core/vnl/algo/vnl_generalized_eigensystem.h
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00001 // This is core/vnl/algo/vnl_generalized_eigensystem.h
00002 #ifndef vnl_generalized_eigensystem_h_
00003 #define vnl_generalized_eigensystem_h_
00004 #ifdef VCL_NEEDS_PRAGMA_INTERFACE
00005 #pragma interface
00006 #endif
00007 //:
00008 // \file
00009 // \brief  Solves the generalized eigenproblem Ax=La
00010 // \author Andrew W. Fitzgibbon, Oxford RRG
00011 // \date   29 Aug 96
00012 //
00013 // \verbatim
00014 // Modifications
00015 //  dac (Manchester) 28/03/2001: tidied up documentation
00016 //   Feb.2002 - Peter Vanroose - brief doxygen comment placed on single line
00017 // \endverbatim
00018 
00019 #include <vnl/vnl_diag_matrix.h>
00020 
00021 //: Solves the generalized eigenproblem Ax=Bx
00022 //  Solves the generalized eigenproblem of $A x = \lambda B x$,
00023 //  with $A$ symmetric and $B$ positive definite. \n
00024 //  See Golub and van Loan, Section 8.7.
00025 
00026 class vnl_generalized_eigensystem
00027 {
00028  public:
00029 // Public data members because they're unique.
00030   long n;
00031 
00032 //: Solves the generalized eigenproblem Ax=Bx
00033 //  Solve real generalized eigensystem $A x = \lambda B x$ for
00034 //  $\lambda$ and $x$, where $A$ symmetric, $B$ positive definite.
00035 //  Initializes storage for the matrix $V = [ x_0 x_1 .. x_n ]$ and
00036 //  the vnl_diag_matrix $D = [ \lambda_0 \lambda_1 ... \lambda_n ]$.
00037 //  The eigenvalues are sorted into increasing order (of value, not
00038 //  absolute value).
00039 //
00040 //  Uses vnl_cholesky decomposition $C^\top C = B$, to convert to
00041 //  $C^{-\top} A C^{-1} x = \lambda x$ and then uses the
00042 //  symmetric eigensystem code.   It will print a verbose warning
00043 //  if $B$ is not positive definite.
00044 
00045   vnl_generalized_eigensystem(const vnl_matrix<double>& A,
00046                               const vnl_matrix<double>& B);
00047 
00048 //: Public eigenvectors.
00049 //  After construction, this contains the matrix of eigenvectors.
00050   vnl_matrix<double> V;
00051 
00052 //: Public eigenvalues.
00053 //  After construction, this contains the diagonal matrix of eigenvalues, stored as a vector.
00054   vnl_diag_matrix<double> D;
00055 };
00056 
00057 #endif // vnl_generalized_eigensystem_h_