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LOGICAL FUNCTION SB02OU( ALPHAR, ALPHAI, BETA )
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 unstable generalized eigenvalues for solving the
C continuous-time algebraic Riccati equation.
C
C ARGUMENTS
C
C Input/Output Parameters
C
C ALPHAR (input) DOUBLE PRECISION
C The real part of the numerator of the current eigenvalue
C considered.
C
C ALPHAI (input) DOUBLE PRECISION
C The imaginary part of the numerator of the current
C eigenvalue considered.
C
C BETA (input) DOUBLE PRECISION
C The (real) denominator of the current eigenvalue
C considered. It is assumed that BETA <> 0 (regular case).
C
C METHOD
C
C The function value SB02OU is set to .TRUE. for an unstable
C eigenvalue and to .FALSE., otherwise.
C
C REFERENCES
C
C None.
C
C NUMERICAL ASPECTS
C
C None.
C
C CONTRIBUTOR
C
C Release 3.0: V. Sima, Katholieke Univ. Leuven, Belgium, Sep. 1997.
C Supersedes Release 2.0 routine SB02CW by P. Van Dooren, Philips
C Research Laboratory, Brussels, Belgium.
C
C REVISIONS
C
C -
C
C KEYWORDS
C
C Algebraic Riccati equation, closed loop system, continuous-time
C system, optimal regulator, Schur form.
C
C ******************************************************************
C
DOUBLE PRECISION ZERO
PARAMETER ( ZERO = 0.0D0 )
C .. Scalar Arguments ..
DOUBLE PRECISION ALPHAR, ALPHAI, BETA
C .. Executable Statements ..
C
SB02OU = ( ALPHAR.LT.ZERO .AND. BETA.LT.ZERO ) .OR.
$ ( ALPHAR.GT.ZERO .AND. BETA.GT.ZERO )
C
RETURN
C *** Last line of SB02OU ***
END
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