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115 lines
2.9 KiB
FortranFixed
115 lines
2.9 KiB
FortranFixed
*> \brief \b DSLECT
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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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* Definition:
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* ===========
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*
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* LOGICAL FUNCTION DSLECT( ZR, ZI )
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*
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* .. Scalar Arguments ..
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* DOUBLE PRECISION ZI, ZR
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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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*> DSLECT returns .TRUE. if the eigenvalue ZR+sqrt(-1)*ZI is to be
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*> selected, and otherwise it returns .FALSE.
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*> It is used by DCHK41 to test if DGEES successfully sorts eigenvalues,
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*> and by DCHK43 to test if DGEESX successfully sorts eigenvalues.
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*>
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*> The common block /SSLCT/ controls how eigenvalues are selected.
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*> If SELOPT = 0, then DSLECT return .TRUE. when ZR is less than zero,
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*> and .FALSE. otherwise.
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*> If SELOPT is at least 1, DSLECT returns SELVAL(SELOPT) and adds 1
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*> to SELOPT, cycling back to 1 at SELMAX.
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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] ZR
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*> \verbatim
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*> ZR is DOUBLE PRECISION
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*> The real part of a complex eigenvalue ZR + i*ZI.
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*> \endverbatim
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*>
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*> \param[in] ZI
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*> \verbatim
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*> ZI is DOUBLE PRECISION
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*> The imaginary part of a complex eigenvalue ZR + i*ZI.
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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 double_eig
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*
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* =====================================================================
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LOGICAL FUNCTION DSLECT( ZR, ZI )
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*
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* -- LAPACK test 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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DOUBLE PRECISION ZI, ZR
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* ..
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*
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* =====================================================================
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*
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* .. Arrays in Common ..
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LOGICAL SELVAL( 20 )
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DOUBLE PRECISION SELWI( 20 ), SELWR( 20 )
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* ..
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* .. Scalars in Common ..
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INTEGER SELDIM, SELOPT
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* ..
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* .. Common blocks ..
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COMMON / SSLCT / SELOPT, SELDIM, SELVAL, SELWR, SELWI
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* ..
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* .. Local Scalars ..
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INTEGER I
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DOUBLE PRECISION RMIN, X
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* ..
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* .. Parameters ..
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DOUBLE PRECISION ZERO
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PARAMETER ( ZERO = 0.0D0 )
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* ..
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* .. External Functions ..
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DOUBLE PRECISION DLAPY2
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EXTERNAL DLAPY2
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* ..
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* .. Executable Statements ..
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*
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IF( SELOPT.EQ.0 ) THEN
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DSLECT = ( ZR.LT.ZERO )
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ELSE
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RMIN = DLAPY2( ZR-SELWR( 1 ), ZI-SELWI( 1 ) )
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DSLECT = SELVAL( 1 )
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DO 10 I = 2, SELDIM
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X = DLAPY2( ZR-SELWR( I ), ZI-SELWI( I ) )
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IF( X.LE.RMIN ) THEN
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RMIN = X
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DSLECT = SELVAL( I )
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END IF
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10 CONTINUE
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END IF
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RETURN
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*
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* End of DSLECT
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*
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END
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