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LOGICAL FUNCTION SB02OV( ALPHAR, ALPHAI, BETA )
C
C RELEASE 4.0, WGS COPYRIGHT 1999.
C
C PURPOSE
C
C To select the unstable generalized eigenvalues for solving the
C discrete-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.
C
C METHOD
C
C The function value SB02OV is set to .TRUE. for an unstable
C eigenvalue (i.e., with modulus greater than or equal to one) and
C 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 SB02CX 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 ONE
PARAMETER ( ONE = 1.0D0 )
C .. Scalar Arguments ..
DOUBLE PRECISION ALPHAR, ALPHAI, BETA
C .. External Functions ..
DOUBLE PRECISION DLAPY2
EXTERNAL DLAPY2
C .. Intrinsic Functions ..
INTRINSIC ABS
C .. Executable Statements ..
C
SB02OV = DLAPY2( ALPHAR, ALPHAI ).GE.ABS( BETA )
C
RETURN
C *** Last line of SB02OV ***
END
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