/// \brief Compute QR factorization [Q,R] = qr(A,0).
///
/// \param A [in/out] On input: the multivector to factor.
/// Overwritten with garbage on output.
///
/// \param Q [out] On output: the (explicitly stored) Q factor in
/// the QR factorization of the (input) multivector A.
///
/// \param R [out] On output: the R factor in the QR factorization
/// of the (input) multivector A.
///
/// \param forceNonnegativeDiagonal [in] If true, then (if
/// necessary) do extra work (modifying both the Q and R
/// factors) in order to force the R factor to have a
/// nonnegative diagonal.
///
/// \warning Currently, this method only works if A and Q have the
/// same communicator and row distribution ("Map," in Petra
/// terms) as those of the multivector given to this adapter
/// instance's constructor. Otherwise, the result of this
/// method is undefined.
void
factorExplicit (MV& A,
MV& Q,
dense_matrix_type& R,
const bool forceNonnegativeDiagonal=false)
{
TEUCHOS_TEST_FOR_EXCEPTION
(! A.isConstantStride (), std::invalid_argument, "TsqrAdaptor::"
"factorExplicit: Input MultiVector A must have constant stride.");
TEUCHOS_TEST_FOR_EXCEPTION
(! Q.isConstantStride (), std::invalid_argument, "TsqrAdaptor::"
"factorExplicit: Input MultiVector Q must have constant stride.");
prepareTsqr (Q); // Finish initializing TSQR.
// FIXME (mfh 16 Jan 2016) Currently, TSQR is a host-only
// implementation.
A.template sync<Kokkos::HostSpace> ();
A.template modify<Kokkos::HostSpace> ();
Q.template sync<Kokkos::HostSpace> ();
Q.template modify<Kokkos::HostSpace> ();
auto A_view = A.template getLocalView<Kokkos::HostSpace> ();
auto Q_view = Q.template getLocalView<Kokkos::HostSpace> ();
scalar_type* const A_ptr =
reinterpret_cast<scalar_type*> (A_view.ptr_on_device ());
scalar_type* const Q_ptr =
reinterpret_cast<scalar_type*> (Q_view.ptr_on_device ());
const bool contiguousCacheBlocks = false;
tsqr_->factorExplicitRaw (A_view.dimension_0 (),
A_view.dimension_1 (),
A_ptr, A.getStride (),
Q_ptr, Q.getStride (),
R.values (), R.stride (),
contiguousCacheBlocks,
forceNonnegativeDiagonal);
}
/// \brief Rank-revealing decomposition
///
/// Using the R factor and explicit Q factor from
/// factorExplicit(), compute the singular value decomposition
/// (SVD) of R: \f$R = U \Sigma V^*\f$. If R is full rank (with
/// respect to the given relative tolerance \c tol), do not modify
/// Q or R. Otherwise, compute \f$Q := Q \cdot U\f$ and \f$R :=
/// \Sigma V^*\f$ in place. If R was modified, then it may not
/// necessarily be upper triangular on output.
///
/// \param Q [in/out] On input: explicit Q factor computed by
/// factorExplicit(). (Must be an orthogonal resp. unitary
/// matrix.) On output: If R is of full numerical rank with
/// respect to the tolerance tol, Q is unmodified. Otherwise, Q
/// is updated so that the first \c rank columns of Q are a
/// basis for the column space of A (the original matrix whose
/// QR factorization was computed by factorExplicit()). The
/// remaining columns of Q are a basis for the null space of A.
///
/// \param R [in/out] On input: N by N upper triangular matrix
/// with leading dimension LDR >= N. On output: if input is
/// full rank, R is unchanged on output. Otherwise, if \f$R = U
/// \Sigma V^*\f$ is the SVD of R, on output R is overwritten
/// with \f$\Sigma \cdot V^*\f$. This is also an N by N matrix,
/// but it may not necessarily be upper triangular.
///
/// \param tol [in] Relative tolerance for computing the numerical
/// rank of the matrix R.
///
/// \return Rank \f$r\f$ of R: \f$ 0 \leq r \leq N\f$.
int
revealRank (MV& Q,
dense_matrix_type& R,
const magnitude_type& tol)
{
TEUCHOS_TEST_FOR_EXCEPTION
(! Q.isConstantStride (), std::invalid_argument, "TsqrAdaptor::"
"revealRank: Input MultiVector Q must have constant stride.");
prepareTsqr (Q); // Finish initializing TSQR.
// FIXME (mfh 18 Oct 2010) Check Teuchos::Comm<int> object in Q
// to make sure it is the same communicator as the one we are
// using in our dist_tsqr_type implementation.
Q.template sync<Kokkos::HostSpace> ();
Q.template modify<Kokkos::HostSpace> ();
auto Q_view = Q.template getLocalView<Kokkos::HostSpace> ();
scalar_type* const Q_ptr =
reinterpret_cast<scalar_type*> (Q_view.ptr_on_device ());
const bool contiguousCacheBlocks = false;
return tsqr_->revealRankRaw (Q_view.dimension_0 (),
Q_view.dimension_1 (),
Q_ptr, Q.getStride (),
R.values (), R.stride (),
tol, contiguousCacheBlocks);
}