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• Memory leak dyld dlopen

  - by imthi

  I am getting leak and I cannot detect from where this is happening. The stack trace does not give full info after dyld open. For few leaks I am not getting any stack trace info. All I get is only object memory address. Is anyone else facing the same issue. I am using XCode 3.2 on show leopard. 18 0x103038 17 0x1033c7 16 0x1034a1 15 0x90145f48 14 dyld dlopen 13 dyld dyld::link(ImageLoader*, bool, ImageLoader::RPathChain const&) 12 dyld ImageLoader::link(ImageLoader::LinkContext const&, bool, bool, ImageLoader::RPathChain const&) 11 dyld ImageLoader::recursiveLoadLibraries(ImageLoader::LinkContext const&, bool, ImageLoader::RPathChain const&) 10 dyld dyld::libraryLocator(char const*, bool, char const*, ImageLoader::RPathChain const*) 9 dyld dyld::load(char const*, dyld::LoadContext const&) 8 dyld dyld::loadPhase0(char const*, dyld::LoadContext const&, std::vector<char const*, std::allocator<char const*> >*) 7 dyld dyld::loadPhase1(char const*, dyld::LoadContext const&, std::vector<char const*, std::allocator<char const*> >*) 6 dyld dyld::loadPhase3(char const*, dyld::LoadContext const&, std::vector<char const*, std::allocator<char const*> >*) 5 dyld dyld::loadPhase4(char const*, dyld::LoadContext const&, std::vector<char const*, std::allocator<char const*> >*) 4 dyld dyld::loadPhase5(char const*, dyld::LoadContext const&, std::vector<char const*, std::allocator<char const*> >*) 3 dyld dyld::mkstringf(char const*, ...) 2 dyld strdup 1 dyld mallocenter

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• Architecture for Qt SIGNAL with subclass-specific, templated argument type

  - by Barry Wark

  I am developing a scientific data acquisition application using Qt. Since I'm not a deep expert in Qt, I'd like some architecture advise from the community on the following problem: The application supports several hardware acquisition interfaces but I would like to provide an common API on top of those interfaces. Each interface has a sample data type and a units for its data. So I'm representing a vector of samples from each device as a std::vector of Boost.Units quantities (i.e. std::vector<boost::units::quantity<unit,sample_type> >). I'd like to use a multi-cast style architecture, where each data source broadcasts newly received data to 1 or more interested parties. Qt's Signal/Slot mechanism is an obvious fit for this style. So, I'd like each data source to emit a signal like typedef std::vector<boost::units::quantity<unit,sample_type> > SampleVector signals: void samplesAcquired(SampleVector sampleVector); for the unit and sample_type appropriate for that device. Since tempalted QObject subclasses aren't supported by the meta-object compiler, there doesn't seem to be a way to have a (tempalted) base class for all data sources which defines the samplesAcquired Signal. In other words, the following won't work: template<T,U> //sample type and units class DataSource : public QObject { Q_OBJECT ... public: typedef std::vector<boost::units::quantity<U,T> > SampleVector signals: void samplesAcquired(SampleVector sampleVector); }; The best option I've been able to come up with is a two-layered approach: template<T,U> //sample type and units class IAcquiredSamples { public: typedef std::vector<boost::units::quantity<U,T> > SampleVector virtual shared_ptr<SampleVector> acquiredData(TimeStamp ts, unsigned long nsamples); }; class DataSource : public QObject { ... signals: void samplesAcquired(TimeStamp ts, unsigned long nsamples); }; The samplesAcquired signal now gives a timestamp and number of samples for the acquisition and clients must use the IAcquiredSamples API to retrieve those samples. Obviously data sources must subclass both DataSource and IAcquiredSamples. The disadvantage of this approach appears to be a loss of simplicity in the API... it would be much nicer if clients could get the acquired samples in the Slot connected. Being able to use Qt's queued connections would also make threading issues easier instead of having to manage them in the acquiredData method within each subclass. One other possibility, is to use a QVariant argument. This necessarily puts the onus on subclass to register their particular sample vector type with Q_REGISTER_METATYPE/qRegisterMetaType. Not really a big deal. Clients of the base class however, will have no way of knowing what type the QVariant value type is, unless a tag struct is also passed with the signal. I consider this solution at least as convoluted as the one above, as it forces clients of the abstract base class API to deal with some of the gnarlier aspects of type system. So, is there a way to achieve the templated signal parameter? Is there a better architecture than the one I've proposed?

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• How to pass parameters to manage_shared_memory.construct() in Boost.Interprocess

  - by recipriversexclusion

  I've stared at the Boost.Interprocess documentation for hours but still haven't been able to figure this out. In the doc, they have an example of creating a vector in shared memory like so: //Define an STL compatible allocator of ints that allocates from the managed_shared_memory. //This allocator will allow placing containers in the segment typedef allocator<int, managed_shared_memory::segment_manager> ShmemAllocator; //Alias a vector that uses the previous STL-like allocator so that allocates //its values from the segment typedef vector<int, ShmemAllocator> MyVector; int main(int argc, char *argv[]) { //Create a new segment with given name and size managed_shared_memory segment(create_only, "MySharedMemory", 65536); //Initialize shared memory STL-compatible allocator const ShmemAllocator alloc_inst (segment.get_segment_manager()); //Construct a vector named "MyVector" in shared memory with argument alloc_inst MyVector *myvector = segment.construct<MyVector>("MyVector")(alloc_inst); Now, I understand this. What I'm stuck is how to pass a second parameter to segment.construct() to specify the number of elements. The interprocess document gives the prototype for construct() as MyType *ptr = managed_memory_segment.construct<MyType>("Name") (par1, par2...); but when I try MyVector *myvector = segment.construct<MyVector>("MyVector")(100, alloc_inst); I get compilation errors. My questions are: Who actually gets passed the parameters par1, par2 from segment.construct, the constructor of the object, e.g. vector? My understanding is that the template allocator parameter is being passed. Is that correct? How can I add another parameter, in addition to alloc_inst that is required by the constructor of the object being created in shared memory? There's very little information other than the terse Boost docs on this.

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• How to create a function with vectors and vertical asymptote using MATLAB

  - by Pedro J Trinidad

  Plot the function f(x) = 1.5x / x-4 for -10 equal or less than X equal or less than 10. Notice that the function have a vertical asymptote at x = 4. Plot the function by creating two vectors for the domain of x. The first vector (call it x1) with elements from -10 to 3.7, and the second vector (calle it x2) with elements from 4.3 to 10. For each of the X vector create a Y vector (call them y1 and y2) with the corresponding values of Y according to the function. To plot the function make two curves in the same plot (y1 vs. x1 and y2 vs. x2).

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• Iterating backward

  - by MBennett

  Suppose I have a vector<int> myvec and I want to loop through all of the elements in reverse. I can think of a few ways of doing this: for (vector<int>::iterator it = myvec.end() - 1; it >= myvec.begin(); --it) { // do stuff here } for (vector<int>::reverse_iterator rit = myvec.rbegin(); rit != myvec.rend(); ++rit) { // do stuff here } for (int i = myvec.size() - 1; i >= 0; --i) { // do stuff here } So my question is when should I use each? Is there a difference? I know that the first one is dangerous because if I pass in an empty vector, then myvec.end() - 1 is undefined, but are there any other hazards or inefficiencies with this?

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• Good way to maintain Muliple level selection menu list in J2ME

  - by geoaxis

  Hello, I need a good way to maintain multiple form level data for menue selection. So for example If I have A and B, each might Have 1 2 3 so A A1 A2 A3 B B1 B2 B3 And this can continue for long, so that I could have A - A1 - A1.1 - A1.1.1 -.... I have the following class in place, works ok But I suspect we could have better. I just need to perform selection ni a selection tree like Widget, but each level of selection comes in another form (in J2ME) import java.util.Vector; public class Tag { private String tag; private Vector childTags; private Tag parent; Tag(String tag, Vector childtag) { this.tag = tag; this.childTags= childTags; } public void setChildTags(Vector childTags) { this.childTags = childTags; } public Vector getChildTags() { return this.childTags; } public String getTag() { return this.tag; } public String toString(int depth) { String a =""; if(depth==0) { a = a + this.getTag(); } if(this.getChildTags()!= null) { for(int k=0;k <this.getChildTags().capacity(); k++) { for (int i=0; i<depth; i++ ) { a = a + ("-"); } a = a+ ( ((Tag)this.getChildTags().elementAt(k)).toString(depth++)); } } return a; } }

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• Detecting Acceleration in a car (iPhone Accelerometer)

  - by TheGazzardian

  Hello, I am working on an iPhone app where we are trying to calculate the acceleration of a moving car. Similar apps have accomplished this (Dynolicious), but the difference is that this app is designed to be used during general city driving, not on a drag strip. This leads us to one big concern that Dynolicious was luckily able to avoid: hills. Yes, hills. There are two important stages to this: calibration, and actual driving. Our initial run was simple and suffered the consequences. During the calibration stage, I took the average force on the phone, and during running, I just subtracted the average force from the current force to get the current acceleration this frame. The problem with this is that the typical car receives much more force than just the forward force - everything from turning to potholes was causing the values to go out of sync with what was really happening. The next run was to add the condition that the iPhone must be oriented in such a way that the screen was facing toward the back of the car. Using this method, I attempted to follow only force on the z-axis, but this obviously lead to problems unless the iPhone was oriented directly upright, because of gravity. Some trigonometry later, and I had managed to work gravity out of the equation, so that the car was actually being read very, very well by the iPhone. Until I hit a slope. As soon as the angle of the car changed, suddenly I was receiving accelerations and decelerations that didn't make sense, and we were once again going out of sync. Talking with someone a lot smarter than me at math lead to a solution that I have been trying to implement for longer than I would like to admit. It's steps are as follows: 1) During calibration, measure gravity as a vector instead of a size. Store that vector. 2) When the car initially moves forward, take the vector of motion and subtract gravity. Use this as the forward momentum. (Ignore, for now, the user cases where this will be difficult and let's concentrate on the math :) 3) From the forward vector and the gravity vector, construct a plane. 4) Whenever a force is received, project it onto said plane to get rid of sideways force/etc. 5) Then, use that force, the known magnitude of gravity, and the known direction of forward motion to essentially solve a triangle to get the forward vector. The problem that is causing the most difficulty in this new system is not step 5, which I have gotten to the point where all the numbers look as they should. The difficult part is actually the detection of the forward vector. I am selecting vectors whose magnitude exceeds gravity, and from there, averaging them and subtracting gravity. (I am doing some error checking to make sure that I am not using a force just because the iPhone accelerometer was off by a bit, which happens more frequently than I would like). But if I plot these vectors that I am using, they actually vary by an angle of about 20-30 degrees, which can lead to some strong inaccuracies. The end result is that the app is even more inaccurate now than before. So basically - all you math and iPhone brains out there - any glaring errors? Any potentially better solutions? Any experience that could be useful at all? Award: offering a bounty of $250 to the first answer that leads to a solution.

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• Seeking STL-aware c++filt

  - by Don Wakefield

  In my development environment, I'm compiling a code base using GNU C++ 3.4.6. Code is under development, and unfortunately crashes now and then. It's nice to be able to run the traceback through a demangler, and I use c++filt 3.4. The problem comes when functions have a number of STL parameters. Consider My_callback::operator()( Status&, std::set<std::string> const&, std::vector<My_parameter*> const&, My_attribute_set const&, std::vector<My_parameter_base*> const&, std::vector<My_parameter> const&, std::set<std::string> const& ) { // ... } When this function is in the traceback, the mangled output on my platform is: (_ZN30My_callbackclER11StatusRKSt3setISsSt4lessISsESaISsEERKSt6vectorIP13My_parameterSaISB_EERK17My_attribute_setRKS9_IP18My_parameter_baseSaISK_EERKS9_ISA_SaISA_EES8_+0x76a) [0x13ffdaa] c++filt kindly demangles it to (My_callback::operator()(Status&, std::set<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::less<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > > const&, std::vector<My_parameter*, std::allocator<My_parameter*> > const&, My_attribute_set const&, std::vector<My_parameter_base*, std::allocator<My_parameter_base*> > const&, std::vector<My_parameter, std::allocator<My_parameter> > const&, std::set<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::less<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > > const&)+0x76a) [0x13ffdaa] This is the same problem as compiler errors encountered when using templates. However, the STL is a fairly regular and recognizable package of templates. So what I'm hoping is that someone out there has created an enhanced version of c++filt which would dump something closer to the original function signature. Any hints?

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• Convert Decimal to ASCII

  - by Dan Snyder

  I'm having difficulty using reinterpret_cast. Before I show you my code I'll let you know what I'm trying to do. I'm trying to get a filename from a vector full of data being used by a MIPS I processor I designed. Basically what I do is compile a binary from a test program for my processor, dump all the hex's from the binary into a vector in my c++ program, convert all of those hex's to decimal integers and store them in a DataMemory vector which is the data memory unit for my processor. I also have instruction memory. So When my processor runs a SYSCALL instruction such as "Open File" my C++ operating system emulator receives a pointer to the beginning of the filename in my data memory. So keep in mind that data memory is full of ints, strings, globals, locals, all sorts of stuff. When I'm told where the filename starts I do the following: Convert the whole decimal integer element that is being pointed to to its ASCII character representation, and then search from left to right to see if the string terminates, if not then just load each character consecutively into a "filename" string. Do this until termination of the string in memory and then store filename in a table. My difficulty is generating filename from my memory. Here is an example of what I'm trying to do: C++ Syntax (Toggle Plain Text) 1.Index Vector NewVector ASCII filename 2.0 240faef0 128123792 'abc7' 'a' 3.0 240faef0 128123792 'abc7' 'ab' 4.0 240faef0 128123792 'abc7' 'abc' 5.0 240faef0 128123792 'abc7' 'abc7' 6.1 1234567a 243225 'k2s0' 'abc7k' 7.1 1234567a 243225 'k2s0' 'abc7k2' 8.1 1234567a 243225 'k2s0' 'abc7k2s' 9. //EXIT LOOP// 10.1 1234567a 243225 'k2s0' 'abc7k2s' Index Vector NewVector ASCII filename 0 240faef0 128123792 'abc7' 'a' 0 240faef0 128123792 'abc7' 'ab' 0 240faef0 128123792 'abc7' 'abc' 0 240faef0 128123792 'abc7' 'abc7' 1 1234567a 243225 'k2s0' 'abc7k' 1 1234567a 243225 'k2s0' 'abc7k2' 1 1234567a 243225 'k2s0' 'abc7k2s' //EXIT LOOP// 1 1234567a 243225 'k2s0' 'abc7k2s' Here is the code that I've written so far to get filename (I'm just applying this to element 1000 of my DataMemory vector to test functionality. 1000 is arbitrary.): C++ Syntax (Toggle Plain Text) 1.int i = 0; 2.int step = 1000;//top->a0; 3.string filename; 4.char *temp = reinterpret_cast<char*>( DataMemory[1000] );//convert to char 5.cout << "a0:" << top->a0 << endl;//pointer supplied 6.cout << "Data:" << DataMemory[top->a0] << endl;//my vector at pointed to location 7.cout << "Data(1000):" << DataMemory[1000] << endl;//the element I'm testing 8.cout << "Characters:" << &temp << endl;//my temporary char array 9. 10.while(&temp[i]!=0) 11.{ 12. filename+=temp[i];//add most recent non-terminated character to string 13. i++; 14. if(i==4)//when 4 chatacters have been added.. 15. { 16. i=0; 17. step+=1;//restart loop at the next element in DataMemory 18. temp = reinterpret_cast<char*>( DataMemory[step] ); 19. } 20. } 21. cout << "Filename:" << filename << endl; int i = 0; int step = 1000;//top-a0; string filename; char *temp = reinterpret_cast( DataMemory[1000] );//convert to char cout << "a0:" << top-a0 << endl;//pointer supplied cout << "Data:" << DataMemory[top-a0] << endl;//my vector at pointed to location cout << "Data(1000):" << DataMemory[1000] << endl;//the element I'm testing cout << "Characters:" << &temp << endl;//my temporary char array while(&temp[i]!=0) { filename+=temp[i];//add most recent non-terminated character to string i++; if(i==3)//when 4 chatacters have been added.. { i=0; step+=1;//restart loop at the next element in DataMemory temp = reinterpret_cast( DataMemory[step] ); } } cout << "Filename:" << filename << endl; So the issue is that when I do the conversion of my decimal element to a char array I assume that 8 hex #'s will give me 4 characters. Why isn't this this case? Here is my output: C++ Syntax (Toggle Plain Text) 1.a0:0 2.Data:0 3.Data(1000):4428576 4.Characters:0x7fff5fbff128 5.Segmentation fault

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• using extends with Java Generics

  - by Sandro

  Lets say that I have the following code: public class Shelter<A extends Animal, B extends Animal> { List<A> topFloor = new Vector<A>(); List<B> bottomFloor = new Vector<B>(); public A getFirstTopFloorAnimal(){return topFloor.firstElement();} public B getFirstBottomFloorAnimal(){return bottomFloor.firstElement();} //This compiles but when I try to use it, it only returns objects public List<Animal> getAnimals() { Vector a = new Vector(topFloor); a.addAll(bottomFloor); return a; } } Now for somereason the following code compiles. But when I try to use getAnimals() I get a of objects instead of Animal. Any ideas why this is? Does this have to do with the List is NOT a List idea in the Generics tutorial? Thank you.

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• The fastest way to iterate through a collection of objects

  - by Trev

  Hello all, First to give you some background: I have some research code which performs a Monte Carlo simulation, essential what happens is I iterate through a collection of objects, compute a number of vectors from their surface then for each vector I iterate through the collection of objects again to see if the vector hits another object (similar to ray tracing). The pseudo code would look something like this for each object { for a number of vectors { do some computations for each object { check if vector intersects } } } As the number of objects can be quite large and the amount of rays is even larger I thought it would be wise to optimise how I iterate through the collection of objects. I created some test code which tests arrays, lists and vectors and for my first test cases found that vectors iterators were around twice as fast as arrays however when I implemented a vector in my code in was somewhat slower than the array I was using before. So I went back to the test code and increased the complexity of the object function each loop was calling (a dummy function equivalent to 'check if vector intersects') and I found that when the complexity of the function increases the execution time gap between arrays and vectors reduces until eventually the array was quicker. Does anyone know why this occurs? It seems strange that execution time inside the loop should effect the outer loop run time.

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• Calling unmanaged c++ code in C# Mixed with STL

  - by Turtle

  Hey, I want to call unmanaged c++ code in C# The function interface is like following(I simplified it to make it easy to understand) Face genMesh(int param1, int param2); Face is a struct defined as: struct Face{ vector<float> nodes; vector<int> indexs; } I googled and read the MSDN docs found ways to call simple c/c++ unmanged code in C#, also know how to hand the struct as return value. And My question is how to handle "vector". I did not find rules about mapping between vector and some types in C# Thanks!

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• map operator [] operands

  - by Jamie Cook

  Hi all I have the following in a member function int tt = 6; vector<set<int>>& temp = m_egressCandidatesByDestAndOtMode[tt]; set<int>& egressCandidateStops = temp.at(dest); and the following declaration of a member variable map<int, vector<set<int>>> m_egressCandidatesByDestAndOtMode; However I get an error when compiling (Intel Compiler 11.0) 1>C:\projects\svn\bdk\Source\ZenithAssignment\src\Iteration\PtBranchAndBoundIterationOriginRunner.cpp(85): error: no operator "[]" matches these operands 1> operand types are: const std::map<int, std::vector<std::set<int, std::less<int>, std::allocator<int>>, std::allocator<std::set<int, std::less<int>, std::allocator<int>>>>, std::less<int>, std::allocator<std::pair<const int, std::vector<std::set<int, std::less<int>, std::allocator<int>>, std::allocator<std::set<int, std::less<int>, std::allocator<int>>>>>>> [ const int ] 1> vector<set<int>>& temp = m_egressCandidatesByDestAndOtMode[tt]; 1> ^ I know it's got to be something silly but I can't see what I've done wrong.

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• Output is different for R-value and L-value. Why?

  - by Leonid Volnitsky

  Can someone explain to me why output for R-value is different from L-value? #include <iostream> #include <vector> using namespace std; template<typename Ct> struct ct_wrapper { Ct&& ct; // R or L ref explicit ct_wrapper(Ct&& ct) : ct(std::forward<Ct>(ct)) { std::cout << this->ct[1];}; }; int main() { // L-val vector<int> v{1,2,3}; ct_wrapper<vector<int>&> lv(v); cout << endl << lv.ct[0] << lv.ct[1] << lv.ct[2] << endl; // R-val ct_wrapper<vector<int>&&> rv(vector<int>{1,2,3}); cout << endl << rv.ct[0] << rv.ct[1] << rv.ct[2] << endl; } Output (same for gcc48 and clang32): 2 123 2 003

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• Are returned locals automatically xvalues

  - by mark

  Following on from a comment I made on this: passing std::vector to constructor and move semantics Is the std::move necessary in the following code, to ensure that the returned value is a xvalue? std::vector<string> buildVector() { std::vector<string> local; // .... build a vector return std::move(local); } It is my understanding that this is required. I have often seen this used when returning a std::unique_ptr from a function, however GManNickG made the following comment: It is my understanding that in a return statement all local variables are automatically xvalues (expiring values) and will be moved, but I'm unsure if that only applies to the returned object itself. So OP should go ahead and put that in there until I'm more confident it shouldn't have to be. :) Can anyone clarify if the std::move is necessary? Is the behaviour compiler dependent?

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• in R, the arguments of "for loop"

  - by alex

  Could anyone please tell me what is wrong with the R code below: i = 1.001 #make SAV and STO become vector SAV = c() STO = c() #set the initial values for the vector SAV[1] = 0 STO[1] = 100 for (t in 2:1000) { if ((price[t]>9.9)&(price[t]<10.1)&(SAV[t-1]!=0)) SAV[t]=SAV[t-1]*i STO[t]=0 } for (t in 2:1000) { if ((price[t]>9.9)&(price[t]<10.1)&(SAV[t-1]=0)) STO[t] = STO [t-1] SAV[t] = 0 } SAV STO What I am trying to do is to find vector for both SAV and STO.

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• C++ converting back and forth from derived and base classes

  - by user127817

  I was wondering if there is a way in C++ to accomplish the following: I have a base class called ResultBase and two class that are Derived from it, Variable and Expression. I have a few methods that do work on vector<ResultBase> . I want to be able to pass in vectors of Variable and Expression into these methods. I can achieve this by creating a vector<ResultBase> and using static_cast to fill it with the members from my vector of Variable/Expression. However, once the vector has run through the methods, I want to be able to get it back as the vector of Result/Expression. I'll know for sure which one I want back. static_cast won't work here as there isn't a method to reconstruct a Variable/Expression from a ResultBase, and more importantly I wouldn't have the original properties of the Variables/Expressions The methods modify some of the properties of the ResultBase and I need those changes to be reflected in the original vectors. (i.e. ResultBase has a property called IsLive, and one of the methods will modify this property. I want this IsLive value to be reflected in the derived class used to create the ResultBase Whats the easiest way to accomplish this?

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• Help thinking "Pythony"

  - by Josh

  I'm brand new to Python and trying to learn it by replicating the following C++ function into python // determines which words in a vector consist of the same letters // outputs the words with the same letters on the same line void equivalentWords(vector <string> words, ofstream & outFile) { outFile << "Equivalent words\n"; // checkedWord is parallel to the words vector. It is // used to make sure each word is only displayed once. vector <bool> checkedWord (words.size(), false); for(int i = 0; i < words.size(); i++) { if (!checkedWord[i]){ outFile << " "; for(int j = i; j < words.size(); j++){ if(equivalentWords(words[i], words[j], outFile)) { outFile << words[j] << " "; checkedWord[j] = true; } } outFile << "\n"; } } } In my python code (below), rather than having a second vector, I have a list ("words") of lists of a string, a sorted list of the chars in the former string (because strings are immutable), and a bool (that tells if the word has been checked yet). However, I can't figure out how to change a value as you iterate through a list. for word, s_word, checked in words: if not checked: for word1, s_word1, checked1 in words: if s_word1 == s_word: checked1 = True # this doesn't work print word1, print "" Any help on doing this or thinking more "Pythony" is appreciated.

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• Simpler array declaration syntax in c++

  - by AareP

  In the spirit of Go-language, where simpler syntax is considered pretty important, here's a proposal for simpler array declaration in c++: int value; int_1 list; int_2 table; int_3 cube; RECT rect; RECT_1 rects; Using typedefs this can expand to: int value; vector<int> list; vector<int> table; vector<int> cube; RECT rect; vector<RECT> rects; Would you use it, or is there such a thing as too simple syntax?

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• Subset and lagging list data structure R

  - by user1234440

  I have a list that is indexed like the following: >list.stuff [[1]] [[1]]$vector ... [[1]]$matrix .... [[1]]$vector [[2]] null [[3]] [[3]]$vector ... [[3]]$matrix .... [[3]]$vector . . . Each segment in the list is indexed according to another vector of indexes: >index.list 1, 3, 5, 10, 15 In list.stuff, only at each of the indexes 1,3,5,10,15 will there be 2 vectors and one matrix; everything else will be null like [[2]]. What I want to do is to lag like the lag.xts function so that whatever is stored in [[1]] will be pushed to [[3]] and the last one drops off. This also requires subsetting the list, if its possible. I was wondering if there exists some functions that handle list manipulation. My thinking is that for xts, a time series can be extracted based on an index you supply: xts.object[index,] #returns the rows 1,3,5,10,15 From here I can lag it with: lag.xts(xts.object[index,]) Any help would be appreciated thanks: EDIT: Here is a reproducible example: list.stuff<-list() vec<-c(1,2,3,4,5,6,7,8,9) vec2<-c(1,2,3,4,5,6,7,8,9) mat<-matrix(c(1,2,3,4,5,6,7,8),4,2) list.vec.mat<-list(vec=vec,mat=mat,vec2=vec2) ind<-c(2,4,6,8,10) for(i in ind){ list.stuff[[i]]<-list.vec.mat }

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• Creating Instance of Python Extension Type in C

  - by Brad Zeis

  I am writing a simple Vector implementation as a Python extension module in C that looks mostly like this: typedef struct { PyObject_HEAD double x; double y; } Vector; static PyTypeObject Vector_Type = { ... }; It is very simple to create instances of Vector while calling from Python, but I need to create a Vector instance in the same extension module. I looked in the documentation but I couldn't find a clear answer. What's the best way to do this?

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• [C++] A minimalistic smart array (container) class template

  - by legends2k

  I've written a (array) container class template (lets call it smart array) for using it in the BREW platform (which doesn't allow many C++ constructs like STD library, exceptions, etc. It has a very minimal C++ runtime support); while writing this my friend said that something like this already exists in Boost called MultiArray, I tried it but the ARM compiler (RVCT) cries with 100s of errors. I've not seen Boost.MultiArray's source, I've just started learning template only lately; template meta programming interests me a lot, although am not sure if this is strictly one, which can be categorised thus. So I want all my fellow C++ aficionados to review it ~ point out flaws, potential bugs, suggestions, optimisations, etc.; somthing like "you've not written your own Big Three which might lead to...". Possibly any criticism that'll help me improve this class and thereby my C++ skills. smart_array.h #include <vector> using std::vector; template <typename T, size_t N> class smart_array { vector < smart_array<T, N - 1> > vec; public: explicit smart_array(vector <size_t> &dimensions) { assert(N == dimensions.size()); vector <size_t>::iterator it = ++dimensions.begin(); vector <size_t> dimensions_remaining(it, dimensions.end()); smart_array <T, N - 1> temp_smart_array(dimensions_remaining); vec.assign(dimensions[0], temp_smart_array); } explicit smart_array(size_t dimension_1 = 1, ...) { static_assert(N > 0, "Error: smart_array expects 1 or more dimension(s)"); assert(dimension_1 > 1); va_list dim_list; vector <size_t> dimensions_remaining(N - 1); va_start(dim_list, dimension_1); for(size_t i = 0; i < N - 1; ++i) { size_t dimension_n = va_arg(dim_list, size_t); assert(dimension_n > 0); dimensions_remaining[i] = dimension_n; } va_end(dim_list); smart_array <T, N - 1> temp_smart_array(dimensions_remaining); vec.assign(dimension_1, temp_smart_array); } smart_array<T, N - 1>& operator[](size_t index) { assert(index < vec.size() && index >= 0); return vec[index]; } size_t length() const { return vec.size(); } }; template<typename T> class smart_array<T, 1> { vector <T> vec; public: explicit smart_array(vector <size_t> &dimension) : vec(dimension[0]) { assert(dimension[0] > 0); } explicit smart_array(size_t dimension_1 = 1) : vec(dimension_1) { assert(dimension_1 > 0); } T& operator[](size_t index) { assert(index < vec.size() && index >= 0); return vec[index]; } size_t length() { return vec.size(); } }; Sample Usage: #include <iostream> using std::cout; using std::endl; int main() { // testing 1 dimension smart_array <int, 1> x(3); x[0] = 0, x[1] = 1, x[2] = 2; cout << "x.length(): " << x.length() << endl; // testing 2 dimensions smart_array <float, 2> y(2, 3); y[0][0] = y[0][1] = y[0][2] = 0; y[1][0] = y[1][1] = y[1][2] = 1; cout << "y.length(): " << y.length() << endl; cout << "y[0].length(): " << y[0].length() << endl; // testing 3 dimensions smart_array <char, 3> z(2, 4, 5); cout << "z.length(): " << z.length() << endl; cout << "z[0].length(): " << z[0].length() << endl; cout << "z[0][0].length(): " << z[0][0].length() << endl; z[0][0][4] = 'c'; cout << z[0][0][4] << endl; // testing 4 dimensions smart_array <bool, 4> r(2, 3, 4, 5); cout << "z.length(): " << r.length() << endl; cout << "z[0].length(): " << r[0].length() << endl; cout << "z[0][0].length(): " << r[0][0].length() << endl; cout << "z[0][0][0].length(): " << r[0][0][0].length() << endl; // testing copy constructor smart_array <float, 2> copy_y(y); cout << "copy_y.length(): " << copy_y.length() << endl; cout << "copy_x[0].length(): " << copy_y[0].length() << endl; cout << copy_y[0][0] << "\t" << copy_y[1][0] << "\t" << copy_y[0][1] << "\t" << copy_y[1][1] << "\t" << copy_y[0][2] << "\t" << copy_y[1][2] << endl; return 0; }

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• Unsort: remembering a permutation and undoing it.

  - by dreeves

  Suppose I have a function f that takes a vector v and returns a new vector with the elements transformed in some way. It does that by calling function g that assumes the vector is sorted. So I want f to be defined like so: f[v_] := Module[{s, r}, s = Sort[v]; (* remember the permutation applied in order to sort v *) r = g[s]; Unsort[r] (* apply the inverse of that permutation *) ] What's the best way to do the "Unsort"? Or could we get really fancy and have this somehow work: answer = Unsort[g[Sort[v]]]; ADDED: Let's make this concrete with a toy example. Suppose we want a function f that takes a vector and transforms it by adding to each element the next smallest element, if any. That's easy to write if we assume the vector is sorted, so let's write a helper function g that makes that assumption: g[v_] := v + Prepend[Most@v, 0] Now for the function we really want, f, that works whether or not v is sorted: f[v_] := (* remember the order; sort it; call g on it; put it back in the original order; return it *)

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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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• Inheritance vs specific types in Financial Modelling for cashflows

  - by BlueTrin

  Hello, I have to program some financial applications where I have to represent a schedule of flows. The flows can be of 3 types: - fee flow (just a lump payment at some date) - floating rate flow (the flow is dependant of an interest rate to be determined at a later date) - fixed rate flow (the flow is dependant of an interest rate determined when the deal is done) I need to keep the whole information and I need to represent a schedule of these flows. Originally I wanted to use inheritance and create three classes FeeFlow, FloatingFlow, FixedFlow all inheriting from ICashFlow and implement some method GetFlowType() returning an enum then I could dynamic_cast the object to the correct type. That would allow me to have only one vector to represent my schedule. What do you think of this design, should I rather use three vectors vector, vector and vector to avoid the dynamic casts ?

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