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  • How are vector patterns used in syntax-rules?

    - by Jay
    Hi, I have been writing Common Lisp macros, so Scheme's R5Rs macros are a bit unnatural to me. I think I got the idea, except that I don't understand how one would use vector patterns in syntax-rules: (define-syntax mac (syntax-rules () ((mac #(a b c d)) (let () (display a) (newline) (display d) (newline))))) (expand '(mac #(1 2 3 4))) ;; Chicken's expand-full extension shows macroexpansion => (let746 () (display747 1) (newline748) (display747 4) (newline748)) I don't see how I'd use a macro that requires its arguments to be written as a vector: (mac #(1 2 3 4)) => 1 4 Is there some kind of technique that uses those patterns? Thank you!

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  • Template problems: No matching function for call

    - by Nick Sweet
    I'm trying to create a template class, and when I define a non-member template function, I get the "No matching function for call to randvec()" error. I have a template class defined as: template <class T> class Vector { T x, y, z; public: //constructors Vector(); Vector(const T& x, const T& y, const T& z); Vector(const Vector& u); //accessors T getx() const; T gety() const; T getz() const; //mutators void setx(const T& x); void sety(const T& y); void setz(const T& z); //operations void operator-(); Vector plus(const Vector& v); Vector minus(const Vector& v); Vector cross(const Vector& v); T dot(const Vector& v); void times(const T& s); T length() const; //Vector<T>& randvec(); //operators Vector& operator=(const Vector& rhs); friend std::ostream& operator<< <T>(std::ostream&, const Vector<T>&); }; and the function in question, which I've defined after all those functions above, is: //random Vector template <class T> Vector<double>& randvec() { const int min=-10, max=10; Vector<double>* r = new Vector<double>; int randx, randy, randz, temp; const int bucket_size = RAND_MAX/(max-min +1); temp = rand(); //voodoo hackery do randx = (rand()/bucket_size)+min; while (randx < min || randx > max); r->setx(randx); do randy = (rand()/bucket_size)+min; while (randy < min || randy > max); r->sety(randy); do randz = (rand()/bucket_size)+min; while (randz < min || randz > max); r->setz(randz); return *r; } Yet, every time I call it in my main function using a line like: Vector<double> a(randvec()); I get that error. However, if I remove the template and define it using 'double' instead of 'T', the call to randvec() works perfectly. Why doesn't it recognize randvec()? P.S. Don't mind the bit labeled voodoo hackery - this is just a cheap hack so that I can get around another problem I encountered.

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  • Finding the intersection of two vector equations.

    - by Matthew Mitchell
    I've been trying to solve this and I found an equation that gives the possibility of zero division errors. Not the best thing: v1 = (a,b) v2 = (c,d) d1 = (e,f) d2 = (h,i) l1: v1 + ?d1 l2: v2 + µd2 Equation to find vector intersection of l1 and l2 programatically by re-arranging for lambda. (a,b) + ?(e,f) = (c,d) + µ(h,i) a + ?e = c + µh b +?f = d + µi µh = a + ?e - c µi = b +?f - d µ = (a + ?e - c)/h µ = (b +?f - d)/i (a + ?e - c)/h = (b +?f - d)/i a/h + ?e/h - c/h = b/i +?f/i - d/i ?e/h - ?f/i = (b/i - d/i) - (a/h - c/h) ?(e/h - f/i) = (b - d)/i - (a - c)/h ? = ((b - d)/i - (a - c)/h)/(e/h - f/i) Intersection vector = (a + ?e,b + ?f) Not sure if it would even work in some cases. I haven't tested it. I need to know how to do this for values as in that example a-i. Thank you.

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  • Class template specializations with shared functionality

    - by Thomas
    I'm writing a simple maths library with a template vector type: template<typename T, size_t N> class Vector { public: Vector<T, N> &operator+=(Vector<T, N> const &other); // ... more operators, functions ... }; Now I want some additional functionality specifically for some of these. Let's say I want functions x() and y() on Vector<T, 2> to access particular coordinates. I could create a partial specialization for this: template<typename T> class Vector<T, 3> { public: Vector<T, 3> &operator+=(Vector<T, 3> const &other); // ... and again all the operators and functions ... T x() const; T y() const; }; But now I'm repeating everything that already existed in the generic template. I could also use inheritance. Renaming the generic template to VectorBase, I could do this: template<typename T, size_t N> class Vector : public VectorBase<T, N> { }; template<typename T> class Vector<T, 3> : public VectorBase<T, 3> { public: T x() const; T y() const; }; However, now the problem is that all operators are defined on VectorBase, so they return VectorBase instances. These cannot be assigned to Vector variables: Vector<float, 3> v; Vector<float, 3> w; w = 5 * v; // error: no conversion from VectorBase<float, 3> to Vector<float, 3> I could give Vector an implicit conversion constructor to make this possible: template<typename T, size_t N> class Vector : public VectorBase<T, N> { public: Vector(VectorBase<T, N> const &other); }; However, now I'm converting from Vector to VectorBase and back again. Even though the types are the same in memory, and the compiler might optimize all this away, it feels clunky and I don't really like to have potential run-time overhead for what is essentially a compile-time problem. Is there any other way to solve this?

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  • How Can I Reference Multiple Primary Keys For A Vector Type Primary Key

    - by AndreiC
    Hi, I have the following scenario: a table of projects and a table of persons, working on one or serveral projects. Also, I have a project id column (of type int), in the first table, which is a primary key there and I have a vector of project ids, as a column of type int, in my second table (persons), that references primary keys from the first table. What is the correct syntax for referencing multiple primary keys, from a vector foreign key. This is the way I am trying to create the table, but I am not sure what to place at the indicated line: CREATE TABLE Persons( Person_Id int, ..., ProjectsList int[], FOREIGN KEY (ProjectsList) REFERENCES Projects(Project_id) -- not sure what how to define the link here ); I hope my explanations are not over-complicated. Thank you in advance for helping!

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  • Pointing to vectors

    - by Matt Munson
    #include <iostream> #include <vector> using namespace std; int main () { vector <int> qwerty; qwerty.push_back(5); vector <int>* p = &qwerty; cout << p[0]; //error: no match for 'operator<<' in 'std::cout << * p' } I'm generally unclear on how to use pointers with vectors, so I'm pretty mystified as to why this is not working. To my mind, this should print 5 to screen.

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  • Splitting a double vector into equal parts

    - by Cosmin
    Greetings, Any input on a way to divide a std::vector into two equal parts ? I need to find the smallest possible difference between |part1 - part2|. This is how I'm doing it now, but from what you can probably tell it will yield a non-optimal split in some cases. auto mid = std::find_if(prim, ultim, [&](double temp) -> bool { if(tempsum >= sum) return true; tempsum += temp; sum -= temp; return false; }); The vector is sorted, highest to lowest, values can indeed appear twice. I'm not expecting part1 and part2 to have the same numbers of elements, but sum(part1) should be as close as possible to sum(part2) For example if we would have { 2.4, 0.12, 1.26, 0.51, 0.70 }, the best split would be { 2.4, 0.12 } and { 1.26, 0.51, 0.70 }. If it helps, I'm trying to achieve the splitting algorithm for the Shannon Fano encoding. Any input is appreciated, thanks!

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  • C++ vector of char array

    - by Stuart
    I am trying to write a program that has a vector of char arrays and am have some problems. char test [] = { 'a', 'b', 'c', 'd', 'e' }; vector<char[]> v; v.push_back(test); Sorry this has to be a char array because I need to be able to generate lists of chars as I am trying to get an output something like. a a a b a c a d a e b a b c Can anyone point me in the right direction? Thanks

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  • why Observable snapshot observer vector

    - by han14466
    In Observable's notifyObservers method, why does the coder use arrLocal = obs.toArray();? Why does not coder iterate vector directly? Thanks public void notifyObservers(Object arg) { Object[] arrLocal; synchronized (this) { /* We don't want the Observer doing callbacks into * arbitrary code while holding its own Monitor. * The code where we extract each Observable from * the Vector and store the state of the Observer * needs synchronization, but notifying observers * does not (should not). The worst result of any * potential race-condition here is that: * 1) a newly-added Observer will miss a * notification in progress * 2) a recently unregistered Observer will be * wrongly notified when it doesn't care */ if (!changed) return; arrLocal = obs.toArray(); clearChanged(); } for (int i = arrLocal.length-1; i>=0; i--) ((Observer)arrLocal[i]).update(this, arg); }

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  • Plotting a grouped 2 dimensional vector in MATLAB

    - by Hossein
    I am trying to make a plot of a 2-dimensional vector (2D Plot). But I don't want all the datapoints to have the same color on the plot. Each datapoint corresponds to a group. I want to have different colors for each group of datapoints. class=[1 3 2 5 2 5 1 3 3 4 2 2 2] says each datapoint belongs to which group X=[x1,y1;x2,y2;x3,y3;.....] the number of these datapoints are the same as the number of elements in the class vector. Now I want to plot these based on colors.

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  • C++ arrays select square number and make new vector

    - by John Smith
    I have to see which of the following from a vector is a square number then make another vector with only the square numbers For example: (4,15,6,25,7,81) the second will be (4,25,81) 4,25,81 because 2x2=4 5x5=25 and 9x9=81 I started like this: { int A[100],n,r,i; cout<<"Number of elements="; cin>>n; for(i=1;i<=n;i++) { cout<<"A["<<i<<"]="; cin>>A[i]; } for(i=1;i<=n;i++) { r=sqrt(A[i]); if(r*r==A[i]) } return 0; } but I am not really sure how to continue

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  • Convert bit vector (array of booleans) to an integer, and integer to bit vector, in Java.

    - by dreeves
    What's the best way to unstub the following functions? // Convert a bit-vector to an integer. int bitvec2int(boolean[] b) { [CODE HERE] } // Convert an integer x to an n-element bit-vector. boolean[] int2bitvec(int x, int n) { [CODE HERE] } Or is there a better way to do that sort of thing than passing boolean arrays around? This comes up in an Android app where we need an array of 20 booleans to persist and the easiest way to do that is to write an integer or string to the key-value store. I'll post the way we (Bee and I) wrote the above as an answer. Thanks!

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  • C++ Vector of pointers

    - by xbonez
    For my latest CS homework, I am required to create a class called Movie which holds title, director, year, rating, actors etc. Then, I am required to read a file which contains a list of this info and store it in a vector of pointers to Movies. I am not sure what the last line means. Does it mean, I read the file, create multiple Movie objects. Then make a vector of pointers where each element (pointer) points to one of those Movie objects? Do I just make two vectors - one of pointers and one of Movies and make a one-to-one mapping of the two vectors?

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  • C++ Memory allocation question involving vectors

    - by TheFuzz
    vector< int > vect; int *int_ptr = new int(10); vect.push_back( *int_ptr ); I under stand that every "new" needs to be followed by a "delete" at some point but does the clear() method clean this memory? What about this method of doing the same thing: vector< int > vect; int int_var = 10; vect.push_back( int_var ); From what I understand, clear() calls the variables destructors, but both vect.push_back() methods in this example push an object on the vector, not a pointer. so does the first example using an int pointer need something other than clear() to clean up memory?

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  • Boost ASIO read X bytes synchroniously into a vector

    - by xeross
    Hey, I've been attempting to write a client/server app with boost now, so far it sends and receives but I can't seem to just read X bytes into a vector. If I use the following code vector<uint8_t> buf; for (;;) { buf.resize(4); boost::system::error_code error; size_t len = socket.read_some(boost::asio::buffer(buf), error); if (error == boost::asio::error::eof) break; // Connection closed cleanly by peer. else if (error) throw boost::system::system_error(error); // Some other error. } And the packet is bigger then 4 bytes then it seems it keeps writing into those 4 bytes until the entire packet has been received, however I want it to fetch 4 bytes, then allow me to parse them, and then get the rest of the packet. Can anyone provide me with a working example, or at least a pointer on how to make it work properly ? Regards, Xeross

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  • List of good Inkscape tutorial

    - by marco.ragogna
    Inkscape seems to be a great open source software to draw and create vector graphics. Now, I would like to learn more how to use it and I would like to ask you to list here good tutorials and articles that helped you in learning Inkscape. Thank you

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  • How to install Uniconverter (command-line app) on Mac OS 10.7.2 (Lion)?

    - by RecentlyAFish
    Uniconverter is a command-line tool that shares code with the sK1 Project. it's used to convert from one type of vector graphic file to another like this: uniconverter before.eps after.svg I'm looking for a step by step solution to install this tool on my laptop. A similar question posted on the Uniconverter Forum back in August is still unanswered. I read about Uniconverter in an answer posted by Neil but don't grok how to send him a message directly for more details.

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  • How does badBIOS jumps airgaps?

    - by Ash
    I was reading this article from Ars on badBIOS and came across this line which states the malware, has the ability to use high-frequency transmissions passed between computer speakers and microphones to bridge airgaps. and wondered if this attack vector was possible ? Not only me , but all other readers were wondering if this had any logical explanation.Can a computer transmit packets via high-frequency sounds broadcast over speakers ?

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  • How do I prevent a curve snapping to a straight line in Flash CS4?

    - by Kelix
    I am trying to do some vector drawing in Flash but am having trouble when "curving" lines. At the moment, unless the curve is significant, it snaps back to a straight line meaning I am finding it impossible to draw shallow curves. Any idea how to turn this snapping off? I have tried turning everything off in View Snapping and it makes no difference.

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  • Java ME scorecard with vector and multiple input fields/screens

    - by proximity
    I have made a scorecard with 5 holes, for each a input field (shots), and a image is shown. The input should be saved into a vector and shown on each hole, eg. hole 2: enter shots, underneath it "total shots: 4" (if you have made 4 shots on hole 1). In the end I would need a sum up of all shots, eg. Hole 1: 4 Hole 2: 3 Hole 3: 2 ... Total: 17 Could someone please help me with this task? { f = new Form("Scorecard"); d = Display.getDisplay(this); mTextField = new TextField("Shots:", "", 2, TextField.NUMERIC); f.append(mTextField); mStatus = new StringItem("Hole 1:", "Par 3, 480m"); f.append(mStatus); try { Image j = Image.createImage("/hole1.png"); ImageItem ii = new ImageItem("", j, 3, "Hole 1"); f.append(ii); } catch (java.io.IOException ioe) {} catch (Exception e) {} f.addCommand(mBackCommand); f.addCommand(mNextCommand); f.addCommand(mExitCommand); f.setCommandListener(this); Display.getDisplay(this).setCurrent(f); } public void startApp() { mBackCommand = new Command("Back", Command.BACK, 0); mNextCommand = new Command("Next", Command.OK, 1); mExitCommand = new Command("Exit", Command.EXIT, 2); } public void pauseApp() { } public void destroyApp(boolean unconditional) { } public void commandAction(Command c, Displayable d) { if (c == mExitCommand) { destroyApp(true); notifyDestroyed(); } else if ( c == mNextCommand) { // -> go to next hole input! save the mTextField input into a vector. } } } ------------------------------ Full code --------------------------------- import java.util.; import javax.microedition.midlet.; import javax.microedition.lcdui.*; public class ScorerMIDlet extends MIDlet implements CommandListener { private Command mExitCommand, mBackCommand, mNextCommand; private Display d; private Form f; private TextField mTextField; private Alert a; private StringItem mHole1; private int b; // repeat holeForm for all five holes and add the input into a vector or array. Display the values in the end after asking for todays date and put todays date in top of the list. Make it possible to go back in the form, eg. hole 3 - hole 2 - hole 1 public void holeForm(int b) { f = new Form("Scorecard"); d = Display.getDisplay(this); mTextField = new TextField("Shots:", "", 2, TextField.NUMERIC); f.append(mTextField); mHole1 = new StringItem("Hole 1:", "Par 5, 480m"); f.append(mHole1); try { Image j = Image.createImage("/hole1.png"); ImageItem ii = new ImageItem("", j, 3, "Hole 1"); f.append(ii); } catch (java.io.IOException ioe) {} catch (Exception e) {} // Set date&time in the end long now = System.currentTimeMillis(); DateField df = new DateField("Playing date:", DateField.DATE_TIME); df.setDate(new Date(now)); f.append(df); f.addCommand(mBackCommand); f.addCommand(mNextCommand); f.addCommand(mExitCommand); f.setCommandListener(this); Display.getDisplay(this).setCurrent(f); } public void startApp() { mBackCommand = new Command("Back", Command.BACK, 0); mNextCommand = new Command("OK-Next", Command.OK, 1); mExitCommand = new Command("Exit", Command.EXIT, 2); b = 0; holeForm(b); } public void pauseApp() {} public void destroyApp(boolean unconditional) {} public void commandAction(Command c, Displayable d) { if (c == mExitCommand) { destroyApp(true); notifyDestroyed(); } else if ( c == mNextCommand) { holeForm(b); } } }

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  • SVG to Android Shape

    - by Buggieboy
    I have started learning about vector drawing in Android with the Shape class. Since Shape is a Drawable, and Drawables are usually defined as XML, it sounds a lot like the vector drawing commands in SVG. My question is this: Has anybody created an XSLT transformation, or other mechanism, for converting an SVG drawing description into Android Shapes?

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  • Why is there no way to resize SRFI-4 vectors in Scheme?

    - by Jay
    I see that SRFI 4 does not mention resizing of vectors. I'm using f64vectors (for which I need fast access), and I'd like to be able to resize them quickly (similar to what realloc does in C), and not necessarily copy the whole vector. Since I didn't find any references to a "resize-f64vector" procedure, I'd like to know why it doesn't exist (and if making a new vector and copying over is my only option).

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