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• Full JSON-RPC specifications

  - by Artyom

  Hello, I'm going to implement JSON-PRC web service. I need specifications for this. So far I had found only one resource that can be called as real specifications: JSON-RPC 1.0 http://json-rpc.org/wiki/specification Proposal of JSON-PRC 2.0: http://groups.google.com/group/json-rpc/web/json-rpc-2-0 (why is it on google groups?) However I've seen that JavaScript frameworks like Dojo actively use JSON-RPC SMD Service Mapping Description proposal But it requires JSON Schema specifications, but it redirects to incorrect URL as reference. So far I had found following: http://tools.ietf.org/html/draft-zyp-json-schema-02 And it is still draft... Can anybody point me to spome actual specifications... At least something official updated? Because it looks like that implementing JSON-RPC 1.0 and 2.0 would not be enought, at least for frameworks like Dojo. Or am I wrong? Questions: Is it enough to implement JSON-RPC 1.0 specifications and 2.0 draft to be on safe side, would this work for most JSON-RPC clients? If I should implement SMD, or it is recommended can somebody point to official specifications of Json Schema and Service Mapping Description or links I found are really "specifications?" Note: do not suggest existing JSON-RPC service implementations.

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• How to best transfer large payloads of data using wsHttp with WCF with message security

  - by jpierson

  I have a case where I need to transfer large amounts of serialized object graphs (via NetDataContractSerializer) using WCF using wsHttp. I'm using message security and would like to continue to do so. Using this setup I would like to transfer serialized object graph which can sometimes approach around 300MB or so but when I try to do so I've started seeing a exception of type System.InsufficientMemoryException appear. After a little research it appears that by default in WCF that a result to a service call is contained within a single message by default which contains the serialized data and this data is buffered by default on the server until the whole message is completely written. Thus the memory exception is being caused by the fact that the server is running out of memory resources that it is allowed to allocate because that buffer is full. The two main recommendations that I've come across are to use streaming or chunking to solve this problem however it is not clear to me what that involves and whether either solution is possible with my current setup (wsHttp/NetDataContractSerializer/Message Security). So far I understand that to use streaming message security would not work because message encryption and decryption need to work on the whole set of data and not a partial message. Chunking however sounds like it might be possible however it is not clear to me how it would be done with the other constraints that I've listed. If anybody could offer some guidance on what solutions are available and how to go about implementing it I would greatly appreciate it. Related resources: Chunking Channel How to: Enable Streaming Large attachments over WCF Custom Message Encoder Another spotting of InsufficientMemoryException I'm also interested in any type of compression that could be done on this data but it looks like I would probably be best off doing this at the transport level once I can transition into .NET 4.0 so that the client will automatically support the gzip headers if I understand this properly.

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• Implement DDD and drawing the line between the an Entity and value object

  - by William

  I am implementing an EMR project. I would like to apply a DDD based approach to the problem. I have identified the "Patient" as being the core object of the system. I understand Patient would be an entity object as well as an aggregrate. I have also identified that every patient must have a "Doctor" and "Medical Records". The medical records would encompass Labs, XRays, Encounter.... I believe those would be entity objects as well. Let us take a Encounter for example. My implementation currently has a few fields as "String" properties, which are the complaint, assessment and plan. The other items necessary for an Encounter are vitals. I have implemented vitals as a value object. Given that it will be necessary to retrieve vitals without haveing to retrieve each Encounter then do vitals become part of the Encounter aggregate and patient aggregrate. I am assuming I could view the Encounter as an aggregrate, because other items are spwaned from the Encounter like prescriptions, lab orders, xrays. Is approach right that I am taking in identifying my entities and aggregates. In the case of vitals, they are specific to a patient, but outside of that there is not any other identity associated with them.

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• How to program a neural network for chess?

  - by marco92w

  Hello! I want to program a chess engine which learns to make good moves and win against other players. I've already coded a representation of the chess board and a function which outputs all possible moves. So I only need an evaluation function which says how good a given situation of the board is. Therefore, I would like to use an artificial neural network which should then evaluate a given position. The output should be a numerical value. The higher the value is, the better is the position for the white player. My approach is to build a network of 385 neurons: There are six unique chess pieces and 64 fields on the board. So for every field we take 6 neurons (1 for every piece). If there is a white piece, the input value is 1. If there is a black piece, the value is -1. And if there is no piece of that sort on that field, the value is 0. In addition to that there should be 1 neuron for the player to move. If it is White's turn, the input value is 1 and if it's Black's turn, the value is -1. I think that configuration of the neural network is quite good. But the main part is missing: How can I implement this neural network into a coding language (e.g. Delphi)? I think the weights for each neuron should be the same in the beginning. Depending on the result of a match, the weights should then be adjusted. But how? I think I should let 2 computer players (both using my engine) play against each other. If White wins, Black gets the feedback that its weights aren't good. So it would be great if you could help me implementing the neural network into a coding language (best would be Delphi, otherwise pseudo-code). Thanks in advance!

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• How do you handle 'SelectedItemChanged' events in a MVVM ViewModel?

  - by Travis

  I have some logic that depends upon two properties being set, as it executes when both properties have a value. For example: private void DoCalc() { if (string.IsNullOrEmpty(Property1) || string.IsNullOrEmpty(Property2)) return; Property3 = Property1 + " " + Property2; } That code would need to be executed every time Property1 or Property2 changed, but I'm having trouble figuring out how to do it in a stylistically acceptable manner. Here are the choices as I see them: 1) Call method from ViewModel I don't have a problem with this conceptually, as the logic is still in the ViewModel - I'm not a 'No code-behind' nazi. However, the 'trigger' logic (when either property changes) is still in the UI layer, which I don't love. The codebehind would look like this: void ComboBox_Property1_SelectedItemChanged(object sender, RoutedEventArgs e) { viewModel.DoCalc(); } 2) Call method from Property Setter This approach seems the most 'pure', but it also seems ugly, as if the logic is hidden. It would look like this: public string Property1 { get {return property1;} set { if (property1 != value) { property1 = value; NotifyPropertyChanged("Property1"); DoCalc(); } } } 3) Hook into the PropertyChanged event I'm now thinking this might be the right approach, but it feels weird to hook into the property changed event in the implementing viewmodel. It would look something like this: public ViewModel() { this.PropertyChanged += new PropertyChangedEventHandler(ViewModel_PropertyChanged); } void ViewModel_PropertyChanged(object sender, PropertyChangedEventArgs e) { if (e.PropertyName == "Property1" || e.PropertyName == "Property2") { DoCalc(); } } So, my question is, if you were browsing through some source code with that requirement, which approach would you prefer to see implemented (and why?). Thanks for any input.

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• Efficient Multiple Linear Regression in C# / .Net

  - by mrnye

  Does anyone know of an efficient way to do multiple linear regression in C#, where the number of simultaneous equations may be in the 1000's (with 3 or 4 different inputs). After reading this article on multiple linear regression I tried implementing it with a matrix equation: Matrix y = new Matrix( new double[,]{{745}, {895}, {442}, {440}, {1598}}); Matrix x = new Matrix( new double[,]{{1, 36, 66}, {1, 37, 68}, {1, 47, 64}, {1, 32, 53}, {1, 1, 101}}); Matrix b = (x.Transpose() * x).Inverse() * x.Transpose() * y; for (int i = 0; i < b.Rows; i++) { Trace.WriteLine("INFO: " + b[i, 0].ToDouble()); } However it does not scale well to the scale of 1000's of equations due to the matrix inversion operation. I can call the R language and use that, however I was hoping there would be a pure .Net solution which will scale to these large sets. Any suggestions? EDIT #1: I have settled using R for the time being. By using statconn (downloaded here) I have found it to be both fast & relatively easy to use this method. I.e. here is a small code snippet, it really isn't much code at all to use the R statconn library (note: this is not all the code!). _StatConn.EvaluateNoReturn(string.Format("output <- lm({0})", equation)); object intercept = _StatConn.Evaluate("coefficients(output)['(Intercept)']"); parameters[0] = (double)intercept; for (int i = 0; i < xColCount; i++) { object parameter = _StatConn.Evaluate(string.Format("coefficients(output)['x{0}']", i)); parameters[i + 1] = (double)parameter; }

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• Are eCommerce platforms worth it for large scale systems?

  - by codeflunky

  My company and I are building a new system for a relatively large client. We are going to be replacing their entire system, which includes some eCommerce aspects to it among many other things. It is not a typical public shopping site, and there are many things about the system (both back end and front end) that are quite different. Some of the people I work for are convinced that we should be using a third party product to implement the eCommerce pieces (shopping cart, catalog management). Their opinion is that it is a solved problem, and we shouldn't have to reinvent it. Given that direction, I have reviewed around ten different .NET based eCommerce platforms, and I struggle to imagine how we will be able to smoothly integrate any of them without a lot of friction. They are so all-encompassing that I feel like they are probably better suited for implementing simple shopping sites rather than larger systems that happen to have some eCommerce aspects to them. We have a really nice architecture planned for everything else (Entity Framework, ASP.NET MVC, etc.), and my gut is telling me that trying to introduce a third party platform will cause unnecessary fragmentation and difficulty. I would love to hear some opinions from people who have been there. Have you used a third party platform for eCommerce? Was it a typical shopping site or something different? Did you feel it was a help or a hinderance? Thanks.

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• What do I do about recurring billing?

  - by phidah

  This might be a subjective question, but I'll give it a go. There are already a number of questions on SO that revolves around subscription billing management. I am currently working on a SaaS solution that will require a fully automated billing system. What I am not looking for when asking this question is not advice on implementing towards a specific payment gateway or stuff like that. Instead I'd like advice on what kind of approach to take. The functionality that I need is a system that can handle upgrades, downgrades, recurring billing, cancellations, etc. Initially for one product only, but it might over time be a requirement that the system can handle multiple products (by products I mean fundamentally different products, not different variations of the same product). As I see it there are a number of possible approaches when you need a solution like this: Code a billing server yourself that supports this and is decoupled from each product so that it can handle multiple independent products. Use a hosted solution like Recurly, Chargify, Spreedly or CheddarGetter. The advantage of using a hosted solution is obviously that you don't need PCI certification, the concern is outsourced and it is a lot faster to get up and running. These advantages come at a cost however: The most important support function for your product - i.e. the billing is not in your control. Additionally you have less control and flexibility. What would you do? If we look beyond the PCI requirements I would definately prefer to have a system coded in-house that could do this kind of job. On the other hand I've heard from numerous sources that coding a system like this is a pain. Any advice is highly appreciated. Also, if you advice to code it yourself, any experiences on how to do it or if there are any opensource projects (no matter the language, what I'm after is not the code but the structure) that I can benefit from would really mean alot. Thanks in advance for your inputs! :-)

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• How to prove writing specifications beats code cowboys?

  - by Andrew Grant

  So I have a problem. Or rather my friend has a problem, since I would never write about my company on an internet forum. At my friend's company specification writing is, shall we say, a little underused. There's a deeply ingrained culture of writing code first and asking questions later, whether it's for a library routine or a new tool to inflict on their long suffering designers. This of course leads to situations where functionality is partially correct, incorrect, or just completely missing ("oh, just save before trying anything you may want to undo"). This usually results in a loss of productivity for those poor designers, or beta periods where bug-fixing is largely spent implementing things correctly. My friend's found his suggestions of writing (and testing against) specifications to be generally well received. Most of his colleagues have embraced the wonderful feeling of discovering false-assumptions on paper, instead of at 11pm on a Sunday in the middle of beta. Viva La Revolution! However there are a few who poo-poo anything that stands between their task and a keyboard. They laugh at the thought of actually designing anything, and write code with merry abandon. Mostly these are senior, long employed developers, reluctant to "waste time". The problem is that this second group of heretics invariably produce things (or at least something) quicker than the first. Subsequently this becomes justification along the lines of "It's pointless to write specifications for something as simple as an image resizer! Oh and those bugs where width!=height or the image uses RLE just need a few tweaks". And now the question :) Other than saying "told you so" at the end of a project, what are some good short-term ways to demonstrate how the practice of writing functional or technical specifications leads to better software in the long run? Cheers!

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• signalR groups - connecting/disconnecting and sending - am I missing something?

  - by Terry_Brown

  very new to signalR, and have rolled up a very simple app that will take questions for moderation at conferences (felt like a straight forward use case) I have 2 hubs at the moment: - Question (for asking questions) - Speaker (these should receive questions and allow moderation, but that will come later) Solution lives at https://github.com/terrybrown/InterASK After watching a video (by David Fowler/Damian Edwards) (http://channel9.msdn.com/Shows/Web+Camps+TV/Damian-Edwards-and-David-Fowler-Demonstrate-SignalR) and another that I can't find the URL for atm, I thought I'd go with 'groups' as the concept to keep messages flowing to the right people. I implemented IConnected, IDisconnect as I'd seen in one of the videos, and upon debugging I can see Connect fire (and on reload I can see disconnect fire), but it seems nothing I do adds a person to a group. The signalR documentation suggests "Groups are not persisted on the server so applications are responsible for keeping track of what connections are in what groups so things like group count can be achieved" which I guess is telling me that I need to keep some method (static or otherwise?) of tracking who is in a group? Certainly I don't seem able to send to groups currently, though I have no problem distributing to anyone currently connected to the app and implementing the same JS method (2 machines on the same page). I suspect I'm just missing something - I read a few of the other questions on here, but none of them seem to mention IConnected/IDisconnect, which tells me these are either new (and nobody is using them) or that they're old (and nobody is using them). I know this could be considered a subjective question, though what I'm looking for is just a simple means of managing the groups so that I can do what I want to - send a question from one hub, and have people connected to a different hub receive it - groups felt the cleanest solution for this? Many thanks folks. Terry

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• Flex HTMLLoader component not raising mouseDown events for all mouse clicks

  - by shane

  I have built a Air 2/Flex 4 kiosk application with Flash Builder 4. Currently I am implementing a touch screen browser to enable users to navigate company training videos. In an attempt to improve the usability of the website on the touchscreen I have placed the HTML component in an adaption of Doug McCune's DragScrollingCanvas (updated to use the flex 4 'Scroller' component) to allow users to scroll the webpage by dragging their finger across the screen. The mouseDown event is used to start scrolling the viewport. In addition the webpage was modified to disable text selection with the following css: html { -webkit-user-select: none; cursor: default; } The problem I face is that the HTMLLoader component only fires a mouseDown if a link/input/button on the webpage is clicked, not when the background or any text is clicked. In addition if I remove the custom css the mouseDown event will not fire when text is being selected, but will if previously highlighted text is clicked. As an alternative I also tried adding a group container with the same dimensions as the HTMLLoader to detect the mouseDown events (so that the group container and HTMLLoader have the same Dragable parent container) and was able to capture mouseDown events and scroll the viewport as expected. However as the mouse event is handled by the group container, I am now unable to navigate the webpage. Does anybody know why the HTMLLoader component is not raising mouseDown events for all mouse clicks?

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• Android Live Wallpaper: waitForCondition(ReallocateCondition)

  - by jstatz

  I've been developing a live wallpaper using GLWallpaperService, and have gotten good results overall. It runs rock-solid in the emulator and looks good. I've dealt with OpenGL many times before so have a solid command of how to do things... unfortunately I'm having a hell of a time getting this to actually be stable on the actual hardware. The basic symption occurs when you slide the physical keyboard on a Motorola Droid in and out a few times. This causes the wallpaper to get destroyed/recreated several times in quick succession -- which would be fine, as I have my assets clearing in onDestroy and reloading in onSurfaceChanged. The problem is after a few iterations of this, (four or five, maybe) the calls to onSurfaceChanged completely stop, and i get an endless string of this printed to the log: 04-02 00:53:18.088: WARN/SharedBufferStack(1032): waitForCondition(ReallocateCondition) timed out (identity=337, status=0). CPU may be pegged. trying again. Is there something I should be implementing here aside from the Android-typical onSurfaceCreated/onSurfaceChanged/onSurfaceDestroyed triumvirate? Browsing through the WallpaperService and WallpaperRenderer classes doesn't pop up anything obvious to me.

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• Pseudocode help

  - by vatsag

  Hello All I've been banging my head over few hours for realising this particular logic My task is to have a masterlist ListM elements of which shall be list(again) in the form of ListA(type A) and ListB(type B) and ListC(type C)(some generic type). Also the lists A and ListB can contain elements of type C(some generic type). Coming to the preconditions 1. ListA can contain only 50 elements of type 'A', rest of the elements can be of generic type C 2. ListB can contain only 50 elements of type 'B', rest of the elements can be of generic type C 3. Also the lists(ListA or ListB) can take at max of 100 elements. 4. ListC can contain elements of generic type C and can take max of 100 elements For ex: Now, If i have 200 elements of type A and 200 elements of type B and 600 elements of type C then i should be able to get 4 Lists(50 elements in each list) of type...ListA (because each ListA can contain at max of 50 elements of type A only, rem 50 is typeC) 4 Lists(50 elements in each list) of type...ListB (because each ListA can contain at max of 50 elements of type B only, rem 50 is typeC) 2 Lists(50 elements in each list) of type...ListC i shall be glad to explain it again if my explanation is quite confusing. Can anyone suggest a better way for implementing such a requirement in the form of a pseudocode ? Thanks in advance VATSAG

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• Manual drag-drop operations in Flex

  - by Yarin

  This is a two-part problem: A) I'm implementing several irregular drag-drop operations in Flex (e.g. DataGrid ItemRenderer into Tree). My preference was modifying DragManager operations to meet my needs, and in fact using DragManager allows me to do everything I need, but I'm having serious issues with performance. For example, dragging anything over a many-columned DataGrid, whether the drag was initiated with DragManager.doDrag, or just using native ListBase drag-drop functionality, slows the drag movement to a crawl. Even if the DataGrid is disabled/ not listenening for any move/drag events, this happens. On the other hand, if the drag is initiated by calling .startDrag() on the Sprite, the drag is smooth and performs great over DataGrids and everything else. So part A would be: Is there a reason why .startDrag() operations work so well, while drags initiated through DragManager.doDrag suffer so badly when over certain components? B) If indeed the solution is to handle drag-drops using .startDrag(), how would I go about determining what component the mouse is over when the drag is released? In my example, my dragged object is brought up to the top level of the display list, and so is being moved around in stage coordinates. mouseMove, mouseOver events don't fire on the components I'm dragging over because the mouse is constantly over the dragged component, so I would need some sort of stage.coordinate - visibleComponentAtThatCoordinate conversion. Any thoughts on this? Thanks alot!-- Yarin

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• Modular Reduction of Polynomials in NTRUEncrypt

  - by Neville

  Hello everyone. I'm implementing the NTRUEncrypt algorithm, according to an NTRU tutorial, a polynomial f has an inverse g such that f*g=1 mod x, basically the polynomial multiplied by its inverse reduced modulo x gives 1. I get the concept but in an example they provide, a polynomial f = -1 + X + X^2 - X4 + X6 + X9 - X10 which we will represent as the array [-1,1,1,0,-1,0,1,0,0,1,-1] has an inverse g of [1,2,0,2,2,1,0,2,1,2,0], so that when we multiply them and reduce the result modulo 3 we get 1, however when I use the NTRU algorithm for multiplying and reducing them I get -2. Here is my algorithm for multiplying them written in Java: public static int[] PolMulFun(int a[],int b[],int c[],int N,int M) { for(int k=N-1;k>=0;k--) { c[k]=0; int j=k+1; for(int i=N-1;i>=0;i--) { if(j==N) { j=0; } if(a[i]!=0 && b[j]!=0) { c[k]=(c[k]+(a[i]*b[j]))%M; } j=j+1; } } return c; } It basicall taken in polynomial a and multiplies it b, resturns teh result in c, N specifies the degree of the polynomials+1, in teh example above N=11; and M is the reuction modulo, in teh exampel above 3. Why am I getting -2 and not 1?

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• SHA1 hashing in Delphi XE

  - by Leonardo Herrera

  Hello, I'm in the process of implementing XML digital signatures. I'm starting with little steps, so right now I want to solve the problem of SHA-1 hashing. There are lots of questions about this in SO: Digitially Sign Key with Lockbox Encryption library for Delphi Convert this php digital signing to Delphi Delphi: is there a version of LockBox for Delphi-XE Delphi 2010 Cryptography libraries ...and probably more. However, I'm using Delphi XE. So far, I've tried LockBox 2 (both the Songbeamer and Sourceforge versions), Lock Box 3, DCPCrypto2 and some others (Hashes is an easy to use unit which uses Windows crypto functions) I prepared a small test rig that gives me the following: LockBox2 FAILED: 1 ('abc') Got: '9f04f41a848514162050e3d68c1a7abb441dc2b5' Expected: 'a9993e364706816aba3e25717850c26c9cd0d89d' FAILED: 2 ('abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq') Got: '51d7d8769ac72c409c5b0e3f69c60adc9a039014' Expected: '84983e441c3bd26ebaae4aa1f95129e5e54670f1' LockBox3 FAILED: 1 ('abc') Got: '9f04f41a848514162050e3d68c1a7abb441dc2b5' Expected: 'a9993e364706816aba3e25717850c26c9cd0d89d' FAILED: 2 ('abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq') Got: '51d7d8769ac72c409c5b0e3f69c60adc9a039014' Expected: '84983e441c3bd26ebaae4aa1f95129e5e54670f1' DCPCrypto2 FAILED: 1 ('abc') Got: '9f04f41a848514162050e3d68c1a7abb441dc2b5' Expected: 'a9993e364706816aba3e25717850c26c9cd0d89d' FAILED: 2 ('abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq') Got: '51d7d8769ac72c409c5b0e3f69c60adc9a039014' Expected: '84983e441c3bd26ebaae4aa1f95129e5e54670f1' Hashes Test 1 passes Test 2 passes Have you succeeded in compile the mentioned libraries under Delphi XE and make them give the appropriate values? I'm particularly interested in DCPCrypt2 SelfTest procedure. Edit: I've added this answer with the fixed source code. Thank you all for your help, it is most appreciated.

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• Disco/MapReduce: Using results of previous iteration as input to new iteration

  - by muckabout

  Currently am implementing PageRank on Disco. As an iterative algorithm, the results of one iteration are used as input to the next iteration. I have a large file which represents all the links, with each row representing a page and the values in the row representing the pages to which it links. For Disco, I break this file into N chunks, then run MapReduce for one round. As a result, I get a set of (page, rank) tuples. I'd like to feed this rank to the next iteration. However, now my mapper needs two inputs: the graph file, and the pageranks. I would like to "zip" together the graph file and the page ranks, such that each line represents a page, it's rank, and it's out links. Since this graph file is separated into N chunks, I need to split the pagerank vector into N parallel chunks, and zip the regions of the pagerank vectors to the graph chunks This all seems more complicated than necessary, and as a pretty straightforward operation (with the quintessential mapreduce algorithm), it seems I'm missing something about Disco that could really simplify the approach. Any thoughts?

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• Resources related to data-mining and gaming on social networks

  - by darren

  Hi all I'm interested in the problem of patterning mining among players of social networking games. For example detecting cheaters of a game, given a company's user database. So far I have been following the usual recipe for a data mining project: construct a data warehouse that aggregates significant information select a classifier, and train it with a subsectio of records from the warehouse validate classifier with another test set lather, rinse, repeat Surprisingly, I've found very little in this area regarding literature, best practices, etc. I am hoping to crowdsource the information gathering problem here. Specifically what I'm looking for: What classifiers have worked will for this type of pattern mining (it seems highly temporal, users playing games, users receiving rewards, users transferring prizes etc). Are there any highly agreed upon attributes specific to social networking / gaming data? What is a practical amount of information that should be considered? One problem I've run into is data overload, where queries and data cleansing may take days to complete. Related to point above, what hardware resources are required to produce results? I've found it difficult to estimate the amount of computing power I will require for production use. It has become apparent that a white box in the corner does not have enough horse-power for such a project. Are companies generally resorting to cloud solutions? Are they buying clusters? Basically, any resources (theoretical, academic, or practical) about implementing a social networking / gaming pattern-mining program would be very much appreciated. Thanks.

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• Microsoft Sync Framework with Mutliple Client and Server Database

  - by David Osborn

  I'm working on changes to an application to have a local data store instead of connecting directly to the database server. The client app will then sync changes both ways between the server database and its local data store. I'm trying to implement the syncing solution using Microsoft Sync Framework. To be clear there is no server application, only the database server, but there are multiple clients. I have started implementing two classes that implement FullEnumerationSimpleSyncProvider, one called LocalSyncProvider and one called ServerSyncProvider. The LocalSyncProvider knows how to enumerate, insert, update, delete items from the local data store, and the ServerSyncProvider knows how to enumerate, insert, update, delete items from the database server. They each use the provided SqlMetadataStore and store the two metadata stores (one for the local and one for the server) on the local drive of the client. This means that each client will have its own metadata store for its local data store and its own metadata store for the server database. Is this actually going to work, does there need to exists only one server metadata store, or do I need to be using the Sync Framework differently?

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• Accurate least-squares fit algorithm needed

  - by ggkmath

  I've experimented with the two ways of implementing a least-squares fit (LSF) algorithm shown here. The first code is simply the textbook approach, as described by Wolfram's page on LSF. The second code re-arranges the equation to minimize machine errors. Both codes produce similar results for my data. I compared these results with Matlab's p=polyfit(x,y,1) function, using correlation coefficients to measure the "goodness" of fit and compare each of the 3 routines. I observed that while all 3 methods produced good results, at least for my data, Matlab's routine had the best fit (the other 2 routines had similar results to each other). Matlab's p=polyfit(x,y,1) function uses a Vandermonde matrix, V (n x 2 matrix) and QR factorization to solve the least-squares problem. In Matlab code, it looks like: V = [x1,1; x2,1; x3,1; ... xn,1] % this line is pseudo-code [Q,R] = qr(V,0); p = R\(Q'*y); % performs same as p = V\y I'm not a mathematician, so I don't understand why it would be more accurate. Although the difference is slight, in my case I need to obtain the slope from the LSF and multiply it by a large number, so any improvement in accuracy shows up in my results. For reasons I can't get into, I cannot use Matlab's routine in my work. So, I'm wondering if anyone has a more accurate equation-based approach recommendation I could use that is an improvement over the above two approaches, in terms of rounding errors/machine accuracy/etc. Any comments appreciated! thanks in advance.

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• Blackberry stopwatch implementation

  - by Michaela

  I'm trying to write a blackberry app that is basically a stopwatch, and displays lap times. First, I'm not sure I'm implementing the stopwatch functionality in the most optimal way. I have a LabelField (_myLabel) that displays the 'clock' - starting at 00:00. Then you hit the start button and every second the _myLabel field gets updated with how many seconds have past since the last update (should only ever increment by 1, but sometimes there is a delay and it will skip a number). I just can't think of a different way to do it - and I am new to GUI development and threads so I guess that's why. EDIT: Here is what calls the stopwatch: _timer = new Timer(); _timer.schedule(new MyTimerTask(), 250, 250); And here is the TimerTask: class MyTimerTask extends TimerTask { long currentTime; long startTime = System.currentTimeMillis(); public void run() { synchronized (Application.getEventLock()) { currentTime = System.currentTimeMillis(); long diff = currentTime - startTime; long min = diff / 60000; long sec = (diff % 60000) / 1000; String minStr = new Long(min).toString(); String secStr = new Long(sec).toString(); if (min < 10) minStr = "0" + minStr; if (sec < 10) secStr = "0" + secStr; _myLabel.setText(minStr + ":" + secStr); timerDisplay.deleteAll(); timerDisplay.add(_timerLabel); } } } Anyway when you stop the stopwatch it updates a historical table of lap time data. When this list gets long, the timer starts to degrade. If you try to scroll, then it gets really bad. Is there a better way to implement my stopwatch?

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• Dynamic State Machine in Ruby? Do State Machines Have to be Classes?

  - by viatropos

  Question is, are state machines always defined statically (on classes)? Or is there a way for me to have it so each instance of the class with has it's own set of states? I'm checking out Stonepath for implementing a Task Engine. I don't really see the distinction between "states" and "tasks" in there, so I'm thinking I could just map a Task directly to a state. This would allow me to be able to define task-lists (or workflows) dynamically, without having to do things like: aasm_event :evaluate do transitions :to => :in_evaluation, :from => :pending end aasm_event :accept do transitions :to => :accepted, :from => :pending end aasm_event :reject do transitions :to => :rejected, :from => :pending end Instead, a WorkItem (the main workflow/task manager model), would just have many tasks. Then the tasks would work like states, so I could do something like this: aasm_initial_state :initial tasks.each do |task| aasm_state task.name.to_sym end previous_state = nil tasks.each do |tasks| aasm_event task.name.to_sym do transitions :to => "#{task.name}_phase".to_sym, :from => previous_state ? "#{task.name}_phase" : "initial" end previous_state = state end However, I can't do that with the aasm gem because those methods (aasm_state and aasm_event) are class methods, so every instance of the class with that state machine has the same states. I want it so a "WorkItem" or "TaskList" dynmically creates a sequence of states and transitions based on the tasks it has. This would allow me to dynamically define workflows and just have states map to tasks. Are state machines ever used like this?

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• Nested Routes and Parameters for Rails URLs (Best Practice)

  - by viatropos

  Hey there, I have a decent understanding of RESTful urls and all the theory behind not nesting urls, but I'm still not quite sure how this looks in an enterprise application, like something like Amazon, StackOverflow, or Google... Google has urls like this: http://code.google.com/apis/ajax/ http://code.google.com/apis/maps/documentation/staticmaps/ https://www.google.com/calendar/render?tab=mc Amazon like this: http://www.amazon.com/books-used-books-textbooks/b/ref=sa_menu_bo0?ie=UTF8&node=283155&pf_rd_p=328655101&pf_rd_s=left-nav-1&pf_rd_t=101&pf_rd_i=507846&pf_rd_m=ATVPDKIKX0DER&pf_rd_r=1PK4ZKN4YWJJ9B86ANC9 http://www.amazon.com/Ruby-Programming-Language-David-Flanagan/dp/0596516177/ref=sr_1_1?ie=UTF8&s=books&qid=1258755625&sr=1-1 And StackOverflow like this: http://stackoverflow.com/users/169992/viatropos http://stackoverflow.com/questions/tagged/html http://stackoverflow.com/questions/tagged?tagnames=html&sort=newest&pagesize=15 So my question is, what is best practice in terms of creating urls for systems like these? When do you start storing parameters in the url, when don't you? These big companies don't seem to be following the rules so hotly debated in the ruby community (that you should almost never nest URLs for example), so I'm wondering how you go about implementing your own urls in larger scale projects because it seems like the idea of not nesting urls breaks down at anything larger than a blog. Any tips?

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• ant deploy to oc4j problem

  - by senzacionale

  BUILD FAILED C:\Projekti\Projekt ANT\build.xml:337: Problem: failed to create task or type antlib:oracle:deploy Cause: The name is undefined. Action: Check the spelling. Action: Check that any custom tasks/types have been declared. Action: Check that any / declarations have taken place. No types or tasks have been defined in this namespace yet This appears to be an antlib declaration. Action: Check that the implementing library exists in one of: -C:\Projekti\Apache ANT\apache-ant-1.8.1\bin..\lib -C:\Documents and Settings\MitjaG.ant\lib -a directory added on the command line with the -lib argument CODE: <target name="deploy" depends="init, ear"> <oracle:deploy moduletype="ear" host="${oc4j.host}" port="${oc4j.admin.port}" userid="${oc4j.admin.user}" password="${oc4j.admin.password}" file="${dest.dir}/${package.name}/${view.dir}/${deploy.dir}/${ear.file}" deploymentname="${app.name}" logfile="${log.dir}/deploy-ear.log"/> <oracle:bindWebApp host="${oc4j.host}" port="${oc4j.admin.port}" userid="${oc4j.admin.user}" password="${oc4j.admin.password}" deploymentname="${app.name}" webmodule="${web.name}" websitename="${oc4j.binding.module}" contextroot="/${app.name}" /> </target> I google and search for whole day but i can not find solution. There is no good docs for oc4j and ant except this from 2005: http://www.it-eye.nl/weblog/2005/08/15/how-to-using-ant-to-deploy-to-oc4j-dp4/

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• PLT Scheme Memory

  - by Eric

  So I need some help with implementing a Make-memory program using Scheme. I need two messages 'write and 'read. So it would be like (mymem 'write 34 -116) and (mymem 'read 99) right? and (define mymem (make-memory 100)).....How would I implement this in scheme? using an Alist???I need some help coding it. I have this code which makes make-memory a procedure and when you run mymem you get ((99.0)) and what i need to do is recur this so i get an alist with dotted pairs to ((0.0)). So any suggestions on how to code this?? Does anyone have any ideas what I could do to recur and make messages Write and read?? (define make-memory (lambda (n) (letrec ((mem '()) (dump (display mem))) (lambda () (if (= n 0) (cons (cons n 0) mem) mem) (cons (cons (- n 1) 0) mem)) (lambda (msg loc val) (cond ((equal? msg 'read) (display (cons n val))(set! n (- n 1))) ((equal? msg 'write) (set! mem (cons val loc)) (set! n (- n 1)) (display mem))))))) (define mymem (make-memory 100)) Yes this is an assignment but I wrote this code. I just need some help or direction. And yes I do know about variable-length argument lists.

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