cslect.f

Go to the documentation of this file.

*> \brief \b CSLECT
*
*  =========== DOCUMENTATION ===========
*
* Online html documentation available at
*            http://www.netlib.org/lapack/explore-html/
*
*  Definition:
*  ===========
*
*       LOGICAL          FUNCTION CSLECT( Z )
*
*       .. Scalar Arguments ..
*       COMPLEX            Z
*       ..
*
*
*> \par Purpose:
*  =============
*>
*> \verbatim
*>
*> CSLECT returns .TRUE. if the eigenvalue Z is to be selected,
*> otherwise it returns .FALSE.
*> It is used by CCHK41 to test if CGEES successfully sorts eigenvalues,
*> and by CCHK43 to test if CGEESX successfully sorts eigenvalues.
*>
*> The common block /SSLCT/ controls how eigenvalues are selected.
*> If SELOPT = 0, then CSLECT return .TRUE. when real(Z) is less than
*> zero, and .FALSE. otherwise.
*> If SELOPT is at least 1, CSLECT returns SELVAL(SELOPT) and adds 1
*> to SELOPT, cycling back to 1 at SELMAX.
*> \endverbatim
*
*  Arguments:
*  ==========
*
*> \param[in] Z
*> \verbatim
*>          Z is COMPLEX
*>          The eigenvalue Z.
*> \endverbatim
*
*  Authors:
*  ========
*
*> \author Univ. of Tennessee
*> \author Univ. of California Berkeley
*> \author Univ. of Colorado Denver
*> \author NAG Ltd.
*
*> \ingroup complex_eig
*
*  =====================================================================
      LOGICAL          FUNCTION cslect( Z )
*
*  -- LAPACK test routine --
*  -- LAPACK is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*
*     .. Scalar Arguments ..
      COMPLEX            z
*     ..
*
*  =====================================================================
*
*     .. Parameters ..
      REAL               zero
      parameter( zero = 0.0e0 )
*     ..
*     .. Local Scalars ..
      INTEGER            i
      REAL               rmin, x
*     ..
*     .. Scalars in Common ..
      INTEGER            seldim, selopt
*     ..
*     .. Arrays in Common ..
      LOGICAL            selval( 20 )
      REAL               selwi( 20 ), selwr( 20 )
*     ..
*     .. Common blocks ..
      COMMON             / sslct / selopt, seldim, selval, selwr, selwi
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC          abs, cmplx, real
*     ..
*     .. Executable Statements ..
*
      IF( selopt.EQ.0 ) THEN
         cslect = ( real( z ).LT.zero )
      ELSE
         rmin = abs( z-cmplx( selwr( 1 ), selwi( 1 ) ) )
         cslect = selval( 1 )
         DO 10 i = 2, seldim
            x = abs( z-cmplx( selwr( i ), selwi( i ) ) )
            IF( x.LE.rmin ) THEN
               rmin = x
               cslect = selval( i )
            END IF
   10    CONTINUE
      END IF
      RETURN
*
*     End of CSLECT
*
      END