LOGICAL FUNCTION DSLECT( ZR, ZI ) * * -- LAPACK test routine (version 3.1.1) -- * Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. * February 2007 * * .. Scalar Arguments .. DOUBLE PRECISION ZI, ZR * .. * * Purpose * ======= * * DSLECT returns .TRUE. if the eigenvalue ZR+sqrt(-1)*ZI is to be * selected, and otherwise it returns .FALSE. * It is used by DCHK41 to test if DGEES succesfully sorts eigenvalues, * and by DCHK43 to test if DGEESX succesfully sorts eigenvalues. * * The common block /SSLCT/ controls how eigenvalues are selected. * If SELOPT = 0, then DSLECT return .TRUE. when ZR is less than zero, * and .FALSE. otherwise. * If SELOPT is at least 1, DSLECT returns SELVAL(SELOPT) and adds 1 * to SELOPT, cycling back to 1 at SELMAX. * * Arguments * ========= * * ZR (input) DOUBLE PRECISION * The real part of a complex eigenvalue ZR + i*ZI. * * ZI (input) DOUBLE PRECISION * The imaginary part of a complex eigenvalue ZR + i*ZI. * * ===================================================================== * * .. Arrays in Common .. LOGICAL SELVAL( 20 ) DOUBLE PRECISION SELWI( 20 ), SELWR( 20 ) * .. * .. Scalars in Common .. INTEGER SELDIM, SELOPT * .. * .. Common blocks .. COMMON / SSLCT / SELOPT, SELDIM, SELVAL, SELWR, SELWI * .. * .. Local Scalars .. INTEGER I DOUBLE PRECISION RMIN, X * .. * .. Parameters .. DOUBLE PRECISION ZERO PARAMETER ( ZERO = 0.0D0 ) * .. * .. External Functions .. DOUBLE PRECISION DLAPY2 EXTERNAL DLAPY2 * .. * .. Executable Statements .. * IF( SELOPT.EQ.0 ) THEN DSLECT = ( ZR.LT.ZERO ) ELSE RMIN = DLAPY2( ZR-SELWR( 1 ), ZI-SELWI( 1 ) ) DSLECT = SELVAL( 1 ) DO 10 I = 2, SELDIM X = DLAPY2( ZR-SELWR( I ), ZI-SELWI( I ) ) IF( X.LE.RMIN ) THEN RMIN = X DSLECT = SELVAL( I ) END IF 10 CONTINUE END IF RETURN * * End of DSLECT * END