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• In R, how do you get the best fitting equation to a set of data?

  - by Matherion

  I'm not sure wether R can do this (I assume it can, but maybe that's just because I tend to assume that R can do anything :-)). What I need is to find the best fitting equation to describe a dataset. For example, if you have these points: df = data.frame(x = c(1, 5, 10, 25, 50, 100), y = c(100, 75, 50, 40, 30, 25)) How do you get the best fitting equation? I know that you can get the best fitting curve with: plot(loess(df$y ~ df$x)) But as I understood you can't extract the equation, see Loess Fit and Resulting Equation. When I try to build it myself (note, I'm not a mathematician, so this is probably not the ideal approach :-)), I end up with smth like: y.predicted = 12.71 + ( 95 / (( (1 + df$x) ^ .5 ) / 1.3)) Which kind of seems to approximate it - but I can't help to think that smth more elegant probably exists :-) I have the feeling that fitting a linear or polynomial model also wouldn't work, because the formula seems different from what those models generally use (i.e. this one seems to need divisions, powers, etc). For example, the approach in Fitting polynomial model to data in R gives pretty bad approximations. I remember from a long time ago that there exist languages (Matlab may be one of them?) that do this kind of stuff. Can R do this as well, or am I just at the wrong place? (Background info: basically, what we need to do is find an equation for determining numbers in the second column based on the numbers in the first column; but we decide the numbers ourselves. We have an idea of how we want the curve to look like, but we can adjust these numbers to an equation if we get a better fit. It's about the pricing for a product (a cheaper alternative to current expensive software for qualitative data analysis); the more 'project credits' you buy, the cheaper it should become. Rather than forcing people to buy a given number (i.e. 5 or 10 or 25), it would be nicer to have a formula so people can buy exactly what they need - but of course this requires a formula. We have an idea for some prices we think are ok, but now we need to translate this into an equation.

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• Visual studio 2010 colourizers, intellisense and the rest. Where to start!!

  - by Owen

  Ok, before I begin I realize that there is a lot of documentation on this subject but I have thus far failed to get even basic colourization working for VS2010. My goal is to simply get to a point where I can open a document and everything is coloured red, from here I can implement the relevant parsing logic. Here's what I have tried/found: 1) Downloaded all the relevent SDK's and such- Found the ook sample (http://code.msdn.microsoft.com/ookLanguage) - didn't build, didn't work. 2) Knowing almost nothing about MEF read through "Implementing a Language Service By Using the Managed Package Framework" - http://msdn.microsoft.com/en-us/library/bb166533(v=VS.100).aspx This was pretty much a copy and paste of all the basic stuff here, and also updating some references which were out of date with the sample see: http://social.msdn.microsoft.com/Forums/en-US/vsx/thread/a310fe67-afd2-4592-b295-3fc86fec7996 Now, I have got to a point where when running the package MEF appears to have hooked up correctly (I know this because with the debugger open I can see that the packages initialize and FDoIdle methods are being hit). When I open a file of the extension I have registered with the ProvideLanguageExtensionAttribute everything dies as if in an endless loop, yet no debug symbols hit (though they are loaded). Looking at the ook sample and the MEF examples they seem to be totally different approaches to the same problem. In the ook sample there are notions of Clasifications and Completion controllers which aren't mentioned in the MEF example. Also, they don't seem to create a Package or Language service, so I have no idea how it should work? With the MEF example, my assumption is that I need to hook into the "IScanner.ScanTokenAndProvideInfoAboutIt" to provide syntax highlighting? Which would be fine if I could ever hit this method. So my first question I guess is which approach should I be taking here? Or do they both somehow tie together? My second questions is, where can I find a basic fully working project that implements bog standard basic syntax highlighting and intellisense or VS2010? Thirdly, in the MEF example when I created a Package there were a bunch of test projects created for me. I appears that the integration tests launch the VS2010 test rig somehow, but the test fails. It would be good to write my service with tests but I have no idea what/how I can test each interaction so any references to testing Language services would be helpful. Finally, please throw any resource/book links my way that I may find useful. Cheers, Chris. N.B. Sorry I realize this is part question part rant, but I have never been so confused.

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• Syntax error while copying an multidimensional array to another in C

  - by mantuko

  We are programming a ST269 microcontroller which has two IR distance sensors. To calibrate these sensors we made one table for each sensor with the distance we measured and the corresponding value we get from the ADC. Now we want to use one function to approximate the values in between. So we defined two two-dimensional arrays (one for each sensor) as global variables. In our function we then want to copy the one array we want to work with to a working array and approximate our values. So here's the code: ... unsigned int ir_werte_re[][] = { {8,553}, ... {83,133} }; unsigned int ir_werte_li[][] = { {8,566}, ... {83,147} }; ... unsigned int geradenaproximation(unsigned int messwert, unsigned int seite) { unsigned int working_array[16][16]; unsigned int i = 0; if (seite == 0) { for (i = 0; i < sizeof(working_array); i++) { working_array[i][0] = ir_werte_li[i][0]; i++; } } else { for (i = 0; i < sizeof(working_array); i++) { working_array[i][0] = ir_werte_re[i][0]; i++; } } i = 0; unsigned int y1 = 0; unsigned int x1 = 0; ... } This code is in a file called sensor.c. We didn't write anything about our global arrays in the sensor.h should we? The sensor.h of course is included in our main.c and there the function is called. We also tried to copy the arrays via memcpy(working_array, ir_werte_li, sizeof(working_array)); And in every way we do this we get a syntax error near unsigned in the line where we're declaring unsigned int y1 = 0; and I'm pretty sure that there is no syntax error in this line : ) The last time I spend coding in C is a few years away so I'm not sure if the way we try to do this is good. Perhaps we can solve this by using a pointer instead of really copying the array or something. So please help me out I'll appreciate your bits on this.

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• Multi domain rails app. How to intelligently use MVC?

  - by denial

  Background: We have app a, b, and plan to add more apps into this same application. The apps are similar enough they could share many views, assets, and actions. Currently a,b live in a single rails app(2.3.10). c will be similar enough that it could also be in this rails app. The problem: As we continue to add more apps to this one app, there's going to be too much case logic that the app will soon become a nightmare to maintain. There will also be potential namespace issues. However, the apps are very similar in function and layout, it also makes sense to keep them in one app so that it's one app to maintain(since roughly 50% of site look/functionality will be shared). What we are trying to do is keep this as clean as possible so it's easy for multiple teams to work on and easy to maintain. Some things we've thought about/are trying: Engines. Make each app an engine. This would let us base routes on the domain. It also allows us to pull out controllers, models and views for the specific app. This solution does not seem ideal as we won't be reusing the apps any time soon. And explicitly stating the host in the routes doesn't seem right. Skinning/themes. The auth logic would be different between the apps. Each user model would be different. So it's not just a skinning problem. In app/view add folder sitea for sitea views, siteb for siteb views and so on. Do the same for controllers and models. This is still pretty messy and since it didn't follow naming conventions, it did not work with rails so nicely and made much of the code messier. Making another rails app. We just didn't want to maintain the same controller or view in 2 apps if they are identical. What we want to do is make the app intelligently use a controller based on the host. So there would be a sessions controller for each app, and perhaps some parent session controller for shared logic(not needed now). In each of these session controllers, it handles authentication for that specific app. So if the domain is a.mysite.com, it would use session controller for app a and know to use app a's views,models,controllers. And if the domain is b.mysite, it would use the session controller for b. And there would be a user model for a and user model for b, which also would be determined by the domain. Does anyone have any suggestions or experience with this situation? And ideally using rails 2.3.x as updating to rails 3 isn't an option right now.

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• iPhone memory management (with specific examples/questions)

  - by donkim

  Hey all. I know this question's been asked but I still don't have a clear picture of memory management in Objective-C. I feel like I have a pretty good grasp of it, but I'd still like some correct answers for the following code. I have a series of examples that I'd love for someone(s) to clarify. Setting a value for an instance variable. Say I have an NSMutableArray variable. In my class, when I initialize it, do I need to call a retain on it? Do I do fooArray = [[[NSMutableArray alloc] init] retain]; or fooArray = [[NSMutableArray alloc] init]; Does doing [[NSMutableArray alloc] init] already set the retain count to 1, so I wouldn't need to call retain on it? On the other hand, if I called a method that I know returns an autoreleased object, I would for sure have to call retain on it, right? Like so: fooString = [[NSString stringWithFormat:@"%d items", someInt] retain]; Properties. I ask about the retain because I'm a bit confused about how @property's automatic setter works. If I had set fooArray to be a @property with retain set, Objective-C will automatically create the following setter, right? - (void)setFooArray:(NSMutableArray *)anArray { [fooArray release]; fooArray = [anArray retain]; } So, if I had code like this: self.fooArray = [[NSMutableArray alloc] init]; (which I believe is valid code), Objective-C creates a setter method that calls retain on the value assigned to fooArray. In this case, will the retain count actually be 2? Correct way of setting a value of a property. I know there are questions on this and (possibly) debates, but which is the right way to set a @property? This? self.fooArray = [[NSMutableArray alloc] init]; Or this? NSMutableArray *anArray = [[NSMutableArray alloc] init]; self.fooArray = anArray; [anArray release]; I'd love to get some clarification on these examples. Thanks!

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• Dynamic Dispatch without Virtual Functions

  - by Kristopher Johnson

  I've got some legacy code that, instead of virtual functions, uses a kind field to do dynamic dispatch. It looks something like this: // Base struct shared by all subtypes // Plain-old data; can't use virtual functions struct POD { int kind; int GetFoo(); int GetBar(); int GetBaz(); int GetXyzzy(); }; enum Kind { Kind_Derived1, Kind_Derived2, Kind_Derived3 }; struct Derived1: POD { Derived1(): kind(Kind_Derived1) {} int GetFoo(); int GetBar(); int GetBaz(); int GetXyzzy(); // plus other type-specific data and function members }; struct Derived2: POD { Derived2(): kind(Kind_Derived2) {} int GetFoo(); int GetBar(); int GetBaz(); int GetXyzzy(); // plus other type-specific data and function members }; struct Derived3: POD { Derived3(): kind(Kind_Derived3) {} int GetFoo(); int GetBar(); int GetBaz(); int GetXyzzy(); // plus other type-specific data and function members }; and then the POD class's function members are implemented like this: int POD::GetFoo() { // Call kind-specific function switch (kind) { case Kind_Derived1: { Derived1 *pDerived1 = static_cast<Derived1*>(this); return pDerived1->GetFoo(); } case Kind_Derived2: { Derived2 *pDerived2 = static_cast<Derived2*>(this); return pDerived2->GetFoo(); } case Kind_Derived3: { Derived3 *pDerived3 = static_cast<Derived3*>(this); return pDerived3->GetFoo(); } default: throw UnknownKindException(kind, "GetFoo"); } } POD::GetBar(), POD::GetBaz(), POD::GetXyzzy(), and other members are implemented similarly. This example is simplified. The actual code has about a dozen different subtypes of POD, and a couple dozen methods. New subtypes of POD and new methods are added pretty frequently, and so every time we do that, we have to update all these switch statements. The typical way to handle this would be to declare the function members virtual in the POD class, but we can't do that because the objects reside in shared memory. There is a lot of code that depends on these structs being plain-old-data, so even if I could figure out some way to have virtual functions in shared-memory objects, I wouldn't want to do that. So, I'm looking for suggestions as to the best way to clean this up so that all the knowledge of how to call the subtype methods is centralized in one place, rather than scattered among a couple dozen switch statements in a couple dozen functions. What occurs to me is that I can create some sort of adapter class that wraps a POD and uses templates to minimize the redundancy. But before I start down that path, I'd like to know how others have dealt with this.

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• Code Golf: Countdown Number Game

  - by Noldorin

  Challenge Here is the task, inspired by the well-known British TV game show Countdown. The challenge should be pretty clear even without any knowledge of the game, but feel free to ask for clarifications. And if you fancy seeing a clip of this game in action, check out this YouTube clip. It features the wonderful late Richard Whitely in 1997. You are given 6 numbers, chosen at random from the set {1, 2, 3, 4, 5, 6, 8, 9, 10, 25, 50, 75, 100}, and a random target number between 100 and 999. The aim is to make use the six given numbers and the four common arithmetic operations (addition, subtraction, multiplication, division; all over the rational numbers) to generate the target - or as close as possible either side. Each number may only be used once at most, while each arithmetic operator may be used any number of times (including zero.) Note that it does not matter how many numbers are used. Write a function that takes the target number and set of 6 numbers (can be represented as list/collection/array/sequence) and returns the solution in any standard numerical notation (e.g. infix, prefix, postfix). The function must always return the closest-possible result to the target, and must run in at most 1 minute on a standard PC. Note that in the case where more than one solution exists, any single solution is sufficient. Examples: {50, 100, 4, 2, 2, 4}, target 203 e.g. 100 * 2 + 2 + (4 / 4) e.g. (100 + 50) * 4 * 2 / (4 + 2) {25, 4, 9, 2, 3, 10}, target 465 e.g. (25 + 10 - 4) * (9 * 2 - 3) {9, 8, 10, 5, 9, 7), target 241 e.g. ((10 + 9) * 9 * 7) + 8) / 5 Rules Other than mentioned in the problem statement, there are no further restrictions. You may write the function in any standard language (standard I/O is not necessary). The aim as always is to solve the task with the smallest number of characters of code. Saying that, I may not simply accept the answer with the shortest code. I'll also be looking at elegance of the code and time complexity of the algorithm! My Solution I'm attempting an F# solution when I find the free time - will post it here when I have something! Format Please post all answers in the following format for the purpose of easy comparison: Language Number of characters: ??? Fully obfuscated function: (code here) Clear (ideally commented) function: (code here) Any notes on the algorithm/clever shortcuts it takes.

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• circles and triangles problem

  - by Faken

  Hello everyone, I have an interesting problem here I've been trying to solve for the last little while: I have 3 circles on a 2D xy plane, each with the same known radius. I know the coordinates of each of the three centers (they are arbitrary and can be anywhere). What is the largest triangle that can be drawn such that each vertice of the triangle sits on a separate circle, what are the coordinates of those verticies? I've been looking at this problem for hours and asked a bunch of people but so far only one person has been able to suggest a plausible solution (though i have no way of proving it). The solution that we have come up with involves first creating a triangle about the three circle centers. Next we look at each circle individually and calculate the equation of a line that passes through the circle's center and is perpendicular to the opposite edge. We then calculate two intersection points of the circle. This is then done for the next two circles with a result of 6 points. We iterate over the 8 possible 3 point triangles that these 6 points create (the restriction is that each point of the big triangle must be on a separate circle) and find the maximum size. The results look reasonable (at least when drawn out on paper) and it passes the special case of when the centers of the circles all fall on a straight line (gives a known largest triangle). Unfortunate i have no way of proving this is correct or not. I'm wondering if anyone has encountered a problem similar to this and if so, how did you solve it? Note: I understand that this is mostly a math question and not programming, however it is going to be implemented in code and it must be optimized to run very fast and efficient. In fact, I already have the above solution in code and tested to be working, if you would like to take a look, please let me know, i chose not to post it because its all in vector form and pretty much impossible to figure out exactly what is going on (because it's been condensed to be more efficient). Lastly, yes this is for school work, though it is NOT a homework question/assignment/project. It's part of my graduate thesis (abet a very very small part, but still technically is part of it). Thanks for your help.

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• Issues querying Access '07 database in C#

  - by Kye

  I'm doing a .NET unit as part of my studies. I've only just started, with a lecturer that as kinda failed to give me the most solid foundation with .NET, so excuse the noobishness. I'm making a pretty simple and generic database-driven application. I'm using C# and I'm accessing a Microsoft Access 2007 database. I've put the database-ish stuff in its own class with the methods just spitting out OleDbDataAdapters that I use for committing. I feed any methods which preform a query a DataSet object from the main program, which is where I'm keeping the data (multiple tables in the db). I've made a very generic private method that I use to perform SQL SELECT queries and have some public methods wrapping that method to get products, orders.etc (it's a generic retail database). The generic method uses a separate Connect method to actually make the connection, and it is as follows: private static OleDbConnection Connect() { OleDbConnection conn = new OleDbConnection( @"Provider=Microsoft.ACE.OLEDB.12.0; Data Source=C:\Temp\db.accdb"); return conn; } The generic method is as follows: private static OleDbDataAdapter GenericSelectQuery( DataSet ds, string namedTable, String selectString) { OleDbCommand oleCommand = new OleDbCommand(); OleDbConnection conn = Connect(); oleCommand.CommandText = selectString; oleCommand.Connection = conn; oleCommand.CommandType = CommandType.Text; OleDbDataAdapter adapter = new OleDbDataAdapter(); adapter.SelectCommand = oleCommand; adapter.MissingSchemaAction = MissingSchemaAction.AddWithKey; adapter.Fill(ds, namedTable); return adapter; } The wrapper methods just pass along the DataSet that they received from the main program, the namedtable string is the name of the table in the dataset, and you pass in the query you wish to make. It doesn't matter which query I give it (even something simple like SELECT * FROM TableName) I still get thrown an OleDbException, stating that there was en error with the FROM clause of the query. I've just resorted to building the queries with Access, but there's still no use. Obviously there's something wrong with my code, which wouldn't actually surprise me. Here are some wrapper methods I'm using. public static OleDbDataAdapter GetOrderLines(DataSet ds) { OleDbDataAdapter adapter = GenericSelectQuery( ds, "orderlines", "SELECT OrderLine.* FROM OrderLine;"); return adapter; } They all look the same, it's just the SQL that changes.

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• Getting up to speed on modern architecture

  - by Matt Thrower

  Hi, I don't have any formal qualifications in computer science, rather I taught myself classic ASP back in the days of the dotcom boom and managed to get myself a job and my career developed from there. I was a confident and, I think, pretty good programmer in ASP 3 but as others have observed one of the problems with classic ASP was that it did a very good job of hiding the nitty-gritty of http so you could become quite competent as a programmer on the basis of relatively poor understanding of the technology you were working with. When I changed on to .NET at first I treated it like classic ASP, developing stand-alone applications as individual websites simply because I didn't know any better at the time. I moved jobs at this point and spent the next several years working on a single site whose architecture relied heavily on custom objects: in other words I gained a lot of experience working with .NET as a middle-tier development tool using a quite old-fashioned approach to OO design along the lines of the classic "car" class example that's so often used to teach OO. Breaking down programs into blocks of functionality and basing your classes and methods around that. Although we worked under an Agile approach to manage the work the whole setup was classic client/server stuff. That suited me and I gradually got to grips with .NET and started using it far more in the manner that it should be, and I began to see the power inherent in the technology and precisely why it was so much better than good old ASP 3. In my latest job I have found myself suddenly dropped in at the deep end with two quite young, skilled and very cutting-edge programmers. They've built a site architecture which is modelling along a lot of stuff which is new to me and which, in truth I'm having a lot of trouble understanding. The application is built on a cloud computing model with multi-tenancy and the architecture is all loosely coupled using a lot of interfaces, factories and the like. They use nHibernate a lot too. Shortly after I joined, both these guys left and I'm now supposedly the senior developer on a system whose technology and architecture I don't really understand and I have no-one to ask questions of. Except you, the internet. Frankly I feel like I've been pitched in at the deep end and I'm sinking. I'm not sure if this is because I lack the educational background to understand this stuff, if I'm simply not mathematically minded enough for modern computing (my maths was never great - my approach to design is often to simply debug until it works, then refactor until it looks neat), or whether I've simply been presented with too much of too radical a nature at once. But the only way to find out which it is is to try and learn it. So can anyone suggest some good places to start? Good books, tutorials or blogs? I've found a lot of internet material simply presupposes a level of understanding that I just don't have. Your advice is much appreciated. Help a middle-aged, stuck in the mud developer get enthusastic again! Please!

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• organizing external libraries and include files

  - by stijn

  Over the years my projects use more and more external libraries, and the way I did it starts feeling more and more awkward (although, that has to be said, it does work flawlessly). I use VS on Windows, CMake on others, and CodeComposer for targetting DSPs on Windows. Except for the DSPs, both 32bit and 64bit platforms are used. Here's a sample of what I am doing now; note that as shown, the different external libraries themselves are not always organized in the same way. Some have different lib/include/src folders, others have a single src folder. Some came ready-to-use with static and/or shared libraries, others were built /path/to/projects /projectA /projectB /path/to/apis /apiA /src /include /lib /apiB /include /i386/lib /amd64/lib /path/to/otherapis /apiC /src /path/to/sharedlibs /apiA_x86.lib -->some libs were built in all possible configurations /apiA_x86d.lib /apiA_x64.lib /apiA_x64d.lib /apiA_static_x86.lib /apiB.lib -->other libs have just one import library /path/to/dlls -->most of this directory also gets distributed to clients /apiA_x86.dll and it's in the PATH /apiB.dll Each time I add an external libary, I roughly use this process: build it, if needed, for different configurations (release/debug/platform) copy it's static and/or import libraries to 'sharedlibs' copy it's shared libraries to 'dlls' add an environment variable, eg 'API_A_DIR' that points to the root for ApiA, like '/path/to/apis/apiA' create a VS property sheet and a CMake file to state include path and eventually the library name, like include = '$(API_A_DIR)/Include' and lib = apiA.lib add the propertysheet/cmake file to the project needing the library It's especially step 4 and 5 that are bothering me. I am pretty sure I am not the only one facing this problem, and would like see how others deal with this. I was thinking to get rid of the environment variables per library, and use just one 'API_INCLUDE_DIR' and populating it with the include files in an organized way: /path/to/api/include /apiA /apiB /apiC This way I do not need the include path in the propertysheets nor the environment variables. For libs that are only used on windows I even don't need a propertysheet at all as I can use #pragmas to instruct the linker what library to link to. Also in the code it will be more clear what gets included, and no need for wrappers to include files having the same name but are from different libraries: #include <apiA/header.h> #include <apiB/header.h> #include <apiC_version1/header.h> The withdrawal is off course that I have to copy include files, and possibly** introduce duplicates on the filesystem, but that looks like a minor price to pay, doesn't it? ** actually once libraries are built, the only thing I need from them is the include files and thie libs. Since each of those would have a dedicated directory, the original source tree is not needed anymore so can be deleted..

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• Truth tables in code? How to structure state machine?

  - by HanClinto

  I have a (somewhat) large truth table / state machine that I need to implement in my code (embedded C). I anticipate the behavior specification of this state machine to change in the future, and so I'd like to keep this easily modifiable in the future. My truth table has 4 inputs and 4 outputs. I have it all in an Excel spreadsheet, and if I could just paste that into my code with a little formatting, that would be ideal. I was thinking I would like to access my truth table like so: u8 newState[] = decisionTable[input1][input2][input3][input4]; And then I could access the output values with: setOutputPin( LINE_0, newState[0] ); setOutputPin( LINE_1, newState[1] ); setOutputPin( LINE_2, newState[2] ); setOutputPin( LINE_3, newState[3] ); But in order to get that, it looks like I would have to do a fairly confusing table like so: static u8 decisionTable[][][][][] = {{{{ 0, 0, 0, 0 }, { 0, 0, 0, 0 }}, {{ 0, 0, 0, 0 }, { 0, 0, 0, 0 }}}, {{{ 0, 0, 1, 1 }, { 0, 1, 1, 1 }}, {{ 0, 1, 0, 1 }, { 1, 1, 1, 1 }}}}, {{{{ 0, 1, 0, 1 }, { 1, 1, 1, 1 }}, {{ 0, 1, 0, 1 }, { 1, 1, 1, 1 }}}, {{{ 0, 1, 1, 1 }, { 0, 1, 1, 1 }}, {{ 0, 1, 0, 1 }, { 1, 1, 1, 1 }}}}; Those nested brackets can be somewhat confusing -- does anyone have a better idea for how I can keep a pretty looking table in my code? Thanks! Edit based on HUAGHAGUAH's answer: Using an amalgamation of everyone's input (thanks -- I wish I could "accept" 3 or 4 of these answers), I think I'm going to try it as a two dimensional array. I'll index into my array using a small bit-shifting macro: #define SM_INPUTS( in0, in1, in2, in3 ) ((in0 << 0) | (in1 << 1) | (in2 << 2) | (in3 << 3)) And that will let my truth table array look like this: static u8 decisionTable[][] = { { 0, 0, 0, 0 }, { 0, 0, 0, 0 }, { 0, 0, 0, 0 }, { 0, 0, 0, 0 }, { 0, 0, 1, 1 }, { 0, 1, 1, 1 }, { 0, 1, 0, 1 }, { 1, 1, 1, 1 }, { 0, 1, 0, 1 }, { 1, 1, 1, 1 }, { 0, 1, 0, 1 }, { 1, 1, 1, 1 }, { 0, 1, 1, 1 }, { 0, 1, 1, 1 }, { 0, 1, 0, 1 }, { 1, 1, 1, 1 }}; And I can then access my truth table like so: decisionTable[ SM_INPUTS( line1, line2, line3, line4 ) ] I'll give that a shot and see how it works out. I'll also be replacing the 0's and 1's with more helpful #defines that express what each state means, along with /**/ comments that explain the inputs for each line of outputs. Thanks for the help, everyone!

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• Javascript: Writing a firefox extension with sockets

  - by Johnny Grass

  I need to write a firefox extension that creates a server socket (I think that's what it's called) and returns the browser's current url when a client application (running on the same computer) sends it a request. The thing is that I have no Java/Javascript background at all and I'm pressed for time so I am trying to hack something together from code samples. So far I've been mildly successful. I've been working with code from this question which is used in the open source Firefox exension PolyChrome I have the following code: var reader = { onInputStreamReady : function(input) { var input_stream = Components.classes["@mozilla.org/scriptableinputstream;1"] .createInstance(Components.interfaces.nsIScriptableInputStream); input_stream.init(input); input_stream.available(); var request = ''; while (input_stream.available()) { request = request + input_stream.read(512); } var checkString = "foo" if (request.toString() == checkString.toString()) { output_console('URL: ' + content.location.href); } else output_console("nothing"); var thread_manager = Components.classes["@mozilla.org/thread-manager;1"].getService(); input.asyncWait(reader,0,0,thread_manager.mainThread); } } var listener = { onSocketAccepted: function(serverSocket, clientSocket) { output_console("Accepted connection on "+clientSocket.host+":"+clientSocket.port); input = clientSocket.openInputStream(0, 0, 0).QueryInterface(Components.interfaces.nsIAsyncInputStream); output = clientSocket.openOutputStream(Components.interfaces.nsITransport.OPEN_BLOCKING, 0, 0); var thread_manager = Components.classes["@mozilla.org/thread-manager;1"].getService(); input.asyncWait(reader,0,0,thread_manager.mainThread); } } var serverSocket = Components.classes["@mozilla.org/network/server-socket;1"]. createInstance(Components.interfaces.nsIServerSocket); serverSocket.init(9999, true, 5); output_console("Opened socket on " + serverSocket.port); serverSocket.asyncListen(listener); I have a few questions. So far I can telnet into localhost and get a response, but my string comparison in the reader seems to fail even if I enter "foo". I don't get why. What am I missing? The sample code I'm using opens up a console window and prints output when I telnet into localhost. Ideally I would like the output to be returned as a response when the client sends a request to the server socket with a passphrase. How do I go about doing that? Is doing this a good idea? Does it create security vulnerabilities on the computer? How can I block connections to the socket from other computers? What is a good place to read about javascript sockets? My google searches have been pretty fruitless but then maybe I'm not using the right keywords.

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• Javascript table construction bug using JQuery in Firefox on Mac OSX

  - by Poita_

  I'm using some code to build up tables using JQuery, but in Firefox 3.5.3 on Mac OSX, the table cells all appear on separate lines by themselves, instead of in their respective rows. Chrome 5.0.342.7 beta on OSX correctly produces the table, as does Safari 4.0.5. Here is a minimal reproduction case: <html> <body> <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js"></script> <script type="text/javascript"> $(document).ready(function() { var b = $('body'); b.append("<table>"); for (var i = 0; i < 3; ++i) { b.append("<tr>"); for (var j = 0; j < 3; ++j) b.append("<td>x</td>"); b.append("</tr>"); } b.append("</table>"); }); </script> </body> </html> In Chrome and Safari, I get this correct output: x x x x x x x x x but Firefox produces: x x x x x x x x x Note that if I manually create that exact table without using Javascript (i.e. direct into the HTML) then the table appears correctly in Firefox. Also, if I change the JS to append then entire table in one call then it also works -- the only time it doesn't work is if you append it part-by-part as I have done before. My question is: is this to be expected, or should I report this as a bug to Firefox? I'm pretty sure this is a Firefox bug, but I'm a bit of a newbie to JS and web development in general, so perhaps there's something I'm missing? P.S. obviously there are easy ways to get around this -- that's not my concern. See above.

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• Facebook Connect from Localhost, doing some weird stuff

  - by Brett

  So maybe the documentation is out of date, or I am just off here. But I have done a slew of FB iframe apps (connect), but I am starting my first FB Connect site. Running it from localhost, and the Connect URL is http:// my_external_IP_address. When I click on the FB login button on my site, it pops up, says waiting for facebook, and it returns my site in that box, with the URL up top with the http:// mysite/?session={session key, user_id, etc.} The user_id is infact my FB id. And so it thinks I am logged in. If I close the popup, I'm not logged in. I'm not sure why the pop up isn't doing the normal fb connect dialog. I'm following these steps. (I added spaces to the http:// as to not be detected as 'spam') html xmlns="http://www.w3.org/1999/xhtml" xmlns:fb="http://www.facebook.com/2008/fbml" right after <body> <script src="http://static.ak.connect.facebook.com/js/api_lib/v0.4/FeatureLoader.js.php" type="text/javascript"> At the end, before the body close tag: script type="text/javascript"> FB.init("fbkey", "http://127.0.0.1/xd_receiver.htm"); I have tried using xd_receiver.htm, /xd_receiver.htm (and other combos), and that brings up a blank page. using the http://127.0.0.1 at least does something. In my config file, which is called before all of those, it checks for a PHP session key to see if they are logged in, if that doesn't exist it looks for a cookie, and if that doesn't exist it does this: require_once('includes/facebook.php'); $facebook = new Facebook($fbkey, $fbsec); $user_id = $facebook->get_loggedin_user(); if($user_id > 0){ $user = $ac->getUserFromFB($user_id); $_SESSION['user_id'] = $user['user_id']; } The user_id is always empty when I echo it out to the screen to test. The session event never occurs as well. So I don't know what it is doing in the popup, but I think Facebook thinks it is logging me in. Not sure. Pretty stumped on this one. Any help would be appreciated. Thanks!

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• iPhone - NSURLConnection does not receive data

  - by Jukurrpa

  Hi, I have a pretty weird problem with NSURLRequest. I'm using them to make an asynchronous image loading in an UITableView. The first time the tableView displays, all connections from NSURLRequests open correctly but receive absolutely no data, regardless of how long I wait. But as soon as I scroll down in the tableView, the newly created requests for the new cells work perfectly! The only way for the images on top of the tableView to load is to make them disappear by scrolling down and then up again, in order to create new requests. Here is what I do in "cellForRowAtIndexPath": UITableViewCell* cell = [tableView dequeueReusableCellWithIdentifier:@"Cell"]; if (cell == nil) { cell = [[UITableViewCell alloc] initWIthFrame:CGRectMake(0, 0, 300, 60)]; AsyncUIImageView imageView = [[AsynUIImageView alloc] initWithFrame:CGRectMake(0, 0, 60, 60)]; imageView.tag = IMG_VIEW // an enum for tags [cell addSubView:imageView]; [imageView release]; } AsyncUIImageView imageView = (AsyncUIImageView*)[cell viewWithTag:IMG_VIEW]; // I do a few cache checks here, but if the image aint cached I do this: [imageView loadImageFromURL:@"http://someurl.com/somepix.jpg"]; // all urls are different, just an example The AsyncUIImageView inherits from UIImageView and contains an NSURLConnection which opens upon calling the loadImageFromURL method: (void) loadImageFromURL:(NSString*)filename { if (self.connection != nil) [self.connection release]; if (self.data != nil) [self.data release]; NSURLRequest* request = [NSURLRequest requestWithURL:[[NSURL alloc] initWithString:fileName] cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:10.0]; self.connection = [[NSURLConnection alloc] initWithRequest:request delegate:self]; if (self.connection == nil) return; self.data = [[NSMutableData data] retain]; } I've created the delegate methods "connection: didReceiveData", which appends received data to self.data and "connectionDidFinishLoading" which sets the image and closes the connection once the transfer is complete. These work, but are never called for the first requests I create. I suspect this bug to come from the main thread not giving the first requests the control so they can execute themselves, as the same behavior happens if I keep my finger on the screen after a scroll: connections open themselves, but no data is received until I stop touching the screen. What am I doing wrong?

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• Twisted + SQLAlchemy and the best way to do it.

  - by Khorkrak

  So I'm writing yet another Twisted based daemon. It'll have an xmlrpc interface as usual so I can easily communicate with it and have other processes interchange data with it as needed. This daemon needs to access a database. We've been using SQL Alchemy in place of hard coding SQL strings for our latest projects - those mostly done for web apps in Pylons. We'd like to do the same for this app and re-use library code that makes use of SQL Alchemy. So what to do? Well of course since that library was written for use in a Pylons app it's all the straight-forward blocking style code that everyone is accustomed to and all of the non-blocking is magically handled by Pylons via threading, thread locals, scoped sessions and so on. So now for Twisted I guess I'm a bit stuck. I could: Just write the sql I need directly if it's minimal and use the dbapi pool in twisted to do runInteractions etc when I need to hit the db. Use the objects and inherently blocking methods in our library and block now and then in my Twisted daemon. Bah. Use sAsync which was last updated in 2008 and kind of reuse the models we have defined already but not really and it does address code that needs to work in Pylons either. Does that even work with the latest version SQL Alchemy? Who knows. That project looked great though - why was it apparently abandoned? Spawn a separate subprocess and have it deal with the library code and all it's blocking, the results being returned back to my daemon when ready as objects marshalled via YAML over xmlrpc. Use deferToThread and then expunge the objects returned having made sure to do eager loads so that I have all my stuff that I might need. Seems kind of ugha to me. I'm also stuck using Python 2.5.4 atm so no 2.6 yet and I don't think I can just do an import from future to get access to the cool new multiprocessing module stuff in there. That's OK though I guess as we've got dealing with interprocess communication down pretty well. So I'm leaning towards option 4 mostly as that would avoid the mortal sin of logic duplication with option 1 while also staying the heck away from threads. Any better ideas?

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• Cocoa's newbie question: is it possible to bind a NSTableView's selection to another tableview's selection?

  - by cocoaOverloaded

  http://img651.imageshack.us/img651/6999/modelsf.jpg Let'say, I've 2 entities in the Core Data's Model file, one being all "transactions" ever done by X company. The "transactions" entity has among other properties, a "DATE" property and a to-one relationship "COMPANY"(specifying the company with which X company has done that particular transaction). The other entity:"companies" of course contains all the companies' info ,with which X company has done transaction. The "companies" entity has a to-many relationships "TRANSACTIONS" which is an inverse relationship to "transactions" entity's "COMPANY" relationship. So within IB, I created a NSTableView(with its own NSArrayController) showing all the transactions on a particular Date (with the help of NSPredicate). Then I create another table view showing the to-many relationship "TRANSACTIONS" of the company of the selected transaction in the first table view(which shows transactions on a particular date). The 2nd table view's NSArrayController binding is like this: ** bind to: "name of the first tableview's controller", Controller Key: selection, Model Key Path:COMPANY.TRANSACTIONS(the to-many relationship in the "companies" entity)** Everythings work fine up to this moment, the 2nd tableview shows all the transactions X company has done with the company of the selected transactions in the 1st table view. But I have a group of textfields showing details of a particular transactions. Binding the these textfields with the controller of the 1st table view(the one showing transactions on a particular date) is pretty straightforward. But what I want to do are: 1/ Look up the transactions on a particular date in the first table view, select any one of them 2/ Then, check all previous transactions of the company of that transaction( selected in the first table view) from the 2nd table view 3/ Select any previous transactions and check the details of the transaction from that group of textfields So naturally I should have bind the textfields' gp to the 2nd table view's controller. But I found the default selected row in the 2nd table view(the one show all previous transactions of a company) wasn't the transaction I've selected in the 1st tableView for a particular date. Of course, i can manually select that transaction in the 2nd table view again.... So I just want to know if it's possible to have the 2nd table view automatically select the transaction according to the transaction I've selected in the 1st table view thr binding?? After hours of googling, I solved the problem by implementing the tableview Delegate protocol: - (void)tableViewSelectionDidChange:(NSNotification *)aNotification { if (["nameOf1stTableView" selectedRow] > -1) { NSArray *objsArray = ["nameOf2ndTableView'sController" arrangedObjects]; for (id obj in objsArray) { if ([[obj valueForKey:@"DATE"] isEqualToDate: ["nameOf1stTableView'sController".selection valueForKey:@"DATE"]]) { ["nameOf2ndTableView" selectRowIndexes:[NSIndexSet indexSetWithIndex:[objsArray indexOfObject:obj]] byExtendingSelection:NO]; } } } } But,this just look too cumbersome... can it be done with binding alone? Thanks in Advance,

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• Why is this line breaking Rails with Passenger on DreamHost?

  - by Frew

  Ok, so I have a Rails app set up on DreamHost and I had it working a while ago and now it's broken. I don't know a lot about deployment environments or anything like that so please forgive my ignorance. Anyway, it looks like the app is crashing at this line in config/environment.rb: require File.join(File.dirname(__FILE__), 'boot') config/boot.rb is pretty much normal, but I'll include it here anyway. # Don't change this file! # Configure your app in config/environment.rb and config/environments/*.rb RAILS_ROOT = "#{File.dirname(__FILE__)}/.." unless defined?(RAILS_ROOT) module Rails class << self def boot! unless booted? preinitialize pick_boot.run end end def booted? defined? Rails::Initializer end def pick_boot (vendor_rails? ? VendorBoot : GemBoot).new end def vendor_rails? File.exist?("#{RAILS_ROOT}/vendor/rails") end def preinitialize load(preinitializer_path) if File.exist?(preinitializer_path) end def preinitializer_path "#{RAILS_ROOT}/config/preinitializer.rb" end end class Boot def run load_initializer Rails::Initializer.run(:set_load_path) end end class VendorBoot < Boot def load_initializer require "#{RAILS_ROOT}/vendor/rails/railties/lib/initializer" Rails::Initializer.run(:install_gem_spec_stubs) end end class GemBoot < Boot def load_initializer self.class.load_rubygems load_rails_gem require 'initializer' end def load_rails_gem if version = self.class.gem_version gem 'rails', version else gem 'rails' end rescue Gem::LoadError => load_error $stderr.puts %(Missing the Rails #{version} gem. Please `gem install -v=#{version} rails`, update your RAILS_GEM_VERSION setting in config/environment.rb for the Rails version you do have installed, or comment out RAILS_GEM_VERSION to use the latest version installed.) exit 1 end class << self def rubygems_version Gem::RubyGemsVersion if defined? Gem::RubyGemsVersion end def gem_version if defined? RAILS_GEM_VERSION RAILS_GEM_VERSION elsif ENV.include?('RAILS_GEM_VERSION') ENV['RAILS_GEM_VERSION'] else parse_gem_version(read_environment_rb) end end def load_rubygems require 'rubygems' min_version = '1.1.1' unless rubygems_version >= min_version $stderr.puts %Q(Rails requires RubyGems >= #{min_version} (you have #{rubygems_version}). Please `gem update --system` and try again.) exit 1 end rescue LoadError $stderr.puts %Q(Rails requires RubyGems >= #{min_version}. Please install RubyGems and try again: http://rubygems.rubyforge.org) exit 1 end def parse_gem_version(text) $1 if text =~ /^[^#]*RAILS_GEM_VERSION\s*=\s*["']([!~<>=]*\s*[\d.]+)["']/ end private def read_environment_rb File.read("#{RAILS_ROOT}/config/environment.rb") end end end end # All that for this: Rails.boot! Does anyone have any ideas? I am not getting any errors in the log or on the page. -fREW

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• Wordpress post query php custom field conditional

  - by Andy

  Here's the situation: In wordpress I'm trying to reset a post WP_Query so that I can rewrite the post link based on whether or not a custom field exists in the post. I'm trying to give the post a NEW link in the custom field. All I've managed to do here is kill the link entirely. Any and all help is greatly appreciated, I'm pretty green to php. Here's my WP_Query: <?php $recentPosts = new WP_Query(); $recentPosts->query('showposts=3'); ?> <?php while ($recentPosts->have_posts()) : $recentPosts->the_post(); ?> <div <?php post_class() ?> id="post-<?php the_ID(); ?>"> <?php $attribute = the_title_attribute(); $title = the_title(); $key = 'NewPostLink'; $newLink = get_post_meta( $post->ID, $key, TRUE ); if ($newLink != '') { $theLink = get_permalink ($post->ID ); if (has_post_thumbnail()) { $image = get_the_post_thumbnail( $post->ID ); echo '<div class="thumbnailbox"><div class="thumbnail"><a href="'.$theLink.'">'.$image.'</a></div></div>'; echo '<h2><a href="'.$theLink.'" rel="bookmark" title="Permanent Link to '.$attribute.'">'.$title.'</a></h2>'; } else { echo '<h2><a href="'.$theLink.'" rel="bookmark" title="Permanent Link to '.$attribute.'">'.$title.'</a></h2>'; } } else { $theLink = $newLink; if (has_post_thumbnail()) { $image = get_the_post_thumbnail( $post->ID ); echo '<div class="thumbnailbox"><div class="thumbnail"><a href="'.$theLink.'">'.$image.'</a></div></div>'; echo '<h2><a href="'.$theLink.'" rel="bookmark" title="Permanent Link to '.$attribute.'">'.$title.'</a></h2>'; } else { echo '<h2><a href="'.$theLink.'" rel="bookmark" title="Permanent Link to '.$attribute.'">'.$title.'</a></h2>'; } } ?> <small><?php the_time('F jS, Y') ?></small> <div class="entry"> <?php the_excerpt(); ?> </div> </div> <?php endwhile; ?>

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• Vector iterators in for loops, return statements, warning, c++

  - by Crystal

  Had 3 questions regarding a hw assignment for C++. The goal was to create a simple palindrome method. Here is my template for that: #ifndef PALINDROME_H #define PALINDROME_H #include <vector> #include <iostream> #include <cmath> template <class T> static bool palindrome(const std::vector<T> &input) { std::vector<T>::const_iterator it = input.begin(); std::vector<T>::const_reverse_iterator rit = input.rbegin(); for (int i = 0; i < input.size()/2; i++, it++, rit++) { if (!(*it == *rit)) { return false; } } return true; } template <class T> static void showVector(const std::vector<T> &input) { for (std::vector<T>::const_iterator it = input.begin(); it != input.end(); it++) { std::cout << *it << " "; } } #endif Regarding the above code, can you have more than one iterator declared in the first part of the for loop? I tried defining both the "it" and "rit" in the palindrome() method, and I kept on getting an error about needing a "," before rit. But when I cut and paste outside the for loop, no errors from the compiler. (I'm using VS 2008). Second question, I pretty much just brain farted on this one. But is the way I have my return statements in the palindrome() method ok? In my head, I think it works like, once the *it and *rit do not equal each other, then the function returns false, and the method exits at this point. Otherwise if it goes all the way through the for loop, then it returns true at the end. I totally brain farted on how return statements work in if blocks and I tried looking up a good example in my book and I couldn't find one. Finally, I get this warnings: \palindrome.h(14) : warning C4018: '<' : signed/unsigned mismatch Now is that because I run my for loop until (i < input.size()/2) and the compiler is telling me that input can be negative? Thanks!

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• Between-request Garbage Collection using Passenger

  - by raphaelcm

  We're using Rails 3.0.7 and REE 1.8.7. Long-term, we will be upgrading, but at the moment it's not feasible. Following the advice of several blog posts, we've been tuning our GC, and have settings that work pretty well. But we would really like to run GC outside of the request-response cycle. I've tried patching Passenger per this post, and using the code supplied in this SO question. In both cases, GC does indeed happen between requests. However, every time the between-request GC happens, I see a bunch of this: MONGODB [INFO] Connecting... MONGODB admin['$cmd'].find({:ismaster=>1}).limit(-1) MONGODB admin['$cmd'].find({:ismaster=>1}).limit(-1) MONGODB admin['$cmd'].find({:ismaster=>1}).limit(-1) Starting the New Relic Agent. Installed New Relic Browser Monitoring middleware SQL (0.0ms) SHOW TABLES SQL (0.0ms) SHOW TABLES RefinerySetting Load (0.0ms) SELECT `refinery_settings`.* FROM `refinery_settings` WHERE `refinery_settings`.`scoping` = 'pages' AND `refinery_settings`.`name` = 'use_marketable_urls' LIMIT 1 SQL (0.0ms) BEGIN RefinerySetting Load (0.0ms) SELECT `refinery_settings`.* FROM `refinery_settings` WHERE `refinery_settings`.`id` = 1 LIMIT 1 AREL (0.0ms) UPDATE `refinery_settings` SET `value` = '--- \"false\"\n', `callback_proc_as_string` = NULL WHERE `refinery_settings`.`id` = 1 SQL (0.0ms) SHOW TABLES RefinerySetting Load (0.0ms) SELECT `refinery_settings`.* FROM `refinery_settings` SQL (0.0ms) COMMIT SQL (0.0ms) SHOW TABLES RefinerySetting Load (4.0ms) SELECT `refinery_settings`.* FROM `refinery_settings` WHERE `refinery_settings`.`scoping` IS NULL AND `refinery_settings`.`name` = 'user_image_sizes' LIMIT 1 SQL (0.0ms) BEGIN RefinerySetting Load (0.0ms) SELECT `refinery_settings`.* FROM `refinery_settings` WHERE `refinery_settings`.`id` = 17 LIMIT 1 AREL (0.0ms) UPDATE `refinery_settings` SET `value` = '--- \n:small: 120x120>\n:medium: 280x280>\n:large: 580x580>\n', `callback_proc_as_string` = NULL WHERE `refinery_settings`.`id` = 17 SQL (0.0ms) SHOW TABLES RefinerySetting Load (0.0ms) SELECT `refinery_settings`.* FROM `refinery_settings` SQL (0.0ms) COMMIT ******** Engine Extend: app/helpers/blog_posts_helper SQL (0.0ms) SHOW TABLES SQL (0.0ms) SHOW TABLES SQL (0.0ms) SHOW TABLES SQL (4.0ms) SHOW TABLES SQL (0.0ms) SHOW TABLES SQL (0.0ms) SHOW TABLES SQL (0.0ms) SHOW TABLES ******** Engine Extend: app/models/user SQL (0.0ms) describe `roles_users` SQL (0.0ms) SHOW TABLES SQL (0.0ms) SHOW TABLES SQL (4.0ms) describe `roles_users` SQL (0.0ms) SHOW TABLES SQL (4.0ms) SHOW TABLES SQL (0.0ms) SHOW TABLES SQL (0.0ms) SHOW TABLES (etc, etc, etc) Which is what happens when rails "loads the world" when the app starts up. Basically, GC.start is re-loading the app for some reason. Because of this, between-request GC is much slower than inline GC. Is there a way around this? I would love to have snappy, between-request GC if possible. Thanks.

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• C# drawing and invalidating 2 lines to meet

  - by BlueMonster

  If i have 2 lines on a page as such: e.Graphics.DrawLine(blackPen, w, h, h, w); e.Graphics.DrawLine(blackPen, w2, h2, h2, w2); how would i animate the first line to reach the second line's position? I have the following method which calculates the distance between two points (i'm assuming i would use this?) public int Distance2D(int x1, int y1, int x2, int y2) { // ______________________ //d = &#8730; (x2-x1)^2 + (y2-y1)^2 // //Our end result int result = 0; //Take x2-x1, then square it double part1 = Math.Pow((x2 - x1), 2); //Take y2-y1, then sqaure it double part2 = Math.Pow((y2 - y1), 2); //Add both of the parts together double underRadical = part1 + part2; //Get the square root of the parts result = (int)Math.Sqrt(underRadical); //Return our result return result; } How would i re-draw the line (on a timer) to reach the second line's position? I've looked a lot into XAML (story-boarding) and such - but i want to know how to do this on my own. Any ideas? I know i would need a method which runs in a loop re-drawing the line after moving the position a tid bit. I would have to call Invalidate() in order to make the line appear as though it's moving... but how would i do this? how would i move that line slowly over to the other line? I'm pretty sure i'd have to use double buffering if i'm doing this as well... as such: SetStyle(ControlStyles.DoubleBuffer | ControlStyles.AllPaintingInWmPaint | ControlStyles.UserPaint, true); This doesn't quiet work, i'm not quiet sure how to fix it. Any ideas? protected override void OnPaint(PaintEventArgs e) { Distance2D(w, h, w2, h2); if (w2 != w && h2 != h) { e.Graphics.DrawLine(blackPen, (w * (int)frame), (h * (int)frame), (h * (int)frame), (w * (int)frame)); e.Graphics.DrawLine(blackPen, w2, h2, h2, w2); } else { t.Abort(); } base.OnPaint(e); } public void MoveLine() { for (int i = 0; i < 126; i++) { frame += .02; Invalidate(); Thread.Sleep(30); } } private void button1_Click(object sender, EventArgs e) { t = new Thread(new ThreadStart(MoveLine)); t.Start(); }

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• Graph Tour with Uniform Cost Search in Java

  - by user324817

  Hi. I'm new to this site, so hopefully you guys don't mind helping a nub. Anyway, I've been asked to write code to find the shortest cost of a graph tour on a particular graph, whose details are read in from file. The graph is shown below: http://img339.imageshack.us/img339/8907/graphr.jpg This is for an Artificial Intelligence class, so I'm expected to use a decent enough search method (brute force has been allowed, but not for full marks). I've been reading, and I think that what I'm looking for is an A* search with constant heuristic value, which I believe is a uniform cost search. I'm having trouble wrapping my head around how to apply this in Java. Basically, here's what I have: Vertex class - ArrayList<Edge> adjacencies; String name; int costToThis; Edge class - final Vertex target; public final int weight; Now at the moment, I'm struggling to work out how to apply the uniform cost notion to my desired goal path. Basically I have to start on a particular node, visit all other nodes, and end on that same node, with the lowest cost. As I understand it, I could use a PriorityQueue to store all of my travelled paths, but I can't wrap my head around how I show the goal state as the starting node with all other nodes visited. Here's what I have so far, which is pretty far off the mark: public static void visitNode(Vertex vertex) { ArrayList<Edge> firstEdges = vertex.getAdjacencies(); for(Edge e : firstEdges) { e.target.costToThis = e.weight + vertex.costToThis; queue.add(e.target); } Vertex next = queue.remove(); visitNode(next); } Initially this takes the starting node, then recursively visits the first node in the PriorityQueue (the path with the next lowest cost). My problem is basically, how do I stop my program from following a path specified in the queue if that path is at the goal state? The queue currently stores Vertex objects, but in my mind this isn't going to work as I can't store whether other vertices have been visited inside a Vertex object. Help is much appreciated! Josh

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• How to store array of NSManagedObjects in an NSManagedObject

  - by David Tay

  I am loading my app with a property list of data from a web site. This property list file contains an NSArray of NSDictionaries which itself contains an NSArray of NSDictionaries. Basically, I'm trying to load a tableView of restaurant menu categories each of which contains menu items. My property list file is fine. I am able to load the file and loop through the nodes structure creating NSEntityDescriptions and am able to save to Core Data. Everything works fine and expectedly except that in my menu category managed object, I have an NSArray of menu items for that category. Later on, when I fetch the categories, the pointers to the menu items in a category is lost and I get all the menu items. Am I suppose to be using predicates or does Core Data keep track of my object graph for me? Can anyone look at how I am loading Core Data and point out the flaw in my logic? I'm pretty good with either SQL and OOP by themselves, but am a little bewildered by ORM. I thought that I should just be able to use aggregation in my managed objects and that the framework would keep track of the pointers for me, but apparently not. NSError *error; NSURL *url = [NSURL URLWithString:@"http://foo.com"]; NSArray *categories = [[NSArray alloc] initWithContentsOfURL:url]; NSMutableArray *menuCategories = [[NSMutableArray alloc] init]; for (int i=0; i<[categories count]; i++){ MenuCategory *menuCategory = [NSEntityDescription insertNewObjectForEntityForName:@"MenuCategory" inManagedObjectContext:[self managedObjectContext]]; NSDictionary *category = [categories objectAtIndex:i]; menuCategory.name = [category objectForKey:@"name"]; NSArray *items = [category objectForKey:@"items"]; NSMutableArray *menuItems = [[NSMutableArray alloc] init]; for (int j=0; j<[items count]; j++){ MenuItem *menuItem = [NSEntityDescription insertNewObjectForEntityForName:@"MenuItem" inManagedObjectContext:[self managedObjectContext]]; NSDictionary *item = [items objectAtIndex:j]; menuItem.name = [item objectForKey:@"name"]; menuItem.price = [item objectForKey:@"price"]; menuItem.image = [item objectForKey:@"image"]; menuItem.details = [item objectForKey:@"details"]; [menuItems addObject:menuItem]; } [menuCategory setValue:menuItems forKey:@"menuItems"]; [menuCategories addObject:menuCategory]; [menuItems release]; } if (![[self managedObjectContext] save:&error]) { NSLog(@"An error occurred: %@", [error localizedDescription]); }

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