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|
SUBROUTINE SB10YD( DISCFL, FLAG, LENDAT, RFRDAT, IFRDAT, OMEGA, N,
$ A, LDA, B, C, D, TOL, IWORK, DWORK, LDWORK,
$ ZWORK, LZWORK, INFO )
C
C SLICOT RELEASE 5.0.
C
C Copyright (c) 2002-2009 NICONET e.V.
C
C This program is free software: you can redistribute it and/or
C modify it under the terms of the GNU General Public License as
C published by the Free Software Foundation, either version 2 of
C the License, or (at your option) any later version.
C
C This program is distributed in the hope that it will be useful,
C but WITHOUT ANY WARRANTY; without even the implied warranty of
C MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
C GNU General Public License for more details.
C
C You should have received a copy of the GNU General Public License
C along with this program. If not, see
C <http://www.gnu.org/licenses/>.
C
C PURPOSE
C
C To fit a supplied frequency response data with a stable, minimum
C phase SISO (single-input single-output) system represented by its
C matrices A, B, C, D. It handles both discrete- and continuous-time
C cases.
C
C ARGUMENTS
C
C Input/Output parameters
C
C DISCFL (input) INTEGER
C Indicates the type of the system, as follows:
C = 0: continuous-time system;
C = 1: discrete-time system.
C
C FLAG (input) INTEGER
C If FLAG = 0, then the system zeros and poles are not
C constrained.
C If FLAG = 1, then the system zeros and poles will have
C negative real parts in the continuous-time case, or moduli
C less than 1 in the discrete-time case. Consequently, FLAG
C must be equal to 1 in mu-synthesis routines.
C
C LENDAT (input) INTEGER
C The length of the vectors RFRDAT, IFRDAT and OMEGA.
C LENDAT >= 2.
C
C RFRDAT (input) DOUBLE PRECISION array, dimension (LENDAT)
C The real part of the frequency data to be fitted.
C
C IFRDAT (input) DOUBLE PRECISION array, dimension (LENDAT)
C The imaginary part of the frequency data to be fitted.
C
C OMEGA (input) DOUBLE PRECISION array, dimension (LENDAT)
C The frequencies corresponding to RFRDAT and IFRDAT.
C These values must be nonnegative and monotonically
C increasing. Additionally, for discrete-time systems
C they must be between 0 and PI.
C
C N (input/output) INTEGER
C On entry, the desired order of the system to be fitted.
C N <= LENDAT-1.
C On exit, the order of the obtained system. The value of N
C could only be modified if N > 0 and FLAG = 1.
C
C A (output) DOUBLE PRECISION array, dimension (LDA,N)
C The leading N-by-N part of this array contains the
C matrix A. If FLAG = 1, then A is in an upper Hessenberg
C form, and corresponds to a minimal realization.
C
C LDA INTEGER
C The leading dimension of the array A. LDA >= MAX(1,N).
C
C B (output) DOUBLE PRECISION array, dimension (N)
C The computed vector B.
C
C C (output) DOUBLE PRECISION array, dimension (N)
C The computed vector C. If FLAG = 1, the first N-1 elements
C are zero (for the exit value of N).
C
C D (output) DOUBLE PRECISION array, dimension (1)
C The computed scalar D.
C
C Tolerances
C
C TOL DOUBLE PRECISION
C The tolerance to be used for determining the effective
C rank of matrices. If the user sets TOL > 0, then the given
C value of TOL is used as a lower bound for the reciprocal
C condition number; a (sub)matrix whose estimated condition
C number is less than 1/TOL is considered to be of full
C rank. If the user sets TOL <= 0, then an implicitly
C computed, default tolerance, defined by TOLDEF = SIZE*EPS,
C is used instead, where SIZE is the product of the matrix
C dimensions, and EPS is the machine precision (see LAPACK
C Library routine DLAMCH).
C
C Workspace
C
C IWORK INTEGER array, dimension max(2,2*N+1)
C
C DWORK DOUBLE PRECISION array, dimension (LDWORK)
C On exit, if INFO = 0, DWORK(1) returns the optimal value
C of LDWORK and DWORK(2) contains the optimal value of
C LZWORK.
C
C LDWORK INTEGER
C The length of the array DWORK.
C LDWORK = max( 2, LW1, LW2, LW3, LW4 ), where
C LW1 = 2*LENDAT + 4*HNPTS; HNPTS = 2048;
C LW2 = LENDAT + 6*HNPTS;
C MN = min( 2*LENDAT, 2*N+1 )
C LW3 = 2*LENDAT*(2*N+1) + max( 2*LENDAT, 2*N+1 ) +
C max( MN + 6*N + 4, 2*MN + 1 ), if N > 0;
C LW3 = 4*LENDAT + 5 , if N = 0;
C LW4 = max( N*N + 5*N, 6*N + 1 + min( 1,N ) ), if FLAG = 1;
C LW4 = 0, if FLAG = 0.
C For optimum performance LDWORK should be larger.
C
C ZWORK COMPLEX*16 array, dimension (LZWORK)
C
C LZWORK INTEGER
C The length of the array ZWORK.
C LZWORK = LENDAT*(2*N+3), if N > 0;
C LZWORK = LENDAT, if N = 0.
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 = 1: if the discrete --> continuous transformation cannot
C be made;
C = 2: if the system poles cannot be found;
C = 3: if the inverse system cannot be found, i.e., D is
C (close to) zero;
C = 4: if the system zeros cannot be found;
C = 5: if the state-space representation of the new
C transfer function T(s) cannot be found;
C = 6: if the continuous --> discrete transformation cannot
C be made.
C
C METHOD
C
C First, if the given frequency data are corresponding to a
C continuous-time system, they are changed to a discrete-time
C system using a bilinear transformation with a scaled alpha.
C Then, the magnitude is obtained from the supplied data.
C Then, the frequency data are linearly interpolated around
C the unit-disc.
C Then, Oppenheim and Schafer complex cepstrum method is applied
C to get frequency data corresponding to a stable, minimum-
C phase system. This is done in the following steps:
C - Obtain LOG (magnitude)
C - Obtain IFFT of the result (DG01MD SLICOT subroutine);
C - halve the data at 0;
C - Obtain FFT of the halved data (DG01MD SLICOT subroutine);
C - Obtain EXP of the result.
C Then, the new frequency data are interpolated back to the
C original frequency.
C Then, based on these newly obtained data, the system matrices
C A, B, C, D are constructed; the very identification is
C performed by Least Squares Method using DGELSY LAPACK subroutine.
C If needed, a discrete-to-continuous time transformation is
C applied on the system matrices by AB04MD SLICOT subroutine.
C Finally, if requested, the poles and zeros of the system are
C checked. If some of them have positive real parts in the
C continuous-time case (or are not inside the unit disk in the
C complex plane in the discrete-time case), they are exchanged with
C their negatives (or reciprocals, respectively), to preserve the
C frequency response, while getting a minimum phase and stable
C system. This is done by SB10ZP SLICOT subroutine.
C
C REFERENCES
C
C [1] Oppenheim, A.V. and Schafer, R.W.
C Discrete-Time Signal Processing.
C Prentice-Hall Signal Processing Series, 1989.
C
C [2] Balas, G., Doyle, J., Glover, K., Packard, A., and Smith, R.
C Mu-analysis and Synthesis toolbox - User's Guide,
C The Mathworks Inc., Natick, MA, USA, 1998.
C
C CONTRIBUTORS
C
C Asparuh Markovski, Technical University of Sofia, July 2003.
C
C REVISIONS
C
C V. Sima, Research Institute for Informatics, Bucharest, Aug. 2003.
C A. Markovski, Technical University of Sofia, October 2003.
C
C KEYWORDS
C
C Bilinear transformation, frequency response, least-squares
C approximation, stability.
C
C ******************************************************************
C
C .. Parameters ..
COMPLEX*16 ZZERO, ZONE
PARAMETER ( ZZERO = ( 0.0D+0, 0.0D+0 ),
$ ZONE = ( 1.0D+0, 0.0D+0 ) )
DOUBLE PRECISION ZERO, ONE, TWO, FOUR, TEN
PARAMETER ( ZERO = 0.0D+0, ONE = 1.0D+0, TWO = 2.0D+0,
$ FOUR = 4.0D+0, TEN = 1.0D+1 )
INTEGER HNPTS
PARAMETER ( HNPTS = 2048 )
C ..
C .. Scalar Arguments ..
INTEGER DISCFL, FLAG, INFO, LDA, LDWORK, LENDAT,
$ LZWORK, N
DOUBLE PRECISION TOL
C ..
C .. Array Arguments ..
INTEGER IWORK(*)
DOUBLE PRECISION A(LDA, *), B(*), C(*), D(*), DWORK(*),
$ IFRDAT(*), OMEGA(*), RFRDAT(*)
COMPLEX*16 ZWORK(*)
C ..
C .. Local Scalars ..
INTEGER CLWMAX, DLWMAX, I, II, INFO2, IP1, IP2, ISTART,
$ ISTOP, IWA0, IWAB, IWBMAT, IWBP, IWBX, IWDME,
$ IWDOMO, IWMAG, IWS, IWVAR, IWXI, IWXR, IWYMAG,
$ K, LW1, LW2, LW3, LW4, MN, N1, N2, P, RANK
DOUBLE PRECISION P1, P2, PI, PW, RAT, TOLB, TOLL
COMPLEX*16 XHAT(HNPTS/2)
C ..
C .. External Functions ..
DOUBLE PRECISION DLAMCH, DLAPY2
EXTERNAL DLAMCH, DLAPY2
C ..
C .. External Subroutines ..
EXTERNAL AB04MD, DCOPY, DG01MD, DGELSY, DLASET, DSCAL,
$ SB10ZP, XERBLA
C ..
C .. Intrinsic Functions ..
INTRINSIC ACOS, ATAN, COS, DBLE, DCMPLX, DIMAG, EXP, LOG,
$ MAX, MIN, SIN, SQRT
C
C Test input parameters and workspace.
C
PI = FOUR*ATAN( ONE )
PW = OMEGA(1)
N1 = N + 1
N2 = N + N1
C
INFO = 0
IF( DISCFL.NE.0 .AND. DISCFL.NE.1 ) THEN
INFO = -1
ELSE IF( FLAG.NE.0 .AND. FLAG.NE.1 ) THEN
INFO = -2
ELSE IF ( LENDAT.LT.2 ) THEN
INFO = -3
ELSE IF ( PW.LT.ZERO ) THEN
INFO = -6
ELSE IF( N.GT.LENDAT - 1 ) THEN
INFO = -7
ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
INFO = -9
ELSE
C
DO 10 K = 2, LENDAT
IF ( OMEGA(K).LT.PW )
$ INFO = -6
PW = OMEGA(K)
10 CONTINUE
C
IF ( DISCFL.EQ.1 .AND. OMEGA(LENDAT).GT.PI )
$ INFO = -6
END IF
C
IF ( INFO.EQ.0 ) THEN
C
C Workspace.
C
LW1 = 2*LENDAT + 4*HNPTS
LW2 = LENDAT + 6*HNPTS
MN = MIN( 2*LENDAT, N2 )
C
IF ( N.GT.0 ) THEN
LW3 = 2*LENDAT*N2 + MAX( 2*LENDAT, N2 ) +
$ MAX( MN + 6*N + 4, 2*MN + 1 )
ELSE
LW3 = 4*LENDAT + 5
END IF
C
IF ( FLAG.EQ.0 ) THEN
LW4 = 0
ELSE
LW4 = MAX( N*N + 5*N, 6*N + 1 + MIN ( 1, N ) )
END IF
C
DLWMAX = MAX( 2, LW1, LW2, LW3, LW4 )
C
IF ( N.GT.0 ) THEN
CLWMAX = LENDAT*( N2 + 2 )
ELSE
CLWMAX = LENDAT
END IF
C
IF ( LDWORK.LT.DLWMAX ) THEN
INFO = -16
ELSE IF ( LZWORK.LT.CLWMAX ) THEN
INFO = -18
END IF
END IF
C
IF ( INFO.NE.0 ) THEN
C
C Error return.
C
CALL XERBLA( 'SB10YD', -INFO )
RETURN
END IF
C
C Set tolerances.
C
TOLB = DLAMCH( 'Epsilon' )
TOLL = TOL
IF ( TOLL.LE.ZERO )
$ TOLL = FOUR*DBLE( LENDAT*N )*TOLB
C
C @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
C
C Workspace usage 1.
C Workspace: need 2*LENDAT + 4*HNPTS.
C
IWDOMO = 1
IWDME = IWDOMO + LENDAT
IWYMAG = IWDME + 2*HNPTS
IWMAG = IWYMAG + 2*HNPTS
C
C Bilinear transformation.
C
IF ( DISCFL.EQ.0 ) THEN
PW = SQRT( OMEGA(1)*OMEGA(LENDAT) + SQRT( TOLB ) )
C
DO 20 K = 1, LENDAT
DWORK(IWDME+K-1) = ( OMEGA(K)/PW )**2
DWORK(IWDOMO+K-1) =
$ ACOS( ( ONE - DWORK(IWDME+K-1) )/
$ ( ONE + DWORK(IWDME+K-1) ) )
20 CONTINUE
C
ELSE
CALL DCOPY( LENDAT, OMEGA, 1, DWORK(IWDOMO), 1 )
END IF
C
C Linear interpolation.
C
DO 30 K = 1, LENDAT
DWORK(IWMAG+K-1) = DLAPY2( RFRDAT(K), IFRDAT(K) )
DWORK(IWMAG+K-1) = ( ONE/LOG( TEN ) ) * LOG( DWORK(IWMAG+K-1) )
30 CONTINUE
C
DO 40 K = 1, HNPTS
DWORK(IWDME+K-1) = ( K - 1 )*PI/HNPTS
DWORK(IWYMAG+K-1) = ZERO
C
IF ( DWORK(IWDME+K-1).LT.DWORK(IWDOMO) ) THEN
DWORK(IWYMAG+K-1) = DWORK(IWMAG)
ELSE IF ( DWORK(IWDME+K-1).GE.DWORK(IWDOMO+LENDAT-1) ) THEN
DWORK(IWYMAG+K-1) = DWORK(IWMAG+LENDAT-1)
END IF
C
40 CONTINUE
C
DO 60 I = 2, LENDAT
P1 = HNPTS*DWORK(IWDOMO+I-2)/PI + ONE
C
IP1 = INT( P1 )
IF ( DBLE( IP1 ).NE.P1 )
$ IP1 = IP1 + 1
C
P2 = HNPTS*DWORK(IWDOMO+I-1)/PI + ONE
C
IP2 = INT( P2 )
IF ( DBLE( IP2 ).NE.P2 )
$ IP2 = IP2 + 1
C
DO 50 P = IP1, IP2 - 1
RAT = DWORK(IWDME+P-1) - DWORK(IWDOMO+I-2)
RAT = RAT/( DWORK(IWDOMO+I-1) - DWORK(IWDOMO+I-2) )
DWORK(IWYMAG+P-1) = ( ONE - RAT )*DWORK(IWMAG+I-2) +
$ RAT*DWORK(IWMAG+I-1)
50 CONTINUE
C
60 CONTINUE
C
DO 70 K = 1, HNPTS
DWORK(IWYMAG+K-1) = EXP( LOG( TEN )*DWORK(IWYMAG+K-1) )
70 CONTINUE
C
C Duplicate data around disc.
C
DO 80 K = 1, HNPTS
DWORK(IWDME+HNPTS+K-1) = TWO*PI - DWORK(IWDME+HNPTS-K)
DWORK(IWYMAG+HNPTS+K-1) = DWORK(IWYMAG+HNPTS-K)
80 CONTINUE
C
C Complex cepstrum to get min phase:
C LOG (Magnitude)
C
DO 90 K = 1, 2*HNPTS
DWORK(IWYMAG+K-1) = TWO*LOG( DWORK(IWYMAG+K-1) )
90 CONTINUE
C
C @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
C
C Workspace usage 2.
C Workspace: need LENDAT + 6*HNPTS.
C
IWXR = IWYMAG
IWXI = IWMAG
C
DO 100 K = 1, 2*HNPTS
DWORK(IWXI+K-1) = ZERO
100 CONTINUE
C
C IFFT
C
CALL DG01MD( 'I', 2*HNPTS, DWORK(IWXR), DWORK(IWXI), INFO2 )
C
C Rescale, because DG01MD doesn't do it.
C
CALL DSCAL( HNPTS, ONE/( TWO*HNPTS ), DWORK(IWXR), 1 )
CALL DSCAL( HNPTS, ONE/( TWO*HNPTS ), DWORK(IWXI), 1 )
C
C Halve the result at 0.
C
DWORK(IWXR) = DWORK(IWXR)/TWO
DWORK(IWXI) = DWORK(IWXI)/TWO
C
C FFT
C
CALL DG01MD( 'D', HNPTS, DWORK(IWXR), DWORK(IWXI), INFO2 )
C
C Get the EXP of the result.
C
DO 110 K = 1, HNPTS/2
XHAT(K) = EXP( DWORK(IWXR+K-1) )*
$ DCMPLX ( COS( DWORK(IWXI+K-1)), SIN( DWORK(IWXI+K-1) ) )
DWORK(IWDME+K-1) = DWORK(IWDME+2*K-2)
110 CONTINUE
C
C Interpolate back to original frequency data.
C
ISTART = 1
ISTOP = LENDAT
C
DO 120 I = 1, LENDAT
ZWORK(I) = ZZERO
IF ( DWORK(IWDOMO+I-1).LE.DWORK(IWDME) ) THEN
ZWORK(I) = XHAT(1)
ISTART = I + 1
ELSE IF ( DWORK(IWDOMO+I-1).GE.DWORK(IWDME+HNPTS/2-1) )
$ THEN
ZWORK(I) = XHAT(HNPTS/2)
ISTOP = ISTOP - 1
END IF
120 CONTINUE
C
DO 140 I = ISTART, ISTOP
II = HNPTS/2
130 CONTINUE
IF ( DWORK(IWDME+II-1).GE.DWORK(IWDOMO+I-1) )
$ P = II
II = II - 1
IF ( II.GT.0 )
$ GOTO 130
RAT = ( DWORK(IWDOMO+I-1) - DWORK(IWDME+P-2) )/
$ ( DWORK(IWDME+P-1) - DWORK(IWDME+P-2) )
ZWORK(I) = RAT*XHAT(P) + ( ONE - RAT )*XHAT(P-1)
140 CONTINUE
C
C CASE N > 0.
C This is the only allowed case in mu-synthesis subroutines.
C
IF ( N.GT.0 ) THEN
C
C Preparation for frequency identification.
C
C @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
C
C Complex workspace usage 1.
C Complex workspace: need 2*LENDAT + LENDAT*(N+1).
C
IWA0 = 1 + LENDAT
IWVAR = IWA0 + LENDAT*N1
C
DO 150 K = 1, LENDAT
IF ( DISCFL.EQ.0 ) THEN
ZWORK(IWVAR+K-1) = DCMPLX( COS( DWORK(IWDOMO+K-1) ),
$ SIN( DWORK(IWDOMO+K-1) ) )
ELSE
ZWORK(IWVAR+K-1) = DCMPLX( COS( OMEGA(K) ),
$ SIN( OMEGA(K) ) )
END IF
150 CONTINUE
C
C Array for DGELSY.
C
DO 160 K = 1, N2
IWORK(K) = 0
160 CONTINUE
C
C Constructing A0.
C
DO 170 K = 1, LENDAT
ZWORK(IWA0+N*LENDAT+K-1) = ZONE
170 CONTINUE
C
DO 190 I = 1, N
DO 180 K = 1, LENDAT
ZWORK(IWA0+(N-I)*LENDAT+K-1) =
$ ZWORK(IWA0+(N1-I)*LENDAT+K-1)*ZWORK(IWVAR+K-1)
180 CONTINUE
190 CONTINUE
C
C @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
C
C Complex workspace usage 2.
C Complex workspace: need 2*LENDAT + LENDAT*(2*N+1).
C
IWBP = IWVAR
IWAB = IWBP + LENDAT
C
C Constructing BP.
C
DO 200 K = 1, LENDAT
ZWORK(IWBP+K-1) = ZWORK(IWA0+K-1)*ZWORK(K)
200 CONTINUE
C
C Constructing AB.
C
DO 220 I = 1, N
DO 210 K = 1, LENDAT
ZWORK(IWAB+(I-1)*LENDAT+K-1) = -ZWORK(K)*
$ ZWORK(IWA0+I*LENDAT+K-1)
210 CONTINUE
220 CONTINUE
C
C @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
C
C Workspace usage 3.
C Workspace: need LW3 = 2*LENDAT*(2*N+1) + max(2*LENDAT,2*N+1).
C
IWBX = 1 + 2*LENDAT*N2
IWS = IWBX + MAX( 2*LENDAT, N2 )
C
C Constructing AX.
C
DO 240 I = 1, N1
DO 230 K = 1, LENDAT
DWORK(2*(I-1)*LENDAT+K) =
$ DBLE( ZWORK(IWA0+(I-1)*LENDAT+K-1) )
DWORK((2*I-1)*LENDAT+K) =
$ DIMAG( ZWORK(IWA0+(I-1)*LENDAT+K-1) )
230 CONTINUE
240 CONTINUE
C
DO 260 I = 1, N
DO 250 K = 1, LENDAT
DWORK(2*N1*LENDAT+2*(I-1)*LENDAT+K) =
$ DBLE( ZWORK(IWAB+(I-1)*LENDAT+K-1) )
DWORK(2*N1*LENDAT+(2*I-1)*LENDAT+K) =
$ DIMAG( ZWORK(IWAB+(I-1)*LENDAT+K-1) )
250 CONTINUE
260 CONTINUE
C
C Constructing BX.
C
DO 270 K = 1, LENDAT
DWORK(IWBX+K-1) = DBLE( ZWORK(IWBP+K-1) )
DWORK(IWBX+LENDAT+K-1) = DIMAG( ZWORK(IWBP+K-1) )
270 CONTINUE
C
C Estimating X.
C Workspace: need LW3 + max( MN+3*(2*N+1)+1, 2*MN+1 ),
C where MN = min( 2*LENDAT, 2*N+1 );
C prefer larger.
C
CALL DGELSY( 2*LENDAT, N2, 1, DWORK, 2*LENDAT, DWORK(IWBX),
$ MAX( 2*LENDAT, N2 ), IWORK, TOLL, RANK,
$ DWORK(IWS), LDWORK-IWS+1, INFO2 )
DLWMAX = MAX( DLWMAX, INT( DWORK(IWS) + IWS - 1 ) )
C
C Constructing A matrix.
C
DO 280 K = 1, N
A(K,1) = -DWORK(IWBX+N1+K-1)
280 CONTINUE
C
IF ( N.GT.1 )
$ CALL DLASET( 'Full', N, N-1, ZERO, ONE, A(1,2), LDA )
C
C Constructing B matrix.
C
DO 290 K = 1, N
B(K) = DWORK(IWBX+N1+K-1)*DWORK(IWBX) - DWORK(IWBX+K)
290 CONTINUE
C
C Constructing C matrix.
C
C(1) = -ONE
C
DO 300 K = 2, N
C(K) = ZERO
300 CONTINUE
C
C Constructing D matrix.
C
D(1) = DWORK(IWBX)
C
C Transform to continuous-time case, if needed.
C Workspace: need max(1,N);
C prefer larger.
C
IF ( DISCFL.EQ.0 ) THEN
CALL AB04MD( 'D', N, 1, 1, ONE, PW, A, LDA, B, LDA, C, 1,
$ D, 1, IWORK, DWORK, LDWORK, INFO2 )
IF ( INFO2.NE.0 ) THEN
INFO = 1
RETURN
END IF
DLWMAX = MAX( DLWMAX, INT( DWORK(1) ) )
END IF
C
C Make all the real parts of the poles and the zeros negative.
C
IF ( FLAG.EQ.1 ) THEN
C
C Workspace: need max(N*N + 5*N, 6*N + 1 + min(1,N));
C prefer larger.
CALL SB10ZP( DISCFL, N, A, LDA, B, C, D, IWORK, DWORK,
$ LDWORK, INFO )
IF ( INFO.NE.0 )
$ RETURN
DLWMAX = MAX( DLWMAX, INT( DWORK(1) ) )
END IF
C
ELSE
C
C CASE N = 0.
C
C @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
C
C Workspace usage 4.
C Workspace: need 4*LENDAT.
C
IWBMAT = 1 + 2*LENDAT
IWS = IWBMAT + 2*LENDAT
C
C Constructing AMAT and BMAT.
C
DO 310 K = 1, LENDAT
DWORK(K) = ONE
DWORK(K+LENDAT) = ZERO
DWORK(IWBMAT+K-1) = DBLE( ZWORK(K) )
DWORK(IWBMAT+LENDAT+K-1) = DIMAG( ZWORK(K) )
310 CONTINUE
C
C Estimating D matrix.
C Workspace: need 4*LENDAT + 5;
C prefer larger.
C
IWORK(1) = 0
CALL DGELSY( 2*LENDAT, 1, 1, DWORK, 2*LENDAT, DWORK(IWBMAT),
$ 2*LENDAT, IWORK, TOLL, RANK, DWORK(IWS),
$ LDWORK-IWS+1, INFO2 )
DLWMAX = MAX( DLWMAX, INT( DWORK(IWS) + IWS - 1 ) )
C
D(1) = DWORK(IWBMAT)
C
END IF
C
C @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
C
DWORK(1) = DLWMAX
DWORK(2) = CLWMAX
RETURN
C
C *** Last line of SB10YD ***
END
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