Re: [eigen] Is it really impossible to modify a column of a matrix with in function?

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On 30.08.2011 11:58, Helmut Jarausch wrote:
void set_Col(VectorXi&  V) {

int main() {
   MatrixXi A(2,3);
   A<<  1,2,3,
   std::cout<<  "A=\n"<<  A<<  std::endl;


It looks as if a column cannot be passed by a non-const reference.
Why doesn't  the col-method return a non-const reference for a non-
const object (the col-method could be overloaded with/without the
const attribute)?

That's because A.col(1) does not return a VectorXi but a view on the corresponding column. Unfortunately passing this to another function is a bit hackish. To stay generic you need to pass a MatrixBase<Derived>& and because A.col() returns a temporary it needs to be a const-ref, which you need to const-cast within your method.
Look here for details:


Dipl.-Inf. Christoph Hertzberg
Cartesium 0.051
Universität Bremen
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28359 Bremen

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