1 LOGICAL FUNCTION SB02OV( ALPHAR, ALPHAI, BETA ) 2C 3C RELEASE 4.0, WGS COPYRIGHT 1999. 4C 5C PURPOSE 6C 7C To select the unstable generalized eigenvalues for solving the 8C discrete-time algebraic Riccati equation. 9C 10C ARGUMENTS 11C 12C Input/Output Parameters 13C 14C ALPHAR (input) DOUBLE PRECISION 15C The real part of the numerator of the current eigenvalue 16C considered. 17C 18C ALPHAI (input) DOUBLE PRECISION 19C The imaginary part of the numerator of the current 20C eigenvalue considered. 21C 22C BETA (input) DOUBLE PRECISION 23C The (real) denominator of the current eigenvalue 24C considered. 25C 26C METHOD 27C 28C The function value SB02OV is set to .TRUE. for an unstable 29C eigenvalue (i.e., with modulus greater than or equal to one) and 30C to .FALSE., otherwise. 31C 32C REFERENCES 33C 34C None. 35C 36C NUMERICAL ASPECTS 37C 38C None. 39C 40C CONTRIBUTOR 41C 42C Release 3.0: V. Sima, Katholieke Univ. Leuven, Belgium, Sep. 1997. 43C Supersedes Release 2.0 routine SB02CX by P. Van Dooren, Philips 44C Research Laboratory, Brussels, Belgium. 45C 46C REVISIONS 47C 48C - 49C 50C KEYWORDS 51C 52C Algebraic Riccati equation, closed loop system, continuous-time 53C system, optimal regulator, Schur form. 54C 55C ****************************************************************** 56C 57 DOUBLE PRECISION ONE 58 PARAMETER ( ONE = 1.0D0 ) 59C .. Scalar Arguments .. 60 DOUBLE PRECISION ALPHAR, ALPHAI, BETA 61C .. External Functions .. 62 DOUBLE PRECISION DLAPY2 63 EXTERNAL DLAPY2 64C .. Intrinsic Functions .. 65 INTRINSIC ABS 66C .. Executable Statements .. 67C 68 SB02OV = DLAPY2( ALPHAR, ALPHAI ).GE.ABS( BETA ) 69C 70 RETURN 71C *** Last line of SB02OV *** 72 END 73