dd/d5e/slctes_8f_source.html

00001       LOGICAL          FUNCTION SLCTES( ZR, ZI, D )
00002 *
00003 *  -- LAPACK test routine (version 3.1) --
00004 *     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
00005 *     November 2006
00006 *
00007 *     .. Scalar Arguments ..
00008       REAL               D, ZI, ZR
00009 *     ..
00010 *
00011 *  Purpose
00012 *  =======
00013 *
00014 *  SLCTES returns .TRUE. if the eigenvalue (ZR/D) + sqrt(-1)*(ZI/D)
00015 *  is to be selected (specifically, in this subroutine, if the real
00016 *  part of the eigenvalue is negative), and otherwise it returns
00017 *  .FALSE..
00018 *
00019 *  It is used by the test routine SDRGES to test whether the driver
00020 *  routine SGGES succesfully sorts eigenvalues.
00021 *
00022 *  Arguments
00023 *  =========
00024 *
00025 *  ZR      (input) REAL
00026 *          The numerator of the real part of a complex eigenvalue
00027 *          (ZR/D) + i*(ZI/D).
00028 *
00029 *  ZI      (input) REAL
00030 *          The numerator of the imaginary part of a complex eigenvalue
00031 *          (ZR/D) + i*(ZI).
00032 *
00033 *  D       (input) REAL
00034 *          The denominator part of a complex eigenvalue
00035 *          (ZR/D) + i*(ZI/D).
00036 *
00037 *  =====================================================================
00038 *
00039 *     .. Parameters ..
00040       REAL               ZERO, ONE
00041       PARAMETER          ( ZERO = 0.0E+0, ONE = 1.0E+0 )
00042 *     ..
00043 *     .. Intrinsic Functions ..
00044       INTRINSIC          SIGN
00045 *     ..
00046 *     .. Executable Statements ..
00047 *
00048       IF( D.EQ.ZERO ) THEN
00049          SLCTES = ( ZR.LT.ZERO )
00050       ELSE
00051          SLCTES = ( SIGN( ONE, ZR ).NE.SIGN( ONE, D ) )
00052       END IF
00053 *
00054       RETURN
00055 *
00056 *     End of SLCTES
00057 *
00058       END