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Add a rank method with threshold control to JacobiSVD, and make solve uses it to return the minimal norm solution for rank-deficient problems

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(grafted from bbd49d194a
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Gael Guennebaud 2013-11-01 18:21:46 +01:00
parent c49421a82b
commit e16e52d493
1 changed files with 69 additions and 2 deletions
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71
Eigen/src/SVD/JacobiSVD.h
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@ -531,6 +531,7 @@ template<typename _MatrixType, int QRPreconditioner> class JacobiSVD
JacobiSVD()
: m_isInitialized(false),
m_isAllocated(false),
m_usePrescribedThreshold(false),
m_computationOptions(0),
m_rows(-1), m_cols(-1)
{}
@ -545,6 +546,7 @@ template<typename _MatrixType, int QRPreconditioner> class JacobiSVD
JacobiSVD(Index rows, Index cols, unsigned int computationOptions = 0)
: m_isInitialized(false),
m_isAllocated(false),
m_usePrescribedThreshold(false),
m_computationOptions(0),
m_rows(-1), m_cols(-1)
{
@ -564,6 +566,7 @@ template<typename _MatrixType, int QRPreconditioner> class JacobiSVD
JacobiSVD(const MatrixType& matrix, unsigned int computationOptions = 0)
: m_isInitialized(false),
m_isAllocated(false),
m_usePrescribedThreshold(false),
m_computationOptions(0),
m_rows(-1), m_cols(-1)
{
@ -665,6 +668,69 @@ template<typename _MatrixType, int QRPreconditioner> class JacobiSVD
eigen_assert(m_isInitialized && "JacobiSVD is not initialized.");
return m_nonzeroSingularValues;
}
/** \returns the rank of the matrix of which \c *this is the SVD.
*
* \note This method has to determine which singular values should be considered nonzero.
* For that, it uses the threshold value that you can control by calling
* setThreshold(const RealScalar&).
*/
inline Index rank() const
{
using std::abs;
eigen_assert(m_isInitialized && "JacobiSVD is not initialized.");
if(m_singularValues.size()==0) return 0;
RealScalar premultiplied_threshold = m_singularValues.coeff(0) * threshold();
Index i = m_nonzeroSingularValues-1;
while(i>=0 && m_singularValues.coeff(i) < premultiplied_threshold) --i;
return i+1;
}
/** Allows to prescribe a threshold to be used by certain methods, such as rank() and solve(),
* which need to determine when singular values are to be considered nonzero.
* This is not used for the SVD decomposition itself.
*
* When it needs to get the threshold value, Eigen calls threshold().
* The default is \c NumTraits<Scalar>::epsilon()
*
* \param threshold The new value to use as the threshold.
*
* A singular value will be considered nonzero if its value is strictly greater than
* \f$ \vert singular value \vert \leqslant threshold \times \vert max singular value \vert \f$.
*
* If you want to come back to the default behavior, call setThreshold(Default_t)
*/
JacobiSVD& setThreshold(const RealScalar& threshold)
{
m_usePrescribedThreshold = true;
m_prescribedThreshold = threshold;
return *this;
}
/** Allows to come back to the default behavior, letting Eigen use its default formula for
* determining the threshold.
*
* You should pass the special object Eigen::Default as parameter here.
* \code svd.setThreshold(Eigen::Default); \endcode
*
* See the documentation of setThreshold(const RealScalar&).
*/
JacobiSVD& setThreshold(Default_t)
{
m_usePrescribedThreshold = false;
return *this;
}
/** Returns the threshold that will be used by certain methods such as rank().
*
* See the documentation of setThreshold(const RealScalar&).
*/
RealScalar threshold() const
{
eigen_assert(m_isInitialized || m_usePrescribedThreshold);
return m_usePrescribedThreshold ? m_prescribedThreshold
: NumTraits<Scalar>::epsilon();
}
inline Index rows() const { return m_rows; }
inline Index cols() const { return m_cols; }
@ -677,11 +743,12 @@ template<typename _MatrixType, int QRPreconditioner> class JacobiSVD
MatrixVType m_matrixV;
SingularValuesType m_singularValues;
WorkMatrixType m_workMatrix;
bool m_isInitialized, m_isAllocated;
bool m_isInitialized, m_isAllocated, m_usePrescribedThreshold;
bool m_computeFullU, m_computeThinU;
bool m_computeFullV, m_computeThinV;
unsigned int m_computationOptions;
Index m_nonzeroSingularValues, m_rows, m_cols, m_diagSize;
RealScalar m_prescribedThreshold;
template<typename __MatrixType, int _QRPreconditioner, bool _IsComplex>
friend struct internal::svd_precondition_2x2_block_to_be_real;
@ -854,7 +921,7 @@ struct solve_retval<JacobiSVD<_MatrixType, QRPreconditioner>, Rhs>
// So A^{-1} = V S^{-1} U^*
Matrix<Scalar, Dynamic, Rhs::ColsAtCompileTime, 0, _MatrixType::MaxRowsAtCompileTime, Rhs::MaxColsAtCompileTime> tmp;
Index nonzeroSingVals = dec().nonzeroSingularValues();
Index nonzeroSingVals = dec().rank();
tmp.noalias() = dec().matrixU().leftCols(nonzeroSingVals).adjoint() * rhs();
tmp = dec().singularValues().head(nonzeroSingVals).asDiagonal().inverse() * tmp;