391 lines
12 KiB
Fortran
391 lines
12 KiB
Fortran
*> \brief \b SSYTRF_ROOK
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*
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* =========== DOCUMENTATION ===========
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*
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* Online html documentation available at
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* http://www.netlib.org/lapack/explore-html/
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*
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*> \htmlonly
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*> Download SSYTRF_ROOK + dependencies
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/ssytrf_rook.f">
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*> [TGZ]</a>
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/ssytrf_rook.f">
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*> [ZIP]</a>
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/ssytrf_rook.f">
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*> [TXT]</a>
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*> \endhtmlonly
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*
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* Definition:
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* ===========
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*
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* SUBROUTINE SSYTRF_ROOK( UPLO, N, A, LDA, IPIV, WORK, LWORK, INFO )
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*
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* .. Scalar Arguments ..
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* CHARACTER UPLO
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* INTEGER INFO, LDA, LWORK, N
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* ..
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* .. Array Arguments ..
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* INTEGER IPIV( * )
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* REAL A( LDA, * ), WORK( * )
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* ..
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*
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*
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*> \par Purpose:
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* =============
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*>
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*> \verbatim
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*>
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*> SSYTRF_ROOK computes the factorization of a real symmetric matrix A
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*> using the bounded Bunch-Kaufman ("rook") diagonal pivoting method.
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*> The form of the factorization is
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*>
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*> A = U*D*U**T or A = L*D*L**T
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*>
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*> where U (or L) is a product of permutation and unit upper (lower)
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*> triangular matrices, and D is symmetric and block diagonal with
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*> 1-by-1 and 2-by-2 diagonal blocks.
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*>
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*> This is the blocked version of the algorithm, calling Level 3 BLAS.
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*> \endverbatim
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*
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* Arguments:
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* ==========
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*
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*> \param[in] UPLO
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*> \verbatim
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*> UPLO is CHARACTER*1
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*> = 'U': Upper triangle of A is stored;
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*> = 'L': Lower triangle of A is stored.
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*> \endverbatim
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*>
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*> \param[in] N
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*> \verbatim
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*> N is INTEGER
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*> The order of the matrix A. N >= 0.
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*> \endverbatim
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*>
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*> \param[in,out] A
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*> \verbatim
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*> A is REAL array, dimension (LDA,N)
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*> On entry, the symmetric matrix A. If UPLO = 'U', the leading
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*> N-by-N upper triangular part of A contains the upper
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*> triangular part of the matrix A, and the strictly lower
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*> triangular part of A is not referenced. If UPLO = 'L', the
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*> leading N-by-N lower triangular part of A contains the lower
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*> triangular part of the matrix A, and the strictly upper
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*> triangular part of A is not referenced.
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*>
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*> On exit, the block diagonal matrix D and the multipliers used
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*> to obtain the factor U or L (see below for further details).
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*> \endverbatim
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*>
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*> \param[in] LDA
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*> \verbatim
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*> LDA is INTEGER
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*> The leading dimension of the array A. LDA >= max(1,N).
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*> \endverbatim
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*>
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*> \param[out] IPIV
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*> \verbatim
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*> IPIV is INTEGER array, dimension (N)
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*> Details of the interchanges and the block structure of D.
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*>
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*> If UPLO = 'U':
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*> If IPIV(k) > 0, then rows and columns k and IPIV(k)
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*> were interchanged and D(k,k) is a 1-by-1 diagonal block.
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*>
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*> If IPIV(k) < 0 and IPIV(k-1) < 0, then rows and
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*> columns k and -IPIV(k) were interchanged and rows and
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*> columns k-1 and -IPIV(k-1) were inerchaged,
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*> D(k-1:k,k-1:k) is a 2-by-2 diagonal block.
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*>
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*> If UPLO = 'L':
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*> If IPIV(k) > 0, then rows and columns k and IPIV(k)
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*> were interchanged and D(k,k) is a 1-by-1 diagonal block.
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*>
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*> If IPIV(k) < 0 and IPIV(k+1) < 0, then rows and
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*> columns k and -IPIV(k) were interchanged and rows and
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*> columns k+1 and -IPIV(k+1) were inerchaged,
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*> D(k:k+1,k:k+1) is a 2-by-2 diagonal block.
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*> \endverbatim
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*>
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*> \param[out] WORK
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*> \verbatim
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*> WORK is REAL array, dimension (MAX(1,LWORK)).
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*> On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
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*> \endverbatim
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*>
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*> \param[in] LWORK
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*> \verbatim
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*> LWORK is INTEGER
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*> The length of WORK. LWORK >=1. For best performance
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*> LWORK >= N*NB, where NB is the block size returned by ILAENV.
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*>
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*> If LWORK = -1, then a workspace query is assumed; the routine
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*> only calculates the optimal size of the WORK array, returns
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*> this value as the first entry of the WORK array, and no error
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*> message related to LWORK is issued by XERBLA.
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*> \endverbatim
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*>
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*> \param[out] INFO
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*> \verbatim
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*> INFO is INTEGER
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*> = 0: successful exit
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*> < 0: if INFO = -i, the i-th argument had an illegal value
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*> > 0: if INFO = i, D(i,i) is exactly zero. The factorization
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*> has been completed, but the block diagonal matrix D is
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*> exactly singular, and division by zero will occur if it
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*> is used to solve a system of equations.
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*> \endverbatim
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*
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* Authors:
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* ========
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*
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*> \author Univ. of Tennessee
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*> \author Univ. of California Berkeley
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*> \author Univ. of Colorado Denver
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*> \author NAG Ltd.
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*
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*> \ingroup realSYcomputational
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*
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*> \par Further Details:
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* =====================
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*>
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*> \verbatim
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*>
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*> If UPLO = 'U', then A = U*D*U**T, where
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*> U = P(n)*U(n)* ... *P(k)U(k)* ...,
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*> i.e., U is a product of terms P(k)*U(k), where k decreases from n to
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*> 1 in steps of 1 or 2, and D is a block diagonal matrix with 1-by-1
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*> and 2-by-2 diagonal blocks D(k). P(k) is a permutation matrix as
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*> defined by IPIV(k), and U(k) is a unit upper triangular matrix, such
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*> that if the diagonal block D(k) is of order s (s = 1 or 2), then
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*>
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*> ( I v 0 ) k-s
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*> U(k) = ( 0 I 0 ) s
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*> ( 0 0 I ) n-k
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*> k-s s n-k
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*>
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*> If s = 1, D(k) overwrites A(k,k), and v overwrites A(1:k-1,k).
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*> If s = 2, the upper triangle of D(k) overwrites A(k-1,k-1), A(k-1,k),
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*> and A(k,k), and v overwrites A(1:k-2,k-1:k).
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*>
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*> If UPLO = 'L', then A = L*D*L**T, where
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*> L = P(1)*L(1)* ... *P(k)*L(k)* ...,
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*> i.e., L is a product of terms P(k)*L(k), where k increases from 1 to
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*> n in steps of 1 or 2, and D is a block diagonal matrix with 1-by-1
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*> and 2-by-2 diagonal blocks D(k). P(k) is a permutation matrix as
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*> defined by IPIV(k), and L(k) is a unit lower triangular matrix, such
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*> that if the diagonal block D(k) is of order s (s = 1 or 2), then
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*>
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*> ( I 0 0 ) k-1
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*> L(k) = ( 0 I 0 ) s
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*> ( 0 v I ) n-k-s+1
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*> k-1 s n-k-s+1
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*>
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*> If s = 1, D(k) overwrites A(k,k), and v overwrites A(k+1:n,k).
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*> If s = 2, the lower triangle of D(k) overwrites A(k,k), A(k+1,k),
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*> and A(k+1,k+1), and v overwrites A(k+2:n,k:k+1).
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*> \endverbatim
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*
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*> \par Contributors:
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* ==================
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*>
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*> \verbatim
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*>
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*> June 2016, Igor Kozachenko,
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*> Computer Science Division,
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*> University of California, Berkeley
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*>
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*> September 2007, Sven Hammarling, Nicholas J. Higham, Craig Lucas,
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*> School of Mathematics,
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*> University of Manchester
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*>
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*> \endverbatim
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*
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* =====================================================================
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SUBROUTINE SSYTRF_ROOK( UPLO, N, A, LDA, IPIV, WORK, LWORK, INFO )
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*
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* -- LAPACK computational routine --
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* -- LAPACK is a software package provided by Univ. of Tennessee, --
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* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
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*
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* .. Scalar Arguments ..
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CHARACTER UPLO
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INTEGER INFO, LDA, LWORK, N
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* ..
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* .. Array Arguments ..
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INTEGER IPIV( * )
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REAL A( LDA, * ), WORK( * )
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* ..
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*
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* =====================================================================
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*
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* .. Local Scalars ..
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LOGICAL LQUERY, UPPER
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INTEGER IINFO, IWS, J, K, KB, LDWORK, LWKOPT, NB, NBMIN
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* ..
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* .. External Functions ..
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LOGICAL LSAME
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INTEGER ILAENV
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EXTERNAL LSAME, ILAENV
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* ..
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* .. External Subroutines ..
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EXTERNAL SLASYF_ROOK, SSYTF2_ROOK, XERBLA
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* ..
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* .. Intrinsic Functions ..
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INTRINSIC MAX
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* ..
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* .. Executable Statements ..
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*
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* Test the input parameters.
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*
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INFO = 0
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UPPER = LSAME( UPLO, 'U' )
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LQUERY = ( LWORK.EQ.-1 )
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IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
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INFO = -1
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ELSE IF( N.LT.0 ) THEN
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INFO = -2
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ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
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INFO = -4
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ELSE IF( LWORK.LT.1 .AND. .NOT.LQUERY ) THEN
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INFO = -7
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END IF
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*
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IF( INFO.EQ.0 ) THEN
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*
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* Determine the block size
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*
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NB = ILAENV( 1, 'SSYTRF_ROOK', UPLO, N, -1, -1, -1 )
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LWKOPT = MAX( 1, N*NB )
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WORK( 1 ) = LWKOPT
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END IF
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*
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IF( INFO.NE.0 ) THEN
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CALL XERBLA( 'SSYTRF_ROOK', -INFO )
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RETURN
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ELSE IF( LQUERY ) THEN
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RETURN
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END IF
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*
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NBMIN = 2
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LDWORK = N
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IF( NB.GT.1 .AND. NB.LT.N ) THEN
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IWS = LDWORK*NB
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IF( LWORK.LT.IWS ) THEN
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NB = MAX( LWORK / LDWORK, 1 )
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NBMIN = MAX( 2, ILAENV( 2, 'SSYTRF_ROOK',
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$ UPLO, N, -1, -1, -1 ) )
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END IF
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ELSE
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IWS = 1
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END IF
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IF( NB.LT.NBMIN )
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$ NB = N
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*
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IF( UPPER ) THEN
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*
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* Factorize A as U*D*U**T using the upper triangle of A
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*
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* K is the main loop index, decreasing from N to 1 in steps of
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* KB, where KB is the number of columns factorized by SLASYF_ROOK;
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* KB is either NB or NB-1, or K for the last block
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*
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K = N
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10 CONTINUE
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*
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* If K < 1, exit from loop
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*
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IF( K.LT.1 )
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$ GO TO 40
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*
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IF( K.GT.NB ) THEN
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*
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* Factorize columns k-kb+1:k of A and use blocked code to
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* update columns 1:k-kb
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*
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CALL SLASYF_ROOK( UPLO, K, NB, KB, A, LDA,
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$ IPIV, WORK, LDWORK, IINFO )
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ELSE
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*
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* Use unblocked code to factorize columns 1:k of A
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*
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CALL SSYTF2_ROOK( UPLO, K, A, LDA, IPIV, IINFO )
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KB = K
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END IF
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*
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* Set INFO on the first occurrence of a zero pivot
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*
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IF( INFO.EQ.0 .AND. IINFO.GT.0 )
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$ INFO = IINFO
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*
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* No need to adjust IPIV
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*
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* Decrease K and return to the start of the main loop
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*
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K = K - KB
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GO TO 10
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*
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ELSE
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*
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* Factorize A as L*D*L**T using the lower triangle of A
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*
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* K is the main loop index, increasing from 1 to N in steps of
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* KB, where KB is the number of columns factorized by SLASYF_ROOK;
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* KB is either NB or NB-1, or N-K+1 for the last block
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*
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K = 1
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20 CONTINUE
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*
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* If K > N, exit from loop
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*
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IF( K.GT.N )
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$ GO TO 40
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*
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IF( K.LE.N-NB ) THEN
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*
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* Factorize columns k:k+kb-1 of A and use blocked code to
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* update columns k+kb:n
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*
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CALL SLASYF_ROOK( UPLO, N-K+1, NB, KB, A( K, K ), LDA,
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$ IPIV( K ), WORK, LDWORK, IINFO )
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ELSE
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*
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* Use unblocked code to factorize columns k:n of A
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*
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CALL SSYTF2_ROOK( UPLO, N-K+1, A( K, K ), LDA, IPIV( K ),
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$ IINFO )
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KB = N - K + 1
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END IF
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*
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* Set INFO on the first occurrence of a zero pivot
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*
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IF( INFO.EQ.0 .AND. IINFO.GT.0 )
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$ INFO = IINFO + K - 1
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*
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* Adjust IPIV
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*
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DO 30 J = K, K + KB - 1
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IF( IPIV( J ).GT.0 ) THEN
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IPIV( J ) = IPIV( J ) + K - 1
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ELSE
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IPIV( J ) = IPIV( J ) - K + 1
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END IF
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30 CONTINUE
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*
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* Increase K and return to the start of the main loop
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*
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K = K + KB
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GO TO 20
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*
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END IF
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*
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40 CONTINUE
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WORK( 1 ) = LWKOPT
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RETURN
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*
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* End of SSYTRF_ROOK
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*
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END
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