698 lines
24 KiB
Fortran
698 lines
24 KiB
Fortran
*> \brief \b STGSNA
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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 STGSNA + dependencies
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/stgsna.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/stgsna.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/stgsna.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 STGSNA( JOB, HOWMNY, SELECT, N, A, LDA, B, LDB, VL,
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* LDVL, VR, LDVR, S, DIF, MM, M, WORK, LWORK,
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* IWORK, INFO )
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*
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* .. Scalar Arguments ..
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* CHARACTER HOWMNY, JOB
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* INTEGER INFO, LDA, LDB, LDVL, LDVR, LWORK, M, MM, N
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* ..
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* .. Array Arguments ..
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* LOGICAL SELECT( * )
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* INTEGER IWORK( * )
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* REAL A( LDA, * ), B( LDB, * ), DIF( * ), S( * ),
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* $ VL( LDVL, * ), VR( LDVR, * ), 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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*> STGSNA estimates reciprocal condition numbers for specified
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*> eigenvalues and/or eigenvectors of a matrix pair (A, B) in
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*> generalized real Schur canonical form (or of any matrix pair
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*> (Q*A*Z**T, Q*B*Z**T) with orthogonal matrices Q and Z, where
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*> Z**T denotes the transpose of Z.
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*>
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*> (A, B) must be in generalized real Schur form (as returned by SGGES),
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*> i.e. A is block upper triangular with 1-by-1 and 2-by-2 diagonal
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*> blocks. B is upper triangular.
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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] JOB
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*> \verbatim
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*> JOB is CHARACTER*1
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*> Specifies whether condition numbers are required for
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*> eigenvalues (S) or eigenvectors (DIF):
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*> = 'E': for eigenvalues only (S);
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*> = 'V': for eigenvectors only (DIF);
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*> = 'B': for both eigenvalues and eigenvectors (S and DIF).
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*> \endverbatim
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*>
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*> \param[in] HOWMNY
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*> \verbatim
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*> HOWMNY is CHARACTER*1
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*> = 'A': compute condition numbers for all eigenpairs;
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*> = 'S': compute condition numbers for selected eigenpairs
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*> specified by the array SELECT.
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*> \endverbatim
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*>
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*> \param[in] SELECT
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*> \verbatim
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*> SELECT is LOGICAL array, dimension (N)
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*> If HOWMNY = 'S', SELECT specifies the eigenpairs for which
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*> condition numbers are required. To select condition numbers
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*> for the eigenpair corresponding to a real eigenvalue w(j),
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*> SELECT(j) must be set to .TRUE.. To select condition numbers
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*> corresponding to a complex conjugate pair of eigenvalues w(j)
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*> and w(j+1), either SELECT(j) or SELECT(j+1) or both, must be
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*> set to .TRUE..
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*> If HOWMNY = 'A', SELECT is not referenced.
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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 square matrix pair (A, B). N >= 0.
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*> \endverbatim
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*>
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*> \param[in] A
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*> \verbatim
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*> A is REAL array, dimension (LDA,N)
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*> The upper quasi-triangular matrix A in the pair (A,B).
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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] B
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*> \verbatim
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*> B is REAL array, dimension (LDB,N)
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*> The upper triangular matrix B in the pair (A,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] VL
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*> \verbatim
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*> VL is REAL array, dimension (LDVL,M)
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*> If JOB = 'E' or 'B', VL must contain left eigenvectors of
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*> (A, B), corresponding to the eigenpairs specified by HOWMNY
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*> and SELECT. The eigenvectors must be stored in consecutive
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*> columns of VL, as returned by STGEVC.
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*> If JOB = 'V', VL is not referenced.
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*> \endverbatim
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*>
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*> \param[in] LDVL
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*> \verbatim
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*> LDVL is INTEGER
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*> The leading dimension of the array VL. LDVL >= 1.
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*> If JOB = 'E' or 'B', LDVL >= N.
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*> \endverbatim
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*>
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*> \param[in] VR
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*> \verbatim
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*> VR is REAL array, dimension (LDVR,M)
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*> If JOB = 'E' or 'B', VR must contain right eigenvectors of
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*> (A, B), corresponding to the eigenpairs specified by HOWMNY
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*> and SELECT. The eigenvectors must be stored in consecutive
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*> columns ov VR, as returned by STGEVC.
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*> If JOB = 'V', VR is not referenced.
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*> \endverbatim
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*>
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*> \param[in] LDVR
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*> \verbatim
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*> LDVR is INTEGER
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*> The leading dimension of the array VR. LDVR >= 1.
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*> If JOB = 'E' or 'B', LDVR >= N.
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*> \endverbatim
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*>
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*> \param[out] S
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*> \verbatim
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*> S is REAL array, dimension (MM)
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*> If JOB = 'E' or 'B', the reciprocal condition numbers of the
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*> selected eigenvalues, stored in consecutive elements of the
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*> array. For a complex conjugate pair of eigenvalues two
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*> consecutive elements of S are set to the same value. Thus
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*> S(j), DIF(j), and the j-th columns of VL and VR all
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*> correspond to the same eigenpair (but not in general the
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*> j-th eigenpair, unless all eigenpairs are selected).
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*> If JOB = 'V', S is not referenced.
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*> \endverbatim
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*>
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*> \param[out] DIF
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*> \verbatim
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*> DIF is REAL array, dimension (MM)
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*> If JOB = 'V' or 'B', the estimated reciprocal condition
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*> numbers of the selected eigenvectors, stored in consecutive
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*> elements of the array. For a complex eigenvector two
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*> consecutive elements of DIF are set to the same value. If
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*> the eigenvalues cannot be reordered to compute DIF(j), DIF(j)
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*> is set to 0; this can only occur when the true value would be
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*> very small anyway.
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*> If JOB = 'E', DIF is not referenced.
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*> \endverbatim
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*>
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*> \param[in] MM
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*> \verbatim
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*> MM is INTEGER
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*> The number of elements in the arrays S and DIF. MM >= M.
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*> \endverbatim
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*>
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*> \param[out] M
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*> \verbatim
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*> M is INTEGER
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*> The number of elements of the arrays S and DIF used to store
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*> the specified condition numbers; for each selected real
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*> eigenvalue one element is used, and for each selected complex
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*> conjugate pair of eigenvalues, two elements are used.
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*> If HOWMNY = 'A', M is set to N.
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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 dimension of the array WORK. LWORK >= max(1,N).
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*> If JOB = 'V' or 'B' LWORK >= 2*N*(N+2)+16.
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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] IWORK
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*> \verbatim
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*> IWORK is INTEGER array, dimension (N + 6)
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*> If JOB = 'E', IWORK is not referenced.
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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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*> \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 realOTHERcomputational
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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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*> The reciprocal of the condition number of a generalized eigenvalue
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*> w = (a, b) is defined as
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*>
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*> S(w) = (|u**TAv|**2 + |u**TBv|**2)**(1/2) / (norm(u)*norm(v))
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*>
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*> where u and v are the left and right eigenvectors of (A, B)
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*> corresponding to w; |z| denotes the absolute value of the complex
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*> number, and norm(u) denotes the 2-norm of the vector u.
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*> The pair (a, b) corresponds to an eigenvalue w = a/b (= u**TAv/u**TBv)
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*> of the matrix pair (A, B). If both a and b equal zero, then (A B) is
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*> singular and S(I) = -1 is returned.
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*>
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*> An approximate error bound on the chordal distance between the i-th
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*> computed generalized eigenvalue w and the corresponding exact
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*> eigenvalue lambda is
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*>
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*> chord(w, lambda) <= EPS * norm(A, B) / S(I)
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*>
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*> where EPS is the machine precision.
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*>
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*> The reciprocal of the condition number DIF(i) of right eigenvector u
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*> and left eigenvector v corresponding to the generalized eigenvalue w
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*> is defined as follows:
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*>
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*> a) If the i-th eigenvalue w = (a,b) is real
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*>
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*> Suppose U and V are orthogonal transformations such that
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*>
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*> U**T*(A, B)*V = (S, T) = ( a * ) ( b * ) 1
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*> ( 0 S22 ),( 0 T22 ) n-1
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*> 1 n-1 1 n-1
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*>
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*> Then the reciprocal condition number DIF(i) is
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*>
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*> Difl((a, b), (S22, T22)) = sigma-min( Zl ),
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*>
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*> where sigma-min(Zl) denotes the smallest singular value of the
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*> 2(n-1)-by-2(n-1) matrix
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*>
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*> Zl = [ kron(a, In-1) -kron(1, S22) ]
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*> [ kron(b, In-1) -kron(1, T22) ] .
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*>
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*> Here In-1 is the identity matrix of size n-1. kron(X, Y) is the
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*> Kronecker product between the matrices X and Y.
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*>
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*> Note that if the default method for computing DIF(i) is wanted
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*> (see SLATDF), then the parameter DIFDRI (see below) should be
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*> changed from 3 to 4 (routine SLATDF(IJOB = 2 will be used)).
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*> See STGSYL for more details.
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*>
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*> b) If the i-th and (i+1)-th eigenvalues are complex conjugate pair,
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*>
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*> Suppose U and V are orthogonal transformations such that
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*>
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*> U**T*(A, B)*V = (S, T) = ( S11 * ) ( T11 * ) 2
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*> ( 0 S22 ),( 0 T22) n-2
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*> 2 n-2 2 n-2
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*>
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*> and (S11, T11) corresponds to the complex conjugate eigenvalue
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*> pair (w, conjg(w)). There exist unitary matrices U1 and V1 such
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*> that
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*>
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*> U1**T*S11*V1 = ( s11 s12 ) and U1**T*T11*V1 = ( t11 t12 )
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*> ( 0 s22 ) ( 0 t22 )
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*>
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*> where the generalized eigenvalues w = s11/t11 and
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*> conjg(w) = s22/t22.
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*>
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*> Then the reciprocal condition number DIF(i) is bounded by
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*>
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*> min( d1, max( 1, |real(s11)/real(s22)| )*d2 )
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*>
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*> where, d1 = Difl((s11, t11), (s22, t22)) = sigma-min(Z1), where
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*> Z1 is the complex 2-by-2 matrix
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*>
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*> Z1 = [ s11 -s22 ]
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*> [ t11 -t22 ],
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*>
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*> This is done by computing (using real arithmetic) the
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*> roots of the characteristical polynomial det(Z1**T * Z1 - lambda I),
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*> where Z1**T denotes the transpose of Z1 and det(X) denotes
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*> the determinant of X.
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*>
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*> and d2 is an upper bound on Difl((S11, T11), (S22, T22)), i.e. an
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*> upper bound on sigma-min(Z2), where Z2 is (2n-2)-by-(2n-2)
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*>
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*> Z2 = [ kron(S11**T, In-2) -kron(I2, S22) ]
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*> [ kron(T11**T, In-2) -kron(I2, T22) ]
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*>
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*> Note that if the default method for computing DIF is wanted (see
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*> SLATDF), then the parameter DIFDRI (see below) should be changed
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*> from 3 to 4 (routine SLATDF(IJOB = 2 will be used)). See STGSYL
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*> for more details.
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*>
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*> For each eigenvalue/vector specified by SELECT, DIF stores a
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*> Frobenius norm-based estimate of Difl.
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*>
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*> An approximate error bound for the i-th computed eigenvector VL(i) or
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*> VR(i) is given by
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*>
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*> EPS * norm(A, B) / DIF(i).
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*>
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*> See ref. [2-3] for more details and further references.
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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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*> 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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*>
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*> [3] B. Kagstrom and P. Poromaa, LAPACK-Style Algorithms and Software
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*> for Solving the Generalized Sylvester Equation and Estimating the
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*> Separation between Regular Matrix Pairs, Report UMINF - 93.23,
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*> Department of Computing Science, Umea University, S-901 87 Umea,
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*> Sweden, December 1993, Revised April 1994, Also as LAPACK Working
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*> Note 75. To appear in ACM Trans. on Math. Software, Vol 22,
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*> No 1, 1996.
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*> \endverbatim
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*>
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* =====================================================================
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SUBROUTINE STGSNA( JOB, HOWMNY, SELECT, N, A, LDA, B, LDB, VL,
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$ LDVL, VR, LDVR, S, DIF, MM, M, WORK, LWORK,
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$ IWORK, 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 HOWMNY, JOB
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INTEGER INFO, LDA, LDB, LDVL, LDVR, LWORK, M, MM, N
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* ..
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* .. Array Arguments ..
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LOGICAL SELECT( * )
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INTEGER IWORK( * )
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REAL A( LDA, * ), B( LDB, * ), DIF( * ), S( * ),
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$ VL( LDVL, * ), VR( LDVR, * ), WORK( * )
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* ..
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*
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* =====================================================================
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*
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* .. Parameters ..
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INTEGER DIFDRI
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PARAMETER ( DIFDRI = 3 )
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REAL ZERO, ONE, TWO, FOUR
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PARAMETER ( ZERO = 0.0E+0, ONE = 1.0E+0, TWO = 2.0E+0,
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$ FOUR = 4.0E+0 )
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* ..
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* .. Local Scalars ..
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LOGICAL LQUERY, PAIR, SOMCON, WANTBH, WANTDF, WANTS
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INTEGER I, IERR, IFST, ILST, IZ, K, KS, LWMIN, N1, N2
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REAL ALPHAI, ALPHAR, ALPRQT, BETA, C1, C2, COND,
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$ EPS, LNRM, RNRM, ROOT1, ROOT2, SCALE, SMLNUM,
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$ TMPII, TMPIR, TMPRI, TMPRR, UHAV, UHAVI, UHBV,
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$ UHBVI
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* ..
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* .. Local Arrays ..
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REAL DUMMY( 1 ), DUMMY1( 1 )
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* ..
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* .. External Functions ..
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LOGICAL LSAME
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REAL SDOT, SLAMCH, SLAPY2, SNRM2
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EXTERNAL LSAME, SDOT, SLAMCH, SLAPY2, SNRM2
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* ..
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* .. External Subroutines ..
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EXTERNAL SGEMV, SLACPY, SLAG2, STGEXC, STGSYL, XERBLA
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* ..
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* .. Intrinsic Functions ..
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INTRINSIC MAX, MIN, SQRT
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* ..
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* .. Executable Statements ..
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*
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* Decode and test the input parameters
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*
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WANTBH = LSAME( JOB, 'B' )
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WANTS = LSAME( JOB, 'E' ) .OR. WANTBH
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WANTDF = LSAME( JOB, 'V' ) .OR. WANTBH
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*
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SOMCON = LSAME( HOWMNY, 'S' )
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*
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INFO = 0
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LQUERY = ( LWORK.EQ.-1 )
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*
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IF( .NOT.WANTS .AND. .NOT.WANTDF ) THEN
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INFO = -1
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ELSE IF( .NOT.LSAME( HOWMNY, 'A' ) .AND. .NOT.SOMCON ) THEN
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INFO = -2
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ELSE IF( N.LT.0 ) THEN
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INFO = -4
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ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
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INFO = -6
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ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
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INFO = -8
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ELSE IF( WANTS .AND. LDVL.LT.N ) THEN
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INFO = -10
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ELSE IF( WANTS .AND. LDVR.LT.N ) THEN
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INFO = -12
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ELSE
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*
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* Set M to the number of eigenpairs for which condition numbers
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* are required, and test MM.
|
|
*
|
|
IF( SOMCON ) THEN
|
|
M = 0
|
|
PAIR = .FALSE.
|
|
DO 10 K = 1, N
|
|
IF( PAIR ) THEN
|
|
PAIR = .FALSE.
|
|
ELSE
|
|
IF( K.LT.N ) THEN
|
|
IF( A( K+1, K ).EQ.ZERO ) THEN
|
|
IF( SELECT( K ) )
|
|
$ M = M + 1
|
|
ELSE
|
|
PAIR = .TRUE.
|
|
IF( SELECT( K ) .OR. SELECT( K+1 ) )
|
|
$ M = M + 2
|
|
END IF
|
|
ELSE
|
|
IF( SELECT( N ) )
|
|
$ M = M + 1
|
|
END IF
|
|
END IF
|
|
10 CONTINUE
|
|
ELSE
|
|
M = N
|
|
END IF
|
|
*
|
|
IF( N.EQ.0 ) THEN
|
|
LWMIN = 1
|
|
ELSE IF( LSAME( JOB, 'V' ) .OR. LSAME( JOB, 'B' ) ) THEN
|
|
LWMIN = 2*N*( N + 2 ) + 16
|
|
ELSE
|
|
LWMIN = N
|
|
END IF
|
|
WORK( 1 ) = LWMIN
|
|
*
|
|
IF( MM.LT.M ) THEN
|
|
INFO = -15
|
|
ELSE IF( LWORK.LT.LWMIN .AND. .NOT.LQUERY ) THEN
|
|
INFO = -18
|
|
END IF
|
|
END IF
|
|
*
|
|
IF( INFO.NE.0 ) THEN
|
|
CALL XERBLA( 'STGSNA', -INFO )
|
|
RETURN
|
|
ELSE IF( LQUERY ) THEN
|
|
RETURN
|
|
END IF
|
|
*
|
|
* Quick return if possible
|
|
*
|
|
IF( N.EQ.0 )
|
|
$ RETURN
|
|
*
|
|
* Get machine constants
|
|
*
|
|
EPS = SLAMCH( 'P' )
|
|
SMLNUM = SLAMCH( 'S' ) / EPS
|
|
KS = 0
|
|
PAIR = .FALSE.
|
|
*
|
|
DO 20 K = 1, N
|
|
*
|
|
* Determine whether A(k,k) begins a 1-by-1 or 2-by-2 block.
|
|
*
|
|
IF( PAIR ) THEN
|
|
PAIR = .FALSE.
|
|
GO TO 20
|
|
ELSE
|
|
IF( K.LT.N )
|
|
$ PAIR = A( K+1, K ).NE.ZERO
|
|
END IF
|
|
*
|
|
* Determine whether condition numbers are required for the k-th
|
|
* eigenpair.
|
|
*
|
|
IF( SOMCON ) THEN
|
|
IF( PAIR ) THEN
|
|
IF( .NOT.SELECT( K ) .AND. .NOT.SELECT( K+1 ) )
|
|
$ GO TO 20
|
|
ELSE
|
|
IF( .NOT.SELECT( K ) )
|
|
$ GO TO 20
|
|
END IF
|
|
END IF
|
|
*
|
|
KS = KS + 1
|
|
*
|
|
IF( WANTS ) THEN
|
|
*
|
|
* Compute the reciprocal condition number of the k-th
|
|
* eigenvalue.
|
|
*
|
|
IF( PAIR ) THEN
|
|
*
|
|
* Complex eigenvalue pair.
|
|
*
|
|
RNRM = SLAPY2( SNRM2( N, VR( 1, KS ), 1 ),
|
|
$ SNRM2( N, VR( 1, KS+1 ), 1 ) )
|
|
LNRM = SLAPY2( SNRM2( N, VL( 1, KS ), 1 ),
|
|
$ SNRM2( N, VL( 1, KS+1 ), 1 ) )
|
|
CALL SGEMV( 'N', N, N, ONE, A, LDA, VR( 1, KS ), 1, ZERO,
|
|
$ WORK, 1 )
|
|
TMPRR = SDOT( N, WORK, 1, VL( 1, KS ), 1 )
|
|
TMPRI = SDOT( N, WORK, 1, VL( 1, KS+1 ), 1 )
|
|
CALL SGEMV( 'N', N, N, ONE, A, LDA, VR( 1, KS+1 ), 1,
|
|
$ ZERO, WORK, 1 )
|
|
TMPII = SDOT( N, WORK, 1, VL( 1, KS+1 ), 1 )
|
|
TMPIR = SDOT( N, WORK, 1, VL( 1, KS ), 1 )
|
|
UHAV = TMPRR + TMPII
|
|
UHAVI = TMPIR - TMPRI
|
|
CALL SGEMV( 'N', N, N, ONE, B, LDB, VR( 1, KS ), 1, ZERO,
|
|
$ WORK, 1 )
|
|
TMPRR = SDOT( N, WORK, 1, VL( 1, KS ), 1 )
|
|
TMPRI = SDOT( N, WORK, 1, VL( 1, KS+1 ), 1 )
|
|
CALL SGEMV( 'N', N, N, ONE, B, LDB, VR( 1, KS+1 ), 1,
|
|
$ ZERO, WORK, 1 )
|
|
TMPII = SDOT( N, WORK, 1, VL( 1, KS+1 ), 1 )
|
|
TMPIR = SDOT( N, WORK, 1, VL( 1, KS ), 1 )
|
|
UHBV = TMPRR + TMPII
|
|
UHBVI = TMPIR - TMPRI
|
|
UHAV = SLAPY2( UHAV, UHAVI )
|
|
UHBV = SLAPY2( UHBV, UHBVI )
|
|
COND = SLAPY2( UHAV, UHBV )
|
|
S( KS ) = COND / ( RNRM*LNRM )
|
|
S( KS+1 ) = S( KS )
|
|
*
|
|
ELSE
|
|
*
|
|
* Real eigenvalue.
|
|
*
|
|
RNRM = SNRM2( N, VR( 1, KS ), 1 )
|
|
LNRM = SNRM2( N, VL( 1, KS ), 1 )
|
|
CALL SGEMV( 'N', N, N, ONE, A, LDA, VR( 1, KS ), 1, ZERO,
|
|
$ WORK, 1 )
|
|
UHAV = SDOT( N, WORK, 1, VL( 1, KS ), 1 )
|
|
CALL SGEMV( 'N', N, N, ONE, B, LDB, VR( 1, KS ), 1, ZERO,
|
|
$ WORK, 1 )
|
|
UHBV = SDOT( N, WORK, 1, VL( 1, KS ), 1 )
|
|
COND = SLAPY2( UHAV, UHBV )
|
|
IF( COND.EQ.ZERO ) THEN
|
|
S( KS ) = -ONE
|
|
ELSE
|
|
S( KS ) = COND / ( RNRM*LNRM )
|
|
END IF
|
|
END IF
|
|
END IF
|
|
*
|
|
IF( WANTDF ) THEN
|
|
IF( N.EQ.1 ) THEN
|
|
DIF( KS ) = SLAPY2( A( 1, 1 ), B( 1, 1 ) )
|
|
GO TO 20
|
|
END IF
|
|
*
|
|
* Estimate the reciprocal condition number of the k-th
|
|
* eigenvectors.
|
|
IF( PAIR ) THEN
|
|
*
|
|
* Copy the 2-by 2 pencil beginning at (A(k,k), B(k, k)).
|
|
* Compute the eigenvalue(s) at position K.
|
|
*
|
|
WORK( 1 ) = A( K, K )
|
|
WORK( 2 ) = A( K+1, K )
|
|
WORK( 3 ) = A( K, K+1 )
|
|
WORK( 4 ) = A( K+1, K+1 )
|
|
WORK( 5 ) = B( K, K )
|
|
WORK( 6 ) = B( K+1, K )
|
|
WORK( 7 ) = B( K, K+1 )
|
|
WORK( 8 ) = B( K+1, K+1 )
|
|
CALL SLAG2( WORK, 2, WORK( 5 ), 2, SMLNUM*EPS, BETA,
|
|
$ DUMMY1( 1 ), ALPHAR, DUMMY( 1 ), ALPHAI )
|
|
ALPRQT = ONE
|
|
C1 = TWO*( ALPHAR*ALPHAR+ALPHAI*ALPHAI+BETA*BETA )
|
|
C2 = FOUR*BETA*BETA*ALPHAI*ALPHAI
|
|
ROOT1 = C1 + SQRT( C1*C1-4.0*C2 )
|
|
ROOT1 = ROOT1 / TWO
|
|
ROOT2 = C2 / ROOT1
|
|
COND = MIN( SQRT( ROOT1 ), SQRT( ROOT2 ) )
|
|
END IF
|
|
*
|
|
* Copy the matrix (A, B) to the array WORK and swap the
|
|
* diagonal block beginning at A(k,k) to the (1,1) position.
|
|
*
|
|
CALL SLACPY( 'Full', N, N, A, LDA, WORK, N )
|
|
CALL SLACPY( 'Full', N, N, B, LDB, WORK( N*N+1 ), N )
|
|
IFST = K
|
|
ILST = 1
|
|
*
|
|
CALL STGEXC( .FALSE., .FALSE., N, WORK, N, WORK( N*N+1 ), N,
|
|
$ DUMMY, 1, DUMMY1, 1, IFST, ILST,
|
|
$ WORK( N*N*2+1 ), LWORK-2*N*N, IERR )
|
|
*
|
|
IF( IERR.GT.0 ) THEN
|
|
*
|
|
* Ill-conditioned problem - swap rejected.
|
|
*
|
|
DIF( KS ) = ZERO
|
|
ELSE
|
|
*
|
|
* Reordering successful, solve generalized Sylvester
|
|
* equation for R and L,
|
|
* A22 * R - L * A11 = A12
|
|
* B22 * R - L * B11 = B12,
|
|
* and compute estimate of Difl((A11,B11), (A22, B22)).
|
|
*
|
|
N1 = 1
|
|
IF( WORK( 2 ).NE.ZERO )
|
|
$ N1 = 2
|
|
N2 = N - N1
|
|
IF( N2.EQ.0 ) THEN
|
|
DIF( KS ) = COND
|
|
ELSE
|
|
I = N*N + 1
|
|
IZ = 2*N*N + 1
|
|
CALL STGSYL( 'N', DIFDRI, N2, N1, WORK( N*N1+N1+1 ),
|
|
$ N, WORK, N, WORK( N1+1 ), N,
|
|
$ WORK( N*N1+N1+I ), N, WORK( I ), N,
|
|
$ WORK( N1+I ), N, SCALE, DIF( KS ),
|
|
$ WORK( IZ+1 ), LWORK-2*N*N, IWORK, IERR )
|
|
*
|
|
IF( PAIR )
|
|
$ DIF( KS ) = MIN( MAX( ONE, ALPRQT )*DIF( KS ),
|
|
$ COND )
|
|
END IF
|
|
END IF
|
|
IF( PAIR )
|
|
$ DIF( KS+1 ) = DIF( KS )
|
|
END IF
|
|
IF( PAIR )
|
|
$ KS = KS + 1
|
|
*
|
|
20 CONTINUE
|
|
WORK( 1 ) = LWMIN
|
|
RETURN
|
|
*
|
|
* End of STGSNA
|
|
*
|
|
END
|