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EigenSolver< _MatrixType > Class Template Reference
Public Types | Public Member Functions

EigenSolver< _MatrixType > Class Template Reference
[Eigenvalues module]

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#include <EigenSolver.h>

Public Types

typedef _MatrixType MatrixType
 Synonym for the template parameter _MatrixType.
typedef MatrixType::Scalar Scalar
 Scalar type for matrices of type MatrixType.
typedef std::complex< RealScalar > ComplexScalar
 Complex scalar type for MatrixType.
typedef Matrix< ComplexScalar,
ColsAtCompileTime, 1, Options
&~RowMajor,
MaxColsAtCompileTime, 1 > 		EigenvalueType
 Type for vector of eigenvalues as returned by eigenvalues().
typedef Matrix< ComplexScalar,
RowsAtCompileTime,
ColsAtCompileTime, Options,
MaxRowsAtCompileTime,
MaxColsAtCompileTime > 		EigenvectorsType
 Type for matrix of eigenvectors as returned by eigenvectors().

Public Member Functions

 EigenSolver ()
 Default constructor.
 EigenSolver (Index size)
 Default constructor with memory preallocation.
 EigenSolver (const MatrixType &matrix, bool computeEigenvectors=true)
 Constructor; computes eigendecomposition of given matrix.
EigenvectorsType eigenvectors () const
 Returns the eigenvectors of given matrix.
const MatrixType & pseudoEigenvectors () const
 Returns the pseudo-eigenvectors of given matrix.
MatrixType pseudoEigenvalueMatrix () const
 Returns the block-diagonal matrix in the pseudo-eigendecomposition.
const EigenvalueType & eigenvalues () const
 Returns the eigenvalues of given matrix.
EigenSolver & compute (const MatrixType &matrix, bool computeEigenvectors=true)
 Computes eigendecomposition of given matrix.
EigenSolver & setMaxIterations (Index maxIters)
 Sets the maximum number of iterations allowed.
Index getMaxIterations ()
 Returns the maximum number of iterations.

Detailed Description

template<typename _MatrixType>
class Eigen::EigenSolver< _MatrixType >

Computes eigenvalues and eigenvectors of general matrices

Template Parameters:
_MatrixTypethe type of the matrix of which we are computing the eigendecomposition; this is expected to be an instantiation of the Matrix class template. Currently, only real matrices are supported.

The eigenvalues and eigenvectors of a matrix $ A $ are scalars $ \lambda $ and vectors $ v $ such that $ Av = \lambda v $. If $ D $ is a diagonal matrix with the eigenvalues on the diagonal, and $ V $ is a matrix with the eigenvectors as its columns, then $ A V = V D $. The matrix $ V $ is almost always invertible, in which case we have $ A = V D V^{-1} $. This is called the eigendecomposition.

The eigenvalues and eigenvectors of a matrix may be complex, even when the matrix is real. However, we can choose real matrices $ V $ and $ D $ satisfying $ A V = V D $, just like the eigendecomposition, if the matrix $ D $ is not required to be diagonal, but if it is allowed to have blocks of the form

\[ \begin{bmatrix} u & v \\ -v & u \end{bmatrix} \]

(where $ u $ and $ v $ are real numbers) on the diagonal. These blocks correspond to complex eigenvalue pairs $ u \pm iv $. We call this variant of the eigendecomposition the pseudo-eigendecomposition.

Call the function compute() to compute the eigenvalues and eigenvectors of a given matrix. Alternatively, you can use the EigenSolver(const MatrixType&, bool) constructor which computes the eigenvalues and eigenvectors at construction time. Once the eigenvalue and eigenvectors are computed, they can be retrieved with the eigenvalues() and eigenvectors() functions. The pseudoEigenvalueMatrix() and pseudoEigenvectors() methods allow the construction of the pseudo-eigendecomposition.

The documentation for EigenSolver(const MatrixType&, bool) contains an example of the typical use of this class.

Note:
The implementation is adapted from JAMA (public domain). Their code is based on EISPACK.
See also:
MatrixBase::eigenvalues(), class ComplexEigenSolver, class SelfAdjointEigenSolver

Definition at line 64 of file EigenSolver.h.

Member Typedef Documentation

typedef std::complex<RealScalar> ComplexScalar

Complex scalar type for MatrixType.

This is std::complex<Scalar> if Scalar is real (e.g., float or double) and just Scalar if Scalar is complex.

Definition at line 90 of file EigenSolver.h.

typedef Matrix<ComplexScalar, ColsAtCompileTime, 1, Options & ~RowMajor, MaxColsAtCompileTime, 1> EigenvalueType

Type for vector of eigenvalues as returned by eigenvalues().

This is a column vector with entries of type ComplexScalar. The length of the vector is the size of MatrixType.

Definition at line 97 of file EigenSolver.h.

typedef Matrix<ComplexScalar, RowsAtCompileTime, ColsAtCompileTime, Options, MaxRowsAtCompileTime, MaxColsAtCompileTime> EigenvectorsType

Type for matrix of eigenvectors as returned by eigenvectors().

This is a square matrix with entries of type ComplexScalar. The size is the same as the size of MatrixType.

Definition at line 104 of file EigenSolver.h.

typedef _MatrixType MatrixType

Synonym for the template parameter _MatrixType.

Definition at line 69 of file EigenSolver.h.

typedef MatrixType::Scalar Scalar

Scalar type for matrices of type MatrixType.

Definition at line 80 of file EigenSolver.h.

Constructor & Destructor Documentation

EigenSolver (  )

Default constructor.

The default constructor is useful in cases in which the user intends to perform decompositions via EigenSolver::compute(const MatrixType&, bool).

See also:
compute() for an example.

Definition at line 113 of file EigenSolver.h.

EigenSolver ( Index  size )

Default constructor with memory preallocation.

Like the default constructor but with preallocation of the internal data according to the specified problem size.

See also:
EigenSolver()

Definition at line 121 of file EigenSolver.h.

EigenSolver ( const MatrixType &  matrix,
bool  computeEigenvectors = true 
)

Constructor; computes eigendecomposition of given matrix.

Parameters:
[in]matrixSquare matrix whose eigendecomposition is to be computed.
[in]computeEigenvectorsIf true, both the eigenvectors and the eigenvalues are computed; if false, only the eigenvalues are computed.

This constructor calls compute() to compute the eigenvalues and eigenvectors.

Example: 

 Output: 


See also:
compute() 



Definition at line 146 of file EigenSolver.h.







Member Function Documentation






      

        

          EigenSolver< MatrixType > & compute 
          (
          const MatrixType & 
           matrix, 
        

        

          
          
          bool 
           computeEigenvectors = true 
        

        

          
          )
          
        

      







Computes eigendecomposition of given matrix. 


Parameters:

  

    
[in]matrixSquare matrix whose eigendecomposition is to be computed. 

    
[in]computeEigenvectorsIf true, both the eigenvectors and the eigenvalues are computed; if false, only the eigenvalues are computed. 

  

  




Returns:
Reference to *this 


This function computes the eigenvalues of the real matrix matrix. The eigenvalues() function can be used to retrieve them. If computeEigenvectors is true, then the eigenvectors are also computed and can be retrieved by calling eigenvectors().


The matrix is first reduced to real Schur form using the RealSchur class. The Schur decomposition is then used to compute the eigenvalues and eigenvectors.


The cost of the computation is dominated by the cost of the Schur decomposition, which is very approximately $ 25n^3 $ (where $ n $ is the size of the matrix) if computeEigenvectors is true, and $ 10n^3 $ if computeEigenvectors is false.


This method reuses of the allocated data in the EigenSolver object.


Example: 


 Output: 


 

Definition at line 372 of file EigenSolver.h.











      

        

          const EigenvalueType& eigenvalues 
          (
           )
           const
        

      







Returns the eigenvalues of given matrix. 


Returns:
A const reference to the column vector containing the eigenvalues.


Precondition:
Either the constructor EigenSolver(const MatrixType&,bool) or the member function compute(const MatrixType&, bool) has been called before.


The eigenvalues are repeated according to their algebraic multiplicity, so there are as many eigenvalues as rows in the matrix. The eigenvalues are not sorted in any particular order.


Example: 


 Output: 


See also:
eigenvectors(), pseudoEigenvalueMatrix(), MatrixBase::eigenvalues() 



Definition at line 243 of file EigenSolver.h.











      

        

          EigenSolver< MatrixType >::EigenvectorsType eigenvectors 
          (
           )
           const
        

      







Returns the eigenvectors of given matrix. 


Returns:
Matrix whose columns are the (possibly complex) eigenvectors.


Precondition:
Either the constructor EigenSolver(const MatrixType&,bool) or the member function compute(const MatrixType&, bool) has been called before, and computeEigenvectors was set to true (the default).


Column $ k $ of the returned matrix is an eigenvector corresponding to eigenvalue number $ k $ as returned by eigenvalues(). The eigenvectors are normalized to have (Euclidean) norm equal to one. The matrix returned by this function is the matrix $ V $ in the eigendecomposition $ A = V D V^{-1} $, if it exists.


Example: 


 Output: 


See also:
eigenvalues(), pseudoEigenvectors() 



Definition at line 340 of file EigenSolver.h.











      

        

          Index getMaxIterations 
          (
           )
          
        

      







Returns the maximum number of iterations. 



Definition at line 292 of file EigenSolver.h.











      

        

          MatrixType pseudoEigenvalueMatrix 
          (
           )
           const
        

      







Returns the block-diagonal matrix in the pseudo-eigendecomposition. 


Returns:
A block-diagonal matrix.


Precondition:
Either the constructor EigenSolver(const MatrixType&,bool) or the member function compute(const MatrixType&, bool) has been called before.


The matrix $ D $ returned by this function is real and block-diagonal. The blocks on the diagonal are either 1-by-1 or 2-by-2 blocks of the form $ \begin{bmatrix} u & v \\ -v & u \end{bmatrix} $. These blocks are not sorted in any particular order. The matrix $ D $ and the matrix $ V $ returned by pseudoEigenvectors() satisfy $ AV = VD $.


See also:
pseudoEigenvectors() for an example, eigenvalues() 



Definition at line 320 of file EigenSolver.h.











      

        

          const MatrixType& pseudoEigenvectors 
          (
           )
           const
        

      







Returns the pseudo-eigenvectors of given matrix. 


Returns:
Const reference to matrix whose columns are the pseudo-eigenvectors.


Precondition:
Either the constructor EigenSolver(const MatrixType&,bool) or the member function compute(const MatrixType&, bool) has been called before, and computeEigenvectors was set to true (the default).


The real matrix $ V $ returned by this function and the block-diagonal matrix $ D $ returned by pseudoEigenvalueMatrix() satisfy $ AV = VD $.


Example: 


 Output: 


See also:
pseudoEigenvalueMatrix(), eigenvectors() 



Definition at line 198 of file EigenSolver.h.











      

        

          EigenSolver& setMaxIterations 
          (
          Index 
           maxIters )
          
        

      







Sets the maximum number of iterations allowed. 



Definition at line 285 of file EigenSolver.h.









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