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.

ZR

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

ZI

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

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