Eigen::VectorBlock< VectorType, Size > Class Template Reference

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

#include <VectorBlock.h>

Inheritance diagram for Eigen::VectorBlock< VectorType, Size >:

Public Member Functions
EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE	VectorBlock (VectorType &vector, Index start, Index size)
EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE	VectorBlock (VectorType &vector, Index start)
Public Member Functions inherited from Eigen::Block< VectorType, internal::traits< VectorType >::Flags &RowMajorBit ? 1 :Size, internal::traits< VectorType >::Flags &RowMajorBit ? Size :1 >
EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE	Block (VectorType &xpr, Index i)
EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE	Block (VectorType &xpr, Index startRow, Index startCol)
EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE	Block (VectorType &xpr, Index startRow, Index startCol, Index blockRows, Index blockCols)
EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE ConstUnwindReturnType	unwind () const
EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE UnwindReturnType	unwind ()

Private Types
enum	{ IsColVector = !(internal::traits<VectorType>::Flags & RowMajorBit) }
typedef Block< VectorType, internal::traits< VectorType >::Flags &RowMajorBit ? 1 :Size, internal::traits< VectorType >::Flags &RowMajorBit ? Size :1 >	Base

Additional Inherited Members
Public Types inherited from Eigen::Block< VectorType, internal::traits< VectorType >::Flags &RowMajorBit ? 1 :Size, internal::traits< VectorType >::Flags &RowMajorBit ? Size :1 >
typedef Impl	Base
typedef internal::remove_all_t< VectorType >	NestedExpression
using	ConstUnwindReturnType = Block< const typename BlockHelper::BaseType, BlockRows, BlockCols, InnerPanel >
using	UnwindReturnType = Block< typename BlockHelper::BaseType, BlockRows, BlockCols, InnerPanel >

Detailed Description

template<typename VectorType, int Size>
class Eigen::VectorBlock< VectorType, Size >

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

Template Parameters

VectorType	the type of the object in which we are taking a sub-vector
Size	size 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 manipulate 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>
 
template <typename Derived>
Eigen::VectorBlock<Derived> segmentFromRange(Eigen::MatrixBase<Derived>& v, int start, int end) {
  return Eigen::VectorBlock<Derived>(v.derived(), start, end - start);
}
 
template <typename Derived>
const Eigen::VectorBlock<const Derived> segmentFromRange(const Eigen::MatrixBase<Derived>& v, int start, int end) {
  return Eigen::VectorBlock<const Derived>(v.derived(), start, end - start);
}
 
int main(int, char**) {
  Eigen::Matrix<int, 1, 6> v;
  v << 1, 2, 3, 4, 5, 6;
  std::cout << segmentFromRange(2 * v, 2, 4) << std::endl;  // calls the const version
  segmentFromRange(v, 1, 3) *= 5;                           // calls the non-const version
  std::cout << "Now the vector v is:" << std::endl << v << std::endl;
  return 0;
}

Output:

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

Output:

See also

class Block, DenseBase::segment(Index,Index,Index,Index), DenseBase::segment(Index,Index)

Member Typedef Documentation

Base

template<typename VectorType , int Size>

typedef Block<VectorType, internal::traits<VectorType>::Flags & RowMajorBit ? 1 : Size, internal::traits<VectorType>::Flags & RowMajorBit ? Size : 1> Eigen::VectorBlock< VectorType, Size >::Base

private

Member Enumeration Documentation

anonymous enum

template<typename VectorType , int Size>

anonymous enum

private

Enumerator
IsColVector

{ IsColVector = !(internal::traits<VectorType>::Flags & RowMajorBit) };

Constructor & Destructor Documentation

VectorBlock() [1/2]

template<typename VectorType , int Size>

EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE Eigen::VectorBlock< VectorType, Size >::VectorBlock ( VectorType &  vector, Index  start, Index  size  )

inline

Dynamic-size constructor

      : Base(vector, IsColVector ? start : 0, IsColVector ? 0 : start, IsColVector ? size : 1, IsColVector ? 1 : size) {
  }

VectorBlock() [2/2]

template<typename VectorType , int Size>

EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE Eigen::VectorBlock< VectorType, Size >::VectorBlock ( VectorType &  vector, Index  start  )

inline

Fixed-size constructor

      : Base(vector, IsColVector ? start : 0, IsColVector ? 0 : start) {}

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The documentation for this class was generated from the following files:

• ForwardDeclarations.h
• VectorBlock.h