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• Why doesn't my Unity DependencyResolver work on shared hosting but works locally?

  - by frennky

  I'm trying to deploy ASP.NET MVC 3 application wich uses Unity as a IoC container. Application works fine on local server, but when deployed it throws an exception: No parameterless constructor defined for this object. And this is thrown for a controller that should get some repository injected by my Unity DependencyResolver. I've installed Unity with NuGet so it should be referenced directly, and I've checked that it gets copied to bin folder. Edit: Here's the stack trace: [MissingMethodException: No parameterless constructor defined for this object.] System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean publicOnly, Boolean noCheck, Boolean& canBeCached, RuntimeMethodHandleInternal& ctor, Boolean& bNeedSecurityCheck) +0 System.RuntimeType.CreateInstanceSlow(Boolean publicOnly, Boolean skipCheckThis, Boolean fillCache) +98 System.RuntimeType.CreateInstanceDefaultCtor(Boolean publicOnly, Boolean skipVisibilityChecks, Boolean skipCheckThis, Boolean fillCache) +241 System.Activator.CreateInstance(Type type, Boolean nonPublic) +69 System.Web.Mvc.DefaultControllerActivator.Create(RequestContext requestContext, Type controllerType) +67 [InvalidOperationException: An error occurred when trying to create a controller of type 'nBlog.Controllers.HomeController'. Make sure that the controller has a parameterless public constructor.] System.Web.Mvc.DefaultControllerActivator.Create(RequestContext requestContext, Type controllerType) +182 System.Web.Mvc.DefaultControllerFactory.GetControllerInstance(RequestContext requestContext, Type controllerType) +80 System.Web.Mvc.DefaultControllerFactory.CreateController(RequestContext requestContext, String controllerName) +74 System.Web.Mvc.MvcHandler.ProcessRequestInit(HttpContextBase httpContext, IController& controller, IControllerFactory& factory) +196 System.Web.Mvc.<>c__DisplayClass6.<BeginProcessRequest>b__2() +49 System.Web.Mvc.<>c__DisplayClassb`1.<ProcessInApplicationTrust>b__a() +13 System.Web.Mvc.SecurityUtil.<GetCallInAppTrustThunk>b__0(Action f) +7 System.Web.Mvc.SecurityUtil.ProcessInApplicationTrust(Action action) +22 System.Web.Mvc.SecurityUtil.ProcessInApplicationTrust(Func`1 func) +124 System.Web.Mvc.MvcHandler.BeginProcessRequest(HttpContextBase httpContext, AsyncCallback callback, Object state) +98 System.Web.Mvc.MvcHandler.BeginProcessRequest(HttpContext httpContext, AsyncCallback callback, Object state) +50 System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.BeginProcessRequest(HttpContext context, AsyncCallback cb, Object extraData) +16 System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +8841400 System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +18 Anyone have an idea what might be the problem?

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• ASP.NEt MVC 2 application error on IIS7 works fine on local machine

  - by aspCoolguy

  My ASP.NET MVC2 application is developed using 1. VS 2010 2. Linq To SQL for Models Here is Call controller code: namespace CallTrackMVC.Controllers { public class CallController : Controller { private CallTrackRepository repository; public CallController():this(new CallTrackRepository()) { } public CallController(CallTrackRepository newRepository) { repository = newRepository; } } } Error on IIS7 when browsing the Call Create page is NullReferenceException: Object reference not set to an instance of an object.] CallTrackMVC.Models.ExecOfficeDataContext..ctor() in C:\ClearCase\rartadi_view\STS_Dev_TEST\CallTrackMVC\Models\ExecOffice.designer.cs:71 CallTrackMVC.Controllers.CallController..ctor() in C:\ClearCase\rartadi_view\STS_Dev_TEST\CallTrackMVC\Controllers\CallController.cs:16 [TargetInvocationException: Exception has been thrown by the target of an invocation.] System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean publicOnly, Boolean noCheck, Boolean& canBeCached, RuntimeMethodHandleInternal& ctor, Boolean& bNeedSecurityCheck) +0 System.RuntimeType.CreateInstanceSlow(Boolean publicOnly, Boolean skipCheckThis, Boolean fillCache) +117 System.RuntimeType.CreateInstanceDefaultCtor(Boolean publicOnly, Boolean skipVisibilityChecks, Boolean skipCheckThis, Boolean fillCache) +247 System.Activator.CreateInstance(Type type, Boolean nonPublic) +106 System.Web.Mvc.DefaultControllerFactory.GetControllerInstance(RequestContext requestContext, Type controllerType) +102 [InvalidOperationException: **An error occurred when trying to create a controller of type 'CallTrackMVC.Controllers.CallController'. Make sure that the controller has a parameterless public constructor.**] System.Web.Mvc.DefaultControllerFactory.GetControllerInstance(RequestContext requestContext, Type controllerType) +541 System.Web.Mvc.DefaultControllerFactory.CreateController(RequestContext requestContext, String controllerName) +85 System.Web.Mvc.MvcHandler.ProcessRequestInit(HttpContextBase httpContext, IController& controller, IControllerFactory& factory) +165 System.Web.Mvc.MvcHandler.BeginProcessRequest(HttpContextBase httpContext, AsyncCallback callback, Object state) +80 System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +389 System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +371 Code in Global.asax is protected void Application_Start() { AreaRegistration.RegisterAllAreas(); RegisterRoutes(RouteTable.Routes); } Any suggestion would be a great help.

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• Interesting SQL Sorting Issue

  - by rofly

  It's crunch time, deadline for my most recent contract is coming in two days and almost everything is complete and working fine (knock on wood) except for one issue. In one of my stored procedures, I'm needing to return a result set as follows. group_id | name A101 | Craig A102 | Craig Z101 | Craig Z102 | Craig A101 | Jim A102 | Jim Z101 | Jim Z102 | Jim B101 | Andy B102 | Andy Z101 | Andy Z102 | Andy The names need to be sorted by the first character of the group id and also include the Z101/Z102 entries. By sorting strictly by the group id, I get a result set as follows: A101 | Craig A102 | Craig A101 | Jim A102 | Jim B101 | Andy B102 | Andy Z101 | Andy Z102 | Andy Z101 | Jim Z102 | Jim I really can't think of a solution that doesn't involve me making a cursor and bloating the stored procedure up more than it already is. I'm sure a great mind out there has an elegant solution and I'm eager to see what the community can come up with. Thanks a ton in advance.

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• Real world Prolog usage

  - by Hank

  Many study Prolog in college, but I have personally not come in contact with it professionally. The traditional examples given are AI and expert system applications, but what have you used it for and what made Prolog a suitable language for the task?

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• Problem setting output flags for ALU in "Nand to Tetris" course

  - by MahlerFive

  Although I tagged this homework, it is actually for a course which I am doing on my own for free. Anyway, the course is called "From Nand to Tetris" and I'm hoping someone here has seen or taken the course so I can get some help. I am at the stage where I am building the ALU with the supplied hdl language. My problem is that I can't get my chip to compile properly. I am getting errors when I try to set the output flags for the ALU. I believe the problem is that I can't subscript any intermediate variable, since when I just try setting the flags to true or false based on some random variable (say an input flag), I do not get the errors. I know the problem is not with the chips I am trying to use since I am using all builtin chips. Here is my ALU chip so far: /** * The ALU. Computes a pre-defined set of functions out = f(x,y) * where x and y are two 16-bit inputs. The function f is selected * by a set of 6 control bits denoted zx, nx, zy, ny, f, no. * The ALU operation can be described using the following pseudocode: * if zx=1 set x = 0 // 16-bit zero constant * if nx=1 set x = !x // Bit-wise negation * if zy=1 set y = 0 // 16-bit zero constant * if ny=1 set y = !y // Bit-wise negation * if f=1 set out = x + y // Integer 2's complement addition * else set out = x & y // Bit-wise And * if no=1 set out = !out // Bit-wise negation * * In addition to computing out, the ALU computes two 1-bit outputs: * if out=0 set zr = 1 else zr = 0 // 16-bit equality comparison * if out<0 set ng = 1 else ng = 0 // 2's complement comparison */ CHIP ALU { IN // 16-bit inputs: x[16], y[16], // Control bits: zx, // Zero the x input nx, // Negate the x input zy, // Zero the y input ny, // Negate the y input f, // Function code: 1 for add, 0 for and no; // Negate the out output OUT // 16-bit output out[16], // ALU output flags zr, // 1 if out=0, 0 otherwise ng; // 1 if out<0, 0 otherwise PARTS: // Zero the x input Mux16( a=x, b=false, sel=zx, out=x2 ); // Zero the y input Mux16( a=y, b=false, sel=zy, out=y2 ); // Negate the x input Not16( in=x, out=notx ); Mux16( a=x, b=notx, sel=nx, out=x3 ); // Negate the y input Not16( in=y, out=noty ); Mux16( a=y, b=noty, sel=ny, out=y3 ); // Perform f Add16( a=x3, b=y3, out=addout ); And16( a=x3, b=y3, out=andout ); Mux16( a=andout, b=addout, sel=f, out=preout ); // Negate the output Not16( in=preout, out=notpreout ); Mux16( a=preout, b=notpreout, sel=no, out=out ); // zr flag Or8way( in=out[0..7], out=zr1 ); // PROBLEM SHOWS UP HERE Or8way( in=out[8..15], out=zr2 ); Or( a=zr1, b=zr2, out=zr ); // ng flag Not( in=out[15], out=ng ); } So the problem shows up when I am trying to send a subscripted version of 'out' to the Or8Way chip. I've tried using a different variable than 'out', but with the same problem. Then I read that you are not able to subscript intermediate variables. I thought maybe if I sent the intermediate variable to some other chip, and that chip subscripted it, it would solve the problem, but it has the same error. Unfortunately I just can't think of a way to set the zr and ng flags without subscripting some intermediate variable, so I'm really stuck! Just so you know, if I replace the problematic lines with the following, it will compile (but not give the right results since I'm just using some random input): // zr flag Not( in=zx, out=zr ); // ng flag Not( in=zx, out=ng ); Anyone have any ideas? Edit: Here is the appendix of the book for the course which specifies how the hdl works. Specifically look at section 5 which talks about buses and says: "An internal pin (like v above) may not be subscripted". Edit: Here is the exact error I get: "Line 68, Can't connect gate's output pin to part". The error message is sort of confusing though, since that does not seem to be the actual problem. If I just replace "Or8way( in=out[0..7], out=zr1 );" with "Or8way( in=false, out=zr1 );" it will not generate this error, which is what lead me to look up in the appendix and find that the out variable, since it was derived as intermediate, could not be subscripted.

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• Comparing (similar) images with Python/PIL

  - by Attila Oláh

  I'm trying to calculate the similarity (read: Levenshtein distance) of two images, using Python 2.6 and PIL. I plan to use the python-levenshtein library for fast comparison. Main question: What is a good strategy for comparing images? My idea is something like: Convert to RGB (transparent - white) (or maybe convert to monochrome?) Scale up the smaller one to the larger one's size Convert each channel (= the only channel, if converted to monochrome) to a sequence (item value = color value of the pixel) Calculate the Levenshtein distance between the two sequences Of course, this will not handle cases like mirrored images, cropped images, etc. But for basic comparison, this should be useful. Is there a better strategy documented somewhere?

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• Using the WF rules engine without workflow in production - implementation experiences

  - by Josh E

  I'm designing an application for a type of case management system that has a big requirement for customizable, flexible business rules. I'm planning on using the WF Rules Engine without workflow (see: here, among other examples and such). One of the points my client brought up (justifiably so!) is whether there are extant examples of using the rules engine for a business rules engine without workflow. My question, of course is: Has anyone used the WF Rules engine sans workflow in a production application before, and what were your experiences?

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• stock management of assemblys and its sub parts

  - by The Disintegrator

  I have to track the stock of individual parts and kits (assembly) and can't find a satisfactory way of doing this. Sample bogus and hyper simplified database: Table prod: prodID 1 prodName Flux capacitor prodCost 900 prodPrice 1350 (900*1.5) prodStock 3 - prodID 2 prodName Mr Fusion prodCost 300 prodPrice 600 (300*2) prodStock 2 - prodID 3 prodName Time travel kit prodCost 1650 (1350+300) prodPrice 2145 (1650*1.3) prodStock 2 Table rels relID 1 relSrc 1 (Flux capacitor) relType 4 (is a subpart of) relDst 3 (Time travel kit) - relID 2 relSrc 2 (Mr Fusion) relType 4 (is a subpart of) relDst 3 (Time travel kit) prodPrice: it's calculated based on the cost but not in a linear way. In this example for costs of 500 or less, the markup is a 200%. For costs of 500-1000 the markup is 150%. For costs of 1000+ the markup is 130% That's why the time travel kit is much cheaper than the individual parts prodStock: here is my problem. I can sell kits or the individual parts, So the stock of the kits is virtual. The problem when I buy: Some providers sell me the Time Travel kit as a whole (with one barcode) and some sells me the individual parts (with a different barcode) So when I load the stock I don't know how to impute it. The problem when I sell: If I only sell kits, calculate the stock would be easy: "I have 3 Flux capacitors and 2 Mr Fusions, so I have 2 Time travel kits and a Flux Capacitor" But I can sell Kits or individual parts. I have to track the stock of the individual parts and the possible kits at the same time (and I have to compensate for the sell price) Probably this is really simple, but I can't see a simple solution. Resuming: I have to find a way of tracking the stock and the database/program is the one who has to do it (I cant ask the clerk to correct the stock) I'm using php+MySql. But this is more a logical problem than a programing one

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• Stock management of assemblies and its sub parts

  - by The Disintegrator

  I have to track the stock of individual parts and kits (assemblies) and can't find a satisfactory way of doing this. Sample bogus and hyper simplified database: Table prod: prodID 1 prodName Flux capacitor prodCost 900 prodPrice 1350 (900*1.5) prodStock 3 - prodID 2 prodName Mr Fusion prodCost 300 prodPrice 600 (300*2) prodStock 2 - prodID 3 prodName Time travel kit prodCost 1650 (1350+300) prodPrice 2145 (1650*1.3) prodStock 2 Table rels relID 1 relSrc 1 (Flux capacitor) relType 4 (is a subpart of) relDst 3 (Time travel kit) - relID 2 relSrc 2 (Mr Fusion) relType 4 (is a subpart of) relDst 3 (Time travel kit) prodPrice: it's calculated based on the cost but not in a linear way. In this example for costs of 500 or less, the markup is a 200%. For costs of 500-1000 the markup is 150%. For costs of 1000+ the markup is 130% That's why the time travel kit is much cheaper than the individual parts prodStock: here is my problem. I can sell kits or the individual parts, So the stock of the kits is virtual. The problem when I buy: Some providers sell me the Time Travel kit as a whole (with one barcode) and some sells me the individual parts (with a different barcode) So when I load the stock I don't know how to impute it. The problem when I sell: If I only sell kits, calculate the stock would be easy: "I have 3 Flux capacitors and 2 Mr Fusions, so I have 2 Time travel kits and a Flux Capacitor" But I can sell Kits or individual parts. So, I have to track the stock of the individual parts and the possible kits at the same time (and I have to compensate for the sell price) Probably this is really simple, but I can't see a simple solution. Resuming: I have to find a way of tracking the stock and the database/program is the one who has to do it (I cant ask the clerk to correct the stock) I'm using php+MySql. But this is more a logical problem than a programing one

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• How should I go about implementing a points-to analysis in Maude?

  - by reprogrammer

  I'm going to implement a points-to analysis algorithm. I'd like to implement this analysis mainly based on the algorithm by Whaley and Lam. Whaley and Lam use a BDD based implementation of Datalog to represent and compute the points-to analysis relations. The following lists some of the relations that are used in a typical points-to analysis. Note that D(w, z) :- A(w, x),B(x, y), C(y, z) means D(w, z) is true if A(w, x), B(x, y), and C(y, z) are all true. BDD is the data structure used to represent these relations. Relations input vP0 (variable : V, heap : H) input store (base : V, field : F, source : V) input load (base : V, field : F, dest : V) input assign (dest : V, source : V) output vP (variable : V, heap : H) output hP (base : H, field : F, target : H) Rules vP(v, h) :- vP0(v, h) vP(v1, h) :- assign(v1, v2), vP(v2, h) hP(h1, f,h2) :- store(v1, f, v2), vP(v1, h1), vP(v2, h2) vP(v2, h2) :- load(v1, f, v2), vP(v1, h1), hP(h1, f, h2) I need to understand if Maude is a good environment for implementing points-to analysis. I noticed that Maude uses a BDD library called BuDDy. But, it looks like that Maude uses BDDs for a different purpose, i.e. unification. So, I thought I might be able to use Maude instead of a Datalog engine to compute the relations of my points-to analysis. I assume Maude propagates independent information concurrently. And this concurrency could potentially make my points-to analysis faster than sequential processing of rules. But, I don't know the best way to represent my relations in Maude. Should I implement BDD in Maude myself, or Maude's internal unification based on BDD has the same effect?

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• Higher-order unification

  - by rwallace

  I'm working on a higher-order theorem prover, of which unification seems to be the most difficult subproblem. If Huet's algorithm is still considered state-of-the-art, does anyone have any links to explanations of it that are written to be understood by a programmer rather than a mathematician? Or even any examples of where it works and the usual first-order algorithm doesn't?

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• redirect prints to log file

  - by lakshmipathi

  Okay. I have completed my first python program.It has around 1000 lines of code. During development I placed plenty of print stmt before running a command using os.system() say something like, print "running command",cmd os.system(cmd) Now I have completed the program.I thought about commenting them but redirecting all these unnecessary print (i can't remove all print stmt- since some provide useful info for user) into a log file will be more useful? Any tricks or tips.

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• Stock management of assemblies and its sub parts (relations)

  - by The Disintegrator

  I have to track the stock of individual parts and kits (assemblies) and can't find a satisfactory way of doing this. Sample bogus and hyper simplified database: Table prod: prodID 1 prodName Flux capacitor prodCost 900 prodPrice 1350 (900*1.5) prodStock 3 - prodID 2 prodName Mr Fusion prodCost 300 prodPrice 600 (300*2) prodStock 2 - prodID 3 prodName Time travel kit prodCost 1650 (1350+300) prodPrice 2145 (1650*1.3) prodStock 2 Table rels relID 1 relSrc 1 (Flux capacitor) relType 4 (is a subpart of) relDst 3 (Time travel kit) - relID 2 relSrc 2 (Mr Fusion) relType 4 (is a subpart of) relDst 3 (Time travel kit) prodPrice: it's calculated based on the cost but not in a linear way. In this example for costs of 500 or less, the markup is a 200%. For costs of 500-1000 the markup is 150%. For costs of 1000+ the markup is 130% That's why the time travel kit is much cheaper than the individual parts prodStock: here is my problem. I can sell kits or the individual parts, So the stock of the kits is virtual. The problem when I buy: Some providers sell me the Time Travel kit as a whole (with one barcode) and some sells me the individual parts (with a different barcode) So when I load the stock I don't know how to impute it. The problem when I sell: If I only sell kits, calculate the stock would be easy: "I have 3 Flux capacitors and 2 Mr Fusions, so I have 2 Time travel kits and a Flux Capacitor" But I can sell Kits or individual parts. So, I have to track the stock of the individual parts and the possible kits at the same time (and I have to compensate for the sell price) Probably this is really simple, but I can't see a simple solution. Resuming: I have to find a way of tracking the stock and the database/program is the one who has to do it (I cant ask the clerk to correct the stock) I'm using php+MySql. But this is more a logical problem than a programing one

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• being able to solve google code jam problem sets

  - by JPro

  This is not a homework question, but rather my intention to know if this is what it takes to learn programming. I keep loggin into TopCoder not to actually participate but to get the basic understand of how the problems are solved. But to my knowledge I don't understand what the problem is and how to translate the problem into an algorithm that can solve it. Just now I happen to look at ACM ICPC 2010 World Finals which is being held in china. The teams were given problem sets and one of them is this: Given at most 100 points on a plan with distinct x-coordinates, find the shortest cycle that passes through each point exactly once, goes from the leftmost point always to the right until it reaches the rightmost point, then goes always to the left until it gets back to the leftmost point. Additionally, two points are given such that the the path from left to right contains the first point, and the path from right to left contains the second point. This seems to be a very simple DP: after processing the last k points, and with the first path ending in point a and the second path ending in point b, what is the smallest total length to achieve that? This is O(n^2) states, transitions in O(n). We deal with the two special points by forcing the first path to contain the first one, and the second path contain the second one. Now I have no idea what I am supposed to solve after reading the problem set. and there's an other one from google code jam: Problem In a big, square room there are two point light sources: one is red and the other is green. There are also n circular pillars. Light travels in straight lines and is absorbed by walls and pillars. The pillars therefore cast shadows: they do not let light through. There are places in the room where no light reaches (black), where only one of the two light sources reaches (red or green), and places where both lights reach (yellow). Compute the total area of each of the four colors in the room. Do not include the area of the pillars. Input * One line containing the number of test cases, T. Each test case contains, in order: * One line containing the coordinates x, y of the red light source. * One line containing the coordinates x, y of the green light source. * One line containing the number of pillars n. * n lines describing the pillars. Each contains 3 numbers x, y, r. The pillar is a disk with the center (x, y) and radius r. The room is the square described by 0 = x, y = 100. Pillars, room walls and light sources are all disjoint, they do not overlap or touch. Output For each test case, output: Case #X: black area red area green area yellow area Is it required that people who program should be should be able to solve these type of problems? I would apprecite if anyone can help me interpret the google code jam problem set as I wish to participate in this years Code Jam to see if I can do anthing or not. Thanks.

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• Breadth-First in Prolog

  - by Ricardo

  What is the general idea of using breadth-first over the default depth-first search scheme in Prolog? Not taking infinite branches? Is there any general way to use breadth-first in Prolog? I've been googling around and I didn't find too much useful info for a novice.

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• Design of Business Layer

  - by Adil Mughal

  Hi, We are currently revamping our architecture and design of application. We have just completed design of Data Access Layer which is generic in the sense that it works using XML and reflection to persist data. Any ways now we are in the phase of designing business layer. We have read some books related to Enterprise Architecture and Design so we have found that there are few patterns that can be applied on business layer. Table Pattern and Domain Model are example of such patterns. Also we have found Domain Driven Design as well. Earlier we decided to build Entities against table objects. But we found that there is difference in Entities and Value Objects when it comes to DDD. For those of you who have gone through such design. Please guide me related to pattern, practice and sample. Thank you in advance! Also please feel free to discuss if you didn't get any point of mine.

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• Any ideas on How to search a 2D array quickly?

  - by Tattat

  I jave a 2D array like this, just like a matrix: {{1, 2, 4, 5, 3, 6}, {8, 3, 4, 4, 5, 2}, {8, 3, 4, 2, 6, 2}, //code skips... ... } I want to get all the "4" position, instead of searching the array one by way, and return the position, how can I search it faster / more efficient? thz in advance.

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• How Does Ctrl-K work in Stackoverflow

  - by harigm

  I am very curious to know how to implement the Ctrl-K feature against code, For sample public static void main(Stirng args[]){ System.out.println.out("welcome"); } That will be nicely formatted? 1)Do we require any package to implement this? 2) Any ready made code avaialble to do this? Can any one help me with this, I am planning to develop a site where this feature would be a real helpful.

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• What's your favourite assisted theorem prover?

  - by Danny King

  Hi all, I'm hoping to pick one of the many assisted theorem provers (rather than automatic ones) but there are rather a lot to choose from! Does anyone have any you prefer and may I ask why? Thanks!

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• Where should I exclude and select information BL or DL?

  - by MRFerocius

  Hi guys; I have another conceptual question. Suppose I have a Data Layer and a Bussines Layer. I have on my data base for example Customers and those customers has an assigned Vendor: Customers(customerID, customerName, customerAddress, vendorID) Vendors(vendorID, vendorName, vendorAddress) Now suppose my Vendor logs into my web application and wants to see all his customers: a) Should I use my Datalayer method and there find his customers on the query? b) Should the data layer return all the customers and on the Buissnes Layer filter that vendor ones? Is B even a good approach because is the one I want to use.... Is it correct? Thanks in advance!!!

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• How to implement "business rules" in Rails?

  - by Zabba

  What is the way to implement "business rules" in Rails? Let us say I have a car and want to sell it: car = Cars.find(24) car.sell car.sell method will check a few things: does current_user own the car? check: car.user_id == current_user.id is the car listed for sale in the sales catalog? check: car.catalogs.ids.include? car.id if all o.k. then car is marked as sold. I was thinking of creating a class called Rules: class Rules def initialize(user,car) @user = user @car = car end def can_sell_car? @car.user_id == @user.id && @car.catalogs.ids.include? @car.id end end And using it like this: def Car def sell if Rules.new(current_user,self).can_sell_car ..sell the car... else @error_message = "Cannot sell this car" nil end end end As for getting the current_user, I was thinking of storing it in a global variable? I think that whenever a controller action is called, it's always a "fresh" call right? If so then storing the current user as a global variable should not introduce any risks..(like some other user being able to access another user's details) Any insights are appreciated! UPDATE So, the global variable route is out! Thanks to PeterWong for pointing out that global variables persist! I've now thinking of using this way: class Rules def self.can_sell_car?(current_user, car) ......checks.... end end And then calling Rules.can_sell_car?(current_user,@car) from the controller action. Any thoughts on this new way?

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• What is natural deduction used for outside of academia?

  - by Danny King

  Hello, I am studying natural deduction as a part of my Formal Specification & Verification Computer Science course at University/College. I find it interesting, however I learn much better when I can find a practical use for things. Could anyone explain to me if and how natural deduction is used other than for formally verifying bits of code? Thanks!

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• SQL - Counting sets of Field-B values for each Field-A value

  - by potrnd

  Hello, First of all sorry that I could not think of a more descriptive title. What I want to do is the following using only SQL: I have some lists of strings, list1, list2 and list3. I have a dataset that contains two interesting columns, A and B. Column A contains a TransactionID and column B contains an ItemID. Naturally, there can be multiple rows that share the same TransactionIDs. I need to catch those transactions that have at least one ItemID in each and every list (list1 AND list2 AND list3). I also need to count how many times does that happen for each transaction. [EDIT] That is, count how many full sets of ItemIDs there are for each TransactionID", "Full Set" being any element of the list1 with any element of the list2 with any element of the list3 I hope that makes enough sense, perhaps I will be able to explain it better with a clear head. Thanks in advance

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• Data mining - parsing a log file in Java

  - by nuvio

  Hello I am carrying on a Java project for the university, where I should analyse poker hands. I found some poker hands in a txt log file. They would typically look like this: PokerStars Zoom Hand #86981279921: Hold'em No Limit ($0.10/$0.25 USD) - 2012/09/30 23:49:51 ET Table 'Whirlpool Zoom 40-100 bb' 9-max Seat #1 is the button Seat 1: lgwong ($30.99 in chips) Seat 2: hastyboots ($28.61 in chips) Seat 3: seula i ($25.31 in chips) Seat 4: fr_kevin01 ($31.81 in chips) Seat 5: limey05 ($27.45 in chips) Seat 6: sanlu ($24.65 in chips) Seat 7: Masterfrank ($25.35 in chips) Seat 8: Refu$e2Lose ($33.23 in chips) Seat 9: 1pepepe0114 ($37.62 in chips) hastyboots: posts small blind $0.10 seula i: posts big blind $0.25 *** HOLE CARDS *** fr_kevin01: folds limey05: folds sanlu: folds Masterfrank: folds Refu$e2Lose: folds 1pepepe0114: folds lgwong: folds hastyboots: folds Uncalled bet ($0.15) returned to seula i seula i collected $0.20 from pot seula i: doesn't show hand *** SUMMARY *** Total pot $0.20 | Rake $0 Seat 1: lgwong (button) folded before Flop (didn't bet) Seat 2: hastyboots (small blind) folded before Flop Seat 3: seula i (big blind) collected ($0.20) Seat 4: fr_kevin01 folded before Flop (didn't bet) Seat 5: limey05 folded before Flop (didn't bet) Seat 6: sanlu folded before Flop (didn't bet) Seat 7: Masterfrank folded before Flop (didn't bet) Seat 8: Refu$e2Lose folded before Flop (didn't bet) Seat 9: 1pepepe0114 folded before Flop (didn't bet) My problem is that I am not sure about how to proceed to parse the log file: the only knowledge I have is "manually" scanning line by line for a particular character or symbol, but I am afraid it would need exhaustive error handling. So I was wandering if there is any other techniques or better way to parse these poker hands? Many thanks for your help

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• Inference engine to calculate matching set according to internal rules

  - by Zecrates

  I have a set of objects with attributes and a bunch of rules that, when applied to the set of objects, provides a subset of those objects. To make this easier to understand I'll provide a concrete example. My objects are persons and each has three attributes: country of origin, gender and age group (all attributes are discrete). I have a bunch of rules, like "all males from the US", which correspond with subsets of this larger set of objects. I'm looking for either an existing Java "inference engine" or something similar, which will be able to map from the rules to a subset of persons, or advice on how to go about creating my own. I have read up on rule engines, but that term seems to be exclusively used for expert systems that externalize the business rules, and usually doesn't include any advanced form of inferencing. Here are some examples of the more complex scenarios I have to deal with: I need the conjunction of rules. So when presented with both "include all males" and "exclude all US persons in the 10 - 20 age group," I'm only interested in the males outside of the US, and the males within the US that are outside the 10 - 20 age group. Rules may have different priorities (explicitly defined). So a rule saying "exclude all males" will override a rule saying "include all US males." Rules may be conflicting. So I could have both an "include all males" and an "exclude all males" in which case the priorities will have to settle the issue. Rules are symmetric. So "include all males" is equivalent to "exclude all females." Rules (or rather subsets) may have meta rules (explicitly defined) associated with them. These meta rules will have to be applied in any case that the original rule is applied, or if the subset is reached via inferencing. So if a meta rule of "exclude the US" is attached to the rule "include all males", and I provide the engine with the rule "exclude all females," it should be able to inference that the "exclude all females" subset is equivalent to the "include all males" subset and as such apply the "exclude the US" rule additionally. I can in all likelihood live without item 5, but I do need all the other properties mentioned. Both my rules and objects are stored in a database and may be updated at any stage, so I'd need to instantiate the 'inference engine' when needed and destroy it afterward.

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