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• C++ boost ublas + units dimension constraints

  - by aaa

  hello. I am seeking advice on design/general idea on how to force matrix dimension constraints on ublas matrix/vector possibly using boost units. For example, let matrix A have dimensions of time x force (for example) // does not have dimensions, time x force and force x time are not distinguished. matrix<double> A; //something like? dimension<time, force, matrix<double> > A; dimension<force, time, matrix<double> > B = trans(A); have you done something like this or do you have some good idea about how to organize such constraints? Thank you

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• How do I write in-code comments and documentation in a proper way? Is there any standard for this?

  - by hkBattousai

  I want to add documentation in my code by means of comment lines. Is there any standard format for this? For example, consider the code below: class Arithmetic { // This method adds two numbers, and returns the result. // dbNum1 is the first number to add, and dbNum2 is second. // The returning value is dbNum1+dbNum2. static double AddTwoNumbers(double dbNum1, double dbNum2); } For this example code, is there any better way of writing the comment lines?

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• template function roundTo int, float -> truncation

  - by Oops

  Hi, according to this question: http://stackoverflow.com/questions/2833730/calling-template-function-without-type-inference the round function I will use in the future now looks like: template < typename TOut, typename TIn > TOut roundTo( TIn value ) { return static_cast<TOut>( value + 0.5 ); } double d = 1.54; int i = rountTo<int>(d); However it makes sense only if it will be used to round to integral datatypes like char, short, int, long, long long int, and it's unsigned counterparts. If it ever will be used with a TOut As float or long double it will deliver s***. double d = 1.54; float f = roundTo<float>(d); // aarrrgh now float is 2.04; I was thinking of a specified overload of the function but ... that's not possible... How would you solve this problem? many thanks in advance Oops

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• floating constants in C

  - by Daziplqa

  Hi floks, I have a question concerning floating constants in C. In Java, the default type of floating point constants in double, so the following will causes a compilation error in java: float f = 100.0; // we either need to uses type case operator or put f at the end of the number constant. This is because the default floating-point constants are of type double and casting from double to float without type cast operator is an error, so we need either add a type case operator or put f at the end of the number. So, Why in C this doesn't produce an error, Is it because the default floating-point constants are of type float, or because the compiler do an implicit down-cast conversion (that doesn't requires type case operator in C)????

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• Maintaining the position of columns in Grails/GORM

  - by firnnauriel

  Is there a way to fix the position of the columns in a domain? I have this domain: class SnbrActVector { int nid String term double weight static mapping = { version false id(generator: 'assigned') } static constraints = { nid(blank:false) term(blank:false) weight(blank:false) } } This is the schema of the table generated: CREATE TABLE `fractor_grailsDEV`.`snbr_act_vector` ( `id` bigint(20) NOT NULL, `weight` double NOT NULL, `term` varchar(255) COLLATE utf8_unicode_ci NOT NULL, `nid` int(11) NOT NULL, PRIMARY KEY (`id`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci It seems that the order of the columns were reversed. Is there a way to make it like this? (order is nid, term, weight) CREATE TABLE `fractor_grailsDEV`.`snbr_act_vector` ( `id` bigint(20) NOT NULL, `nid` int(11) NOT NULL, `term` varchar(255) COLLATE utf8_unicode_ci NOT NULL, `weight` double NOT NULL, PRIMARY KEY (`id`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci

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• What is the best way to mock a 3rd party object in ruby?

  - by spinlock

  I'm writing a test app using the twitter gem and I'd like to write an integration test but I can't figure out how to mock the objects in the Twitter namespace. Here's the function that I want to test: def build_twitter(omniauth) Twitter.configure do |config| config.consumer_key = TWITTER_KEY config.consumer_secret = TWITTER_SECRET config.oauth_token = omniauth['credentials']['token'] config.oauth_token_secret = omniauth['credentials']['secret'] end client = Twitter::Client.new user = client.current_user self.name = user.name end and here's the rspec test that I'm trying to write: feature 'testing oauth' do before(:each) do @twitter = double("Twitter") @twitter.stub!(:configure).and_return true @client = double("Twitter::Client") @client.stub!(:current_user).and_return(@user) @user = double("Twitter::User") @user.stub!(:name).and_return("Tester") end scenario 'twitter' do visit root_path login_with_oauth page.should have_content("Pages#home") end end But, I'm getting this error: 1) testing oauth twitter Failure/Error: login_with_oauth Twitter::Error::Unauthorized: GET https://api.twitter.com/1/account/verify_credentials.json: 401: Invalid / expired Token # ./app/models/user.rb:40:in `build_twitter' # ./app/models/user.rb:16:in `build_authentication' # ./app/controllers/authentications_controller.rb:47:in `create' # ./spec/support/integration_spec_helper.rb:3:in `login_with_oauth' # ./spec/integration/twit_test.rb:16:in `block (2 levels) in <top (required)>' The mocks above are using rspec but I'm open to trying mocha too. Any help would be greatly appreciated.

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• static, define, and const in C

  - by yCalleecharan

  Hi, I've read that static variables are used inside function when one doesn't want the variable value to change/initialize each time the function is called. But what about defining a variable static in the main program before "main" e.g. #include <stdio.h> static double m = 30000; int main(void) { value = m * 2 + 3; } Here the variable m has a constant value that won't get modified later in the main program. In the same line of thought what difference does it make to have these instead of using the static definition: const double m = 30000; or #define m 30000 //m or M and then making sure here to use double operations in the main code so as to convert m to the right data type. Thanks a lot...

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• C# Creating thumbnail (low quality and big size problem)

  - by ile

  public void CreateThumbnail(Image img1, Photo photo, string targetDirectoryThumbs) { int newWidth = 700; int newHeight = 700; double ratio = 0; if (img1.Width > img1.Height) { ratio = img1.Width / (double)img1.Height; newHeight = (int)(newHeight / ratio); } else { ratio = img1.Height / (double)img1.Width; newWidth = (int)(newWidth / ratio); } Image bmp1 = img1.GetThumbnailImage(newWidth, newHeight, null, IntPtr.Zero); bmp1.Save(targetDirectoryThumbs + photo.PhotoID + ".jpg"); img1.Dispose(); bmp1.Dispose(); } I've put 700px so that you can have better insight of the problem. Here is original image and resized one. Any good recommendation? Thanks, Ile

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• boost timer usage question

  - by stefita

  I have a really simple question, yet I can't find an answer for it. I guess I am missing something in the usage of the boost timer.hpp. Here is my code, that unfortunately gives me an error message: include <boost/timer.hpp> int main() { boost::timer t; } And the error messages are as follows: /usr/include/boost/timer.hpp: In member function ‘double boost::timer::elapsed_max() const’: /usr/include/boost/timer.hpp:59: error: ‘numeric_limits’ is not a member of ‘std’ /usr/include/boost/timer.hpp:59: error: ‘::max’ has not been declared /usr/include/boost/timer.hpp:59: error: expected primary-expression before ‘double’ /usr/include/boost/timer.hpp:59: error: expected `)' before ‘double’ The used library is boost 1.36 (SUSE 11.1). Thanks in advance!

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• recursive program

  - by wilson88

  I am trying to make a recursive program that calculates interest per year.It prompts the user for the startup amount (1000), the interest rate (10%)and number of years(1).(in brackets are samples) Manually I realised that the interest comes from the formula YT(1 + R)----- interest for the first year which is 1100. 2nd year YT(1 + R/2 + R2/2) //R squared 2nd year YT(1 + R/3 + R2/3 + 3R3/) // R cubed How do I write a recursive program that will calculate the interest? Below is the function which I tried //Latest after editing double calculateInterest2(double start, double rate, int duration) { if (0 == duration) { return start; } else { return (1+rate) * calculateInterest2(start, rate, duration - 1); } }

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• Define and return a struct in c

  - by nevan

  I'm trying to convert some code from Javascript to c. The function creates an array (which always has a fixed number of items) and then returns the array. I've learned that in c it's not straightforward to return an array, so I'd like to return this as a struct instead. My c is not all that great, so I'd like to check that returning a struct is the right thing to do in this situation, and that I'm doing it the right way. Thanks. typedef struct { double x; double y; double z; } Xyz; Xyz xyzPlusOne(Xyz addOne) { Xyz xyz; xyz.x = addOne.x + 1; xyz.y = addOne.y + 1; xyz.z = addOne.z + 1; return xyz; }

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• C# is there a problem with division?

  - by Tom

  This is a piece of my code, it is called every second, after about 10 seconds the values start to become weird (see below): double a; double b; for (int i = 0; i < currAC.Length; i++ ) { a = currAC[i]; b = aveACValues[i]; divisor = (a/b); Console.WriteLine("a = " + a.ToString("N2") + "\t" + "b = " + b.ToString("N2")); Console.WriteLine("divisor = " + divisor); Console.WriteLine("a+b = " + (a+b)); } and the output: a = -0.05 b = 0.00 divisor = 41 a+b = -0.0524010372273268 currAC and aveACValues are double[] what on earth is going on???? The addition result is correct every time, but the division value is wrong, yet it is reading a and b correctly?? EDIT: '41' is the value of the first calculation, ie when a = currAC[0], but this should not remain???

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• problem while converting object into datetime in c#

  - by Lalit

  Hi, I am getting string value in object let say "28/05/2010". While i am converting it in to DateTime it is throwing exception as : String was not recognized as a valid DateTime. The Code is: object obj = ((Excel.Range)worksheet.Cells[iRowindex, colIndex_q17]).Value2; Type type = obj.GetType(); string strDate3 = string.Empty; double dbl = 0.0; if (type == typeof(System.Double)) { dbl = Convert.ToDouble(((Excel.Range)worksheet.Cells[iRowindex, colIndex_q17]).Value2); strDate3 = DateTime.FromOADate(dbl).ToShortDateString(); } else { DateTime dt = new DateTime().Date; //////////dt = DateTime.Parse(Convert.ToString(obj)); **dt = Convert.ToDateTime(obj).Date;** strDate3 = dt.ToShortDateString(); } The double star "**" line gets exception.

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• Make the Enter key act like the submit button

  - by Michael Quiles

  How can I make it where some one presses the enter key on my form it will submit this code ? Ive tried the ligtning bolt events etc... but I can't seem to figure it out. private void xTripSubmitButton_Click(object sender, EventArgs e) { // Calculates the numbers from the input and output boxes/labels Miles = double.Parse(this.xTripDestinationTextBox.Text); Mpg = double.Parse(this.xTripMpgTextBox.Text); Price = double.Parse(this.xTripPricepgTextBox.Text); Output = Miles / Mpg; Coutput = Output * Price; //displays a message and the result for the numbers the user inputs this.xTripOutputLabel.Text = "Total gallons you would use: " + Output.ToString("0") + Environment.NewLine + "Total amount it will cost you: " + Coutput.ToString("C"); }

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• Array::ConvertAll in managed C++

  - by danny.lesnik

  This is a continuation from this post. I'm trying to parse this string in managed C++: String ^ rgba = "[0.09019608,0.5176471,0.9058824,1]"; cli::array<System::Double> ^ RGB = System::Array::ConvertAll<String,cli::array<System::Double> >((rgba->Substring(1,rgba->Length-2)->Split(',')),double::Parse); Compiler throws me the following error: Error 15 error C2770: invalid explicit generic argument(s) for 'cli::array<Type,dimension> ^System::Array::ConvertAll(cli::array<TInput,1> ^,System::Converter<TInput,TOutput> ^)' What am I doing wrong?

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• Haskell: Why is it saying my function type is off?

  - by linkmaster03

  I wrote a little Haskell program to find the area of a triangle, primarily to practice custom types, but it keeps throwing the following error on compile: areafinder.hs:7:4: Couldn't match expected type 'Triangle' against inferred type 'm b' In a stmt of a 'do' expression: putStr "Base: " In the expression: do { putStr "Base: "; baseStr I'm not sure where 'm b' comes from, so I'm at a loss here. Why is it throwing this error, and what can I do to fix it? Here is my code: module Main where data Triangle = Triangle Double Double -- base, height getTriangle :: Triangle getTriangle = do putStr "Base: " baseStr Double calcTriangle (Triangle base height) = base * height main = putStrLn ("Area = " ++ show (calcTriangle getTriangle)) Thanks. :)

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• F# operator over-loading question

  - by jyoung

  The following code fails in 'Evaluate' with: "This expression was expected to have type Complex but here has type double list" Am I breaking some rule on operator over-loading on '(+)'? Things are OK if I change '(+)' to 'Add'. open Microsoft.FSharp.Math /// real power series [kn; ...; k0] => kn*S^n + ... + k0*S^0 type Powers = double List let (+) (ls:Powers) (rs:Powers) = let rec AddReversed (ls:Powers) (rs:Powers) = match ( ls, rs ) with | ( l::ltail, r::rtail ) -> ( l + r ) :: AddReversed ltail rtail | ([], _) -> rs | (_, []) -> ls ( AddReversed ( ls |> List.rev ) ( rs |> List.rev) ) |> List.rev let Evaluate (ks:Powers) ( value:Complex ) = ks |> List.fold (fun (acc:Complex) (k:double)-> acc * value + Complex.Create(k, 0.0) ) Complex.Zero

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• Why this friend function can't access a private member of the class?

  - by Alceu Costa

  I am getting the following error when I try to access bins private member of the GHistogram class from within the extractHistogram() implementation: error: 'QVector<double> MyNamespace::GHistogram::bins' is private error: within this context Where the 'within this context' error points to the extractHistogram() implementation. Does anyone knows what's wrong with my friend function declaration? Here's the code: namespace MyNamespace{ class GHistogram { public: GHistogram(qint32 numberOfBins); qint32 getNumberOfBins(); /** * Returns the frequency of the value i. */ double getValueAt(qint32 i); friend GHistogram * Gbdi::extractHistogram(GImage *image, qint32 numberOfBins); private: QVector<double> bins; }; GHistogram * extractHistogram(GImage * image, qint32 numberOfBins); }

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• There is more then one Point class

  - by Dmitry

  Today I hit something very annoying while working with one of my colleagues. It seems there are two Point classes in .NET and by mistake we were trying for a good few minutes to figure out why our "Point(x,y)" wouldn’t take double, but only Int. Turns out we were using the wrong one since the XAML element in question needed the version with Double. So, based on what you actually want to do, make sure you’re using the right namespace. Please see below for MSDN reference links for each namespace version of Point, hope this saves you some time. System.Windows Point (MSDN Ref - Double version) System.Dawing Point (MSDN Ref - Int version)

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• Convert Decimal number into Fraction

  - by alankrita

  I am trying to convert decimal number into its fraction. Decimal numbers will be having a maximum 4 digits after the decimal place. example:- 12.34 = 1234/100 12.3456 = 123456/10000 my code :- #include <stdio.h> int main(void) { double a=12.34; int c=10000; double b=(a-floor(a))*c; int d=(int)floor(a)*c+(int)b; while(1) { if(d%10==0) { d=d/10; c=c/10; } else break; } printf("%d/%d",d,c); return 0; } but I am not getting correct output, Decimal numbers will be of double precision only.Please guide me what I should do.

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• C++ return type overload hack

  - by aaa

  I was bored and came up with such hack (pseudocode): 1 struct proxy { 2 operator int(); // int function 3 operator double(); // double function 4 proxy(arguments); 5 arguments &arguments_; 6 }; 7 8 proxy function(arguments &args) { 9 return proxy(args); 10 } 11 int v = function(...); 12 double u = function(...); is it evil to use in real code?

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• Strange calculation problem in C multiply by 1.2 fails

  - by DoomStone

  I have this c code, where i need to calculate a dobule from a long. double result; long t2_value; t2_value = 72; result = t2_value * 1.2; Now this code crashes at "result = t2_value * 1.2;" only with the error "Vector 0000000006". Here is the strange thing, if i replace result = t2_value * 1.2; with result = 72 * 1.2; evything works just as it should, i have tryed type casting t2_value as an double result = ((double)t2_value * 1.2); or making it an int istead of a long, but nothing helps.

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• why this with excel sheet reading?

  - by Lalit

  Hi, I am reading the excel sheet from c# interop services cell by cell. where as my excel sheet have Date cells. It generates some double values , I am converting them in date by : double dbl = Convert.ToDouble(((Excel.Range)worksheet.Cells[iRowindex, colIndex_q17]).Value2); string strDate3 = DateTime.FromOADate(dbl).ToShortDateString(); drRow[dtSourceEXLData.Columns[constants.VisualDate]] = strDate3; ok? but some time happening the value of ((Excel.Range)worksheet.Cells[iRowindex,colIndex_q17]).Value2 getting date formate.why this is happeing? plaease guide me. it throws excepion of "input string not in correct format".why it is not generating double value like other cell of same column?

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• Measuring execution time of a call to system() in C++

  - by jm1234567890

  I have found some code on measuring execution time here http://www.dreamincode.net/forums/index.php?showtopic=24685 However, it does not seem to work for calls to system(). I imagine this is because the execution jumps out of the current process. clock_t begin=clock(); system(something); clock_t end=clock(); cout<<"Execution time: "<<diffclock(end,begin)<<" s."<<endl; Then double diffclock(clock_t clock1,clock_t clock2) { double diffticks=clock1-clock2; double diffms=(diffticks)/(CLOCKS_PER_SEC); return diffms; } However this always returns 0 seconds... Is there another method that will work? Also, this is in Linux. Thanks!

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• Is it possible to write a generic +1 method for numeric box types in Java?

  - by polygenelubricants

  This is NOT homework. Part 1 Is it possible to write a generic method, something like this: <T extends Number> T plusOne(T num) { return num + 1; // DOESN'T COMPILE! How to fix??? } Short of using a bunch of instanceof and casts, is this possible? Part 2 The following 3 methods compile: Integer plusOne(Integer num) { return num + 1; } Double plusOne(Double num) { return num + 1; } Long plusOne(Long num) { return num + 1; } Is it possible to write a generic version that bound T to only Integer, Double, or Long?

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