Eigen
3.4.90 (git rev a4098ac676528a83cfb73d4d26ce1b42ec05f47c)

Base class of SVD algorithms.
Derived  the type of the actual SVD decomposition 
SVD decomposition consists in decomposing any nbyp matrix A as a product
\[ A = U S V^* \]
where U is a nbyn unitary, V is a pbyp unitary, and S is a nbyp real positive matrix which is zero outside of its main diagonal; the diagonal entries of S are known as the singular values of A and the columns of U and V are known as the left and right singular vectors of A respectively.
Singular values are always sorted in decreasing order.
You can ask for only thin U or V to be computed, meaning the following. In case of a rectangular nbyp matrix, letting m be the smaller value among n and p, there are only m singular vectors; the remaining columns of U and V do not correspond to actual singular vectors. Asking for thin U or V means asking for only their m first columns to be formed. So U is then a nbym matrix, and V is then a pbym matrix. Notice that thin U and V are all you need for (least squares) solving.
The status of the computation can be retrieved using the info() method. Unless info() returns Success, the results should be not considered well defined.
If the input matrix has inf or nan coefficients, the result of the computation is undefined, and info() will return InvalidInput, but the computation is guaranteed to terminate in finite (and reasonable) time.
Public Types  
typedef Eigen::Index  Index 
Public Types inherited from Eigen::EigenBase< Derived >  
typedef Eigen::Index  Index 
The interface type of indices. More...  
Public Member Functions  
bool  computeU () const 
bool  computeV () const 
ComputationInfo  info () const 
Reports whether previous computation was successful. More...  
const MatrixUType &  matrixU () const 
const MatrixVType &  matrixV () const 
Index  nonzeroSingularValues () const 
Index  rank () const 
Derived &  setThreshold (const RealScalar &threshold) 
Derived &  setThreshold (Default_t) 
const SingularValuesType &  singularValues () const 
template<typename Rhs >  
const Solve< Derived, Rhs >  solve (const MatrixBase< Rhs > &b) const 
RealScalar  threshold () const 
Public Member Functions inherited from Eigen::SolverBase< SVDBase< Derived > >  
AdjointReturnType  adjoint () const 
SVDBase< Derived > &  derived () 
const SVDBase< Derived > &  derived () const 
const Solve< SVDBase< Derived >, Rhs >  solve (const MatrixBase< Rhs > &b) const 
SolverBase ()  
ConstTransposeReturnType  transpose () const 
Public Member Functions inherited from Eigen::EigenBase< Derived >  
EIGEN_CONSTEXPR Index  cols () const EIGEN_NOEXCEPT 
Derived &  derived () 
const Derived &  derived () const 
EIGEN_CONSTEXPR Index  rows () const EIGEN_NOEXCEPT 
EIGEN_CONSTEXPR Index  size () const EIGEN_NOEXCEPT 
Protected Member Functions  
SVDBase ()  
Default Constructor. More...  
typedef Eigen::Index Eigen::SVDBase< Derived >::Index 

inlineprotected 
Default Constructor.
Default constructor of SVDBase

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Reports whether previous computation was successful.
Success
if computation was successful.

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For the SVD decomposition of a nbyp matrix, letting m be the minimum of n and p, the U matrix is nbyn if you asked for ComputeFullU , and is nbym if you asked for ComputeThinU .
The m first columns of U are the left singular vectors of the matrix being decomposed.
This method asserts that you asked for U to be computed.

inline 
For the SVD decomposition of a nbyp matrix, letting m be the minimum of n and p, the V matrix is pbyp if you asked for ComputeFullV , and is pbym if you asked for ComputeThinV .
The m first columns of V are the right singular vectors of the matrix being decomposed.
This method asserts that you asked for V to be computed.

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*this
is the SVD.

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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 NumTraits<Scalar>::epsilon()
threshold  The new value to use as the threshold. 
A singular value will be considered nonzero if its value is strictly greater than \( \vert singular value \vert \leqslant threshold \times \vert max singular value \vert \).
If you want to come back to the default behavior, call setThreshold(Default_t)

inline 
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.
See the documentation of setThreshold(const RealScalar&).

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For the SVD decomposition of a nbyp matrix, letting m be the minimum of n and p, the returned vector has size m. Singular values are always sorted in decreasing order.

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b  the righthandside of the equation to solve. 

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Returns the threshold that will be used by certain methods such as rank().
See the documentation of setThreshold(const RealScalar&).