute a command chain repeatedly meta-grouping (lists-tables-hypertables) Example (No, I am not looking for a solution to this, it is just an example): You want to read xml strings embedded in a binary file with variable length records. Your tool reads the record length and deletes the junk surrounding your text. Now it splits open the xml and extracts the strings. Being Indian number glyphs and containing decimal commas instead of decimal points, your tool transforms it into ASCII and replaces commas with points. Now the results must be stored into matrices of variable length....etc. etc. I am searching for a good language / language-design and if possible, an implementation. Which design do you like or even, if it does not fulfill the conditions, wouldn't you want to miss ? EDIT: The question is if a solution for the problem exists and if yes, which implementations are available. You DO NOT implement your own sorting algorithm if Quicksort, Mergesort and Heapsort is available. You DO NOT invent your own text parsing method if you have regular expressions. You DO NOT invent your own 3D language for graphics if OpenGL/Direct3D is available. There are existing solutions or at least papers describing the problem and giving suggestions. And there are people who may have worked and experienced such problems and who can give ideas and suggestions. The idea that this problem is totally new and I should work out and implement it myself without background knowledge seems for me, I must admit, totally off the mark.

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• Runge-Kutta Method with adaptive step

  - by infoholic_anonymous

  I am implementing Runge-Kutta method with adaptive step in matlab. I get different results as compared to matlab's own ode45 and my own implementation of Runge-Kutta method with fixed step. What am I doing wrong in my code? Is it possible? function [ result ] = rk4_modh( f, int, init, h, h_min ) % % f - function handle % int - interval - pair (x_min, x_max) % init - initial conditions - pair (y1(0),y2(0)) % h_min - lower limit for h (step length) % h - initial step length % x - independent variable ( for example time ) % y - dependent variable - vertical vector - in our case ( y1, y2 ) function [ k1, k2, k3, k4, ka, y ] = iteration( f, h, x, y ) % core functionality performed within loop k1 = h * f(x,y); k2 = h * f(x+h/2, y+k1/2); k3 = h * f(x+h/2, y+k2/2); k4 = h * f(x+h, y+k3); ka = (k1 + 2*k2 + 2*k3 + k4)/6; y = y + ka; end % constants % relative error eW = 1e-10; % absolute error eB = 1e-10; s = 0.9; b = 5; % initialization i = 1; x = int(1); y = init; while true hy = y; hx = x; %algorithm [ k1, k2, k3, k4, ka, y ] = iteration( f, h, x, y ); % error estimation for j=1:2 [ hk1, hk2, hk3, hk4, hka, hy ] = iteration( f, h/2, hx, hy ); hx = hx + h/2; end err(:,i) = abs(hy - y); % step adjustment e = abs( hy ) * eW + eB; a = min( e ./ err(:,i) )^(0.2); mul = a * s; if mul >= 1 % step length admitted keepH(i) = h; k(:,:,i) = [ k1, k2, k3, k4, ka ]; previous(i,:) = [ x+h, y' ]; %' i = i + 1; if floor( x + h + eB ) == int(2) break; else h = min( [mul*h, b*h, int(2)-x] ); x = x + keepH(i-1); end else % step length requires further adjustments h = mul * h; if ( h < h_min ) error('Computation with given precision impossible'); end end end result = struct( 'val', previous, 'k', k, 'err', err, 'h', keepH ); end The function in question is: function [ res ] = fun( x, y ) % res(1) = y(2) + y(1) * ( 0.9 - y(1)^2 - y(2)^2 ); res(2) = -y(1) + y(2) * ( 0.9 - y(1)^2 - y(2)^2 ); res = res'; %' end The call is: res = rk4( @fun, [0,20], [0.001; 0.001], 0.008 ); The resulting plot for x1 : The result of ode45( @fun, [0, 20], [0.001, 0.001] ) is:

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