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fix stupid numerical stability issue in SVD::solve (though it is not yet as stable as LU with full pivoting)

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This commit is contained in:
Gael Guennebaud 2008-09-04 14:38:42 +00:00
parent 6add33e2c2
commit 12e9de4abb
2 changed files with 44 additions and 5 deletions
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2
Eigen/src/Core/MatrixBase.h
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@ -573,7 +573,7 @@ template<typename Derived> class MatrixBase
/////////// SVD module ///////////
const SVD<EvalType> svd() const;
SVD<EvalType> svd() const;
/////////// Geometry module ///////////

47
Eigen/src/SVD/SVD.h
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@ -76,6 +76,7 @@ template<typename MatrixType> class SVD
const MatrixVType& matrixV() const { return m_matV; }
void compute(const MatrixType& matrix);
SVD& sort();
protected:
/** \internal */
@ -464,6 +465,43 @@ void SVD<MatrixType>::compute(const MatrixType& matrix)
} // end iterations
}
template<typename MatrixType>
SVD<MatrixType>& SVD<MatrixType>::sort()
{
int mu = m_matU.rows();
int mv = m_matV.rows();
int n = m_matU.cols();
for (int i=0; i<n; i++)
{
int k = i;
Scalar p = m_sigma.coeff(i);
for (int j=i+1; j<n; j++)
{
if (m_sigma.coeff(j) > p)
{
k = j;
p = m_sigma.coeff(j);
}
}
if (k != i)
{
m_sigma.coeffRef(k) = m_sigma.coeff(i); // i.e.
m_sigma.coeffRef(i) = p; // swaps the i-th and the k-th elements
int j = mu;
for(int s=0; j!=0; ++s, --j)
std::swap(m_matU.coeffRef(s,i), m_matU.coeffRef(s,k));
j = mv;
for (int s=0; j!=0; ++s, --j)
std::swap(m_matV.coeffRef(s,i), m_matV.coeffRef(s,k));
}
}
return *this;
}
/** \returns the solution of \f$ A x = b \f$ using the current SVD decomposition of A.
* The parts of the solution corresponding to zero singular values are ignored.
*
@ -476,6 +514,7 @@ void SVD<MatrixType>::solve(const MatrixBase<OtherDerived> &b, ResultType* resul
const int rows = m_matU.rows();
ei_assert(b.rows() == rows);
Scalar maxVal = m_sigma.cwise().abs().maxCoeff();
for (int j=0; j<b.cols(); ++j)
{
Matrix<Scalar,MatrixUType::RowsAtCompileTime,1> aux = m_matU.transpose() * b.col(j);
@ -483,10 +522,10 @@ void SVD<MatrixType>::solve(const MatrixBase<OtherDerived> &b, ResultType* resul
for (int i = 0; i <m_matU.cols(); i++)
{
Scalar si = m_sigma.coeff(i);
if (si != 0)
aux.coeffRef(i) /= si;
else
if (ei_isMuchSmallerThan(ei_abs(si),maxVal))
aux.coeffRef(i) = 0;
else
aux.coeffRef(i) /= si;
}
result->col(j) = m_matV * aux;
@ -497,7 +536,7 @@ void SVD<MatrixType>::solve(const MatrixBase<OtherDerived> &b, ResultType* resul
* \returns the SVD decomposition of \c *this
*/
template<typename Derived>
inline const SVD<typename MatrixBase<Derived>::EvalType>
inline SVD<typename MatrixBase<Derived>::EvalType>
MatrixBase<Derived>::svd() const
{
return SVD<typename ei_eval<Derived>::type>(derived());