1075 lines
36 KiB
Fortran
1075 lines
36 KiB
Fortran
*> \brief \b STREVC
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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 STREVC + dependencies
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/strevc.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/strevc.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/strevc.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 STREVC( SIDE, HOWMNY, SELECT, N, T, LDT, VL, LDVL, VR,
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* LDVR, MM, M, WORK, INFO )
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*
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* .. Scalar Arguments ..
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* CHARACTER HOWMNY, SIDE
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* INTEGER INFO, LDT, LDVL, LDVR, M, MM, N
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* ..
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* .. Array Arguments ..
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* LOGICAL SELECT( * )
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* REAL T( LDT, * ), VL( LDVL, * ), VR( LDVR, * ),
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* $ 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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*> STREVC computes some or all of the right and/or left eigenvectors of
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*> a real upper quasi-triangular matrix T.
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*> Matrices of this type are produced by the Schur factorization of
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*> a real general matrix: A = Q*T*Q**T, as computed by SHSEQR.
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*>
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*> The right eigenvector x and the left eigenvector y of T corresponding
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*> to an eigenvalue w are defined by:
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*>
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*> T*x = w*x, (y**H)*T = w*(y**H)
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*>
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*> where y**H denotes the conjugate transpose of y.
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*> The eigenvalues are not input to this routine, but are read directly
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*> from the diagonal blocks of T.
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*>
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*> This routine returns the matrices X and/or Y of right and left
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*> eigenvectors of T, or the products Q*X and/or Q*Y, where Q is an
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*> input matrix. If Q is the orthogonal factor that reduces a matrix
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*> A to Schur form T, then Q*X and Q*Y are the matrices of right and
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*> left eigenvectors of A.
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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] SIDE
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*> \verbatim
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*> SIDE is CHARACTER*1
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*> = 'R': compute right eigenvectors only;
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*> = 'L': compute left eigenvectors only;
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*> = 'B': compute both right and left eigenvectors.
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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 all right and/or left eigenvectors;
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*> = 'B': compute all right and/or left eigenvectors,
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*> backtransformed by the matrices in VR and/or VL;
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*> = 'S': compute selected right and/or left eigenvectors,
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*> as indicated by the logical array SELECT.
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*> \endverbatim
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*>
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*> \param[in,out] 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 eigenvectors to be
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*> computed.
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*> If w(j) is a real eigenvalue, the corresponding real
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*> eigenvector is computed if SELECT(j) is .TRUE..
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*> If w(j) and w(j+1) are the real and imaginary parts of a
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*> complex eigenvalue, the corresponding complex eigenvector is
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*> computed if either SELECT(j) or SELECT(j+1) is .TRUE., and
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*> on exit SELECT(j) is set to .TRUE. and SELECT(j+1) is set to
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*> .FALSE..
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*> Not referenced if HOWMNY = 'A' or 'B'.
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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 T. N >= 0.
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*> \endverbatim
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*>
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*> \param[in] T
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*> \verbatim
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*> T is REAL array, dimension (LDT,N)
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*> The upper quasi-triangular matrix T in Schur canonical form.
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*> \endverbatim
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*>
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*> \param[in] LDT
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*> \verbatim
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*> LDT is INTEGER
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*> The leading dimension of the array T. LDT >= max(1,N).
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*> \endverbatim
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*>
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*> \param[in,out] VL
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*> \verbatim
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*> VL is REAL array, dimension (LDVL,MM)
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*> On entry, if SIDE = 'L' or 'B' and HOWMNY = 'B', VL must
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*> contain an N-by-N matrix Q (usually the orthogonal matrix Q
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*> of Schur vectors returned by SHSEQR).
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*> On exit, if SIDE = 'L' or 'B', VL contains:
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*> if HOWMNY = 'A', the matrix Y of left eigenvectors of T;
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*> if HOWMNY = 'B', the matrix Q*Y;
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*> if HOWMNY = 'S', the left eigenvectors of T specified by
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*> SELECT, stored consecutively in the columns
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*> of VL, in the same order as their
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*> eigenvalues.
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*> A complex eigenvector corresponding to a complex eigenvalue
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*> is stored in two consecutive columns, the first holding the
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*> real part, and the second the imaginary part.
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*> Not referenced if SIDE = 'R'.
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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, and if
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*> SIDE = 'L' or 'B', LDVL >= N.
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*> \endverbatim
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*>
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*> \param[in,out] VR
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*> \verbatim
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*> VR is REAL array, dimension (LDVR,MM)
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*> On entry, if SIDE = 'R' or 'B' and HOWMNY = 'B', VR must
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*> contain an N-by-N matrix Q (usually the orthogonal matrix Q
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*> of Schur vectors returned by SHSEQR).
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*> On exit, if SIDE = 'R' or 'B', VR contains:
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*> if HOWMNY = 'A', the matrix X of right eigenvectors of T;
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*> if HOWMNY = 'B', the matrix Q*X;
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*> if HOWMNY = 'S', the right eigenvectors of T specified by
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*> SELECT, stored consecutively in the columns
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*> of VR, in the same order as their
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*> eigenvalues.
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*> A complex eigenvector corresponding to a complex eigenvalue
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*> is stored in two consecutive columns, the first holding the
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*> real part and the second the imaginary part.
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*> Not referenced if SIDE = 'L'.
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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, and if
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*> SIDE = 'R' or 'B', LDVR >= N.
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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 columns in the arrays VL and/or VR. 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 columns in the arrays VL and/or VR actually
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*> used to store the eigenvectors.
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*> If HOWMNY = 'A' or 'B', M is set to N.
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*> Each selected real eigenvector occupies one column and each
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*> selected complex eigenvector occupies two columns.
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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 (3*N)
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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 algorithm used in this program is basically backward (forward)
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*> substitution, with scaling to make the the code robust against
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*> possible overflow.
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*>
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*> Each eigenvector is normalized so that the element of largest
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*> magnitude has magnitude 1; here the magnitude of a complex number
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*> (x,y) is taken to be |x| + |y|.
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*> \endverbatim
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*>
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* =====================================================================
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SUBROUTINE STREVC( SIDE, HOWMNY, SELECT, N, T, LDT, VL, LDVL, VR,
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$ LDVR, MM, M, WORK, 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, SIDE
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INTEGER INFO, LDT, LDVL, LDVR, M, MM, N
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* ..
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* .. Array Arguments ..
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LOGICAL SELECT( * )
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REAL T( LDT, * ), VL( LDVL, * ), VR( LDVR, * ),
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$ 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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REAL ZERO, ONE
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PARAMETER ( ZERO = 0.0E+0, ONE = 1.0E+0 )
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* ..
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* .. Local Scalars ..
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LOGICAL ALLV, BOTHV, LEFTV, OVER, PAIR, RIGHTV, SOMEV
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INTEGER I, IERR, II, IP, IS, J, J1, J2, JNXT, K, KI, N2
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REAL BETA, BIGNUM, EMAX, OVFL, REC, REMAX, SCALE,
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$ SMIN, SMLNUM, ULP, UNFL, VCRIT, VMAX, WI, WR,
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$ XNORM
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* ..
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* .. External Functions ..
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LOGICAL LSAME
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INTEGER ISAMAX
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REAL SDOT, SLAMCH
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EXTERNAL LSAME, ISAMAX, SDOT, SLAMCH
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* ..
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* .. External Subroutines ..
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EXTERNAL SAXPY, SCOPY, SGEMV, SLABAD, SLALN2, SSCAL,
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$ XERBLA
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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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* .. Local Arrays ..
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REAL X( 2, 2 )
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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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BOTHV = LSAME( SIDE, 'B' )
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RIGHTV = LSAME( SIDE, 'R' ) .OR. BOTHV
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LEFTV = LSAME( SIDE, 'L' ) .OR. BOTHV
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*
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ALLV = LSAME( HOWMNY, 'A' )
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OVER = LSAME( HOWMNY, 'B' )
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SOMEV = LSAME( HOWMNY, 'S' )
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*
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INFO = 0
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IF( .NOT.RIGHTV .AND. .NOT.LEFTV ) THEN
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INFO = -1
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ELSE IF( .NOT.ALLV .AND. .NOT.OVER .AND. .NOT.SOMEV ) 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( LDT.LT.MAX( 1, N ) ) THEN
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INFO = -6
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ELSE IF( LDVL.LT.1 .OR. ( LEFTV .AND. LDVL.LT.N ) ) THEN
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INFO = -8
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ELSE IF( LDVR.LT.1 .OR. ( RIGHTV .AND. LDVR.LT.N ) ) THEN
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INFO = -10
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ELSE
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*
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* Set M to the number of columns required to store the selected
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* eigenvectors, standardize the array SELECT if necessary, and
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* test MM.
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*
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IF( SOMEV ) THEN
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M = 0
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PAIR = .FALSE.
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DO 10 J = 1, N
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IF( PAIR ) THEN
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PAIR = .FALSE.
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SELECT( J ) = .FALSE.
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ELSE
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IF( J.LT.N ) THEN
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IF( T( J+1, J ).EQ.ZERO ) THEN
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IF( SELECT( J ) )
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$ M = M + 1
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ELSE
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PAIR = .TRUE.
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IF( SELECT( J ) .OR. SELECT( J+1 ) ) THEN
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SELECT( J ) = .TRUE.
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M = M + 2
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END IF
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END IF
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ELSE
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IF( SELECT( N ) )
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$ M = M + 1
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END IF
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END IF
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10 CONTINUE
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ELSE
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M = N
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END IF
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*
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IF( MM.LT.M ) THEN
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INFO = -11
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END IF
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END IF
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IF( INFO.NE.0 ) THEN
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CALL XERBLA( 'STREVC', -INFO )
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RETURN
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END IF
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*
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* Quick return if possible.
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*
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IF( N.EQ.0 )
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$ RETURN
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*
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* Set the constants to control overflow.
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*
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UNFL = SLAMCH( 'Safe minimum' )
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OVFL = ONE / UNFL
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CALL SLABAD( UNFL, OVFL )
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ULP = SLAMCH( 'Precision' )
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SMLNUM = UNFL*( N / ULP )
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BIGNUM = ( ONE-ULP ) / SMLNUM
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*
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* Compute 1-norm of each column of strictly upper triangular
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* part of T to control overflow in triangular solver.
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*
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WORK( 1 ) = ZERO
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DO 30 J = 2, N
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WORK( J ) = ZERO
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DO 20 I = 1, J - 1
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WORK( J ) = WORK( J ) + ABS( T( I, J ) )
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20 CONTINUE
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30 CONTINUE
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*
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* Index IP is used to specify the real or complex eigenvalue:
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* IP = 0, real eigenvalue,
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* 1, first of conjugate complex pair: (wr,wi)
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* -1, second of conjugate complex pair: (wr,wi)
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*
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N2 = 2*N
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*
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IF( RIGHTV ) THEN
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*
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* Compute right eigenvectors.
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*
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IP = 0
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IS = M
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DO 140 KI = N, 1, -1
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*
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IF( IP.EQ.1 )
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$ GO TO 130
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IF( KI.EQ.1 )
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$ GO TO 40
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IF( T( KI, KI-1 ).EQ.ZERO )
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$ GO TO 40
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IP = -1
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*
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40 CONTINUE
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IF( SOMEV ) THEN
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IF( IP.EQ.0 ) THEN
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IF( .NOT.SELECT( KI ) )
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$ GO TO 130
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ELSE
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IF( .NOT.SELECT( KI-1 ) )
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$ GO TO 130
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END IF
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END IF
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*
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* Compute the KI-th eigenvalue (WR,WI).
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*
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WR = T( KI, KI )
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WI = ZERO
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IF( IP.NE.0 )
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$ WI = SQRT( ABS( T( KI, KI-1 ) ) )*
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$ SQRT( ABS( T( KI-1, KI ) ) )
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SMIN = MAX( ULP*( ABS( WR )+ABS( WI ) ), SMLNUM )
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*
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IF( IP.EQ.0 ) THEN
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*
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* Real right eigenvector
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*
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WORK( KI+N ) = ONE
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*
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* Form right-hand side
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*
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DO 50 K = 1, KI - 1
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WORK( K+N ) = -T( K, KI )
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50 CONTINUE
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*
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* Solve the upper quasi-triangular system:
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* (T(1:KI-1,1:KI-1) - WR)*X = SCALE*WORK.
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*
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JNXT = KI - 1
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DO 60 J = KI - 1, 1, -1
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IF( J.GT.JNXT )
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$ GO TO 60
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J1 = J
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J2 = J
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JNXT = J - 1
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IF( J.GT.1 ) THEN
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IF( T( J, J-1 ).NE.ZERO ) THEN
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J1 = J - 1
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JNXT = J - 2
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END IF
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END IF
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*
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IF( J1.EQ.J2 ) THEN
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*
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* 1-by-1 diagonal block
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*
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CALL SLALN2( .FALSE., 1, 1, SMIN, ONE, T( J, J ),
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$ LDT, ONE, ONE, WORK( J+N ), N, WR,
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$ ZERO, X, 2, SCALE, XNORM, IERR )
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*
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* Scale X(1,1) to avoid overflow when updating
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* the right-hand side.
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*
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IF( XNORM.GT.ONE ) THEN
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IF( WORK( J ).GT.BIGNUM / XNORM ) THEN
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X( 1, 1 ) = X( 1, 1 ) / XNORM
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SCALE = SCALE / XNORM
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END IF
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END IF
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*
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* Scale if necessary
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*
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IF( SCALE.NE.ONE )
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$ CALL SSCAL( KI, SCALE, WORK( 1+N ), 1 )
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WORK( J+N ) = X( 1, 1 )
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*
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* Update right-hand side
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*
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CALL SAXPY( J-1, -X( 1, 1 ), T( 1, J ), 1,
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$ WORK( 1+N ), 1 )
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*
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ELSE
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*
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* 2-by-2 diagonal block
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*
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CALL SLALN2( .FALSE., 2, 1, SMIN, ONE,
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$ T( J-1, J-1 ), LDT, ONE, ONE,
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$ WORK( J-1+N ), N, WR, ZERO, X, 2,
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$ SCALE, XNORM, IERR )
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*
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* Scale X(1,1) and X(2,1) to avoid overflow when
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* updating the right-hand side.
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*
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IF( XNORM.GT.ONE ) THEN
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BETA = MAX( WORK( J-1 ), WORK( J ) )
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IF( BETA.GT.BIGNUM / XNORM ) THEN
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X( 1, 1 ) = X( 1, 1 ) / XNORM
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X( 2, 1 ) = X( 2, 1 ) / XNORM
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SCALE = SCALE / XNORM
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END IF
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END IF
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*
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* Scale if necessary
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*
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IF( SCALE.NE.ONE )
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$ CALL SSCAL( KI, SCALE, WORK( 1+N ), 1 )
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WORK( J-1+N ) = X( 1, 1 )
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WORK( J+N ) = X( 2, 1 )
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*
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* Update right-hand side
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*
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CALL SAXPY( J-2, -X( 1, 1 ), T( 1, J-1 ), 1,
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$ WORK( 1+N ), 1 )
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CALL SAXPY( J-2, -X( 2, 1 ), T( 1, J ), 1,
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$ WORK( 1+N ), 1 )
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END IF
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60 CONTINUE
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*
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* Copy the vector x or Q*x to VR and normalize.
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*
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IF( .NOT.OVER ) THEN
|
|
CALL SCOPY( KI, WORK( 1+N ), 1, VR( 1, IS ), 1 )
|
|
*
|
|
II = ISAMAX( KI, VR( 1, IS ), 1 )
|
|
REMAX = ONE / ABS( VR( II, IS ) )
|
|
CALL SSCAL( KI, REMAX, VR( 1, IS ), 1 )
|
|
*
|
|
DO 70 K = KI + 1, N
|
|
VR( K, IS ) = ZERO
|
|
70 CONTINUE
|
|
ELSE
|
|
IF( KI.GT.1 )
|
|
$ CALL SGEMV( 'N', N, KI-1, ONE, VR, LDVR,
|
|
$ WORK( 1+N ), 1, WORK( KI+N ),
|
|
$ VR( 1, KI ), 1 )
|
|
*
|
|
II = ISAMAX( N, VR( 1, KI ), 1 )
|
|
REMAX = ONE / ABS( VR( II, KI ) )
|
|
CALL SSCAL( N, REMAX, VR( 1, KI ), 1 )
|
|
END IF
|
|
*
|
|
ELSE
|
|
*
|
|
* Complex right eigenvector.
|
|
*
|
|
* Initial solve
|
|
* [ (T(KI-1,KI-1) T(KI-1,KI) ) - (WR + I* WI)]*X = 0.
|
|
* [ (T(KI,KI-1) T(KI,KI) ) ]
|
|
*
|
|
IF( ABS( T( KI-1, KI ) ).GE.ABS( T( KI, KI-1 ) ) ) THEN
|
|
WORK( KI-1+N ) = ONE
|
|
WORK( KI+N2 ) = WI / T( KI-1, KI )
|
|
ELSE
|
|
WORK( KI-1+N ) = -WI / T( KI, KI-1 )
|
|
WORK( KI+N2 ) = ONE
|
|
END IF
|
|
WORK( KI+N ) = ZERO
|
|
WORK( KI-1+N2 ) = ZERO
|
|
*
|
|
* Form right-hand side
|
|
*
|
|
DO 80 K = 1, KI - 2
|
|
WORK( K+N ) = -WORK( KI-1+N )*T( K, KI-1 )
|
|
WORK( K+N2 ) = -WORK( KI+N2 )*T( K, KI )
|
|
80 CONTINUE
|
|
*
|
|
* Solve upper quasi-triangular system:
|
|
* (T(1:KI-2,1:KI-2) - (WR+i*WI))*X = SCALE*(WORK+i*WORK2)
|
|
*
|
|
JNXT = KI - 2
|
|
DO 90 J = KI - 2, 1, -1
|
|
IF( J.GT.JNXT )
|
|
$ GO TO 90
|
|
J1 = J
|
|
J2 = J
|
|
JNXT = J - 1
|
|
IF( J.GT.1 ) THEN
|
|
IF( T( J, J-1 ).NE.ZERO ) THEN
|
|
J1 = J - 1
|
|
JNXT = J - 2
|
|
END IF
|
|
END IF
|
|
*
|
|
IF( J1.EQ.J2 ) THEN
|
|
*
|
|
* 1-by-1 diagonal block
|
|
*
|
|
CALL SLALN2( .FALSE., 1, 2, SMIN, ONE, T( J, J ),
|
|
$ LDT, ONE, ONE, WORK( J+N ), N, WR, WI,
|
|
$ X, 2, SCALE, XNORM, IERR )
|
|
*
|
|
* Scale X(1,1) and X(1,2) to avoid overflow when
|
|
* updating the right-hand side.
|
|
*
|
|
IF( XNORM.GT.ONE ) THEN
|
|
IF( WORK( J ).GT.BIGNUM / XNORM ) THEN
|
|
X( 1, 1 ) = X( 1, 1 ) / XNORM
|
|
X( 1, 2 ) = X( 1, 2 ) / XNORM
|
|
SCALE = SCALE / XNORM
|
|
END IF
|
|
END IF
|
|
*
|
|
* Scale if necessary
|
|
*
|
|
IF( SCALE.NE.ONE ) THEN
|
|
CALL SSCAL( KI, SCALE, WORK( 1+N ), 1 )
|
|
CALL SSCAL( KI, SCALE, WORK( 1+N2 ), 1 )
|
|
END IF
|
|
WORK( J+N ) = X( 1, 1 )
|
|
WORK( J+N2 ) = X( 1, 2 )
|
|
*
|
|
* Update the right-hand side
|
|
*
|
|
CALL SAXPY( J-1, -X( 1, 1 ), T( 1, J ), 1,
|
|
$ WORK( 1+N ), 1 )
|
|
CALL SAXPY( J-1, -X( 1, 2 ), T( 1, J ), 1,
|
|
$ WORK( 1+N2 ), 1 )
|
|
*
|
|
ELSE
|
|
*
|
|
* 2-by-2 diagonal block
|
|
*
|
|
CALL SLALN2( .FALSE., 2, 2, SMIN, ONE,
|
|
$ T( J-1, J-1 ), LDT, ONE, ONE,
|
|
$ WORK( J-1+N ), N, WR, WI, X, 2, SCALE,
|
|
$ XNORM, IERR )
|
|
*
|
|
* Scale X to avoid overflow when updating
|
|
* the right-hand side.
|
|
*
|
|
IF( XNORM.GT.ONE ) THEN
|
|
BETA = MAX( WORK( J-1 ), WORK( J ) )
|
|
IF( BETA.GT.BIGNUM / XNORM ) THEN
|
|
REC = ONE / XNORM
|
|
X( 1, 1 ) = X( 1, 1 )*REC
|
|
X( 1, 2 ) = X( 1, 2 )*REC
|
|
X( 2, 1 ) = X( 2, 1 )*REC
|
|
X( 2, 2 ) = X( 2, 2 )*REC
|
|
SCALE = SCALE*REC
|
|
END IF
|
|
END IF
|
|
*
|
|
* Scale if necessary
|
|
*
|
|
IF( SCALE.NE.ONE ) THEN
|
|
CALL SSCAL( KI, SCALE, WORK( 1+N ), 1 )
|
|
CALL SSCAL( KI, SCALE, WORK( 1+N2 ), 1 )
|
|
END IF
|
|
WORK( J-1+N ) = X( 1, 1 )
|
|
WORK( J+N ) = X( 2, 1 )
|
|
WORK( J-1+N2 ) = X( 1, 2 )
|
|
WORK( J+N2 ) = X( 2, 2 )
|
|
*
|
|
* Update the right-hand side
|
|
*
|
|
CALL SAXPY( J-2, -X( 1, 1 ), T( 1, J-1 ), 1,
|
|
$ WORK( 1+N ), 1 )
|
|
CALL SAXPY( J-2, -X( 2, 1 ), T( 1, J ), 1,
|
|
$ WORK( 1+N ), 1 )
|
|
CALL SAXPY( J-2, -X( 1, 2 ), T( 1, J-1 ), 1,
|
|
$ WORK( 1+N2 ), 1 )
|
|
CALL SAXPY( J-2, -X( 2, 2 ), T( 1, J ), 1,
|
|
$ WORK( 1+N2 ), 1 )
|
|
END IF
|
|
90 CONTINUE
|
|
*
|
|
* Copy the vector x or Q*x to VR and normalize.
|
|
*
|
|
IF( .NOT.OVER ) THEN
|
|
CALL SCOPY( KI, WORK( 1+N ), 1, VR( 1, IS-1 ), 1 )
|
|
CALL SCOPY( KI, WORK( 1+N2 ), 1, VR( 1, IS ), 1 )
|
|
*
|
|
EMAX = ZERO
|
|
DO 100 K = 1, KI
|
|
EMAX = MAX( EMAX, ABS( VR( K, IS-1 ) )+
|
|
$ ABS( VR( K, IS ) ) )
|
|
100 CONTINUE
|
|
*
|
|
REMAX = ONE / EMAX
|
|
CALL SSCAL( KI, REMAX, VR( 1, IS-1 ), 1 )
|
|
CALL SSCAL( KI, REMAX, VR( 1, IS ), 1 )
|
|
*
|
|
DO 110 K = KI + 1, N
|
|
VR( K, IS-1 ) = ZERO
|
|
VR( K, IS ) = ZERO
|
|
110 CONTINUE
|
|
*
|
|
ELSE
|
|
*
|
|
IF( KI.GT.2 ) THEN
|
|
CALL SGEMV( 'N', N, KI-2, ONE, VR, LDVR,
|
|
$ WORK( 1+N ), 1, WORK( KI-1+N ),
|
|
$ VR( 1, KI-1 ), 1 )
|
|
CALL SGEMV( 'N', N, KI-2, ONE, VR, LDVR,
|
|
$ WORK( 1+N2 ), 1, WORK( KI+N2 ),
|
|
$ VR( 1, KI ), 1 )
|
|
ELSE
|
|
CALL SSCAL( N, WORK( KI-1+N ), VR( 1, KI-1 ), 1 )
|
|
CALL SSCAL( N, WORK( KI+N2 ), VR( 1, KI ), 1 )
|
|
END IF
|
|
*
|
|
EMAX = ZERO
|
|
DO 120 K = 1, N
|
|
EMAX = MAX( EMAX, ABS( VR( K, KI-1 ) )+
|
|
$ ABS( VR( K, KI ) ) )
|
|
120 CONTINUE
|
|
REMAX = ONE / EMAX
|
|
CALL SSCAL( N, REMAX, VR( 1, KI-1 ), 1 )
|
|
CALL SSCAL( N, REMAX, VR( 1, KI ), 1 )
|
|
END IF
|
|
END IF
|
|
*
|
|
IS = IS - 1
|
|
IF( IP.NE.0 )
|
|
$ IS = IS - 1
|
|
130 CONTINUE
|
|
IF( IP.EQ.1 )
|
|
$ IP = 0
|
|
IF( IP.EQ.-1 )
|
|
$ IP = 1
|
|
140 CONTINUE
|
|
END IF
|
|
*
|
|
IF( LEFTV ) THEN
|
|
*
|
|
* Compute left eigenvectors.
|
|
*
|
|
IP = 0
|
|
IS = 1
|
|
DO 260 KI = 1, N
|
|
*
|
|
IF( IP.EQ.-1 )
|
|
$ GO TO 250
|
|
IF( KI.EQ.N )
|
|
$ GO TO 150
|
|
IF( T( KI+1, KI ).EQ.ZERO )
|
|
$ GO TO 150
|
|
IP = 1
|
|
*
|
|
150 CONTINUE
|
|
IF( SOMEV ) THEN
|
|
IF( .NOT.SELECT( KI ) )
|
|
$ GO TO 250
|
|
END IF
|
|
*
|
|
* Compute the KI-th eigenvalue (WR,WI).
|
|
*
|
|
WR = T( KI, KI )
|
|
WI = ZERO
|
|
IF( IP.NE.0 )
|
|
$ WI = SQRT( ABS( T( KI, KI+1 ) ) )*
|
|
$ SQRT( ABS( T( KI+1, KI ) ) )
|
|
SMIN = MAX( ULP*( ABS( WR )+ABS( WI ) ), SMLNUM )
|
|
*
|
|
IF( IP.EQ.0 ) THEN
|
|
*
|
|
* Real left eigenvector.
|
|
*
|
|
WORK( KI+N ) = ONE
|
|
*
|
|
* Form right-hand side
|
|
*
|
|
DO 160 K = KI + 1, N
|
|
WORK( K+N ) = -T( KI, K )
|
|
160 CONTINUE
|
|
*
|
|
* Solve the quasi-triangular system:
|
|
* (T(KI+1:N,KI+1:N) - WR)**T*X = SCALE*WORK
|
|
*
|
|
VMAX = ONE
|
|
VCRIT = BIGNUM
|
|
*
|
|
JNXT = KI + 1
|
|
DO 170 J = KI + 1, N
|
|
IF( J.LT.JNXT )
|
|
$ GO TO 170
|
|
J1 = J
|
|
J2 = J
|
|
JNXT = J + 1
|
|
IF( J.LT.N ) THEN
|
|
IF( T( J+1, J ).NE.ZERO ) THEN
|
|
J2 = J + 1
|
|
JNXT = J + 2
|
|
END IF
|
|
END IF
|
|
*
|
|
IF( J1.EQ.J2 ) THEN
|
|
*
|
|
* 1-by-1 diagonal block
|
|
*
|
|
* Scale if necessary to avoid overflow when forming
|
|
* the right-hand side.
|
|
*
|
|
IF( WORK( J ).GT.VCRIT ) THEN
|
|
REC = ONE / VMAX
|
|
CALL SSCAL( N-KI+1, REC, WORK( KI+N ), 1 )
|
|
VMAX = ONE
|
|
VCRIT = BIGNUM
|
|
END IF
|
|
*
|
|
WORK( J+N ) = WORK( J+N ) -
|
|
$ SDOT( J-KI-1, T( KI+1, J ), 1,
|
|
$ WORK( KI+1+N ), 1 )
|
|
*
|
|
* Solve (T(J,J)-WR)**T*X = WORK
|
|
*
|
|
CALL SLALN2( .FALSE., 1, 1, SMIN, ONE, T( J, J ),
|
|
$ LDT, ONE, ONE, WORK( J+N ), N, WR,
|
|
$ ZERO, X, 2, SCALE, XNORM, IERR )
|
|
*
|
|
* Scale if necessary
|
|
*
|
|
IF( SCALE.NE.ONE )
|
|
$ CALL SSCAL( N-KI+1, SCALE, WORK( KI+N ), 1 )
|
|
WORK( J+N ) = X( 1, 1 )
|
|
VMAX = MAX( ABS( WORK( J+N ) ), VMAX )
|
|
VCRIT = BIGNUM / VMAX
|
|
*
|
|
ELSE
|
|
*
|
|
* 2-by-2 diagonal block
|
|
*
|
|
* Scale if necessary to avoid overflow when forming
|
|
* the right-hand side.
|
|
*
|
|
BETA = MAX( WORK( J ), WORK( J+1 ) )
|
|
IF( BETA.GT.VCRIT ) THEN
|
|
REC = ONE / VMAX
|
|
CALL SSCAL( N-KI+1, REC, WORK( KI+N ), 1 )
|
|
VMAX = ONE
|
|
VCRIT = BIGNUM
|
|
END IF
|
|
*
|
|
WORK( J+N ) = WORK( J+N ) -
|
|
$ SDOT( J-KI-1, T( KI+1, J ), 1,
|
|
$ WORK( KI+1+N ), 1 )
|
|
*
|
|
WORK( J+1+N ) = WORK( J+1+N ) -
|
|
$ SDOT( J-KI-1, T( KI+1, J+1 ), 1,
|
|
$ WORK( KI+1+N ), 1 )
|
|
*
|
|
* Solve
|
|
* [T(J,J)-WR T(J,J+1) ]**T* X = SCALE*( WORK1 )
|
|
* [T(J+1,J) T(J+1,J+1)-WR] ( WORK2 )
|
|
*
|
|
CALL SLALN2( .TRUE., 2, 1, SMIN, ONE, T( J, J ),
|
|
$ LDT, ONE, ONE, WORK( J+N ), N, WR,
|
|
$ ZERO, X, 2, SCALE, XNORM, IERR )
|
|
*
|
|
* Scale if necessary
|
|
*
|
|
IF( SCALE.NE.ONE )
|
|
$ CALL SSCAL( N-KI+1, SCALE, WORK( KI+N ), 1 )
|
|
WORK( J+N ) = X( 1, 1 )
|
|
WORK( J+1+N ) = X( 2, 1 )
|
|
*
|
|
VMAX = MAX( ABS( WORK( J+N ) ),
|
|
$ ABS( WORK( J+1+N ) ), VMAX )
|
|
VCRIT = BIGNUM / VMAX
|
|
*
|
|
END IF
|
|
170 CONTINUE
|
|
*
|
|
* Copy the vector x or Q*x to VL and normalize.
|
|
*
|
|
IF( .NOT.OVER ) THEN
|
|
CALL SCOPY( N-KI+1, WORK( KI+N ), 1, VL( KI, IS ), 1 )
|
|
*
|
|
II = ISAMAX( N-KI+1, VL( KI, IS ), 1 ) + KI - 1
|
|
REMAX = ONE / ABS( VL( II, IS ) )
|
|
CALL SSCAL( N-KI+1, REMAX, VL( KI, IS ), 1 )
|
|
*
|
|
DO 180 K = 1, KI - 1
|
|
VL( K, IS ) = ZERO
|
|
180 CONTINUE
|
|
*
|
|
ELSE
|
|
*
|
|
IF( KI.LT.N )
|
|
$ CALL SGEMV( 'N', N, N-KI, ONE, VL( 1, KI+1 ), LDVL,
|
|
$ WORK( KI+1+N ), 1, WORK( KI+N ),
|
|
$ VL( 1, KI ), 1 )
|
|
*
|
|
II = ISAMAX( N, VL( 1, KI ), 1 )
|
|
REMAX = ONE / ABS( VL( II, KI ) )
|
|
CALL SSCAL( N, REMAX, VL( 1, KI ), 1 )
|
|
*
|
|
END IF
|
|
*
|
|
ELSE
|
|
*
|
|
* Complex left eigenvector.
|
|
*
|
|
* Initial solve:
|
|
* ((T(KI,KI) T(KI,KI+1) )**T - (WR - I* WI))*X = 0.
|
|
* ((T(KI+1,KI) T(KI+1,KI+1)) )
|
|
*
|
|
IF( ABS( T( KI, KI+1 ) ).GE.ABS( T( KI+1, KI ) ) ) THEN
|
|
WORK( KI+N ) = WI / T( KI, KI+1 )
|
|
WORK( KI+1+N2 ) = ONE
|
|
ELSE
|
|
WORK( KI+N ) = ONE
|
|
WORK( KI+1+N2 ) = -WI / T( KI+1, KI )
|
|
END IF
|
|
WORK( KI+1+N ) = ZERO
|
|
WORK( KI+N2 ) = ZERO
|
|
*
|
|
* Form right-hand side
|
|
*
|
|
DO 190 K = KI + 2, N
|
|
WORK( K+N ) = -WORK( KI+N )*T( KI, K )
|
|
WORK( K+N2 ) = -WORK( KI+1+N2 )*T( KI+1, K )
|
|
190 CONTINUE
|
|
*
|
|
* Solve complex quasi-triangular system:
|
|
* ( T(KI+2,N:KI+2,N) - (WR-i*WI) )*X = WORK1+i*WORK2
|
|
*
|
|
VMAX = ONE
|
|
VCRIT = BIGNUM
|
|
*
|
|
JNXT = KI + 2
|
|
DO 200 J = KI + 2, N
|
|
IF( J.LT.JNXT )
|
|
$ GO TO 200
|
|
J1 = J
|
|
J2 = J
|
|
JNXT = J + 1
|
|
IF( J.LT.N ) THEN
|
|
IF( T( J+1, J ).NE.ZERO ) THEN
|
|
J2 = J + 1
|
|
JNXT = J + 2
|
|
END IF
|
|
END IF
|
|
*
|
|
IF( J1.EQ.J2 ) THEN
|
|
*
|
|
* 1-by-1 diagonal block
|
|
*
|
|
* Scale if necessary to avoid overflow when
|
|
* forming the right-hand side elements.
|
|
*
|
|
IF( WORK( J ).GT.VCRIT ) THEN
|
|
REC = ONE / VMAX
|
|
CALL SSCAL( N-KI+1, REC, WORK( KI+N ), 1 )
|
|
CALL SSCAL( N-KI+1, REC, WORK( KI+N2 ), 1 )
|
|
VMAX = ONE
|
|
VCRIT = BIGNUM
|
|
END IF
|
|
*
|
|
WORK( J+N ) = WORK( J+N ) -
|
|
$ SDOT( J-KI-2, T( KI+2, J ), 1,
|
|
$ WORK( KI+2+N ), 1 )
|
|
WORK( J+N2 ) = WORK( J+N2 ) -
|
|
$ SDOT( J-KI-2, T( KI+2, J ), 1,
|
|
$ WORK( KI+2+N2 ), 1 )
|
|
*
|
|
* Solve (T(J,J)-(WR-i*WI))*(X11+i*X12)= WK+I*WK2
|
|
*
|
|
CALL SLALN2( .FALSE., 1, 2, SMIN, ONE, T( J, J ),
|
|
$ LDT, ONE, ONE, WORK( J+N ), N, WR,
|
|
$ -WI, X, 2, SCALE, XNORM, IERR )
|
|
*
|
|
* Scale if necessary
|
|
*
|
|
IF( SCALE.NE.ONE ) THEN
|
|
CALL SSCAL( N-KI+1, SCALE, WORK( KI+N ), 1 )
|
|
CALL SSCAL( N-KI+1, SCALE, WORK( KI+N2 ), 1 )
|
|
END IF
|
|
WORK( J+N ) = X( 1, 1 )
|
|
WORK( J+N2 ) = X( 1, 2 )
|
|
VMAX = MAX( ABS( WORK( J+N ) ),
|
|
$ ABS( WORK( J+N2 ) ), VMAX )
|
|
VCRIT = BIGNUM / VMAX
|
|
*
|
|
ELSE
|
|
*
|
|
* 2-by-2 diagonal block
|
|
*
|
|
* Scale if necessary to avoid overflow when forming
|
|
* the right-hand side elements.
|
|
*
|
|
BETA = MAX( WORK( J ), WORK( J+1 ) )
|
|
IF( BETA.GT.VCRIT ) THEN
|
|
REC = ONE / VMAX
|
|
CALL SSCAL( N-KI+1, REC, WORK( KI+N ), 1 )
|
|
CALL SSCAL( N-KI+1, REC, WORK( KI+N2 ), 1 )
|
|
VMAX = ONE
|
|
VCRIT = BIGNUM
|
|
END IF
|
|
*
|
|
WORK( J+N ) = WORK( J+N ) -
|
|
$ SDOT( J-KI-2, T( KI+2, J ), 1,
|
|
$ WORK( KI+2+N ), 1 )
|
|
*
|
|
WORK( J+N2 ) = WORK( J+N2 ) -
|
|
$ SDOT( J-KI-2, T( KI+2, J ), 1,
|
|
$ WORK( KI+2+N2 ), 1 )
|
|
*
|
|
WORK( J+1+N ) = WORK( J+1+N ) -
|
|
$ SDOT( J-KI-2, T( KI+2, J+1 ), 1,
|
|
$ WORK( KI+2+N ), 1 )
|
|
*
|
|
WORK( J+1+N2 ) = WORK( J+1+N2 ) -
|
|
$ SDOT( J-KI-2, T( KI+2, J+1 ), 1,
|
|
$ WORK( KI+2+N2 ), 1 )
|
|
*
|
|
* Solve 2-by-2 complex linear equation
|
|
* ([T(j,j) T(j,j+1) ]**T-(wr-i*wi)*I)*X = SCALE*B
|
|
* ([T(j+1,j) T(j+1,j+1)] )
|
|
*
|
|
CALL SLALN2( .TRUE., 2, 2, SMIN, ONE, T( J, J ),
|
|
$ LDT, ONE, ONE, WORK( J+N ), N, WR,
|
|
$ -WI, X, 2, SCALE, XNORM, IERR )
|
|
*
|
|
* Scale if necessary
|
|
*
|
|
IF( SCALE.NE.ONE ) THEN
|
|
CALL SSCAL( N-KI+1, SCALE, WORK( KI+N ), 1 )
|
|
CALL SSCAL( N-KI+1, SCALE, WORK( KI+N2 ), 1 )
|
|
END IF
|
|
WORK( J+N ) = X( 1, 1 )
|
|
WORK( J+N2 ) = X( 1, 2 )
|
|
WORK( J+1+N ) = X( 2, 1 )
|
|
WORK( J+1+N2 ) = X( 2, 2 )
|
|
VMAX = MAX( ABS( X( 1, 1 ) ), ABS( X( 1, 2 ) ),
|
|
$ ABS( X( 2, 1 ) ), ABS( X( 2, 2 ) ), VMAX )
|
|
VCRIT = BIGNUM / VMAX
|
|
*
|
|
END IF
|
|
200 CONTINUE
|
|
*
|
|
* Copy the vector x or Q*x to VL and normalize.
|
|
*
|
|
IF( .NOT.OVER ) THEN
|
|
CALL SCOPY( N-KI+1, WORK( KI+N ), 1, VL( KI, IS ), 1 )
|
|
CALL SCOPY( N-KI+1, WORK( KI+N2 ), 1, VL( KI, IS+1 ),
|
|
$ 1 )
|
|
*
|
|
EMAX = ZERO
|
|
DO 220 K = KI, N
|
|
EMAX = MAX( EMAX, ABS( VL( K, IS ) )+
|
|
$ ABS( VL( K, IS+1 ) ) )
|
|
220 CONTINUE
|
|
REMAX = ONE / EMAX
|
|
CALL SSCAL( N-KI+1, REMAX, VL( KI, IS ), 1 )
|
|
CALL SSCAL( N-KI+1, REMAX, VL( KI, IS+1 ), 1 )
|
|
*
|
|
DO 230 K = 1, KI - 1
|
|
VL( K, IS ) = ZERO
|
|
VL( K, IS+1 ) = ZERO
|
|
230 CONTINUE
|
|
ELSE
|
|
IF( KI.LT.N-1 ) THEN
|
|
CALL SGEMV( 'N', N, N-KI-1, ONE, VL( 1, KI+2 ),
|
|
$ LDVL, WORK( KI+2+N ), 1, WORK( KI+N ),
|
|
$ VL( 1, KI ), 1 )
|
|
CALL SGEMV( 'N', N, N-KI-1, ONE, VL( 1, KI+2 ),
|
|
$ LDVL, WORK( KI+2+N2 ), 1,
|
|
$ WORK( KI+1+N2 ), VL( 1, KI+1 ), 1 )
|
|
ELSE
|
|
CALL SSCAL( N, WORK( KI+N ), VL( 1, KI ), 1 )
|
|
CALL SSCAL( N, WORK( KI+1+N2 ), VL( 1, KI+1 ), 1 )
|
|
END IF
|
|
*
|
|
EMAX = ZERO
|
|
DO 240 K = 1, N
|
|
EMAX = MAX( EMAX, ABS( VL( K, KI ) )+
|
|
$ ABS( VL( K, KI+1 ) ) )
|
|
240 CONTINUE
|
|
REMAX = ONE / EMAX
|
|
CALL SSCAL( N, REMAX, VL( 1, KI ), 1 )
|
|
CALL SSCAL( N, REMAX, VL( 1, KI+1 ), 1 )
|
|
*
|
|
END IF
|
|
*
|
|
END IF
|
|
*
|
|
IS = IS + 1
|
|
IF( IP.NE.0 )
|
|
$ IS = IS + 1
|
|
250 CONTINUE
|
|
IF( IP.EQ.-1 )
|
|
$ IP = 0
|
|
IF( IP.EQ.1 )
|
|
$ IP = -1
|
|
*
|
|
260 CONTINUE
|
|
*
|
|
END IF
|
|
*
|
|
RETURN
|
|
*
|
|
* End of STREVC
|
|
*
|
|
END
|