sslect()

logical function sslect	(	real	zr,
		real	zi
	)

SSLECT

Purpose:

 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.

Parameters

[in]	ZR	ZR is REAL The real part of a complex eigenvalue ZR + i*ZI.
[in]	ZI	ZI is REAL 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 sslect.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 ..
      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
*

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