Re: [eigen] 3.0.1 released!

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Hi,
 
The later includes exceptions safety and the automatic uses of the
math functions declared in the scalar type's namespace.

Eigen 3.0.0 called math function(s) from std namespace (e.g. std::ceil ) with RealScalar as a parameter -  which wasn't right for custom scalars.
I was going to report this bug today, but 3.0.1 already fixed this - thank you so much!!

I'm testing Eigen step-by-step regarding arbitrary precision support - I'll let you know if something will come up. 

There are other question I want to discuss:

I.
I needed (Moore-Penrose) pseudo inverse lately.. There are two versions available:
http://eigen.tuxfamily.org/index.php?title=FAQ#Is_there_a_method_to_compute_the_.28Moore-Penrose.29_pseudo_inverse_.3F 
http://listengine.tuxfamily.org/lists.tuxfamily.org/eigen/2010/01/msg00187.html

Both of them seems little outdated/flawed, (first doesn't support custom scalar types, second doesn't work with Eigen 3.x and both are not optimized) .  

To cure the situation I've added two functions to JacobiSVD class:

MatrixType pinverse(const RealScalar& tolerance) const; // use user-defined tolerance
MatrixType pinverse() const; // use default tolerance

Please see modified JacobiSVD.h in attach, whether this  pinverse() worth to be added in Eigen.

II.
I see there is some work was done on porting LAPACK routines on Eigen natively (not just linking to Fortran binaries), e.g. getrf (\lapack\lu.cpp).

Although this is huge chunk of work it is the only decent way for porting LAPACK to C++ - to be implemented in Eigen natively, benefiting from its generic architecture, expressiveness, etc.

Besides I am sure this is the only and correct way to enable LAPACK with multi-precision. 

I'm very interested in this direction of development, to say the least.

Are there any plans/priorities in this direction?

III.
Just quick question - maybe I'm missing something.
Is there any way to select matrix coefficients using custom binary operation as a criterion?

For example, to find sum of all elements greater than tolerance:

(m > tolerance).sum();

or choose elements based on arbitrary custom rule (proxy)

(m.choose(rule))

where rule can be an unary function which accepts one coefficient at a time, returning true/false (choose/not choose).
E.g. to select coefficients with sin > 0.5:

rule(x)
{
 if sin(x)> 0.5 return true; else return false;
}

IV.
Could you update URL of  MPFR C++ to http://www.holoborodko.com/pavel/mpfr/  in "unsupported/Eigen/MPRealSupport"?
I've changed numerical URLs on my site to be more meaningful. 

*****
I've been working with and studying Eigen for a few months. I must say this is absolutely the best C++ library I've ever saw. 
Both in design and masterful implementation. I really enjoy working with.
Thank you.

Pavel Holoborodko
http://www.holoborodko.com

On Mon, May 30, 2011 at 10:43 PM, Gael Guennebaud <gael.guennebaud@xxxxxxxxx> wrote:
Hi,

Eigen 3.0.1 is released!

The source archive is at:
http://bitbucket.org/eigen/eigen/get/3.0.1.tar.bz2

In addition to various minor bug fixes, this release brings official
support for gcc 4.6 and ARM NEON as well as an improved support for
custom scalar types.
The later includes exceptions safety and the automatic uses of the
math functions declared in the scalar type's namespace.
The support for ARM NEON has been possible thanks to the GCC Compile
Farm Project.

Complete changelog:
http://eigen.tuxfamily.org/index.php?title=ChangeLog#Eigen_3.0.1

gael



// This file is part of Eigen, a lightweight C++ template library
// for linear algebra.
//
// Copyright (C) 2009-2010 Benoit Jacob <jacob.benoit.1@xxxxxxxxx>
//
// Eigen is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 3 of the License, or (at your option) any later version.
//
// Alternatively, you can redistribute it and/or
// modify it under the terms of the GNU General Public License as
// published by the Free Software Foundation; either version 2 of
// the License, or (at your option) any later version.
//
// Eigen is distributed in the hope that it will be useful, but WITHOUT ANY
// WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
// FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License or the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License and a copy of the GNU General Public License along with
// Eigen. If not, see <http://www.gnu.org/licenses/>.

#ifndef EIGEN_JACOBISVD_H
#define EIGEN_JACOBISVD_H

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>
struct qr_preconditioner_impl<MatrixType, QRPreconditioner, Case, false>
{
  static bool run(JacobiSVD<MatrixType, QRPreconditioner>&, const MatrixType&)
  {
    return false;
  }
};

/*** preconditioner using FullPivHouseholderQR ***/

template<typename MatrixType>
struct qr_preconditioner_impl<MatrixType, FullPivHouseholderQRPreconditioner, PreconditionIfMoreRowsThanCols, true>
{
  static bool run(JacobiSVD<MatrixType, FullPivHouseholderQRPreconditioner>& svd, const MatrixType& matrix)
  {
    if(matrix.rows() > matrix.cols())
    {
      FullPivHouseholderQR<MatrixType> qr(matrix);
      svd.m_workMatrix = qr.matrixQR().block(0,0,matrix.cols(),matrix.cols()).template triangularView<Upper>();
      if(svd.m_computeFullU) svd.m_matrixU = qr.matrixQ();
      if(svd.computeV()) svd.m_matrixV = qr.colsPermutation();
      return true;
    }
    return false;
  }
};

template<typename MatrixType>
struct qr_preconditioner_impl<MatrixType, FullPivHouseholderQRPreconditioner, PreconditionIfMoreColsThanRows, true>
{
  static bool run(JacobiSVD<MatrixType, FullPivHouseholderQRPreconditioner>& svd, const MatrixType& matrix)
  {
    if(matrix.cols() > matrix.rows())
    {
      typedef Matrix<typename MatrixType::Scalar, MatrixType::ColsAtCompileTime, MatrixType::RowsAtCompileTime,
                     MatrixType::Options, MatrixType::MaxColsAtCompileTime, MatrixType::MaxRowsAtCompileTime>
              TransposeTypeWithSameStorageOrder;
      FullPivHouseholderQR<TransposeTypeWithSameStorageOrder> qr(matrix.adjoint());
      svd.m_workMatrix = qr.matrixQR().block(0,0,matrix.rows(),matrix.rows()).template triangularView<Upper>().adjoint();
      if(svd.m_computeFullV) svd.m_matrixV = qr.matrixQ();
      if(svd.computeU()) svd.m_matrixU = qr.colsPermutation();
      return true;
    }
    else return false;
  }
};

/*** preconditioner using ColPivHouseholderQR ***/

template<typename MatrixType>
struct qr_preconditioner_impl<MatrixType, ColPivHouseholderQRPreconditioner, PreconditionIfMoreRowsThanCols, true>
{
  static bool run(JacobiSVD<MatrixType, ColPivHouseholderQRPreconditioner>& svd, const MatrixType& matrix)
  {
    if(matrix.rows() > matrix.cols())
    {
      ColPivHouseholderQR<MatrixType> qr(matrix);
      svd.m_workMatrix = qr.matrixQR().block(0,0,matrix.cols(),matrix.cols()).template triangularView<Upper>();
      if(svd.m_computeFullU) svd.m_matrixU = qr.householderQ();
      else if(svd.m_computeThinU) {
        svd.m_matrixU.setIdentity(matrix.rows(), matrix.cols());
        qr.householderQ().applyThisOnTheLeft(svd.m_matrixU);
      }
      if(svd.computeV()) svd.m_matrixV = qr.colsPermutation();
      return true;
    }
    return false;
  }
};

template<typename MatrixType>
struct qr_preconditioner_impl<MatrixType, ColPivHouseholderQRPreconditioner, PreconditionIfMoreColsThanRows, true>
{
  static bool run(JacobiSVD<MatrixType, ColPivHouseholderQRPreconditioner>& svd, const MatrixType& matrix)
  {
    if(matrix.cols() > matrix.rows())
    {
      typedef Matrix<typename MatrixType::Scalar, MatrixType::ColsAtCompileTime, MatrixType::RowsAtCompileTime,
                     MatrixType::Options, MatrixType::MaxColsAtCompileTime, MatrixType::MaxRowsAtCompileTime>
              TransposeTypeWithSameStorageOrder;
      ColPivHouseholderQR<TransposeTypeWithSameStorageOrder> qr(matrix.adjoint());
      svd.m_workMatrix = qr.matrixQR().block(0,0,matrix.rows(),matrix.rows()).template triangularView<Upper>().adjoint();
      if(svd.m_computeFullV) svd.m_matrixV = qr.householderQ();
      else if(svd.m_computeThinV) {
        svd.m_matrixV.setIdentity(matrix.cols(), matrix.rows());
        qr.householderQ().applyThisOnTheLeft(svd.m_matrixV);
      }
      if(svd.computeU()) svd.m_matrixU = qr.colsPermutation();
      return true;
    }
    else return false;
  }
};

/*** preconditioner using HouseholderQR ***/

template<typename MatrixType>
struct qr_preconditioner_impl<MatrixType, HouseholderQRPreconditioner, PreconditionIfMoreRowsThanCols, true>
{
  static bool run(JacobiSVD<MatrixType, HouseholderQRPreconditioner>& svd, const MatrixType& matrix)
  {
    if(matrix.rows() > matrix.cols())
    {
      HouseholderQR<MatrixType> qr(matrix);
      svd.m_workMatrix = qr.matrixQR().block(0,0,matrix.cols(),matrix.cols()).template triangularView<Upper>();
      if(svd.m_computeFullU) svd.m_matrixU = qr.householderQ();
      else if(svd.m_computeThinU) {
        svd.m_matrixU.setIdentity(matrix.rows(), matrix.cols());
        qr.householderQ().applyThisOnTheLeft(svd.m_matrixU);
      }
      if(svd.computeV()) svd.m_matrixV.setIdentity(matrix.cols(), matrix.cols());
      return true;
    }
    return false;
  }
};

template<typename MatrixType>
struct qr_preconditioner_impl<MatrixType, HouseholderQRPreconditioner, PreconditionIfMoreColsThanRows, true>
{
  static bool run(JacobiSVD<MatrixType, HouseholderQRPreconditioner>& svd, const MatrixType& matrix)
  {
    if(matrix.cols() > matrix.rows())
    {
      typedef Matrix<typename MatrixType::Scalar, MatrixType::ColsAtCompileTime, MatrixType::RowsAtCompileTime,
                     MatrixType::Options, MatrixType::MaxColsAtCompileTime, MatrixType::MaxRowsAtCompileTime>
              TransposeTypeWithSameStorageOrder;
      HouseholderQR<TransposeTypeWithSameStorageOrder> qr(matrix.adjoint());
      svd.m_workMatrix = qr.matrixQR().block(0,0,matrix.rows(),matrix.rows()).template triangularView<Upper>().adjoint();
      if(svd.m_computeFullV) svd.m_matrixV = qr.householderQ();
      else if(svd.m_computeThinV) {
        svd.m_matrixV.setIdentity(matrix.cols(), matrix.rows());
        qr.householderQ().applyThisOnTheLeft(svd.m_matrixV);
      }
      if(svd.computeU()) svd.m_matrixU.setIdentity(matrix.rows(), matrix.rows());
      return true;
    }
    else return false;
  }
};

/*** 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)
  {
    Scalar z;
    JacobiRotation<Scalar> rot;
    RealScalar n = sqrt(abs2(work_matrix.coeff(p,p)) + 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);
      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);
    }
    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)
{
  Matrix<RealScalar,2,2> m;
  m << real(matrix.coeff(p,p)), real(matrix.coeff(p,q)),
       real(matrix.coeff(q,p)), 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 u = d / t;
    rot1.c() = RealScalar(1) / sqrt(RealScalar(1) + abs2(u));
    rot1.s() = rot1.c() * u;
  }
  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_computationOptions(0),
        m_rows(-1), m_cols(-1)
    {}


    /** \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_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_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 Moore?Penrose pseudoinverse of the matrix of which *this is the SVD decomposition.
      *
	  * \note  A^{+} = V S^{+} U^*. 
      * \param tolerance is used for pseudoinversion of S, S(i) = {1/S(i), if |S(i)| > tolerance; 0 otherwise} 
      */
	MatrixType pinverse(const RealScalar& tolerance) const;
	
    /** \returns Moore?Penrose pseudoinverse of the matrix of which *this is the SVD decomposition.
      *
	  * \note  A^{+} = V S^{+} U^*. Tolerance for S^{+} is taken to be t = machine_epsilon*max(rows(),cols())*max(abs(S)).
      */
	MatrixType pinverse() const;

    /** \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;
    }

    inline Index rows() const { return m_rows; }
    inline Index cols() const { return m_cols; }

  private:
    void allocate(Index rows, Index cols, unsigned int computationOptions);

  protected:
    MatrixUType m_matrixU;
    MatrixVType m_matrixV;
    SingularValuesType m_singularValues;
    WorkMatrixType m_workMatrix;
    bool m_isInitialized, m_isAllocated;
    bool m_computeFullU, m_computeThinU;
    bool m_computeFullV, m_computeThinV;
    unsigned int m_computationOptions;
    Index m_nonzeroSingularValues, m_rows, m_cols, m_diagSize;

    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;
};

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);
  m_matrixU.resize(m_rows, m_computeFullU ? m_rows
                          : m_computeThinU ? m_diagSize
                          : 0);
  m_matrixV.resize(m_cols, m_computeFullV ? m_cols
                          : m_computeThinV ? m_diagSize
                          : 0);
  m_workMatrix.resize(m_diagSize, m_diagSize);
}

template<typename MatrixType, int QRPreconditioner>
JacobiSVD<MatrixType, QRPreconditioner>&
JacobiSVD<MatrixType, QRPreconditioner>::compute(const MatrixType& matrix, unsigned int computationOptions)
{
  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();

  /*** step 1. The R-SVD step: we use a QR decomposition to reduce to the case of a square matrix */

  if(!internal::qr_preconditioner_impl<MatrixType, QRPreconditioner, internal::PreconditionIfMoreColsThanRows>::run(*this, matrix)
  && !internal::qr_preconditioner_impl<MatrixType, QRPreconditioner, internal::PreconditionIfMoreRowsThanCols>::run(*this, matrix))
  {
    m_workMatrix = matrix.block(0,0,m_diagSize,m_diagSize);
    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.
        using std::max;
        if(max(internal::abs(m_workMatrix.coeff(p,q)),internal::abs(m_workMatrix.coeff(q,p)))
            > max(internal::abs(m_workMatrix.coeff(p,p)),internal::abs(m_workMatrix.coeff(q,q)))*precision)
        {
          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 = internal::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_isInitialized = true;
  return *this;
}

template<typename MatrixType, int QRPreconditioner>
MatrixType JacobiSVD<MatrixType, QRPreconditioner>::pinverse() const
{
	eigen_assert(m_isInitialized && "JacobiSVD is not initialized.");
	eigen_assert(computeU() && computeV() && "JacobiSVD::pinverse() requires both unitaries U and V to be computed (thin unitaries suffice).");

	RealScalar tolerance = NumTraits<Scalar>::epsilon() * std::max(m_rows,m_cols) * m_singularValues.cwiseAbs().maxCoeff();

	return pinverse(tolerance);
}

template<typename MatrixType, int QRPreconditioner>
MatrixType JacobiSVD<MatrixType, QRPreconditioner>::pinverse(const RealScalar& tolerance) const
{
	eigen_assert(m_isInitialized && "JacobiSVD is not initialized.");
	eigen_assert(computeU() && computeV() && "JacobiSVD::pinverse() requires both unitaries U and V to be computed (thin unitaries suffice).");

	// A = U S V^*
	// A^{+} = V S^{+} U^*
	typename JacobiSVD<MatrixType, QRPreconditioner>::SingularValuesType invertedSingVals(m_diagSize);

	Index i = 0;

	// Singular values are positive and stored in descending order
	// It is really simplifies S inversion.
	while( i < m_nonzeroSingularValues && m_singularValues(i) > tolerance)
	{
		RealScalar s(1);

		s /= m_singularValues(i);

		invertedSingVals(i) = s;

		i++;
	}

	invertedSingVals.tail(m_diagSize - i).setZero();	

	return m_matrixV * invertedSingVals.asDiagonal() * m_matrixU.adjoint();
}

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^*

    Index diagSize = std::min(dec().rows(), dec().cols());
    typename JacobiSVDType::SingularValuesType invertedSingVals(diagSize);

    Index nonzeroSingVals = dec().nonzeroSingularValues();
    invertedSingVals.head(nonzeroSingVals) = dec().singularValues().head(nonzeroSingVals).array().inverse();
    invertedSingVals.tail(diagSize - nonzeroSingVals).setZero();

    dst = dec().matrixV().leftCols(diagSize)
        * invertedSingVals.asDiagonal()
        * dec().matrixU().leftCols(diagSize).adjoint()
        * rhs();
  }
};
} // end namespace internal

template<typename Derived>
JacobiSVD<typename MatrixBase<Derived>::PlainObject>
MatrixBase<Derived>::jacobiSvd(unsigned int computationOptions) const
{
  return JacobiSVD<PlainObject>(*this, computationOptions);
}



#endif // EIGEN_JACOBISVD_H


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