dslect()

logical function dslect	(	double precision	zr,
		double precision	zi
	)

DSLECT

Purpose:

 DSLECT returns .TRUE. if the eigenvalue ZR+sqrt(-1)*ZI is to be
 selected, and otherwise it returns .FALSE.
 It is used by DCHK41 to test if DGEES successfully sorts eigenvalues,
 and by DCHK43 to test if DGEESX successfully sorts eigenvalues.

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

Parameters

[in]	ZR	ZR is DOUBLE PRECISION The real part of a complex eigenvalue ZR + i*ZI.
[in]	ZI	ZI is DOUBLE PRECISION The imaginary part of a complex eigenvalue ZR + i*ZI.

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line 61 of file dslect.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 ..
      DOUBLE PRECISION   ZI, ZR
*     ..
*
*  =====================================================================
*
*     .. Arrays in Common ..
      LOGICAL            SELVAL( 20 )
      DOUBLE PRECISION   SELWI( 20 ), SELWR( 20 )
*     ..
*     .. Scalars in Common ..
      INTEGER            SELDIM, SELOPT
*     ..
*     .. Common blocks ..
      COMMON             / sslct / selopt, seldim, selval, selwr, selwi
*     ..
*     .. Local Scalars ..
      INTEGER            I
      DOUBLE PRECISION   RMIN, X
*     ..
*     .. Parameters ..
      DOUBLE PRECISION   ZERO
      parameter( zero = 0.0d0 )
*     ..
*     .. External Functions ..
      DOUBLE PRECISION   DLAPY2
      EXTERNAL           dlapy2
*     ..
*     .. Executable Statements ..
*
      IF( selopt.EQ.0 ) THEN
         dslect = ( zr.LT.zero )
      ELSE
         rmin = dlapy2( zr-selwr( 1 ), zi-selwi( 1 ) )
         dslect = selval( 1 )
         DO 10 i = 2, seldim
            x = dlapy2( zr-selwr( i ), zi-selwi( i ) )
            IF( x.LE.rmin ) THEN
               rmin = x
               dslect = selval( i )
            END IF
   10    CONTINUE
      END IF
      RETURN
*
*     End of DSLECT
*

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