713 lines
24 KiB
Fortran
713 lines
24 KiB
Fortran
*> \brief \b STGEX2 swaps adjacent diagonal blocks in an upper (quasi) triangular matrix pair by an orthogonal equivalence transformation.
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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 STGEX2 + dependencies
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/stgex2.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/stgex2.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/stgex2.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 STGEX2( WANTQ, WANTZ, N, A, LDA, B, LDB, Q, LDQ, Z,
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* LDZ, J1, N1, N2, WORK, LWORK, INFO )
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*
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* .. Scalar Arguments ..
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* LOGICAL WANTQ, WANTZ
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* INTEGER INFO, J1, LDA, LDB, LDQ, LDZ, LWORK, N, N1, N2
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* ..
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* .. Array Arguments ..
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* REAL A( LDA, * ), B( LDB, * ), Q( LDQ, * ),
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* $ WORK( * ), Z( LDZ, * )
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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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*> STGEX2 swaps adjacent diagonal blocks (A11, B11) and (A22, B22)
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*> of size 1-by-1 or 2-by-2 in an upper (quasi) triangular matrix pair
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*> (A, B) by an orthogonal equivalence transformation.
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*>
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*> (A, B) must be in generalized real Schur canonical form (as returned
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*> by SGGES), i.e. A is block upper triangular with 1-by-1 and 2-by-2
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*> diagonal blocks. B is upper triangular.
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*>
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*> Optionally, the matrices Q and Z of generalized Schur vectors are
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*> updated.
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*>
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*> Q(in) * A(in) * Z(in)**T = Q(out) * A(out) * Z(out)**T
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*> Q(in) * B(in) * Z(in)**T = Q(out) * B(out) * Z(out)**T
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*>
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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] WANTQ
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*> \verbatim
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*> WANTQ is LOGICAL
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*> .TRUE. : update the left transformation matrix Q;
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*> .FALSE.: do not update Q.
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*> \endverbatim
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*>
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*> \param[in] WANTZ
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*> \verbatim
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*> WANTZ is LOGICAL
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*> .TRUE. : update the right transformation matrix Z;
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*> .FALSE.: do not update Z.
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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 matrices A and B. 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 matrix A in the pair (A, B).
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*> On exit, the updated matrix A.
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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[in,out] B
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*> \verbatim
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*> B is REAL array, dimension (LDB,N)
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*> On entry, the matrix B in the pair (A, B).
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*> On exit, the updated matrix B.
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*> \endverbatim
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*>
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*> \param[in] LDB
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*> \verbatim
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*> LDB is INTEGER
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*> The leading dimension of the array B. LDB >= max(1,N).
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*> \endverbatim
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*>
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*> \param[in,out] Q
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*> \verbatim
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*> Q is REAL array, dimension (LDQ,N)
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*> On entry, if WANTQ = .TRUE., the orthogonal matrix Q.
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*> On exit, the updated matrix Q.
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*> Not referenced if WANTQ = .FALSE..
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*> \endverbatim
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*>
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*> \param[in] LDQ
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*> \verbatim
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*> LDQ is INTEGER
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*> The leading dimension of the array Q. LDQ >= 1.
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*> If WANTQ = .TRUE., LDQ >= N.
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*> \endverbatim
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*>
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*> \param[in,out] Z
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*> \verbatim
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*> Z is REAL array, dimension (LDZ,N)
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*> On entry, if WANTZ =.TRUE., the orthogonal matrix Z.
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*> On exit, the updated matrix Z.
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*> Not referenced if WANTZ = .FALSE..
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*> \endverbatim
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*>
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*> \param[in] LDZ
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*> \verbatim
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*> LDZ is INTEGER
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*> The leading dimension of the array Z. LDZ >= 1.
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*> If WANTZ = .TRUE., LDZ >= N.
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*> \endverbatim
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*>
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*> \param[in] J1
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*> \verbatim
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*> J1 is INTEGER
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*> The index to the first block (A11, B11). 1 <= J1 <= N.
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*> \endverbatim
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*>
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*> \param[in] N1
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*> \verbatim
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*> N1 is INTEGER
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*> The order of the first block (A11, B11). N1 = 0, 1 or 2.
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*> \endverbatim
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*>
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*> \param[in] N2
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*> \verbatim
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*> N2 is INTEGER
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*> The order of the second block (A22, B22). N2 = 0, 1 or 2.
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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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*> \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 dimension of the array WORK.
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*> LWORK >= MAX( N*(N2+N1), (N2+N1)*(N2+N1)*2 )
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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 = 1, the transformed matrix (A, B) would be
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*> too far from generalized Schur form; the blocks are
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*> not swapped and (A, B) and (Q, Z) are unchanged.
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*> The problem of swapping is too ill-conditioned.
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*> <0: If INFO = -16: LWORK is too small. Appropriate value
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*> for LWORK is returned in WORK(1).
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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 realGEauxiliary
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*
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*> \par Further Details:
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* =====================
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*>
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*> In the current code both weak and strong stability tests are
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*> performed. The user can omit the strong stability test by changing
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*> the internal logical parameter WANDS to .FALSE.. See ref. [2] for
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*> details.
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*
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*> \par Contributors:
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* ==================
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*>
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*> Bo Kagstrom and Peter Poromaa, Department of Computing Science,
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*> Umea University, S-901 87 Umea, Sweden.
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*
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*> \par References:
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* ================
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*>
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*> \verbatim
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*>
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*> [1] B. Kagstrom; A Direct Method for Reordering Eigenvalues in the
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*> Generalized Real Schur Form of a Regular Matrix Pair (A, B), in
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*> M.S. Moonen et al (eds), Linear Algebra for Large Scale and
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*> Real-Time Applications, Kluwer Academic Publ. 1993, pp 195-218.
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*>
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*> [2] B. Kagstrom and P. Poromaa; Computing Eigenspaces with Specified
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*> Eigenvalues of a Regular Matrix Pair (A, B) and Condition
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*> Estimation: Theory, Algorithms and Software,
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*> Report UMINF - 94.04, Department of Computing Science, Umea
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*> University, S-901 87 Umea, Sweden, 1994. Also as LAPACK Working
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*> Note 87. To appear in Numerical Algorithms, 1996.
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*> \endverbatim
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*>
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* =====================================================================
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SUBROUTINE STGEX2( WANTQ, WANTZ, N, A, LDA, B, LDB, Q, LDQ, Z,
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$ LDZ, J1, N1, N2, WORK, LWORK, INFO )
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*
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* -- LAPACK auxiliary 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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LOGICAL WANTQ, WANTZ
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INTEGER INFO, J1, LDA, LDB, LDQ, LDZ, LWORK, N, N1, N2
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* ..
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* .. Array Arguments ..
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REAL A( LDA, * ), B( LDB, * ), Q( LDQ, * ),
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$ WORK( * ), Z( LDZ, * )
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* ..
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*
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* =====================================================================
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* Replaced various illegal calls to SCOPY by calls to SLASET, or by DO
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* loops. Sven Hammarling, 1/5/02.
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*
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* .. Parameters ..
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REAL ZERO, ONE
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PARAMETER ( ZERO = 0.0E+0, ONE = 1.0E+0 )
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REAL TWENTY
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PARAMETER ( TWENTY = 2.0E+01 )
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INTEGER LDST
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PARAMETER ( LDST = 4 )
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LOGICAL WANDS
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PARAMETER ( WANDS = .TRUE. )
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* ..
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* .. Local Scalars ..
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LOGICAL STRONG, WEAK
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INTEGER I, IDUM, LINFO, M
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REAL BQRA21, BRQA21, DDUM, DNORMA, DNORMB,
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$ DSCALE,
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$ DSUM, EPS, F, G, SA, SB, SCALE, SMLNUM,
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$ THRESHA, THRESHB
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* ..
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* .. Local Arrays ..
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INTEGER IWORK( LDST )
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REAL AI( 2 ), AR( 2 ), BE( 2 ), IR( LDST, LDST ),
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$ IRCOP( LDST, LDST ), LI( LDST, LDST ),
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$ LICOP( LDST, LDST ), S( LDST, LDST ),
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$ SCPY( LDST, LDST ), T( LDST, LDST ),
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$ TAUL( LDST ), TAUR( LDST ), TCPY( LDST, LDST )
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* ..
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* .. External Functions ..
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REAL SLAMCH
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EXTERNAL SLAMCH
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* ..
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* .. External Subroutines ..
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EXTERNAL SGEMM, SGEQR2, SGERQ2, SLACPY, SLAGV2, SLARTG,
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$ SLASET, SLASSQ, SORG2R, SORGR2, SORM2R, SORMR2,
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$ SROT, SSCAL, STGSY2
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* ..
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* .. Intrinsic Functions ..
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INTRINSIC ABS, MAX, SQRT
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* ..
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* .. Executable Statements ..
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*
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INFO = 0
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*
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* Quick return if possible
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*
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IF( N.LE.1 .OR. N1.LE.0 .OR. N2.LE.0 )
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$ RETURN
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IF( N1.GT.N .OR. ( J1+N1 ).GT.N )
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$ RETURN
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M = N1 + N2
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IF( LWORK.LT.MAX( N*M, M*M*2 ) ) THEN
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INFO = -16
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WORK( 1 ) = MAX( N*M, M*M*2 )
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RETURN
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END IF
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*
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WEAK = .FALSE.
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STRONG = .FALSE.
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*
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* Make a local copy of selected block
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*
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CALL SLASET( 'Full', LDST, LDST, ZERO, ZERO, LI, LDST )
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CALL SLASET( 'Full', LDST, LDST, ZERO, ZERO, IR, LDST )
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CALL SLACPY( 'Full', M, M, A( J1, J1 ), LDA, S, LDST )
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CALL SLACPY( 'Full', M, M, B( J1, J1 ), LDB, T, LDST )
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*
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* Compute threshold for testing acceptance of swapping.
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*
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EPS = SLAMCH( 'P' )
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SMLNUM = SLAMCH( 'S' ) / EPS
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DSCALE = ZERO
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DSUM = ONE
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CALL SLACPY( 'Full', M, M, S, LDST, WORK, M )
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CALL SLASSQ( M*M, WORK, 1, DSCALE, DSUM )
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DNORMA = DSCALE*SQRT( DSUM )
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DSCALE = ZERO
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DSUM = ONE
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CALL SLACPY( 'Full', M, M, T, LDST, WORK, M )
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CALL SLASSQ( M*M, WORK, 1, DSCALE, DSUM )
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DNORMB = DSCALE*SQRT( DSUM )
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*
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* THRES has been changed from
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* THRESH = MAX( TEN*EPS*SA, SMLNUM )
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* to
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* THRESH = MAX( TWENTY*EPS*SA, SMLNUM )
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* on 04/01/10.
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* "Bug" reported by Ondra Kamenik, confirmed by Julie Langou, fixed by
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* Jim Demmel and Guillaume Revy. See forum post 1783.
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*
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THRESHA = MAX( TWENTY*EPS*DNORMA, SMLNUM )
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THRESHB = MAX( TWENTY*EPS*DNORMB, SMLNUM )
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*
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IF( M.EQ.2 ) THEN
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*
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* CASE 1: Swap 1-by-1 and 1-by-1 blocks.
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*
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* Compute orthogonal QL and RQ that swap 1-by-1 and 1-by-1 blocks
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* using Givens rotations and perform the swap tentatively.
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*
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F = S( 2, 2 )*T( 1, 1 ) - T( 2, 2 )*S( 1, 1 )
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G = S( 2, 2 )*T( 1, 2 ) - T( 2, 2 )*S( 1, 2 )
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SA = ABS( S( 2, 2 ) ) * ABS( T( 1, 1 ) )
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SB = ABS( S( 1, 1 ) ) * ABS( T( 2, 2 ) )
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CALL SLARTG( F, G, IR( 1, 2 ), IR( 1, 1 ), DDUM )
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IR( 2, 1 ) = -IR( 1, 2 )
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IR( 2, 2 ) = IR( 1, 1 )
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CALL SROT( 2, S( 1, 1 ), 1, S( 1, 2 ), 1, IR( 1, 1 ),
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$ IR( 2, 1 ) )
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CALL SROT( 2, T( 1, 1 ), 1, T( 1, 2 ), 1, IR( 1, 1 ),
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$ IR( 2, 1 ) )
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IF( SA.GE.SB ) THEN
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CALL SLARTG( S( 1, 1 ), S( 2, 1 ), LI( 1, 1 ), LI( 2, 1 ),
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$ DDUM )
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ELSE
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CALL SLARTG( T( 1, 1 ), T( 2, 1 ), LI( 1, 1 ), LI( 2, 1 ),
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$ DDUM )
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END IF
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CALL SROT( 2, S( 1, 1 ), LDST, S( 2, 1 ), LDST, LI( 1, 1 ),
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$ LI( 2, 1 ) )
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CALL SROT( 2, T( 1, 1 ), LDST, T( 2, 1 ), LDST, LI( 1, 1 ),
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$ LI( 2, 1 ) )
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LI( 2, 2 ) = LI( 1, 1 )
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LI( 1, 2 ) = -LI( 2, 1 )
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*
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* Weak stability test: |S21| <= O(EPS F-norm((A)))
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* and |T21| <= O(EPS F-norm((B)))
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*
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WEAK = ABS( S( 2, 1 ) ) .LE. THRESHA .AND.
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$ ABS( T( 2, 1 ) ) .LE. THRESHB
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IF( .NOT.WEAK )
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$ GO TO 70
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*
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IF( WANDS ) THEN
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*
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* Strong stability test:
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* F-norm((A-QL**H*S*QR)) <= O(EPS*F-norm((A)))
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* and
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* F-norm((B-QL**H*T*QR)) <= O(EPS*F-norm((B)))
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*
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CALL SLACPY( 'Full', M, M, A( J1, J1 ), LDA, WORK( M*M+1 ),
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$ M )
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CALL SGEMM( 'N', 'N', M, M, M, ONE, LI, LDST, S, LDST, ZERO,
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$ WORK, M )
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CALL SGEMM( 'N', 'T', M, M, M, -ONE, WORK, M, IR, LDST, ONE,
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$ WORK( M*M+1 ), M )
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DSCALE = ZERO
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DSUM = ONE
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CALL SLASSQ( M*M, WORK( M*M+1 ), 1, DSCALE, DSUM )
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SA = DSCALE*SQRT( DSUM )
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*
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CALL SLACPY( 'Full', M, M, B( J1, J1 ), LDB, WORK( M*M+1 ),
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$ M )
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CALL SGEMM( 'N', 'N', M, M, M, ONE, LI, LDST, T, LDST, ZERO,
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$ WORK, M )
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CALL SGEMM( 'N', 'T', M, M, M, -ONE, WORK, M, IR, LDST, ONE,
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$ WORK( M*M+1 ), M )
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DSCALE = ZERO
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DSUM = ONE
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CALL SLASSQ( M*M, WORK( M*M+1 ), 1, DSCALE, DSUM )
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SB = DSCALE*SQRT( DSUM )
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STRONG = SA.LE.THRESHA .AND. SB.LE.THRESHB
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IF( .NOT.STRONG )
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$ GO TO 70
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END IF
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*
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* Update (A(J1:J1+M-1, M+J1:N), B(J1:J1+M-1, M+J1:N)) and
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* (A(1:J1-1, J1:J1+M), B(1:J1-1, J1:J1+M)).
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*
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CALL SROT( J1+1, A( 1, J1 ), 1, A( 1, J1+1 ), 1, IR( 1, 1 ),
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$ IR( 2, 1 ) )
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CALL SROT( J1+1, B( 1, J1 ), 1, B( 1, J1+1 ), 1, IR( 1, 1 ),
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$ IR( 2, 1 ) )
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CALL SROT( N-J1+1, A( J1, J1 ), LDA, A( J1+1, J1 ), LDA,
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$ LI( 1, 1 ), LI( 2, 1 ) )
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CALL SROT( N-J1+1, B( J1, J1 ), LDB, B( J1+1, J1 ), LDB,
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$ LI( 1, 1 ), LI( 2, 1 ) )
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*
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* Set N1-by-N2 (2,1) - blocks to ZERO.
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*
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A( J1+1, J1 ) = ZERO
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B( J1+1, J1 ) = ZERO
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*
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* Accumulate transformations into Q and Z if requested.
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*
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IF( WANTZ )
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$ CALL SROT( N, Z( 1, J1 ), 1, Z( 1, J1+1 ), 1, IR( 1, 1 ),
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$ IR( 2, 1 ) )
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IF( WANTQ )
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$ CALL SROT( N, Q( 1, J1 ), 1, Q( 1, J1+1 ), 1, LI( 1, 1 ),
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$ LI( 2, 1 ) )
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*
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* Exit with INFO = 0 if swap was successfully performed.
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*
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RETURN
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*
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ELSE
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*
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* CASE 2: Swap 1-by-1 and 2-by-2 blocks, or 2-by-2
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* and 2-by-2 blocks.
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*
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* Solve the generalized Sylvester equation
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* S11 * R - L * S22 = SCALE * S12
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* T11 * R - L * T22 = SCALE * T12
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* for R and L. Solutions in LI and IR.
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*
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CALL SLACPY( 'Full', N1, N2, T( 1, N1+1 ), LDST, LI, LDST )
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CALL SLACPY( 'Full', N1, N2, S( 1, N1+1 ), LDST,
|
|
$ IR( N2+1, N1+1 ), LDST )
|
|
CALL STGSY2( 'N', 0, N1, N2, S, LDST, S( N1+1, N1+1 ), LDST,
|
|
$ IR( N2+1, N1+1 ), LDST, T, LDST, T( N1+1, N1+1 ),
|
|
$ LDST, LI, LDST, SCALE, DSUM, DSCALE, IWORK, IDUM,
|
|
$ LINFO )
|
|
IF( LINFO.NE.0 )
|
|
$ GO TO 70
|
|
*
|
|
* Compute orthogonal matrix QL:
|
|
*
|
|
* QL**T * LI = [ TL ]
|
|
* [ 0 ]
|
|
* where
|
|
* LI = [ -L ]
|
|
* [ SCALE * identity(N2) ]
|
|
*
|
|
DO 10 I = 1, N2
|
|
CALL SSCAL( N1, -ONE, LI( 1, I ), 1 )
|
|
LI( N1+I, I ) = SCALE
|
|
10 CONTINUE
|
|
CALL SGEQR2( M, N2, LI, LDST, TAUL, WORK, LINFO )
|
|
IF( LINFO.NE.0 )
|
|
$ GO TO 70
|
|
CALL SORG2R( M, M, N2, LI, LDST, TAUL, WORK, LINFO )
|
|
IF( LINFO.NE.0 )
|
|
$ GO TO 70
|
|
*
|
|
* Compute orthogonal matrix RQ:
|
|
*
|
|
* IR * RQ**T = [ 0 TR],
|
|
*
|
|
* where IR = [ SCALE * identity(N1), R ]
|
|
*
|
|
DO 20 I = 1, N1
|
|
IR( N2+I, I ) = SCALE
|
|
20 CONTINUE
|
|
CALL SGERQ2( N1, M, IR( N2+1, 1 ), LDST, TAUR, WORK, LINFO )
|
|
IF( LINFO.NE.0 )
|
|
$ GO TO 70
|
|
CALL SORGR2( M, M, N1, IR, LDST, TAUR, WORK, LINFO )
|
|
IF( LINFO.NE.0 )
|
|
$ GO TO 70
|
|
*
|
|
* Perform the swapping tentatively:
|
|
*
|
|
CALL SGEMM( 'T', 'N', M, M, M, ONE, LI, LDST, S, LDST, ZERO,
|
|
$ WORK, M )
|
|
CALL SGEMM( 'N', 'T', M, M, M, ONE, WORK, M, IR, LDST, ZERO, S,
|
|
$ LDST )
|
|
CALL SGEMM( 'T', 'N', M, M, M, ONE, LI, LDST, T, LDST, ZERO,
|
|
$ WORK, M )
|
|
CALL SGEMM( 'N', 'T', M, M, M, ONE, WORK, M, IR, LDST, ZERO, T,
|
|
$ LDST )
|
|
CALL SLACPY( 'F', M, M, S, LDST, SCPY, LDST )
|
|
CALL SLACPY( 'F', M, M, T, LDST, TCPY, LDST )
|
|
CALL SLACPY( 'F', M, M, IR, LDST, IRCOP, LDST )
|
|
CALL SLACPY( 'F', M, M, LI, LDST, LICOP, LDST )
|
|
*
|
|
* Triangularize the B-part by an RQ factorization.
|
|
* Apply transformation (from left) to A-part, giving S.
|
|
*
|
|
CALL SGERQ2( M, M, T, LDST, TAUR, WORK, LINFO )
|
|
IF( LINFO.NE.0 )
|
|
$ GO TO 70
|
|
CALL SORMR2( 'R', 'T', M, M, M, T, LDST, TAUR, S, LDST, WORK,
|
|
$ LINFO )
|
|
IF( LINFO.NE.0 )
|
|
$ GO TO 70
|
|
CALL SORMR2( 'L', 'N', M, M, M, T, LDST, TAUR, IR, LDST, WORK,
|
|
$ LINFO )
|
|
IF( LINFO.NE.0 )
|
|
$ GO TO 70
|
|
*
|
|
* Compute F-norm(S21) in BRQA21. (T21 is 0.)
|
|
*
|
|
DSCALE = ZERO
|
|
DSUM = ONE
|
|
DO 30 I = 1, N2
|
|
CALL SLASSQ( N1, S( N2+1, I ), 1, DSCALE, DSUM )
|
|
30 CONTINUE
|
|
BRQA21 = DSCALE*SQRT( DSUM )
|
|
*
|
|
* Triangularize the B-part by a QR factorization.
|
|
* Apply transformation (from right) to A-part, giving S.
|
|
*
|
|
CALL SGEQR2( M, M, TCPY, LDST, TAUL, WORK, LINFO )
|
|
IF( LINFO.NE.0 )
|
|
$ GO TO 70
|
|
CALL SORM2R( 'L', 'T', M, M, M, TCPY, LDST, TAUL, SCPY, LDST,
|
|
$ WORK, INFO )
|
|
CALL SORM2R( 'R', 'N', M, M, M, TCPY, LDST, TAUL, LICOP, LDST,
|
|
$ WORK, INFO )
|
|
IF( LINFO.NE.0 )
|
|
$ GO TO 70
|
|
*
|
|
* Compute F-norm(S21) in BQRA21. (T21 is 0.)
|
|
*
|
|
DSCALE = ZERO
|
|
DSUM = ONE
|
|
DO 40 I = 1, N2
|
|
CALL SLASSQ( N1, SCPY( N2+1, I ), 1, DSCALE, DSUM )
|
|
40 CONTINUE
|
|
BQRA21 = DSCALE*SQRT( DSUM )
|
|
*
|
|
* Decide which method to use.
|
|
* Weak stability test:
|
|
* F-norm(S21) <= O(EPS * F-norm((S)))
|
|
*
|
|
IF( BQRA21.LE.BRQA21 .AND. BQRA21.LE.THRESHA ) THEN
|
|
CALL SLACPY( 'F', M, M, SCPY, LDST, S, LDST )
|
|
CALL SLACPY( 'F', M, M, TCPY, LDST, T, LDST )
|
|
CALL SLACPY( 'F', M, M, IRCOP, LDST, IR, LDST )
|
|
CALL SLACPY( 'F', M, M, LICOP, LDST, LI, LDST )
|
|
ELSE IF( BRQA21.GE.THRESHA ) THEN
|
|
GO TO 70
|
|
END IF
|
|
*
|
|
* Set lower triangle of B-part to zero
|
|
*
|
|
CALL SLASET( 'Lower', M-1, M-1, ZERO, ZERO, T(2,1), LDST )
|
|
*
|
|
IF( WANDS ) THEN
|
|
*
|
|
* Strong stability test:
|
|
* F-norm((A-QL**H*S*QR)) <= O(EPS*F-norm((A)))
|
|
* and
|
|
* F-norm((B-QL**H*T*QR)) <= O(EPS*F-norm((B)))
|
|
*
|
|
CALL SLACPY( 'Full', M, M, A( J1, J1 ), LDA, WORK( M*M+1 ),
|
|
$ M )
|
|
CALL SGEMM( 'N', 'N', M, M, M, ONE, LI, LDST, S, LDST, ZERO,
|
|
$ WORK, M )
|
|
CALL SGEMM( 'N', 'N', M, M, M, -ONE, WORK, M, IR, LDST, ONE,
|
|
$ WORK( M*M+1 ), M )
|
|
DSCALE = ZERO
|
|
DSUM = ONE
|
|
CALL SLASSQ( M*M, WORK( M*M+1 ), 1, DSCALE, DSUM )
|
|
SA = DSCALE*SQRT( DSUM )
|
|
*
|
|
CALL SLACPY( 'Full', M, M, B( J1, J1 ), LDB, WORK( M*M+1 ),
|
|
$ M )
|
|
CALL SGEMM( 'N', 'N', M, M, M, ONE, LI, LDST, T, LDST, ZERO,
|
|
$ WORK, M )
|
|
CALL SGEMM( 'N', 'N', M, M, M, -ONE, WORK, M, IR, LDST, ONE,
|
|
$ WORK( M*M+1 ), M )
|
|
DSCALE = ZERO
|
|
DSUM = ONE
|
|
CALL SLASSQ( M*M, WORK( M*M+1 ), 1, DSCALE, DSUM )
|
|
SB = DSCALE*SQRT( DSUM )
|
|
STRONG = SA.LE.THRESHA .AND. SB.LE.THRESHB
|
|
IF( .NOT.STRONG )
|
|
$ GO TO 70
|
|
*
|
|
END IF
|
|
*
|
|
* If the swap is accepted ("weakly" and "strongly"), apply the
|
|
* transformations and set N1-by-N2 (2,1)-block to zero.
|
|
*
|
|
CALL SLASET( 'Full', N1, N2, ZERO, ZERO, S(N2+1,1), LDST )
|
|
*
|
|
* copy back M-by-M diagonal block starting at index J1 of (A, B)
|
|
*
|
|
CALL SLACPY( 'F', M, M, S, LDST, A( J1, J1 ), LDA )
|
|
CALL SLACPY( 'F', M, M, T, LDST, B( J1, J1 ), LDB )
|
|
CALL SLASET( 'Full', LDST, LDST, ZERO, ZERO, T, LDST )
|
|
*
|
|
* Standardize existing 2-by-2 blocks.
|
|
*
|
|
CALL SLASET( 'Full', M, M, ZERO, ZERO, WORK, M )
|
|
WORK( 1 ) = ONE
|
|
T( 1, 1 ) = ONE
|
|
IDUM = LWORK - M*M - 2
|
|
IF( N2.GT.1 ) THEN
|
|
CALL SLAGV2( A( J1, J1 ), LDA, B( J1, J1 ), LDB, AR, AI, BE,
|
|
$ WORK( 1 ), WORK( 2 ), T( 1, 1 ), T( 2, 1 ) )
|
|
WORK( M+1 ) = -WORK( 2 )
|
|
WORK( M+2 ) = WORK( 1 )
|
|
T( N2, N2 ) = T( 1, 1 )
|
|
T( 1, 2 ) = -T( 2, 1 )
|
|
END IF
|
|
WORK( M*M ) = ONE
|
|
T( M, M ) = ONE
|
|
*
|
|
IF( N1.GT.1 ) THEN
|
|
CALL SLAGV2( A( J1+N2, J1+N2 ), LDA, B( J1+N2, J1+N2 ), LDB,
|
|
$ TAUR, TAUL, WORK( M*M+1 ), WORK( N2*M+N2+1 ),
|
|
$ WORK( N2*M+N2+2 ), T( N2+1, N2+1 ),
|
|
$ T( M, M-1 ) )
|
|
WORK( M*M ) = WORK( N2*M+N2+1 )
|
|
WORK( M*M-1 ) = -WORK( N2*M+N2+2 )
|
|
T( M, M ) = T( N2+1, N2+1 )
|
|
T( M-1, M ) = -T( M, M-1 )
|
|
END IF
|
|
CALL SGEMM( 'T', 'N', N2, N1, N2, ONE, WORK, M, A( J1, J1+N2 ),
|
|
$ LDA, ZERO, WORK( M*M+1 ), N2 )
|
|
CALL SLACPY( 'Full', N2, N1, WORK( M*M+1 ), N2, A( J1, J1+N2 ),
|
|
$ LDA )
|
|
CALL SGEMM( 'T', 'N', N2, N1, N2, ONE, WORK, M, B( J1, J1+N2 ),
|
|
$ LDB, ZERO, WORK( M*M+1 ), N2 )
|
|
CALL SLACPY( 'Full', N2, N1, WORK( M*M+1 ), N2, B( J1, J1+N2 ),
|
|
$ LDB )
|
|
CALL SGEMM( 'N', 'N', M, M, M, ONE, LI, LDST, WORK, M, ZERO,
|
|
$ WORK( M*M+1 ), M )
|
|
CALL SLACPY( 'Full', M, M, WORK( M*M+1 ), M, LI, LDST )
|
|
CALL SGEMM( 'N', 'N', N2, N1, N1, ONE, A( J1, J1+N2 ), LDA,
|
|
$ T( N2+1, N2+1 ), LDST, ZERO, WORK, N2 )
|
|
CALL SLACPY( 'Full', N2, N1, WORK, N2, A( J1, J1+N2 ), LDA )
|
|
CALL SGEMM( 'N', 'N', N2, N1, N1, ONE, B( J1, J1+N2 ), LDB,
|
|
$ T( N2+1, N2+1 ), LDST, ZERO, WORK, N2 )
|
|
CALL SLACPY( 'Full', N2, N1, WORK, N2, B( J1, J1+N2 ), LDB )
|
|
CALL SGEMM( 'T', 'N', M, M, M, ONE, IR, LDST, T, LDST, ZERO,
|
|
$ WORK, M )
|
|
CALL SLACPY( 'Full', M, M, WORK, M, IR, LDST )
|
|
*
|
|
* Accumulate transformations into Q and Z if requested.
|
|
*
|
|
IF( WANTQ ) THEN
|
|
CALL SGEMM( 'N', 'N', N, M, M, ONE, Q( 1, J1 ), LDQ, LI,
|
|
$ LDST, ZERO, WORK, N )
|
|
CALL SLACPY( 'Full', N, M, WORK, N, Q( 1, J1 ), LDQ )
|
|
*
|
|
END IF
|
|
*
|
|
IF( WANTZ ) THEN
|
|
CALL SGEMM( 'N', 'N', N, M, M, ONE, Z( 1, J1 ), LDZ, IR,
|
|
$ LDST, ZERO, WORK, N )
|
|
CALL SLACPY( 'Full', N, M, WORK, N, Z( 1, J1 ), LDZ )
|
|
*
|
|
END IF
|
|
*
|
|
* Update (A(J1:J1+M-1, M+J1:N), B(J1:J1+M-1, M+J1:N)) and
|
|
* (A(1:J1-1, J1:J1+M), B(1:J1-1, J1:J1+M)).
|
|
*
|
|
I = J1 + M
|
|
IF( I.LE.N ) THEN
|
|
CALL SGEMM( 'T', 'N', M, N-I+1, M, ONE, LI, LDST,
|
|
$ A( J1, I ), LDA, ZERO, WORK, M )
|
|
CALL SLACPY( 'Full', M, N-I+1, WORK, M, A( J1, I ), LDA )
|
|
CALL SGEMM( 'T', 'N', M, N-I+1, M, ONE, LI, LDST,
|
|
$ B( J1, I ), LDB, ZERO, WORK, M )
|
|
CALL SLACPY( 'Full', M, N-I+1, WORK, M, B( J1, I ), LDB )
|
|
END IF
|
|
I = J1 - 1
|
|
IF( I.GT.0 ) THEN
|
|
CALL SGEMM( 'N', 'N', I, M, M, ONE, A( 1, J1 ), LDA, IR,
|
|
$ LDST, ZERO, WORK, I )
|
|
CALL SLACPY( 'Full', I, M, WORK, I, A( 1, J1 ), LDA )
|
|
CALL SGEMM( 'N', 'N', I, M, M, ONE, B( 1, J1 ), LDB, IR,
|
|
$ LDST, ZERO, WORK, I )
|
|
CALL SLACPY( 'Full', I, M, WORK, I, B( 1, J1 ), LDB )
|
|
END IF
|
|
*
|
|
* Exit with INFO = 0 if swap was successfully performed.
|
|
*
|
|
RETURN
|
|
*
|
|
END IF
|
|
*
|
|
* Exit with INFO = 1 if swap was rejected.
|
|
*
|
|
70 CONTINUE
|
|
*
|
|
INFO = 1
|
|
RETURN
|
|
*
|
|
* End of STGEX2
|
|
*
|
|
END
|