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JacobiSVD.h
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// This file is part of Eigen, a lightweight C++ template library
// for linear algebra.
//
// Copyright (C) 2009-2010 Benoit Jacob <jacob.benoit.1@gmail.com>
//
// This Source Code Form is subject to the terms of the Mozilla
// Public License v. 2.0. If a copy of the MPL was not distributed
// with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
#ifndef EIGEN_JACOBISVD_H
#define EIGEN_JACOBISVD_H
namespace Eigen {
namespace internal {
// forward declaration (needed by ICC)
// the empty body is required by MSVC
template<typename MatrixType, int QRPreconditioner,
bool IsComplex = NumTraits<typename MatrixType::Scalar>::IsComplex>
struct svd_precondition_2x2_block_to_be_real {};
/*** QR preconditioners (R-SVD)
***
*** Their role is to reduce the problem of computing the SVD to the case of a square matrix.
*** This approach, known as R-SVD, is an optimization for rectangular-enough matrices, and is a requirement for
*** JacobiSVD which by itself is only able to work on square matrices.
***/
enum { PreconditionIfMoreColsThanRows, PreconditionIfMoreRowsThanCols };
template<typename MatrixType, int QRPreconditioner, int Case>
struct qr_preconditioner_should_do_anything
{
enum { a = MatrixType::RowsAtCompileTime != Dynamic &&
MatrixType::ColsAtCompileTime != Dynamic &&
MatrixType::ColsAtCompileTime <= MatrixType::RowsAtCompileTime,
b = MatrixType::RowsAtCompileTime != Dynamic &&
MatrixType::ColsAtCompileTime != Dynamic &&
MatrixType::RowsAtCompileTime <= MatrixType::ColsAtCompileTime,
ret = !( (QRPreconditioner == NoQRPreconditioner) ||
(Case == PreconditionIfMoreColsThanRows && bool(a)) ||
(Case == PreconditionIfMoreRowsThanCols && bool(b)) )
};
};
template<typename MatrixType, int QRPreconditioner, int Case,
bool DoAnything = qr_preconditioner_should_do_anything<MatrixType, QRPreconditioner, Case>::ret
> struct qr_preconditioner_impl {};
template<typename MatrixType, int QRPreconditioner, int Case>
class qr_preconditioner_impl<MatrixType, QRPreconditioner, Case, false>
{
public:
typedef typename MatrixType::Index Index;
void allocate(const JacobiSVD<MatrixType, QRPreconditioner>&) {}
bool run(JacobiSVD<MatrixType, QRPreconditioner>&, const MatrixType&)
{
return false;
}
};
/*** preconditioner using FullPivHouseholderQR ***/
template<typename MatrixType>
class qr_preconditioner_impl<MatrixType, FullPivHouseholderQRPreconditioner, PreconditionIfMoreRowsThanCols, true>
{
public:
typedef typename MatrixType::Index Index;
typedef typename MatrixType::Scalar Scalar;
enum
{
RowsAtCompileTime = MatrixType::RowsAtCompileTime,
MaxRowsAtCompileTime = MatrixType::MaxRowsAtCompileTime
};
typedef Matrix<Scalar, 1, RowsAtCompileTime, RowMajor, 1, MaxRowsAtCompileTime> WorkspaceType;
void allocate(const JacobiSVD<MatrixType, FullPivHouseholderQRPreconditioner>& svd)
{
if (svd.rows() != m_qr.rows() || svd.cols() != m_qr.cols())
{
m_qr.~QRType();
::new (&m_qr) QRType(svd.rows(), svd.cols());
}
if (svd.m_computeFullU) m_workspace.resize(svd.rows());
}
bool run(JacobiSVD<MatrixType, FullPivHouseholderQRPreconditioner>& svd, const MatrixType& matrix)
{
if(matrix.rows() > matrix.cols())
{
m_qr.compute(matrix);
svd.m_workMatrix = m_qr.matrixQR().block(0,0,matrix.cols(),matrix.cols()).template triangularView<Upper>();
if(svd.m_computeFullU) m_qr.matrixQ().evalTo(svd.m_matrixU, m_workspace);
if(svd.computeV()) svd.m_matrixV = m_qr.colsPermutation();
return true;
}
return false;
}
private:
typedef FullPivHouseholderQR<MatrixType> QRType;
QRType m_qr;
WorkspaceType m_workspace;
};
template<typename MatrixType>
class qr_preconditioner_impl<MatrixType, FullPivHouseholderQRPreconditioner, PreconditionIfMoreColsThanRows, true>
{
public:
typedef typename MatrixType::Index Index;
typedef typename MatrixType::Scalar Scalar;
enum
{
RowsAtCompileTime = MatrixType::RowsAtCompileTime,
ColsAtCompileTime = MatrixType::ColsAtCompileTime,
MaxRowsAtCompileTime = MatrixType::MaxRowsAtCompileTime,
MaxColsAtCompileTime = MatrixType::MaxColsAtCompileTime,
Options = MatrixType::Options
};
typedef Matrix<Scalar, ColsAtCompileTime, RowsAtCompileTime, Options, MaxColsAtCompileTime, MaxRowsAtCompileTime>
TransposeTypeWithSameStorageOrder;
void allocate(const JacobiSVD<MatrixType, FullPivHouseholderQRPreconditioner>& svd)
{
if (svd.cols() != m_qr.rows() || svd.rows() != m_qr.cols())
{
m_qr.~QRType();
::new (&m_qr) QRType(svd.cols(), svd.rows());
}
m_adjoint.resize(svd.cols(), svd.rows());
if (svd.m_computeFullV) m_workspace.resize(svd.cols());
}
bool run(JacobiSVD<MatrixType, FullPivHouseholderQRPreconditioner>& svd, const MatrixType& matrix)
{
if(matrix.cols() > matrix.rows())
{
m_adjoint = matrix.adjoint();
m_qr.compute(m_adjoint);
svd.m_workMatrix = m_qr.matrixQR().block(0,0,matrix.rows(),matrix.rows()).template triangularView<Upper>().adjoint();
if(svd.m_computeFullV) m_qr.matrixQ().evalTo(svd.m_matrixV, m_workspace);
if(svd.computeU()) svd.m_matrixU = m_qr.colsPermutation();
return true;
}
else return false;
}
private:
typedef FullPivHouseholderQR<TransposeTypeWithSameStorageOrder> QRType;
QRType m_qr;
TransposeTypeWithSameStorageOrder m_adjoint;
typename internal::plain_row_type<MatrixType>::type m_workspace;
};
/*** preconditioner using ColPivHouseholderQR ***/
template<typename MatrixType>
class qr_preconditioner_impl<MatrixType, ColPivHouseholderQRPreconditioner, PreconditionIfMoreRowsThanCols, true>
{
public:
typedef typename MatrixType::Index Index;
void allocate(const JacobiSVD<MatrixType, ColPivHouseholderQRPreconditioner>& svd)
{
if (svd.rows() != m_qr.rows() || svd.cols() != m_qr.cols())
{
m_qr.~QRType();
::new (&m_qr) QRType(svd.rows(), svd.cols());
}
if (svd.m_computeFullU) m_workspace.resize(svd.rows());
else if (svd.m_computeThinU) m_workspace.resize(svd.cols());
}
bool run(JacobiSVD<MatrixType, ColPivHouseholderQRPreconditioner>& svd, const MatrixType& matrix)
{
if(matrix.rows() > matrix.cols())
{
m_qr.compute(matrix);
svd.m_workMatrix = m_qr.matrixQR().block(0,0,matrix.cols(),matrix.cols()).template triangularView<Upper>();
if(svd.m_computeFullU) m_qr.householderQ().evalTo(svd.m_matrixU, m_workspace);
else if(svd.m_computeThinU)
{
svd.m_matrixU.setIdentity(matrix.rows(), matrix.cols());
m_qr.householderQ().applyThisOnTheLeft(svd.m_matrixU, m_workspace);
}
if(svd.computeV()) svd.m_matrixV = m_qr.colsPermutation();
return true;
}
return false;
}
private:
typedef ColPivHouseholderQR<MatrixType> QRType;
QRType m_qr;
typename internal::plain_col_type<MatrixType>::type m_workspace;
};
template<typename MatrixType>
class qr_preconditioner_impl<MatrixType, ColPivHouseholderQRPreconditioner, PreconditionIfMoreColsThanRows, true>
{
public:
typedef typename MatrixType::Index Index;
typedef typename MatrixType::Scalar Scalar;
enum
{
RowsAtCompileTime = MatrixType::RowsAtCompileTime,
ColsAtCompileTime = MatrixType::ColsAtCompileTime,
MaxRowsAtCompileTime = MatrixType::MaxRowsAtCompileTime,
MaxColsAtCompileTime = MatrixType::MaxColsAtCompileTime,
Options = MatrixType::Options
};
typedef Matrix<Scalar, ColsAtCompileTime, RowsAtCompileTime, Options, MaxColsAtCompileTime, MaxRowsAtCompileTime>
TransposeTypeWithSameStorageOrder;
void allocate(const JacobiSVD<MatrixType, ColPivHouseholderQRPreconditioner>& svd)
{
if (svd.cols() != m_qr.rows() || svd.rows() != m_qr.cols())
{
m_qr.~QRType();
::new (&m_qr) QRType(svd.cols(), svd.rows());
}
if (svd.m_computeFullV) m_workspace.resize(svd.cols());
else if (svd.m_computeThinV) m_workspace.resize(svd.rows());
m_adjoint.resize(svd.cols(), svd.rows());
}
bool run(JacobiSVD<MatrixType, ColPivHouseholderQRPreconditioner>& svd, const MatrixType& matrix)
{
if(matrix.cols() > matrix.rows())
{
m_adjoint = matrix.adjoint();
m_qr.compute(m_adjoint);
svd.m_workMatrix = m_qr.matrixQR().block(0,0,matrix.rows(),matrix.rows()).template triangularView<Upper>().adjoint();
if(svd.m_computeFullV) m_qr.householderQ().evalTo(svd.m_matrixV, m_workspace);
else if(svd.m_computeThinV)
{
svd.m_matrixV.setIdentity(matrix.cols(), matrix.rows());
m_qr.householderQ().applyThisOnTheLeft(svd.m_matrixV, m_workspace);
}
if(svd.computeU()) svd.m_matrixU = m_qr.colsPermutation();
return true;
}
else return false;
}
private:
typedef ColPivHouseholderQR<TransposeTypeWithSameStorageOrder> QRType;
QRType m_qr;
TransposeTypeWithSameStorageOrder m_adjoint;
typename internal::plain_row_type<MatrixType>::type m_workspace;
};
/*** preconditioner using HouseholderQR ***/
template<typename MatrixType>
class qr_preconditioner_impl<MatrixType, HouseholderQRPreconditioner, PreconditionIfMoreRowsThanCols, true>
{
public:
typedef typename MatrixType::Index Index;
void allocate(const JacobiSVD<MatrixType, HouseholderQRPreconditioner>& svd)
{
if (svd.rows() != m_qr.rows() || svd.cols() != m_qr.cols())
{
m_qr.~QRType();
::new (&m_qr) QRType(svd.rows(), svd.cols());
}
if (svd.m_computeFullU) m_workspace.resize(svd.rows());
else if (svd.m_computeThinU) m_workspace.resize(svd.cols());
}
bool run(JacobiSVD<MatrixType, HouseholderQRPreconditioner>& svd, const MatrixType& matrix)
{
if(matrix.rows() > matrix.cols())
{
m_qr.compute(matrix);
svd.m_workMatrix = m_qr.matrixQR().block(0,0,matrix.cols(),matrix.cols()).template triangularView<Upper>();
if(svd.m_computeFullU) m_qr.householderQ().evalTo(svd.m_matrixU, m_workspace);
else if(svd.m_computeThinU)
{
svd.m_matrixU.setIdentity(matrix.rows(), matrix.cols());
m_qr.householderQ().applyThisOnTheLeft(svd.m_matrixU, m_workspace);
}
if(svd.computeV()) svd.m_matrixV.setIdentity(matrix.cols(), matrix.cols());
return true;
}
return false;
}
private:
typedef HouseholderQR<MatrixType> QRType;
QRType m_qr;
typename internal::plain_col_type<MatrixType>::type m_workspace;
};
template<typename MatrixType>
class qr_preconditioner_impl<MatrixType, HouseholderQRPreconditioner, PreconditionIfMoreColsThanRows, true>
{
public:
typedef typename MatrixType::Index Index;
typedef typename MatrixType::Scalar Scalar;
enum
{
RowsAtCompileTime = MatrixType::RowsAtCompileTime,
ColsAtCompileTime = MatrixType::ColsAtCompileTime,
MaxRowsAtCompileTime = MatrixType::MaxRowsAtCompileTime,
MaxColsAtCompileTime = MatrixType::MaxColsAtCompileTime,
Options = MatrixType::Options
};
typedef Matrix<Scalar, ColsAtCompileTime, RowsAtCompileTime, Options, MaxColsAtCompileTime, MaxRowsAtCompileTime>
TransposeTypeWithSameStorageOrder;
void allocate(const JacobiSVD<MatrixType, HouseholderQRPreconditioner>& svd)
{
if (svd.cols() != m_qr.rows() || svd.rows() != m_qr.cols())
{
m_qr.~QRType();
::new (&m_qr) QRType(svd.cols(), svd.rows());
}
if (svd.m_computeFullV) m_workspace.resize(svd.cols());
else if (svd.m_computeThinV) m_workspace.resize(svd.rows());
m_adjoint.resize(svd.cols(), svd.rows());
}
bool run(JacobiSVD<MatrixType, HouseholderQRPreconditioner>& svd, const MatrixType& matrix)
{
if(matrix.cols() > matrix.rows())
{
m_adjoint = matrix.adjoint();
m_qr.compute(m_adjoint);
svd.m_workMatrix = m_qr.matrixQR().block(0,0,matrix.rows(),matrix.rows()).template triangularView<Upper>().adjoint();
if(svd.m_computeFullV) m_qr.householderQ().evalTo(svd.m_matrixV, m_workspace);
else if(svd.m_computeThinV)
{
svd.m_matrixV.setIdentity(matrix.cols(), matrix.rows());
m_qr.householderQ().applyThisOnTheLeft(svd.m_matrixV, m_workspace);
}
if(svd.computeU()) svd.m_matrixU.setIdentity(matrix.rows(), matrix.rows());
return true;
}
else return false;
}
private:
typedef HouseholderQR<TransposeTypeWithSameStorageOrder> QRType;
QRType m_qr;
TransposeTypeWithSameStorageOrder m_adjoint;
typename internal::plain_row_type<MatrixType>::type m_workspace;
};
/*** 2x2 SVD implementation
***
*** JacobiSVD consists in performing a series of 2x2 SVD subproblems
***/
template<typename MatrixType, int QRPreconditioner>
struct svd_precondition_2x2_block_to_be_real<MatrixType, QRPreconditioner, false>
{
typedef JacobiSVD<MatrixType, QRPreconditioner> SVD;
typedef typename SVD::Index Index;
static void run(typename SVD::WorkMatrixType&, SVD&, Index, Index) {}
};
template<typename MatrixType, int QRPreconditioner>
struct svd_precondition_2x2_block_to_be_real<MatrixType, QRPreconditioner, true>
{
typedef JacobiSVD<MatrixType, QRPreconditioner> SVD;
typedef typename MatrixType::Scalar Scalar;
typedef typename MatrixType::RealScalar RealScalar;
typedef typename SVD::Index Index;
static void run(typename SVD::WorkMatrixType& work_matrix, SVD& svd, Index p, Index q)
{
using std::sqrt;
Scalar z;
JacobiRotation<Scalar> rot;
RealScalar n = sqrt(numext::abs2(work_matrix.coeff(p,p)) + numext::abs2(work_matrix.coeff(q,p)));
if(n==0)
{
z = abs(work_matrix.coeff(p,q)) / work_matrix.coeff(p,q);
work_matrix.row(p) *= z;
if(svd.computeU()) svd.m_matrixU.col(p) *= conj(z);
if(work_matrix.coeff(q,q)!=Scalar(0))
{
z = abs(work_matrix.coeff(q,q)) / work_matrix.coeff(q,q);
work_matrix.row(q) *= z;
if(svd.computeU()) svd.m_matrixU.col(q) *= conj(z);
}
// otherwise the second row is already zero, so we have nothing to do.
}
else
{
rot.c() = conj(work_matrix.coeff(p,p)) / n;
rot.s() = work_matrix.coeff(q,p) / n;
work_matrix.applyOnTheLeft(p,q,rot);
if(svd.computeU()) svd.m_matrixU.applyOnTheRight(p,q,rot.adjoint());
if(work_matrix.coeff(p,q) != Scalar(0))
{
Scalar z = abs(work_matrix.coeff(p,q)) / work_matrix.coeff(p,q);
work_matrix.col(q) *= z;
if(svd.computeV()) svd.m_matrixV.col(q) *= z;
}
if(work_matrix.coeff(q,q) != Scalar(0))
{
z = abs(work_matrix.coeff(q,q)) / work_matrix.coeff(q,q);
work_matrix.row(q) *= z;
if(svd.computeU()) svd.m_matrixU.col(q) *= conj(z);
}
}
}
};
template<typename MatrixType, typename RealScalar, typename Index>
void real_2x2_jacobi_svd(const MatrixType& matrix, Index p, Index q,
JacobiRotation<RealScalar> *j_left,
JacobiRotation<RealScalar> *j_right)
{
using std::sqrt;
using std::abs;
Matrix<RealScalar,2,2> m;
m << numext::real(matrix.coeff(p,p)), numext::real(matrix.coeff(p,q)),
numext::real(matrix.coeff(q,p)), numext::real(matrix.coeff(q,q));
JacobiRotation<RealScalar> rot1;
RealScalar t = m.coeff(0,0) + m.coeff(1,1);
RealScalar d = m.coeff(1,0) - m.coeff(0,1);
if(t == RealScalar(0))
{
rot1.c() = RealScalar(0);
rot1.s() = d > RealScalar(0) ? RealScalar(1) : RealScalar(-1);
}
else
{
RealScalar t2d2 = numext::hypot(t,d);
rot1.c() = abs(t)/t2d2;
rot1.s() = d/t2d2;
if(t<RealScalar(0))
rot1.s() = -rot1.s();
}
m.applyOnTheLeft(0,1,rot1);
j_right->makeJacobi(m,0,1);
*j_left = rot1 * j_right->transpose();
}
} // end namespace internal
/** \ingroup SVD_Module
*
*
* \class JacobiSVD
*
* \brief Two-sided Jacobi SVD decomposition of a rectangular matrix
*
* \param MatrixType the type of the matrix of which we are computing the SVD decomposition
* \param QRPreconditioner this optional parameter allows to specify the type of QR decomposition that will be used internally
* for the R-SVD step for non-square matrices. See discussion of possible values below.
*
* SVD decomposition consists in decomposing any n-by-p matrix \a A as a product
* \f[ A = U S V^* \f]
* where \a U is a n-by-n unitary, \a V is a p-by-p unitary, and \a S is a n-by-p real positive matrix which is zero outside of its main diagonal;
* the diagonal entries of S are known as the \em singular \em values of \a A and the columns of \a U and \a V are known as the left
* and right \em singular \em vectors of \a A respectively.
*
* Singular values are always sorted in decreasing order.
*
* This JacobiSVD decomposition computes only the singular values by default. If you want \a U or \a V, you need to ask for them explicitly.
*
* You can ask for only \em thin \a U or \a V to be computed, meaning the following. In case of a rectangular n-by-p matrix, letting \a m be the
* smaller value among \a n and \a p, there are only \a m singular vectors; the remaining columns of \a U and \a V do not correspond to actual
* singular vectors. Asking for \em thin \a U or \a V means asking for only their \a m first columns to be formed. So \a U is then a n-by-m matrix,
* and \a V is then a p-by-m matrix. Notice that thin \a U and \a V are all you need for (least squares) solving.
*
* Here's an example demonstrating basic usage:
* \include JacobiSVD_basic.cpp
* Output: \verbinclude JacobiSVD_basic.out
*
* This JacobiSVD class is a two-sided Jacobi R-SVD decomposition, ensuring optimal reliability and accuracy. The downside is that it's slower than
* bidiagonalizing SVD algorithms for large square matrices; however its complexity is still \f$ O(n^2p) \f$ where \a n is the smaller dimension and
* \a p is the greater dimension, meaning that it is still of the same order of complexity as the faster bidiagonalizing R-SVD algorithms.
* In particular, like any R-SVD, it takes advantage of non-squareness in that its complexity is only linear in the greater dimension.
*
* If the input matrix has inf or nan coefficients, the result of the computation is undefined, but the computation is guaranteed to
* terminate in finite (and reasonable) time.
*
* The possible values for QRPreconditioner are:
* \li ColPivHouseholderQRPreconditioner is the default. In practice it's very safe. It uses column-pivoting QR.
* \li FullPivHouseholderQRPreconditioner, is the safest and slowest. It uses full-pivoting QR.
* Contrary to other QRs, it doesn't allow computing thin unitaries.
* \li HouseholderQRPreconditioner is the fastest, and less safe and accurate than the pivoting variants. It uses non-pivoting QR.
* This is very similar in safety and accuracy to the bidiagonalization process used by bidiagonalizing SVD algorithms (since bidiagonalization
* is inherently non-pivoting). However the resulting SVD is still more reliable than bidiagonalizing SVDs because the Jacobi-based iterarive
* process is more reliable than the optimized bidiagonal SVD iterations.
* \li NoQRPreconditioner allows not to use a QR preconditioner at all. This is useful if you know that you will only be computing
* JacobiSVD decompositions of square matrices. Non-square matrices require a QR preconditioner. Using this option will result in
* faster compilation and smaller executable code. It won't significantly speed up computation, since JacobiSVD is always checking
* if QR preconditioning is needed before applying it anyway.
*
* \sa MatrixBase::jacobiSvd()
*/
template<typename _MatrixType, int QRPreconditioner> class JacobiSVD
{
public:
typedef _MatrixType MatrixType;
typedef typename MatrixType::Scalar Scalar;
typedef typename NumTraits<typename MatrixType::Scalar>::Real RealScalar;
typedef typename MatrixType::Index Index;
enum {
RowsAtCompileTime = MatrixType::RowsAtCompileTime,
ColsAtCompileTime = MatrixType::ColsAtCompileTime,
DiagSizeAtCompileTime = EIGEN_SIZE_MIN_PREFER_DYNAMIC(RowsAtCompileTime,ColsAtCompileTime),
MaxRowsAtCompileTime = MatrixType::MaxRowsAtCompileTime,
MaxColsAtCompileTime = MatrixType::MaxColsAtCompileTime,
MaxDiagSizeAtCompileTime = EIGEN_SIZE_MIN_PREFER_FIXED(MaxRowsAtCompileTime,MaxColsAtCompileTime),
MatrixOptions = MatrixType::Options
};
typedef Matrix<Scalar, RowsAtCompileTime, RowsAtCompileTime,
MatrixOptions, MaxRowsAtCompileTime, MaxRowsAtCompileTime>
MatrixUType;
typedef Matrix<Scalar, ColsAtCompileTime, ColsAtCompileTime,
MatrixOptions, MaxColsAtCompileTime, MaxColsAtCompileTime>
MatrixVType;
typedef typename internal::plain_diag_type<MatrixType, RealScalar>::type SingularValuesType;
typedef typename internal::plain_row_type<MatrixType>::type RowType;
typedef typename internal::plain_col_type<MatrixType>::type ColType;
typedef Matrix<Scalar, DiagSizeAtCompileTime, DiagSizeAtCompileTime,
MatrixOptions, MaxDiagSizeAtCompileTime, MaxDiagSizeAtCompileTime>
WorkMatrixType;
/** \brief Default Constructor.
*
* The default constructor is useful in cases in which the user intends to
* perform decompositions via JacobiSVD::compute(const MatrixType&).
*/
JacobiSVD()
: m_isInitialized(false),
m_isAllocated(false),
m_usePrescribedThreshold(false),
m_computationOptions(0),
m_rows(-1), m_cols(-1), m_diagSize(0)
{}
/** \brief Default Constructor with memory preallocation
*
* Like the default constructor but with preallocation of the internal data
* according to the specified problem size.
* \sa 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)
{
allocate(rows, cols, computationOptions);
}
/** \brief Constructor performing the decomposition of given matrix.
*
* \param matrix the matrix to decompose
* \param computationOptions optional parameter allowing to specify if you want full or thin U or V unitaries to be computed.
* By default, none is computed. This is a bit-field, the possible bits are #ComputeFullU, #ComputeThinU,
* #ComputeFullV, #ComputeThinV.
*
* Thin unitaries are only available if your matrix type has a Dynamic number of columns (for example MatrixXf). They also are not
* available with the (non-default) FullPivHouseholderQR preconditioner.
*/
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)
{
compute(matrix, computationOptions);
}
/** \brief Method performing the decomposition of given matrix using custom options.
*
* \param matrix the matrix to decompose
* \param computationOptions optional parameter allowing to specify if you want full or thin U or V unitaries to be computed.
* By default, none is computed. This is a bit-field, the possible bits are #ComputeFullU, #ComputeThinU,
* #ComputeFullV, #ComputeThinV.
*
* Thin unitaries are only available if your matrix type has a Dynamic number of columns (for example MatrixXf). They also are not
* available with the (non-default) FullPivHouseholderQR preconditioner.
*/
JacobiSVD& compute(const MatrixType& matrix, unsigned int computationOptions);
/** \brief Method performing the decomposition of given matrix using current options.
*
* \param matrix the matrix to decompose
*
* This method uses the current \a computationOptions, as already passed to the constructor or to compute(const MatrixType&, unsigned int).
*/
JacobiSVD& compute(const MatrixType& matrix)
{
return compute(matrix, m_computationOptions);
}
/** \returns the \a U matrix.
*
* For the SVD decomposition of a n-by-p matrix, letting \a m be the minimum of \a n and \a p,
* the U matrix is n-by-n if you asked for #ComputeFullU, and is n-by-m if you asked for #ComputeThinU.
*
* The \a m first columns of \a U are the left singular vectors of the matrix being decomposed.
*
* This method asserts that you asked for \a U to be computed.
*/
const MatrixUType& matrixU() const
{
eigen_assert(m_isInitialized && "JacobiSVD is not initialized.");
eigen_assert(computeU() && "This JacobiSVD decomposition didn't compute U. Did you ask for it?");
return m_matrixU;
}
/** \returns the \a V matrix.
*
* For the SVD decomposition of a n-by-p matrix, letting \a m be the minimum of \a n and \a p,
* the V matrix is p-by-p if you asked for #ComputeFullV, and is p-by-m if you asked for ComputeThinV.
*
* The \a m first columns of \a V are the right singular vectors of the matrix being decomposed.
*
* This method asserts that you asked for \a V to be computed.
*/
const MatrixVType& matrixV() const
{
eigen_assert(m_isInitialized && "JacobiSVD is not initialized.");
eigen_assert(computeV() && "This JacobiSVD decomposition didn't compute V. Did you ask for it?");
return m_matrixV;
}
/** \returns the vector of singular values.
*
* For the SVD decomposition of a n-by-p matrix, letting \a m be the minimum of \a n and \a p, the
* returned vector has size \a m. Singular values are always sorted in decreasing order.
*/
const SingularValuesType& singularValues() const
{
eigen_assert(m_isInitialized && "JacobiSVD is not initialized.");
return m_singularValues;
}
/** \returns true if \a U (full or thin) is asked for in this SVD decomposition */
inline bool computeU() const { return m_computeFullU || m_computeThinU; }
/** \returns true if \a V (full or thin) is asked for in this SVD decomposition */
inline bool computeV() const { return m_computeFullV || m_computeThinV; }
/** \returns a (least squares) solution of \f$ A x = b \f$ using the current SVD decomposition of A.
*
* \param b the right-hand-side of the equation to solve.
*
* \note Solving requires both U and V to be computed. Thin U and V are enough, there is no need for full U or V.
*
* \note SVD solving is implicitly least-squares. Thus, this method serves both purposes of exact solving and least-squares solving.
* In other words, the returned solution is guaranteed to minimize the Euclidean norm \f$ \Vert A x - b \Vert \f$.
*/
template<typename Rhs>
inline const internal::solve_retval<JacobiSVD, Rhs>
solve(const MatrixBase<Rhs>& b) const
{
eigen_assert(m_isInitialized && "JacobiSVD is not initialized.");
eigen_assert(computeU() && computeV() && "JacobiSVD::solve() requires both unitaries U and V to be computed (thin unitaries suffice).");
return internal::solve_retval<JacobiSVD, Rhs>(*this, b.derived());
}
/** \returns the number of singular values that are not exactly 0 */
Index nonzeroSingularValues() const
{
eigen_assert(m_isInitialized && "JacobiSVD is not initialized.");
return m_nonzeroSingularValues;
}
/** \returns the rank of the matrix of which \c *this is the SVD.
*
* \note This method has to determine which singular values should be considered nonzero.
* For that, it uses the threshold value that you can control by calling
* setThreshold(const RealScalar&).
*/
inline Index rank() const
{
using std::abs;
eigen_assert(m_isInitialized && "JacobiSVD is not initialized.");
if(m_singularValues.size()==0) return 0;
RealScalar premultiplied_threshold = m_singularValues.coeff(0) * threshold();
Index i = m_nonzeroSingularValues-1;
while(i>=0 && m_singularValues.coeff(i) < premultiplied_threshold) --i;
return i+1;
}
/** Allows to prescribe a threshold to be used by certain methods, such as rank() and solve(),
* which need to determine when singular values are to be considered nonzero.
* This is not used for the SVD decomposition itself.
*
* When it needs to get the threshold value, Eigen calls threshold().
* The default is \c NumTraits<Scalar>::epsilon()
*
* \param threshold The new value to use as the threshold.
*
* A singular value will be considered nonzero if its value is strictly greater than
* \f$ \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
: (std::max<Index>)(1,m_diagSize)*NumTraits<Scalar>::epsilon();
}
inline Index rows() const { return m_rows; }
inline Index cols() const { return m_cols; }
private:
void allocate(Index rows, Index cols, unsigned int computationOptions);
static void check_template_parameters()
{
EIGEN_STATIC_ASSERT_NON_INTEGER(Scalar);
}
protected:
MatrixUType m_matrixU;
MatrixVType m_matrixV;
SingularValuesType m_singularValues;
WorkMatrixType m_workMatrix;
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;
template<typename __MatrixType, int _QRPreconditioner, int _Case, bool _DoAnything>
friend struct internal::qr_preconditioner_impl;
internal::qr_preconditioner_impl<MatrixType, QRPreconditioner, internal::PreconditionIfMoreColsThanRows> m_qr_precond_morecols;
internal::qr_preconditioner_impl<MatrixType, QRPreconditioner, internal::PreconditionIfMoreRowsThanCols> m_qr_precond_morerows;
MatrixType m_scaledMatrix;
};
template<typename MatrixType, int QRPreconditioner>
void JacobiSVD<MatrixType, QRPreconditioner>::allocate(Index rows, Index cols, unsigned int computationOptions)
{
eigen_assert(rows >= 0 && cols >= 0);
if (m_isAllocated &&
rows == m_rows &&
cols == m_cols &&
computationOptions == m_computationOptions)
{
return;
}
m_rows = rows;
m_cols = cols;
m_isInitialized = false;
m_isAllocated = true;
m_computationOptions = computationOptions;
m_computeFullU = (computationOptions & ComputeFullU) != 0;
m_computeThinU = (computationOptions & ComputeThinU) != 0;
m_computeFullV = (computationOptions & ComputeFullV) != 0;
m_computeThinV = (computationOptions & ComputeThinV) != 0;
eigen_assert(!(m_computeFullU && m_computeThinU) && "JacobiSVD: you can't ask for both full and thin U");
eigen_assert(!(m_computeFullV && m_computeThinV) && "JacobiSVD: you can't ask for both full and thin V");
eigen_assert(EIGEN_IMPLIES(m_computeThinU || m_computeThinV, MatrixType::ColsAtCompileTime==Dynamic) &&
"JacobiSVD: thin U and V are only available when your matrix has a dynamic number of columns.");
if (QRPreconditioner == FullPivHouseholderQRPreconditioner)
{
eigen_assert(!(m_computeThinU || m_computeThinV) &&
"JacobiSVD: can't compute thin U or thin V with the FullPivHouseholderQR preconditioner. "
"Use the ColPivHouseholderQR preconditioner instead.");
}
m_diagSize = (std::min)(m_rows, m_cols);
m_singularValues.resize(m_diagSize);
if(RowsAtCompileTime==Dynamic)
m_matrixU.resize(m_rows, m_computeFullU ? m_rows
: m_computeThinU ? m_diagSize
: 0);
if(ColsAtCompileTime==Dynamic)
m_matrixV.resize(m_cols, m_computeFullV ? m_cols
: m_computeThinV ? m_diagSize
: 0);
m_workMatrix.resize(m_diagSize, m_diagSize);
if(m_cols>m_rows) m_qr_precond_morecols.allocate(*this);
if(m_rows>m_cols) m_qr_precond_morerows.allocate(*this);
if(m_rows!=m_cols) m_scaledMatrix.resize(rows,cols);
}
template<typename MatrixType, int QRPreconditioner>
JacobiSVD<MatrixType, QRPreconditioner>&
JacobiSVD<MatrixType, QRPreconditioner>::compute(const MatrixType& matrix, unsigned int computationOptions)
{
check_template_parameters();
using std::abs;
allocate(matrix.rows(), matrix.cols(), computationOptions);
// currently we stop when we reach precision 2*epsilon as the last bit of precision can require an unreasonable number of iterations,
// only worsening the precision of U and V as we accumulate more rotations
const RealScalar precision = RealScalar(2) * NumTraits<Scalar>::epsilon();
// limit for very small denormal numbers to be considered zero in order to avoid infinite loops (see bug 286)
const RealScalar considerAsZero = RealScalar(2) * std::numeric_limits<RealScalar>::denorm_min();
// Scaling factor to reduce over/under-flows
RealScalar scale = matrix.cwiseAbs().maxCoeff();
if(scale==RealScalar(0)) scale = RealScalar(1);
/*** step 1. The R-SVD step: we use a QR decomposition to reduce to the case of a square matrix */
if(m_rows!=m_cols)
{
m_scaledMatrix = matrix / scale;
m_qr_precond_morecols.run(*this, m_scaledMatrix);
m_qr_precond_morerows.run(*this, m_scaledMatrix);
}
else
{
m_workMatrix = matrix.block(0,0,m_diagSize,m_diagSize) / scale;
if(m_computeFullU) m_matrixU.setIdentity(m_rows,m_rows);
if(m_computeThinU) m_matrixU.setIdentity(m_rows,m_diagSize);
if(m_computeFullV) m_matrixV.setIdentity(m_cols,m_cols);
if(m_computeThinV) m_matrixV.setIdentity(m_cols, m_diagSize);
}
/*** step 2. The main Jacobi SVD iteration. ***/
bool finished = false;
while(!finished)
{
finished = true;
// do a sweep: for all index pairs (p,q), perform SVD of the corresponding 2x2 sub-matrix
for(Index p = 1; p < m_diagSize; ++p)
{
for(Index q = 0; q < p; ++q)
{
// if this 2x2 sub-matrix is not diagonal already...
// notice that this comparison will evaluate to false if any NaN is involved, ensuring that NaN's don't
// keep us iterating forever. Similarly, small denormal numbers are considered zero.
using std::max;
RealScalar threshold = (max)(considerAsZero, precision * (max)(abs(m_workMatrix.coeff(p,p)),
abs(m_workMatrix.coeff(q,q))));
// We compare both values to threshold instead of calling max to be robust to NaN (See bug 791)
if(abs(m_workMatrix.coeff(p,q))>threshold || abs(m_workMatrix.coeff(q,p)) > threshold)
{
finished = false;
// perform SVD decomposition of 2x2 sub-matrix corresponding to indices p,q to make it diagonal
internal::svd_precondition_2x2_block_to_be_real<MatrixType, QRPreconditioner>::run(m_workMatrix, *this, p, q);
JacobiRotation<RealScalar> j_left, j_right;
internal::real_2x2_jacobi_svd(m_workMatrix, p, q, &j_left, &j_right);
// accumulate resulting Jacobi rotations
m_workMatrix.applyOnTheLeft(p,q,j_left);
if(computeU()) m_matrixU.applyOnTheRight(p,q,j_left.transpose());
m_workMatrix.applyOnTheRight(p,q,j_right);
if(computeV()) m_matrixV.applyOnTheRight(p,q,j_right);
}
}
}
}
/*** step 3. The work matrix is now diagonal, so ensure it's positive so its diagonal entries are the singular values ***/
for(Index i = 0; i < m_diagSize; ++i)
{
RealScalar a = abs(m_workMatrix.coeff(i,i));
m_singularValues.coeffRef(i) = a;
if(computeU() && (a!=RealScalar(0))) m_matrixU.col(i) *= m_workMatrix.coeff(i,i)/a;
}
/*** step 4. Sort singular values in descending order and compute the number of nonzero singular values ***/
m_nonzeroSingularValues = m_diagSize;
for(Index i = 0; i < m_diagSize; i++)
{
Index pos;
RealScalar maxRemainingSingularValue = m_singularValues.tail(m_diagSize-i).maxCoeff(&pos);
if(maxRemainingSingularValue == RealScalar(0))
{
m_nonzeroSingularValues = i;
break;
}
if(pos)
{
pos += i;
std::swap(m_singularValues.coeffRef(i), m_singularValues.coeffRef(pos));
if(computeU()) m_matrixU.col(pos).swap(m_matrixU.col(i));
if(computeV()) m_matrixV.col(pos).swap(m_matrixV.col(i));
}
}
m_singularValues *= scale;
m_isInitialized = true;
return *this;
}
namespace internal {
template<typename _MatrixType, int QRPreconditioner, typename Rhs>
struct solve_retval<JacobiSVD<_MatrixType, QRPreconditioner>, Rhs>
: solve_retval_base<JacobiSVD<_MatrixType, QRPreconditioner>, Rhs>
{
typedef JacobiSVD<_MatrixType, QRPreconditioner> JacobiSVDType;
EIGEN_MAKE_SOLVE_HELPERS(JacobiSVDType,Rhs)
template<typename Dest> void evalTo(Dest& dst) const
{
eigen_assert(rhs().rows() == dec().rows());
// A = U S V^*
// So A^{-1} = V S^{-1} U^*
Matrix<Scalar, Dynamic, Rhs::ColsAtCompileTime, 0, _MatrixType::MaxRowsAtCompileTime, Rhs::MaxColsAtCompileTime> tmp;
Index rank = dec().rank();
tmp.noalias() = dec().matrixU().leftCols(rank).adjoint() * rhs();
tmp = dec().singularValues().head(rank).asDiagonal().inverse() * tmp;
dst = dec().matrixV().leftCols(rank) * tmp;
}
};
} // end namespace internal
/** \svd_module
*
* \return the singular value decomposition of \c *this computed by two-sided
* Jacobi transformations.
*
* \sa class JacobiSVD
*/
template<typename Derived>
JacobiSVD<typename MatrixBase<Derived>::PlainObject>
MatrixBase<Derived>::jacobiSvd(unsigned int computationOptions) const
{
return JacobiSVD<PlainObject>(*this, computationOptions);
}
} // end namespace Eigen
#endif // EIGEN_JACOBISVD_H

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