LOGICAL FUNCTION SB02OU( ALPHAR, ALPHAI, BETA )
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