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1 // This file is part of Eigen, a lightweight C++ template library
2 // for linear algebra.
3 //
4 // Copyright (C) 2008-2010 Gael Guennebaud <gael.guennebaud@inria.fr>
5 // Copyright (C) 2006-2008 Benoit Jacob <jacob.benoit.1@gmail.com>
6 //
7 // This Source Code Form is subject to the terms of the Mozilla
8 // Public License v. 2.0. If a copy of the MPL was not distributed
9 // with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
10 
11 #ifndef EIGEN_VECTORBLOCK_H
12 #define EIGEN_VECTORBLOCK_H
13 
14 namespace Eigen {
15 
16 /** \class VectorBlock
17   * \ingroup Core_Module
18   *
19   * \brief Expression of a fixed-size or dynamic-size sub-vector
20   *
21   * \param VectorType the type of the object in which we are taking a sub-vector
22   * \param Size size of the sub-vector we are taking at compile time (optional)
23   *
24   * This class represents an expression of either a fixed-size or dynamic-size sub-vector.
25   * It is the return type of DenseBase::segment(Index,Index) and DenseBase::segment<int>(Index) and
26   * most of the time this is the only way it is used.
27   *
28   * However, if you want to directly maniputate sub-vector expressions,
29   * for instance if you want to write a function returning such an expression, you
30   * will need to use this class.
31   *
32   * Here is an example illustrating the dynamic case:
33   * \include class_VectorBlock.cpp
34   * Output: \verbinclude class_VectorBlock.out
35   *
36   * \note Even though this expression has dynamic size, in the case where \a VectorType
37   * has fixed size, this expression inherits a fixed maximal size which means that evaluating
38   * it does not cause a dynamic memory allocation.
39   *
40   * Here is an example illustrating the fixed-size case:
41   * \include class_FixedVectorBlock.cpp
42   * Output: \verbinclude class_FixedVectorBlock.out
43   *
44   * \sa class Block, DenseBase::segment(Index,Index,Index,Index), DenseBase::segment(Index,Index)
45   */
46 
47 namespace internal {
48 template<typename VectorType, int Size>
49 struct traits<VectorBlock<VectorType, Size> >
50   : public traits<Block<VectorType,
51                      traits<VectorType>::Flags & RowMajorBit ? 1 : Size,
52                      traits<VectorType>::Flags & RowMajorBit ? Size : 1> >
53 {
54 };
55 }
56 
57 template<typename VectorType, int Size> class VectorBlock
58   : public Block<VectorType,
59                      internal::traits<VectorType>::Flags & RowMajorBit ? 1 : Size,
60                      internal::traits<VectorType>::Flags & RowMajorBit ? Size : 1>
61 {
62     typedef Block<VectorType,
63                      internal::traits<VectorType>::Flags & RowMajorBit ? 1 : Size,
64                      internal::traits<VectorType>::Flags & RowMajorBit ? Size : 1> Base;
65     enum {
66       IsColVector = !(internal::traits<VectorType>::Flags & RowMajorBit)
67     };
68   public:
69     EIGEN_DENSE_PUBLIC_INTERFACE(VectorBlock)
70 
71     using Base::operator=;
72 
73     /** Dynamic-size constructor
74       */
75     inline VectorBlock(VectorType& vector, Index start, Index size)
76       : Base(vector,
77              IsColVector ? start : 0, IsColVector ? 0 : start,
78              IsColVector ? size  : 1, IsColVector ? 1 : size)
79     {
80       EIGEN_STATIC_ASSERT_VECTOR_ONLY(VectorBlock);
81     }
82 
83     /** Fixed-size constructor
84       */
85     inline VectorBlock(VectorType& vector, Index start)
86       : Base(vector, IsColVector ? start : 0, IsColVector ? 0 : start)
87     {
88       EIGEN_STATIC_ASSERT_VECTOR_ONLY(VectorBlock);
89     }
90 };
91 
92 
93 } // end namespace Eigen
94 
95 #endif // EIGEN_VECTORBLOCK_H
96