zslect()

logical function zslect

(

complex*16

Z

)

ZSLECT

Purpose:

 ZSLECT returns .TRUE. if the eigenvalue Z is to be selected,
 otherwise it returns .FALSE.
 It is used by ZCHK41 to test if ZGEES successfully sorts eigenvalues,
 and by ZCHK43 to test if ZGEESX successfully sorts eigenvalues.

 The common block /SSLCT/ controls how eigenvalues are selected.
 If SELOPT = 0, then ZSLECT return .TRUE. when real(Z) is less than
 zero, and .FALSE. otherwise.
 If SELOPT is at least 1, ZSLECT returns SELVAL(SELOPT) and adds 1
 to SELOPT, cycling back to 1 at SELMAX.

Parameters

[in]

Z

Z is COMPLEX*16 The eigenvalue Z.

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line 55 of file zslect.f.

*
*  -- 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*16         Z
*     ..
*
*  =====================================================================
*
*     .. Parameters ..
      DOUBLE PRECISION   ZERO
      parameter( zero = 0.0d0 )
*     ..
*     .. Local Scalars ..
      INTEGER            I
      DOUBLE PRECISION   RMIN, X
*     ..
*     .. Scalars in Common ..
      INTEGER            SELDIM, SELOPT
*     ..
*     .. Arrays in Common ..
      LOGICAL            SELVAL( 20 )
      DOUBLE PRECISION   SELWI( 20 ), SELWR( 20 )
*     ..
*     .. Common blocks ..
      COMMON             / sslct / selopt, seldim, selval, selwr, selwi
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC          abs, dble, dcmplx
*     ..
*     .. Executable Statements ..
*
      IF( selopt.EQ.0 ) THEN
         zslect = ( dble( z ).LT.zero )
      ELSE
         rmin = abs( z-dcmplx( selwr( 1 ), selwi( 1 ) ) )
         zslect = selval( 1 )
         DO 10 i = 2, seldim
            x = abs( z-dcmplx( selwr( i ), selwi( i ) ) )
            IF( x.LE.rmin ) THEN
               rmin = x
               zslect = selval( i )
            END IF
   10    CONTINUE
      END IF
      RETURN
*
*     End of ZSLECT
*