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• propositional theorems

  - by gcc

  wang's theorem to prove theorems in propositonal calculus Label Sequent Comment S1: P ? Q, Q ? R, ¬R ? ¬P Initial sequent. S2: ¬P ? Q, ¬Q ? R, ¬R ? ¬P Two applications of R5. S3: ¬P ? Q, ¬Q ? R ? ¬P, R Rl. S4: ¬P, ¬Q ? R ? ¬P, R S4 and S5 are obtained from S3 with R3. Note that S4 is an axiom since P appears on both sides of the sequent ar- row at the top level. S5: Q, ¬Q ? R ? ¬P, R The other sequent generated by the ap- plication of R3. S6: Q, ¬Q ? ¬P, R S6 and S7 are obtained from S5 using R3. S7: Q, R ? ¬P, R This is an axiom. S8: Q ? ¬P, R, Q Obtained from S6 using R1. S8 is an axiom. The original sequent is now proved, since it has successfully been transformed into a set of three axioms with no unproved sequents left over. //R1,R2,R3,R4,R5 is transformation myhomework is so complicate as you can see and i must finish homework in 4 days i just want help ,can you show me how i should construct the algorithm or how i should take and store the input

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• .NET ValidationRule problem

  - by PaN1C_Showt1Me

  Hi ! I have a control with this validation <MyPicker.SelectedItem> <Binding Path="Person.Value" Mode="TwoWay" UpdateSourceTrigger="PropertyChanged" NotifyOnValidationError="True"> <Binding.ValidationRules> <rules:MyValidationRule ValidationType="notnull"/> </Binding.ValidationRules> </Binding> </MyPicker.SelectedItem> This is the Validation Class: class MyValidationRule : ValidationRule { private string _validationType; public string ValidationType { get { return _validationType; } set { _validationType = value; } } public override ValidationResult Validate(object value, CultureInfo cultureInfo) { ValidationResult trueResult = new ValidationResult(true, null); switch (_validationType.ToLower()) { case "notnull": return value == null ? new ValidationResult(false, "EMPTY FIELD") : trueResult; default: return trueResult; } } } Question: When the property is changed, then the Validate( ) method is called which is correct. But to call this method at the very beginning when the MyControl is created? I need to prove immediate after initialize if the there's a null value in the control (and display a validation error)

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• Pecking order of pigeons?

  - by sc_ray

  I was going though problems on graph theory posted by Prof. Ericksson from my alma-mater and came across this rather unique question about pigeons and their innate tendency to form pecking orders. The question goes as follows: Whenever groups of pigeons gather, they instinctively establish a pecking order. For any pair of pigeons, one pigeon always pecks the other, driving it away from food or potential mates. The same pair of pigeons always chooses the same pecking order, even after years of separation, no matter what other pigeons are around. Surprisingly, the overall pecking order can contain cycles—for example, pigeon A pecks pigeon B, which pecks pigeon C, which pecks pigeon A. Prove that any finite set of pigeons can be arranged in a row from left to right so that every pigeon pecks the pigeon immediately to its left. Since this is a question on Graph theory, the first things that crossed my mind that is this just asking for a topological sort of a graphs of relationships(relationships being the pecking order). What made this a little more complex was the fact that there can be cyclic relationships between the pigeons. If we have a cyclic dependency as follows: A-B-C-A where A pecks on B,B pecks on C and C goes back and pecks on A If we represent it in the way suggested by the problem, we have something as follows: C B A But the above given row ordering does not factor in the pecking order between C and A. I had another idea of solving it by mathematical induction where the base case is for two pigeons arranged according to their pecking order, assuming the pecking order arrangement is valid for n pigeons and then proving it to be true for n+1 pigeons. I am not sure if I am going down the wrong track here. Some insights into how I should be analyzing this problem will be helpful. Thanks

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• ArrayCollection loop through for matching items

  - by charlie

  Hi I hope someone can help me..... i am trying to build a dynamic form for a questionnaire module. Building on some previous posts I am using the process similar to that in question "http://stackoverflow.com/questions/629021/how-to-generate-a-formmxform-dynamically-in-flex" i have managed to prove out the fact of extending the XML to include a calendar, combobox etc. my problem is that now need to get the data from an ArrayCollection rather than from an xml file. I am looking to loop through the AC and where type = "text" render a textinput field, where a type ="calendar" render a Calendar etc etc. my code so far just looking at a textinput field (and sorry for all the comments included ;) is:- [Bindable] public var AC:ArrayCollection = new ArrayCollection( [ {type:'text', direction:'horizontal', tooltip:'test tooltip', label:'my textbox label', id:'1'}, {type:'text', direction:'horizontal', tooltip:'another tooltip', label:'another label', id:'2'} ]); private function init():void { var form:Form = new Form(); for each(var elements:XML in AC) { switch( [email protected]()) { case "text": var fi:FormItem = new FormItem(); // fi.toolTip = elements.tooltip.toString(); // fi.required = getglobalprofile.required.toString(); // fi.direction = getglobalprofileb[i].@direction; var li:Label = new Label(); // li.text = getglobalprofileb[i].@label; // li.width = 100; var ti:TextInput = new TextInput(); ti.text = "test"; ti.width = 200; form.addChild(fi); fi.addChild(li); fi.addChild(ti); // break; } } this.addChild( form); } ]] <mx:Form id="form" name="form"> </mx:Form> if you are interested in the working xml version (rendering only) let me know and i will post this as well

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• what makes a Tomcat5.5 cannot be "aware" of new Java Web Applications?

  - by Michael Mao

  This is for uni homework, but I reckon it is more a generic problem to the Tomcat Server(version 5.5.27) on my uni. The problem is, I first did a skeleton Java Web Application (Just a simple Servlet and a welcome-file, nothing complicated, no lib included) using NetBeans 6.8 with the bundled Tomcat 6.0.20 (localhost:8084/WSD) Then, to test and prove it is "portable" and "auto-deploy-able", I cleaned and built a WSD.war file and dropped it onto my Xampp Tomcat (localhost:8080/WSD). The war extracted everything accordingly and I can see identical output from this Tomcat. So far, so good. However, after I tried to drop to war onto uni server, funny thing happens: uni server Even though I've changed the war permission to 755, it is simply not "responding". I then copied the extracted files to uni server, the MainServlet cannot be recognized from within its Context Path "/WSD", basically nothing works, expect the static index.jsp. I tried several times to stop and restart uni Tomcat, it doesn't help? I wonder what makes this happen? Is there anything I did wrong with my approach? To be frank I paid no attention to a server not under my control, and I am unfortunately not a real active day-to-day Java Programmer now. I understand the fundamentals of MVC, Servelets, JSPs, JavaBeans, but I really feel frustrated by this, as I cannot see why... Or, should I ask, a Java Web Application, after cleaned and built by NetBeans6.8, is self-contained and self-configured so ready to be deployed to any Java Web Container? I know, I can certainly program everything in plain old JSP, but this is soooo... unacceptable to myself... Update : I am now wondering if there is any free Tomcat Hosting so that I would like to see if my war file and/or my web app can go with them without any configuration at all?

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• Simple encryption - Sum of Hashes in C

  - by Dogbert

  I am attempting to demonstrate a simple proof of concept with respect to a vulnerability in a piece of code in a game written in C. Let's say that we want to validate a character login. The login is handled by the user choosing n items, (let's just assume n=5 for now) from a graphical menu. The items are all medieval themed: eg: _______________________________ | | | | | Bow | Sword | Staff | |-----------|-----------|-------| | Shield | Potion | Gold | |___________|___________|_______| The user must click on each item, then choose a number for each item. The validation algorithm then does the following: Determines which items were selected Drops each string to lowercase (ie: Bow becomes bow, etc) Calculates a simple string hash for each string (ie: `bow = b=2, o=15, w=23, sum = (2+15+23=40) Multiplies the hash by the value the user selected for the corresponding item; This new value is called the key Sums together the keys for each of the selected items; this is the final validation hash IMPORTANT: The validator will accept this hash, along with non-zero multiples of it (ie: if the final hash equals 1111, then 2222, 3333, 8888, etc are also valid). So, for example, let's say I select: Bow (1) Sword (2) Staff (10) Shield (1) Potion (6) The algorithm drops each of these strings to lowercase, calculates their string hashes, multiplies that hash by the number selected for each string, then sums these keys together. eg: Final_Validation_Hash = 1*HASH(Bow) + 2*HASH(Sword) + 10*HASH(Staff) + 1*HASH(Shield) + 6*HASH(Potion) By application of Euler's Method, I plan to demonstrate that these hashes are not unique, and want to devise a simple application to prove it. in my case, for 5 items, I would essentially be trying to calculate: (B)(y) = (A_1)(x_1) + (A_2)(x_2) + (A_3)(x_3) + (A_4)(x_4) + (A_5)(x_5) Where: B is arbitrary A_j are the selected coefficients/values for each string/category x_j are the hash values for each string/category y is the final validation hash (eg: 1111 above) B,y,A_j,x_j are all discrete-valued, positive, and non-zero (ie: natural numbers) Can someone either assist me in solving this problem or point me to a similar example (ie: code, worked out equations, etc)? I just need to solve the final step (ie: (B)(Y) = ...). Thank you all in advance.

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• Ad distribution problem: an optimal solution?

  - by Mokuchan

  I'm asked to find a 2 approximate solution to this problem: You’re consulting for an e-commerce site that receives a large number of visitors each day. For each visitor i, where i € {1, 2 ..... n}, the site has assigned a value v[i], representing the expected revenue that can be obtained from this customer. Each visitor i is shown one of m possible ads A1, A2 ..... An as they enter the site. The site wants a selection of one ad for each customer so that each ad is seen, overall, by a set of customers of reasonably large total weight. Thus, given a selection of one ad for each customer, we will define the spread of this selection to be the minimum, over j = 1, 2 ..... m, of the total weight of all customers who were shown ad Aj. Example Suppose there are six customers with values 3, 4, 12, 2, 4, 6, and there are m = 3 ads. Then, in this instance, one could achieve a spread of 9 by showing ad A1 to customers 1, 2, 4, ad A2 to customer 3, and ad A3 to customers 5 and 6. The ultimate goal is to find a selection of an ad for each customer that maximizes the spread. Unfortunately, this optimization problem is NP-hard (you don’t have to prove this). So instead give a polynomial-time algorithm that approximates the maximum spread within a factor of 2. The solution I found is the following: Order visitors values in descending order Add the next visitor value (i.e. assign the visitor) to the Ad with the current lowest total value Repeat This solution actually seems to always find the optimal solution, or I simply can't find a counterexample. Can you find it? Is this a non-polinomial solution and I just can't see it?

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• Xcode "Build and Archive" from command line

  - by Dan Fabulich

  Xcode 3.2 provides an awesome new feature under the Build menu, "Build and Archive" which generates an .ipa file suitable for Ad Hoc distribution. You can also open the Organizer, go to "Archived Applications," and "Submit Application to iTunesConnect." Is there a way to use "Build and Archive" from the command line (as part of a build script)? I'd assume that xcodebuild would be involved somehow, but the man page doesn't seem to say anything about this. UPDATE Michael Grinich requested clarification; here's what exactly you can't do with command-line builds, features you can ONLY do with Xcode's Organizer after you "Build and Archive." You can click "Share Application..." to share your IPA with beta testers. As Guillaume points out below, due to some Xcode magic, this IPA file does not require a separately distributed .mobileprovision file that beta testers need to install; that's magical. No command-line script can do it. For example, Arrix's script (submitted May 1) does not meet that requirement. More importantly, after you've beta tested a build, you can click "Submit Application to iTunes Connect" to submit that EXACT same build to Apple, the very binary you tested, without rebuilding it. That's impossible from the command line, because signing the app is part of the build process; you can sign bits for Ad Hoc beta testing OR you can sign them for submission to the App Store, but not both. No IPA built on the command-line can be beta tested on phones and then submitted directly to Apple. I'd love for someone to come along and prove me wrong: both of these features work great in the Xcode GUI and cannot be replicated from the command line.

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• WPF Usercontrol with textboxes

  - by benPearce

  I have a WPF user control with a number of textboxes, this is hosted on a WPF window. The textboxes are not currently bound but I cannot type into any of them. I have put a breakpoint in the KeyDown event of one of the textboxes and it hits it fine and I can see the key I pressed. The textboxes are declared as <TextBox Grid.Row="3" Grid.Column="4" x:Name="PostcodeSearch" Style="{StaticResource SearchTextBox}" KeyDown="PostcodeSearch_KeyDown"/> The style is implemented as <Style x:Key="SearchTextBox" TargetType="{x:Type TextBox}"> <Setter Property="Control.Margin" Value="2"/> <Setter Property="Height" Value="20"/> <Setter Property="Width" Value="140"/> <Setter Property="HorizontalAlignment" Value="Left"/> </Style> I am hoping I have overlooked something obvious. EDIT: I only added the KeyDown and KeyUp events just to prove that the keys presses were getting through. I do not have any custom functionality.

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• Select statement with multiple 'where' fields using same value without duplicating text

  - by kdbdallas

  I will start by saying that I don't think what I want can be done, but that said, I am hoping I am wrong and someone knows more than me. So here is your chance... Prove you are smarter than me :) I want to do a search against a SQLite table looking for any records that "are similar" without having to write out the query in long hand. To clarify this is how I know I can write the query: select * from Articles where title like '%Bla%' or category like '%Bla%' or post like '%Bla%' This works and is not a huge deal if you are only checking against a couple of columns, but if you need to check against a bunch then your query can get really long and nasty looking really fast, not to mention the chance for typos. (ie: 'Bla%' instead of '%Bla%') What I am wondering is if there is a short hand way to do this? *This next code does not work the way I want, but just shows kind of what I am looking for select * from Articles where title or category or post like '%Bla%' Anyone know if there is a way to specify that multiple 'where' columns should use the same search value without listing that same search value for every column? Thanks in advance!

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• Plotting a graph with GD

  - by Nayena

  Here it goes. I have been thinking about this for a long time, and havent really been able to put up a proper way to do it yet. I havent implemented anything yet, as im still designing the thing. The idea is that i crawl a website for internal links, i got this settled, its easy, but after the crawling, i end up with an array with lots of links, and how many times those particular link appears on the site that i crawled (and how they're connected). With this huge array, i want to draw a graph somehow. Assuming i can handle the data correctly, the real question here is how i can draw this in a image by the use of the GD library. I figured if theres less than 12 elements, i can align them up on a unit circle spacing them up as a circle and then connecting them accordingly, so anything up to 12 elements shouldn't be a problem, but if theres more than 12, it could be awesome getting them lined up like this Or well, thats just a rough drawing, but i guess its just to prove a point. So i'm here looking for guidance or tips towards getting the math down to getting the stuff lined up in a good way. I have previously made bar-graphs, so i have little experience doing math with GD. If possible, id prefer not using some plotter-library - in the end, it gives me a better understanding on how things are supposed to be.

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• How can i mock or test my deferred execution functionality?

  - by cottsak

  I have what could be seen as a bizarre hybrid of IQueryable<T> and IList<T> collections of domain objects passed up my application stack. I'm trying to maintain as much of the 'late querying' or 'lazy loading' as possible. I do this in two ways: By using a LinqToSql data layer and passing IQueryable<T>s through by repositories and to my app layer. Then after my app layer passing IList<T>s but where certain elements in the object/aggregate graph are 'chained' with delegates so as to defer their loading. Sometimes even the delegate contents rely on IQueryable<T> sources and the DataContext are injected. This works for me so far. What is blindingly difficult is proving that this design actually works. Ie. If i defeat the 'lazy' part somewhere and my execution happens early then the whole thing is a waste of time. I'd like to be able to TDD this somehow. I don't know a lot about delegates or thread safety as it applies to delegates acting on the same source. I'd like to be able to mock the DataContext and somehow trace both methods of deferring (IQueryable<T>'s SQL and the delegates) the loading so that i can have tests that prove that both functions are working at different levels/layers of the app/stack. As it's crucial that the deferring works for the design to be of any value, i'd like to see tests fail when i break the design at a given level (separate from the live implementation). Is this possible?

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• Anyone NOT using a Web Framework? Why?

  - by tom

  I'm well aware of the many reasons to use a web framework. I'm just wondering whether anyone out there is using absolutely no web framework whatsoever to develop their web projects. I would really love to know the reason(s) why you're not using a web framework. For the sake of this discussion, your programming language of choice does not matter. Some possibilities for discussion: You don't hide behind an ORM. You don't rely on any sort of templating system. You think MVC is a really nice TLA but lacks an essential vowel or two. No need for any additional javascript framework tomfoolery. You just write as much code as possible in your native programming language(s). Summary of reasons thus far: Language learning opportunities. Specific performance reasons (write-intensive transaction processing). Seeking more nuanced control over your data and applications (less abstraction). You're building your own framework! Prove to yourself that you can succeed (or fail) just like the big framework-building gurus. Integration issues with unpopular/legacy technologies (exotic databases or protocols come to mind). Big company, lots of code, no talent nor buy-in present to move to a web framework. Some frameworks really lock you in and cannot perpetually grow along with your needs. These few black sheep don't make it easy to jump outside of the framework, write some custom code, and easily jump back in. When you finally escape the asylum, you'll never look back.

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• Rewriting jQuery to plain old javascript - are the performance gains worth it?

  - by Swader

  Since jQuery is an incredibly easy and banal library, I've developed a rather complex project fairly quickly with it. The entire interface is jQuery based, and memory is cleaned regularly to maintain optimum performance. Everything works very well in Firefox, and exceptionally so in Chrome (other browsers are of no concern for me as this is not a commercial or publicly available product). What I'm wondering now is - since pure plain old javascript is really not a complicated language to master, would it be performance enhancing to rewrite the whole thing in plain old JS, and if so, how much of a boost would you expect to get from it? If the answers prove positive enough, I'll go ahead and do it, run a benchmark and report back with the precise findings. Cheers Edit: Thanks guys, valuable insight. The purpose was not to "re-invent the wheel" - it was just for experience and personal improvement. Just because something exists, doesn't mean you shouldn't explore it into greater detail, know how it works or try to recreate it. This is the same reason I seldom use frameworks, I would much rather use my own code and iron it out and gain massive experience doing it, than start off by using someone else's code, regardless of how ironed out it is. Anyway, won't be doing it, thanks for saving me the effort :)

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• Best way to sign data in web form with user certificate

  - by salgiza

  We have a C# web app where users will connect using a digital certificate stored in their browsers. From the examples that we have seen, verifying their identity will be easy once we enable SSL, as we can access the fields in the certificate, using Request.ClientCertificate, to check the user's name. We have also been requested, however, to sign the data sent by the user (a few simple fields and a binary file) so that we can prove, without doubt, which user entered each record in our database. Our first thought was creating a small text signature including the fields (and, if possible, the md5 of the file) and encrypt it with the private key of the certificate, but... As far as I know we can't access the private key of the certificate to sign the data, and I don't know if there is any way to sign the fields in the browser, or we have no other option than using a Java applet. And if it's the latter, how we would do it (Is there any open source applet we can use? Would it be better if we create one ourselves?) Of course, it would be better if there was any way to "sign" the fields received in the server, using the data that we can access from the user's certificate. But if not, any info on the best way to solve the problem would be appreciated.

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• Why does this code sample produce a memory leak?

  - by citronas

  In the university we were given the following code sample and we were being told, that there is a memory leak when running this code. The sample should demonstrate that this is a situation where the garbage collector can't work. As far as my object oriented programming goes, the only codeline able to create a memory leak would be items=Arrays.copyOf(items,2 * size+1); The documentation says, that the elements are copied. Does that mean the reference is copied (and therefore another entry on the heap is created) or the object itself is being copied? As far as I know, Object and therefore Object[] are implemented as a reference type. So assigning a new value to 'items' would allow the garbage collector to find that the old 'item' is no longer referenced and can therefore be collected. In my eyes, this the codesample does not produce a memory leak. Could somebody prove me wrong? =) import java.util.Arrays; public class Foo { private Object[] items; private int size=0; private static final int ISIZE=10; public Foo() { items= new Object[ISIZE]; } public void push(final Object o){ checkSize(); items[size++]=o; } public Object pop(){ if (size==0) throw new ///... return items[--size]; } private void checkSize(){ if (items.length==size){ items=Arrays.copyOf(items,2 * size+1); } } }

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• Complicated .NET factory design

  - by Tom W

  Hello SO; I'm planning to ask a fairly elaborate question that is also something of a musing here, so bear with me... I'm trying to design a factory implementation for a simulation application. The simulation will consist of different sorts of entities i.e. it is not a homogenous simulation in any respect. As a result, there will be numerous very different concrete implementations and only the very general properties will be abstracted at the top level. What I'd like to be able to do is create new simulation entities by calling a method on the model with a series of named arguments representing the parameters of the entity, and have the model infer what type of object is being described by the inbound parameters (from the names of the parameters and potentially the sequence they occur in) and call a factory method on the appropriate derived class. For example, if I pass the model a pair of parameters (Param1=5000, Param2="Bacon") I would like it to infer that the names Param1 and Param2 'belong' to the class "Blob1" and call a shared function "getBlob1" with named parameters Param1:=5000, Param2:="Bacon" whereas if I pass the model (Param1=5000, Param3=50) it would call a similar factory method for Blob2; because Param1 and Param3 in that order 'belong' to Blob2. I foresee several issues to resolve: Whether or not I can reflect on the available types with string parameter names and how to do this if it's possible Whether or not there's a neat way of doing the appropriate constructor inference from the combinatoric properties of the argument list or whether I'm going to have to bodge something to do it 'by hand'. If possible I'd like the model class to be able to accept parameters as parameters rather than as some collection of keys and values, which would require the model to expose a large number of parametrised methods at runtime without me having to code them explicitly - presumably one for every factory method available in the relevant namespace. What I'm really asking is how you'd go about implementing such a system, rather than whether or not it's fundamentally possible. I don't have the foresight or experience with .NET reflection to be able to figure out a way by myself. Hopefully this will prove an informative discussion.

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• Point covering problem

  - by Sean

  I recently had this problem on a test: given a set of points m (all on the x-axis) and a set n of lines with endpoints [l, r] (again on the x-axis), find the minimum subset of n such that all points are covered by a line. Prove that your solution always finds the minimum subset. The algorithm I wrote for it was something to the effect of: (say lines are stored as arrays with the left endpoint in position 0 and the right in position 1) algorithm coverPoints(set[] m, set[][] n): chosenLines = [] while m is not empty: minX = min(m) bestLine = n[0] for i=1 to length of n: if n[i][0] <= m and n[i][1] > bestLine[1] then bestLine = n[i] add bestLine to chosenLines for i=0 to length of m: if m <= bestLine[1] then delete m[i] from m return chosenLines I'm just not sure if this always finds the minimum solution. It's a simple greedy algorithm so my gut tells me it won't, but one of my friends who is much better than me at this says that for this problem a greedy algorithm like this always finds the minimal solution. For proving mine always finds the minimal solution I did a very hand wavy proof by contradiction where I made an assumption that probably isn't true at all. I forget exactly what I did. If this isn't a minimal solution, is there a way to do it in less than something like O(n!) time? Thanks

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• Cost of logic in a query

  - by FrustratedWithFormsDesigner

  I have a query that looks something like this: select xmlelement("rootNode", (case when XH.ID is not null then xmlelement("xhID", XH.ID) else xmlelement("xhID", xmlattributes('true' AS "xsi:nil"), XH.ID) end), (case when XH.SER_NUM is not null then xmlelement("serialNumber", XH.SER_NUM) else xmlelement("serialNumber", xmlattributes('true' AS "xsi:nil"), XH.SER_NUM) end), /*repeat this pattern for many more columns from the same table...*/ FROM XH WHERE XH.ID = 'SOMETHINGOROTHER' It's ugly and I don't like it, and it is also the slowest executing query (there are others of similar form, but much smaller and they aren't causing any major problems - yet). Maintenance is relatively easy as this is mostly a generated query, but my concern now is for performance. I am wondering how much of an overhead there is for all of these case expressions. To see if there was any difference, I wrote another version of this query as: select xmlelement("rootNode", xmlforest(XH.ID, XH.SER_NUM,... (I know that this query does not produce exactly the same, thing, my plan was to move the logic to PL/SQL or XSL) I tried to get execution plans for both versions, but they are the same. I'm guessing that the logic does not get factored into the execution plan. My gut tells me the second version should execute faster, but I'd like some way to prove that (other than writing a PL/SQL test function with timing statements before and after the query and running that code over and over again to get a test sample). Is it possible to get a good idea of how much the case-when will cost? Also, I could write the case-when using the decode function instead. Would that perform better (than case-statements)?

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• Batch insert mode with hibernate and oracle: seems to be dropping back to slow mode silently

  - by Chris

  I'm trying to get a batch insert working with Hibernate into Oracle, according to what i've read here: http://docs.jboss.org/hibernate/core/3.3/reference/en/html/batch.html , but with my benchmarking it doesn't seem any faster than before. Can anyone suggest a way to prove whether hibernate is using batch mode or not? I hear that there are numerous reasons why it may silently drop into normal mode (eg associations and generated ids) so is there some way to find out why it has gone non-batch? My hibernate.cfg.xml contains this line which i believe is all i need to enable batch mode: <property name="jdbc.batch_size">50</property> My insert code looks like this: List<LogEntry> entries = ..a list of 100 LogEntry data classes... Session sess = sessionFactory.getCurrentSession(); for(LogEntry e : entries) { sess.save(e); } sess.flush(); sess.clear(); My 'logentry' class has no associations, the only interesting field is the id: @Entity @Table(name="log_entries") public class LogEntry { @Id @GeneratedValue public Long id; ..other fields - strings and ints... However, since it is oracle, i believe the @GeneratedValue will use the sequence generator. And i believe that only the 'identity' generator will stop bulk inserts. So if anyone can explain why it isn't running in batch mode, or how i can find out for sure if it is or isn't in batch mode, or find out why hibernate is silently dropping back to slow mode, i'd be most grateful. Thanks

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• How to render all records from a nested set into a real html tree

  - by Christoph Schiessl

  I'm using the awesome_nested_set plugin in my Rails project. I have two models that look like this (simplified): class Customer < ActiveRecord::Base has_many :categories end class Category < ActiveRecord::Base belongs_to :customer # Columns in the categories table: lft, rgt and parent_id acts_as_nested_set :scope => :customer_id validates_presence_of :name # Further validations... end The tree in the database is constructed as expected. All the values of parent_id, lft and rgt are correct. The tree has multiple root nodes (which is of course allowed in awesome_nested_set). Now, I want to render all categories of a given customer in a correctly sorted tree like structure: for example nested <ul> tags. This wouldn't be too difficult but I need it to be efficient (the less sql queries the better). Update: Figured out that it is possible to calculate the number of children for any given Node in the tree without further SQL queries: number_of_children = (node.rgt - node.lft - 1)/2. This doesn't solve the problem but it may prove to be helpful.

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• What is the fastest way to check if files are identical?

  - by ojblass

  If you have 1,000,0000 source files, you suspect they are all the same, and you want to compare them what is the current fasted method to compare those files? Assume they are Java files and platform where the comparison is done is not important. cksum is making me cry. When I mean identical I mean ALL identical. Update: I know about generating checksums. diff is laughable ... I want speed. Update: Don't get stuck on the fact they are source files. Pretend for example you took a million runs of a program with very regulated output. You want to prove all 1,000,000 versions of the output are the same. Update: read the number of blocks rather than bytes? Immediatly throw out those? Is that faster than finding the number of bytes? Update: Is this ANY different than the fastest way to compare two files?

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• AJAX Request Erroring

  - by 30secondstosam

  I can not figure out for the life of me why this is erroring - can someone please cast a second pair of eyes over this - it's probably something really stupid, thanks in advance for the help: EDIT Stupidly I was putting the wrong URL in - HOWEVER... Now I have put the correct URL in, the site just hangs and crashes. Any ideas please? HTML: <input id="pc" class="sfc" name="ProdCat[]" type="checkbox" value=""> <input id="psc" class="sfc" name="ProdSubCat[]" type="checkbox" value=""> <input id="bf" class="sfc" name="BrandFil[]" type="checkbox" value=""> JQuery: $('input[type="checkbox"]').change(function(){ var name = $(this).attr("name"); var ProdCatFil = []; var ProdSubCatFil = []; var BrandFil = []; // Loop through the checked checkboxes in the same group // and add their values to an array $('input[type="checkbox"]:checked').each(function(){ switch(name) { case 'ProdCatFil[]': ProdCatFil.push($(this).val()); break; case 'ProdSubCatFil[]': ProdSubCatFil.push($(this).val()); break; case 'BrandFil[]': BrandFil.push($(this).val()); break; } }); $("#loading").ajaxStart(function(){ $(this).show(); $('.content_area').hide(); }); $("#loading").ajaxStop(function(){ $(this).hide(); $('.content_area').show(); }); $.ajax({ type: "GET", url: '../ajax/ajax.php', data: 'ProdCatFil='+ProdCatFil+'&ProdSubCatFil='+ProdSubCatFil+'&BrandFil='+BrandFil, success: function(data) { $('.content_area').html(data); } }).error(function (event, jqXHR, ajaxSettings, thrownError) { $('.content_area').html("<h2>Could not retrieve data</h2>"); //alert('[event:' + event + '], [jqXHR:' + jqXHR + '], [ajaxSettings:' + ajaxSettings + '], [thrownError:' + thrownError + '])'); }); PHP (just to prove it's working): echo '<h1>TEST TEST TEST </h1>'; The errors from JQuery alert box: [event:[object Object]], [jqXHR:error], [ajaxSettings:Not Found], [thrownError:undefined])

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• Why won't Internet Explorer (or Chrome) display my 'Loading...' gif but Firefox will?

  - by codeLes

  I have a page that fires several xmlHttp requests (synchronous, plain-vanilla javascript, I'd love to be using jquery thanks for mentioning that). I'm hiding/showing a div with a loading image based on starting/stopping the related javascript functions (at times I have a series of 3 xmlhttp request spawning functions nested). div = document.getElementById("loadingdiv"); if(div) { if(stillLoading) { div.style.visibility='visible'; div.style.display=''; } else { div.style.visibility='hidden'; div.style.display='none'; } } In Firefox this seems to work fine. The div displays and shows the gif for the required processing. In IE/Chrome however I get no such feedback. I am only able to prove that the div/image will even display by putting alert() methods in place with I call the above code, this stops the process and seems to give the browsers in question the window they need to render the dom change. I want IE/Chrome to work like it works in Firefox. What gives?

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• change postgres date format

  - by Jay

  Is there a way to change the default format of a date in Postgres? Normally when I query a Postgres database, dates come out as yyyy-mm-dd hh:mm:ss+tz, like 2011-02-21 11:30:00-05. But one particular program the dates come out yyyy-mm-dd hh:mm:ss.s, that is, there is no time zone and it shows tenths of a second. Apparently something is changing the default date format, but I don't know what or where. I don't think it's a server-side configuration parameter, because I can access the same database with a different program and I get the format with the timezone. I care because it appears to be ignoring my "set timezone" calls in addition to changing the format. All times come out EST. Additional info: If I write "select somedate from sometable" I get the "no timezone" format. But if I write "select to_char(somedate::timestamptz, 'yyyy-mm-dd hh24:mi:ss-tz')" then timezones work as I would expect. This really sounds to me like something is setting all timestamps to implicitly be "to_char(date::timestamp, 'yyyy-mm-dd hh24:mi:ss.m')". But I can't find anything in the documentation about how I would do this if I wanted to, nor can I find anything in the code that appears to do this. Though as I don't know what to look for, that doesn't prove much.

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