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Eigen  3.3.71
Eigen::VectorBlock Class Reference

Detailed Description

Expression of a fixed-size or dynamic-size sub-vector.

Template Parameters
VectorTypethe type of the object in which we are taking a sub-vector
Sizesize of the sub-vector we are taking at compile time (optional)

This class represents an expression of either a fixed-size or dynamic-size sub-vector. It is the return type of DenseBase::segment(Index,Index) and DenseBase::segment<int>(Index) and most of the time this is the only way it is used.

However, if you want to directly maniputate sub-vector expressions, for instance if you want to write a function returning such an expression, you will need to use this class.

Here is an example illustrating the dynamic case:

#include <Eigen/Core>
#include <iostream>
using namespace Eigen;
using namespace std;
template<typename Derived>
segmentFromRange(MatrixBase<Derived>& v, int start, int end)
{
return Eigen::VectorBlock<Derived>(v.derived(), start, end-start);
}
template<typename Derived>
segmentFromRange(const MatrixBase<Derived>& v, int start, int end)
{
return Eigen::VectorBlock<const Derived>(v.derived(), start, end-start);
}
int main(int, char**)
{
Matrix<int,1,6> v; v << 1,2,3,4,5,6;
cout << segmentFromRange(2*v, 2, 4) << endl; // calls the const version
segmentFromRange(v, 1, 3) *= 5; // calls the non-const version
cout << "Now the vector v is:" << endl << v << endl;
return 0;
}

Output:

6 8
Now the vector v is:
 1 10 15  4  5  6
Note
Even though this expression has dynamic size, in the case where VectorType has fixed size, this expression inherits a fixed maximal size which means that evaluating it does not cause a dynamic memory allocation.

Here is an example illustrating the fixed-size case:

#include <Eigen/Core>
#include <iostream>
using namespace Eigen;
using namespace std;
template<typename Derived>
firstTwo(MatrixBase<Derived>& v)
{
return Eigen::VectorBlock<Derived, 2>(v.derived(), 0);
}
template<typename Derived>
firstTwo(const MatrixBase<Derived>& v)
{
return Eigen::VectorBlock<const Derived, 2>(v.derived(), 0);
}
int main(int, char**)
{
Matrix<int,1,6> v; v << 1,2,3,4,5,6;
cout << firstTwo(4*v) << endl; // calls the const version
firstTwo(v) *= 2; // calls the non-const version
cout << "Now the vector v is:" << endl << v << endl;
return 0;
}

Output:

4 8
Now the vector v is:
2 4 3 4 5 6
See also
class Block, DenseBase::segment(Index,Index,Index,Index), DenseBase::segment(Index,Index)

Public Member Functions

 VectorBlock (VectorType &vector, Index start)
 
 VectorBlock (VectorType &vector, Index start, Index size)
 

Constructor & Destructor Documentation

◆ VectorBlock() [1/2]

Eigen::VectorBlock::VectorBlock ( VectorType &  vector,
Index  start,
Index  size 
)
inline

Dynamic-size constructor

◆ VectorBlock() [2/2]

Eigen::VectorBlock::VectorBlock ( VectorType &  vector,
Index  start 
)
inline

Fixed-size constructor


The documentation for this class was generated from the following files:
Eigen
Namespace containing all symbols from the Eigen library.
Definition: Core:309
Eigen::VectorBlock
Expression of a fixed-size or dynamic-size sub-vector.
Definition: ForwardDeclarations.h:83
Eigen::Matrix
The matrix class, also used for vectors and row-vectors.
Definition: Matrix.h:178
Eigen::MatrixBase
Base class for all dense matrices, vectors, and expressions.
Definition: MatrixBase.h:48