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SUBROUTINE IB01OY( NS, NMAX, N, SV, INFO )

C

C PURPOSE

C

C To ask for user's confirmation of the system order found by

C SLICOT Library routine IB01OD. This routine may be modified,

C but its interface must be preserved.

C

C ARGUMENTS

C

C Input/Output Parameters

C

C NS (input) INTEGER

C The number of singular values. NS > 0.

C

C NMAX (input) INTEGER

C The maximum value of the system order. 0 <= NMAX <= NS.

C

C N (input/output) INTEGER

C On entry, the estimate of the system order computed by

C IB01OD routine. 0 <= N <= NS.

C On exit, the user's estimate of the system order, which

C could be identical with the input value of N.

C Note that the output value of N should be less than

C or equal to NMAX.

C

C SV (input) DOUBLE PRECISION array, dimension ( NS )

C The singular values, in descending order, used for

C determining the system order.

C

C Error Indicator

C

C INFO INTEGER

C = 0: successful exit;

C < 0: if INFO = -i, the i-th argument had an illegal

C value.

C

C CONTRIBUTORS

C

C V. Sima, Research Institute for Informatics, Bucharest, Aug. 1999.

C

C REVISIONS

C

C -

C

C KEYWORDS

C

C Identification, parameter estimation, singular values, structure

C identification.

C

C *********************************************************************

C

C .. Parameters ..

INTEGER INTRMN, OUTRMN

PARAMETER ( INTRMN = 5, OUTRMN = 6 )

C INTRMN is the unit number for the (terminal) input device.

C OUTRMN is the unit number for the (terminal) output device.

C ..

C .. Scalar Arguments ..

INTEGER INFO, N, NMAX, NS

C ..

C .. Array Arguments ..

DOUBLE PRECISION SV( * )

C ..

C .. Local Scalars ..

LOGICAL YES

INTEGER I

CHARACTER ANS

C ..

C .. External Functions ..

LOGICAL LSAME

EXTERNAL LSAME

C ..

C .. External Subroutines ..

EXTERNAL XERBLA

C

C .. Executable Statements ..

C

C Check the scalar input parameters.

C

INFO = 0

IF( NS.LE.0 ) THEN

INFO = -1

ELSE IF( NMAX.LT.0 .OR. NMAX.GT.NS ) THEN

INFO = -2

ELSE IF( N.LT.0 .OR. N.GT.NS ) THEN

INFO = -3

END IF

C

IF( INFO.NE.0 ) THEN

CALL XERBLA( 'IB01OY', -INFO )

RETURN

END IF

C

WRITE( OUTRMN, '(/'' Singular values (in descending order) used'',

$ '' to estimate the system order:'', //

$ (5D15.8) )' ) ( SV(I), I = 1, NS )

WRITE( OUTRMN, '(/'' Estimated order of the system, n = '', I5 )'

$ ) N

WRITE( OUTRMN, '(/'' Do you want this value of n to be used'',

$ '' to determine the system matrices?'' )' )

C

10 CONTINUE

WRITE( OUTRMN, '(/'' Type "yes" or "no": '' )' )

READ ( INTRMN, '( A )' ) ANS

YES = LSAME( ANS, 'Y' )

IF( YES ) THEN

IF( N.LE.NMAX ) THEN

C

C The value of n is adequate and has been confirmed.

C

RETURN

ELSE

C

C The estimated value of n is not acceptable.

C

WRITE( OUTRMN, '(/'' n should be less than or equal'',

$ '' to '', I5 )' ) NMAX

WRITE( OUTRMN, '( '' (It may be useful to restart'',

$ '' with a larger tolerance.)'' )' )

GO TO 20

END IF

C

ELSE IF( LSAME( ANS, 'N' ) ) THEN

GO TO 20

ELSE

C

C Wrong answer should be re-entered.

C

GO TO 10

END IF

C

C Enter the desired value of n.

C

20 CONTINUE

WRITE( OUTRMN,'(/'' Enter the desired value of n (n <= '', I5,

$ ''); n = '' )' ) NMAX

READ ( INTRMN, * ) N

IF ( N.LT.0 ) THEN

C

C The specified value of n is not acceptable.

C

WRITE( OUTRMN, '(/'' n should be larger than zero.'' )' )

GO TO 20

ELSE IF ( N.GT.NMAX ) THEN

C

C The specified value of n is not acceptable.

C

WRITE( OUTRMN, '(/'' n should be less than or equal to '',

$ I5 )' ) NMAX

GO TO 20

END IF

C

RETURN

C

C *** Last line of IB01OY ***

END