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Return a reference to a Armadillo vector element


Return a reference to a Armadillo vector element

By : Rizwan Hassan
Date : November 19 2020, 01:01 AM
Hope this helps at(0) is almost certainly returning a proxy object, which can be converted to double, or be assigned a double, but is not actually a reference. This may be to avoid dangling references, or to allow for efficient storage of sparse matrices. The documentation for Armadillo is unfortunately pretty quiet on the semantics, but it does not specify that at returns a reference.
This would suggest that you are discouraged from returning a reference. Is there another way to achieve what you want?
code :


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Return vector element by reference

Return vector element by reference


By : dhia haf
Date : March 29 2020, 07:55 AM
should help you out The getElement method is correctly returning a reference to a B instance but the local ele is not a reference it is a value. What is essentially happening under the hood here is the following
code :
// Copy constructor B::B(B& other) is being called 
B ele = B(A.getElement());
B& ele = A.getElement();
Return vector element reference by [] operator

Return vector element reference by [] operator


By : Rares Ursu
Date : March 29 2020, 07:55 AM
I hope this helps you . Your operator[] seems to be fine. You do seem to be missing a semi-colon after the name your struct.
code :
#include <iostream>
#include <vector>

struct A
{
    void Function () {
        std::cout << "A::Function()" "\n" ;
    }
};

template <typename type> struct Container {
    std::vector <type *> v;

    void Function () {
        std::cout << "Container::Function ()" "\n" ;
    }

    type* operator[] (int i) { 
          return (v)[i];
    }
};

int main (void)
{
    A a ;

    Container <A> c ;

    c.Function () ;

    c.v.push_back (&a) ;
    c[0]->Function () ;

    return 0 ;
}
int main (void)
{
    A a ;

    Container <A> *pC = new Container <A> ;

    pC->Function () ;

    pC->v.push_back (&a) ;
    (*pC) [0]->Function () ;

    delete pC ;

    return 0 ;
}
Return double from vector multiplication with Armadillo C++

Return double from vector multiplication with Armadillo C++


By : Santie van niekerk
Date : March 29 2020, 07:55 AM
I think the issue was by ths following , The result of the product is an expression template called arma::Glue which can be converted to a 1x1 matrix. To do this inline and assign it to a double evaluate it explicitly using .eval() and take the only element which is (0,0).
code :
#include <armadillo>

int main() {
  using arma::rowvec;
  using arma::vec;
  double A = (rowvec({1,3,4})*vec({5,6,7})).eval()(0,0);
};
#include <armadillo>

int main() {
  using arma::rowvec;
  using arma::vec;
  using arma::dot;
  double A = dot(rowvec({1,3,4}), vec({5,6,7}));
};
C++ - Return reference to a vector element

C++ - Return reference to a vector element


By : user2432
Date : March 29 2020, 07:55 AM
I hope this helps you . You're passing the vector by value so you're returning a reference to a temporary element. If you pass the vector by reference you should be fine.
element wise vector or matrix multiplication in Armadillo C++

element wise vector or matrix multiplication in Armadillo C++


By : AlexanderHB
Date : March 29 2020, 07:55 AM
This might help you It's explained in the Armadillo documentation. You should read all relevant documentation before posting questions on Stackoverflow.
See the section on operators, which states that % is used for element-wise multiplication:
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