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LOGICAL FUNCTION SB02CX( REIG, IEIG )
C
C SLICOT RELEASE 5.0.
C
C Copyright (c) 2002-2009 NICONET e.V.
C
C This program is free software: you can redistribute it and/or
C modify it under the terms of the GNU General Public License as
C published by the Free Software Foundation, either version 2 of
C the License, or (at your option) any later version.
C
C This program is distributed in the hope that it will be useful,
C but WITHOUT ANY WARRANTY; without even the implied warranty of
C MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
C GNU General Public License for more details.
C
C You should have received a copy of the GNU General Public License
C along with this program. If not, see
C <http://www.gnu.org/licenses/>.
C
C PURPOSE
C
C To select the purely imaginary eigenvalues in computing the
C H-infinity norm of a system.
C
C ARGUMENTS
C
C Input/Output Parameters
C
C REIG (input) DOUBLE PRECISION
C The real part of the current eigenvalue considered.
C
C IEIG (input) DOUBLE PRECISION
C The imaginary part of the current eigenvalue considered.
C
C METHOD
C
C The function value SB02CX is set to .TRUE. for a purely imaginary
C eigenvalue and to .FALSE., otherwise.
C
C REFERENCES
C
C None.
C
C NUMERICAL ASPECTS
C
C None.
C
C CONTRIBUTOR
C
C P. Hr. Petkov, Technical University of Sofia, May, 1999.
C
C REVISIONS
C
C P. Hr. Petkov, Technical University of Sofia, Oct. 2000.
C
C KEYWORDS
C
C H-infinity norm, robust control.
C
C ******************************************************************
C
C .. Parameters ..
DOUBLE PRECISION HUNDRD
PARAMETER ( HUNDRD = 100.0D+0 )
C ..
C .. Scalar Arguments ..
DOUBLE PRECISION IEIG, REIG
C ..
C .. Local Scalars ..
DOUBLE PRECISION EPS, TOL
C ..
C .. External Functions ..
DOUBLE PRECISION DLAMCH
EXTERNAL DLAMCH
C ..
C .. Intrinsic Functions ..
INTRINSIC ABS
C ..
C .. Executable Statements ..
C
C Get the machine precision.
C
EPS = DLAMCH( 'Epsilon' )
C
C Set the tolerance in the determination of the purely
C imaginary eigenvalues.
C
TOL = HUNDRD*EPS
SB02CX = ABS( REIG ).LT.TOL
C
RETURN
C *** Last line of SB02CX ***
END
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