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*> \brief \b SSLECT
*
* =========== DOCUMENTATION ===========
*
* Online html documentation available at
* http://www.netlib.org/lapack/explore-html/
*
* Definition:
* ===========
*
* LOGICAL FUNCTION SSLECT( ZR, ZI )
*
* .. Scalar Arguments ..
* REAL ZI, ZR
* ..
*
*
*> \par Purpose:
* =============
*>
*> \verbatim
*>
*> SSLECT returns .TRUE. if the eigenvalue ZR+sqrt(-1)*ZI is to be
*> selected, and otherwise it returns .FALSE.
*> It is used by SCHK41 to test if SGEES successfully sorts eigenvalues,
*> and by SCHK43 to test if SGEESX successfully sorts eigenvalues.
*>
*> The common block /SSLCT/ controls how eigenvalues are selected.
*> If SELOPT = 0, then SSLECT return .TRUE. when ZR is less than zero,
*> and .FALSE. otherwise.
*> If SELOPT is at least 1, SSLECT returns SELVAL(SELOPT) and adds 1
*> to SELOPT, cycling back to 1 at SELMAX.
*> \endverbatim
*
* Arguments:
* ==========
*
*> \param[in] ZR
*> \verbatim
*> ZR is REAL
*> The real part of a complex eigenvalue ZR + i*ZI.
*> \endverbatim
*>
*> \param[in] ZI
*> \verbatim
*> ZI is REAL
*> The imaginary part of a complex eigenvalue ZR + i*ZI.
*> \endverbatim
*
* Authors:
* ========
*
*> \author Univ. of Tennessee
*> \author Univ. of California Berkeley
*> \author Univ. of Colorado Denver
*> \author NAG Ltd.
*
*> \date June 2016
*
*> \ingroup single_eig
*
* =====================================================================
LOGICAL FUNCTION SSLECT( ZR, ZI )
*
* -- LAPACK test routine (version 3.7.0) --
* -- LAPACK is a software package provided by Univ. of Tennessee, --
* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
* June 2016
*
* .. Scalar Arguments ..
REAL ZI, ZR
* ..
*
* =====================================================================
*
* .. Arrays in Common ..
LOGICAL SELVAL( 20 )
REAL SELWI( 20 ), SELWR( 20 )
* ..
* .. Scalars in Common ..
INTEGER SELDIM, SELOPT
* ..
* .. Common blocks ..
COMMON / SSLCT / SELOPT, SELDIM, SELVAL, SELWR, SELWI
* ..
* .. Local Scalars ..
INTEGER I
REAL RMIN, X
* ..
* .. Parameters ..
REAL ZERO
PARAMETER ( ZERO = 0.0E0 )
* ..
* .. External Functions ..
REAL SLAPY2
EXTERNAL SLAPY2
* ..
* .. Executable Statements ..
*
IF( SELOPT.EQ.0 ) THEN
SSLECT = ( ZR.LT.ZERO )
ELSE
RMIN = SLAPY2( ZR-SELWR( 1 ), ZI-SELWI( 1 ) )
SSLECT = SELVAL( 1 )
DO 10 I = 2, SELDIM
X = SLAPY2( ZR-SELWR( I ), ZI-SELWI( I ) )
IF( X.LE.RMIN ) THEN
RMIN = X
SSLECT = SELVAL( I )
END IF
10 CONTINUE
END IF
RETURN
*
* End of SSLECT
*
END
|
