364 lines
13 KiB
Fortran
364 lines
13 KiB
Fortran
SUBROUTINE AB09AD( DICO, JOB, EQUIL, ORDSEL, N, M, P, NR, A, LDA,
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$ B, LDB, C, LDC, HSV, TOL, IWORK, DWORK, LDWORK,
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$ IWARN, INFO )
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C
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C SLICOT RELEASE 5.0.
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C
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C Copyright (c) 2002-2009 NICONET e.V.
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C
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C This program is free software: you can redistribute it and/or
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C modify it under the terms of the GNU General Public License as
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C published by the Free Software Foundation, either version 2 of
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C the License, or (at your option) any later version.
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C
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C This program is distributed in the hope that it will be useful,
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C but WITHOUT ANY WARRANTY; without even the implied warranty of
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C MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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C GNU General Public License for more details.
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C
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C You should have received a copy of the GNU General Public License
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C along with this program. If not, see
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C <http://www.gnu.org/licenses/>.
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C
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C PURPOSE
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C
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C To compute a reduced order model (Ar,Br,Cr) for a stable original
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C state-space representation (A,B,C) by using either the square-root
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C or the balancing-free square-root Balance & Truncate (B & T)
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C model reduction method.
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C
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C ARGUMENTS
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C
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C Mode Parameters
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C
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C DICO CHARACTER*1
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C Specifies the type of the original system as follows:
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C = 'C': continuous-time system;
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C = 'D': discrete-time system.
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C
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C JOB CHARACTER*1
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C Specifies the model reduction approach to be used
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C as follows:
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C = 'B': use the square-root Balance & Truncate method;
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C = 'N': use the balancing-free square-root
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C Balance & Truncate method.
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C
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C EQUIL CHARACTER*1
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C Specifies whether the user wishes to preliminarily
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C equilibrate the triplet (A,B,C) as follows:
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C = 'S': perform equilibration (scaling);
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C = 'N': do not perform equilibration.
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C
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C ORDSEL CHARACTER*1
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C Specifies the order selection method as follows:
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C = 'F': the resulting order NR is fixed;
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C = 'A': the resulting order NR is automatically determined
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C on basis of the given tolerance TOL.
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C
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C Input/Output Parameters
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C
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C N (input) INTEGER
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C The order of the original state-space representation, i.e.
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C the order of the matrix A. N >= 0.
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C
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C M (input) INTEGER
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C The number of system inputs. M >= 0.
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C
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C P (input) INTEGER
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C The number of system outputs. P >= 0.
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C
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C NR (input/output) INTEGER
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C On entry with ORDSEL = 'F', NR is the desired order of the
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C resulting reduced order system. 0 <= NR <= N.
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C On exit, if INFO = 0, NR is the order of the resulting
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C reduced order model. NR is set as follows:
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C if ORDSEL = 'F', NR is equal to MIN(NR,NMIN), where NR
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C is the desired order on entry and NMIN is the order of a
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C minimal realization of the given system; NMIN is
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C determined as the number of Hankel singular values greater
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C than N*EPS*HNORM(A,B,C), where EPS is the machine
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C precision (see LAPACK Library Routine DLAMCH) and
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C HNORM(A,B,C) is the Hankel norm of the system (computed
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C in HSV(1));
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C if ORDSEL = 'A', NR is equal to the number of Hankel
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C singular values greater than MAX(TOL,N*EPS*HNORM(A,B,C)).
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C
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C A (input/output) DOUBLE PRECISION array, dimension (LDA,N)
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C On entry, the leading N-by-N part of this array must
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C contain the state dynamics matrix A.
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C On exit, if INFO = 0, the leading NR-by-NR part of this
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C array contains the state dynamics matrix Ar of the reduced
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C order system.
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C
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C LDA INTEGER
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C The leading dimension of array A. LDA >= MAX(1,N).
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C
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C B (input/output) DOUBLE PRECISION array, dimension (LDB,M)
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C On entry, the leading N-by-M part of this array must
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C contain the original input/state matrix B.
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C On exit, if INFO = 0, the leading NR-by-M part of this
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C array contains the input/state matrix Br of the reduced
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C order system.
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C
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C LDB INTEGER
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C The leading dimension of array B. LDB >= MAX(1,N).
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C
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C C (input/output) DOUBLE PRECISION array, dimension (LDC,N)
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C On entry, the leading P-by-N part of this array must
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C contain the original state/output matrix C.
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C On exit, if INFO = 0, the leading P-by-NR part of this
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C array contains the state/output matrix Cr of the reduced
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C order system.
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C
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C LDC INTEGER
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C The leading dimension of array C. LDC >= MAX(1,P).
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C
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C HSV (output) DOUBLE PRECISION array, dimension (N)
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C If INFO = 0, it contains the Hankel singular values of
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C the original system ordered decreasingly. HSV(1) is the
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C Hankel norm of the system.
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C
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C Tolerances
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C
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C TOL DOUBLE PRECISION
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C If ORDSEL = 'A', TOL contains the tolerance for
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C determining the order of reduced system.
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C For model reduction, the recommended value is
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C TOL = c*HNORM(A,B,C), where c is a constant in the
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C interval [0.00001,0.001], and HNORM(A,B,C) is the
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C Hankel-norm of the given system (computed in HSV(1)).
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C For computing a minimal realization, the recommended
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C value is TOL = N*EPS*HNORM(A,B,C), where EPS is the
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C machine precision (see LAPACK Library Routine DLAMCH).
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C This value is used by default if TOL <= 0 on entry.
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C If ORDSEL = 'F', the value of TOL is ignored.
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C
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C Workspace
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C
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C IWORK INTEGER array, dimension (LIWORK)
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C LIWORK = 0, if JOB = 'B';
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C LIWORK = N, if JOB = 'N'.
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C
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C DWORK DOUBLE PRECISION array, dimension (LDWORK)
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C On exit, if INFO = 0, DWORK(1) returns the optimal value
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C of LDWORK.
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C
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C LDWORK INTEGER
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C The length of the array DWORK.
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C LDWORK >= MAX(1,N*(2*N+MAX(N,M,P)+5)+N*(N+1)/2).
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C For optimum performance LDWORK should be larger.
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C
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C Warning Indicator
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C
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C IWARN INTEGER
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C = 0: no warning;
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C = 1: with ORDSEL = 'F', the selected order NR is greater
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C than the order of a minimal realization of the
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C given system. In this case, the resulting NR is
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C set automatically to a value corresponding to the
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C order of a minimal realization of the system.
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C
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C Error Indicator
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C
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C INFO INTEGER
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C = 0: successful exit;
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C < 0: if INFO = -i, the i-th argument had an illegal
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C value;
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C = 1: the reduction of A to the real Schur form failed;
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C = 2: the state matrix A is not stable (if DICO = 'C')
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C or not convergent (if DICO = 'D');
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C = 3: the computation of Hankel singular values failed.
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C
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C METHOD
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C
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C Let be the stable linear system
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C
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C d[x(t)] = Ax(t) + Bu(t)
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C y(t) = Cx(t) (1)
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C
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C where d[x(t)] is dx(t)/dt for a continuous-time system and x(t+1)
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C for a discrete-time system. The subroutine AB09AD determines for
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C the given system (1), the matrices of a reduced order system
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C
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C d[z(t)] = Ar*z(t) + Br*u(t)
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C yr(t) = Cr*z(t) (2)
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C
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C such that
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C
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C HSV(NR) <= INFNORM(G-Gr) <= 2*[HSV(NR+1) + ... + HSV(N)],
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C
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C where G and Gr are transfer-function matrices of the systems
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C (A,B,C) and (Ar,Br,Cr), respectively, and INFNORM(G) is the
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C infinity-norm of G.
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C
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C If JOB = 'B', the square-root Balance & Truncate method of [1]
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C is used and, for DICO = 'C', the resulting model is balanced.
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C By setting TOL <= 0, the routine can be used to compute balanced
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C minimal state-space realizations of stable systems.
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C
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C If JOB = 'N', the balancing-free square-root version of the
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C Balance & Truncate method [2] is used.
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C By setting TOL <= 0, the routine can be used to compute minimal
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C state-space realizations of stable systems.
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C
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C REFERENCES
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C
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C [1] Tombs M.S. and Postlethwaite I.
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C Truncated balanced realization of stable, non-minimal
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C state-space systems.
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C Int. J. Control, Vol. 46, pp. 1319-1330, 1987.
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C
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C [2] Varga A.
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C Efficient minimal realization procedure based on balancing.
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C Proc. of IMACS/IFAC Symp. MCTS, Lille, France, May 1991,
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C A. El Moudui, P. Borne, S. G. Tzafestas (Eds.),
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C Vol. 2, pp. 42-46.
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C
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C NUMERICAL ASPECTS
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C
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C The implemented methods rely on accuracy enhancing square-root or
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C balancing-free square-root techniques.
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C 3
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C The algorithms require less than 30N floating point operations.
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C
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C CONTRIBUTOR
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C
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C C. Oara and A. Varga, German Aerospace Center,
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C DLR Oberpfaffenhofen, March 1998.
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C Based on the RASP routines SRBT and SRBFT.
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C
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C REVISIONS
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C
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C May 2, 1998.
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C November 11, 1998, V. Sima, Research Institute for Informatics,
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C Bucharest.
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C
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C KEYWORDS
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C
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C Balancing, minimal state-space representation, model reduction,
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C multivariable system, state-space model.
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C
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C ******************************************************************
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C
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C .. Parameters ..
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DOUBLE PRECISION ONE, C100
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PARAMETER ( ONE = 1.0D0, C100 = 100.0D0 )
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C .. Scalar Arguments ..
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CHARACTER DICO, EQUIL, JOB, ORDSEL
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INTEGER INFO, IWARN, LDA, LDB, LDC, LDWORK, M, N, NR, P
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DOUBLE PRECISION TOL
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C .. Array Arguments ..
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INTEGER IWORK(*)
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DOUBLE PRECISION A(LDA,*), B(LDB,*), C(LDC,*), DWORK(*), HSV(*)
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C .. Local Scalars ..
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LOGICAL FIXORD
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INTEGER IERR, KI, KR, KT, KTI, KW, NN
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DOUBLE PRECISION MAXRED, WRKOPT
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C .. External Functions ..
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LOGICAL LSAME
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EXTERNAL LSAME
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C .. External Subroutines ..
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EXTERNAL AB09AX, TB01ID, TB01WD, XERBLA
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C .. Intrinsic Functions ..
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INTRINSIC DBLE, MAX, MIN
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C .. Executable Statements ..
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C
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INFO = 0
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IWARN = 0
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FIXORD = LSAME( ORDSEL, 'F' )
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C
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C Test the input scalar arguments.
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C
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IF( .NOT. ( LSAME( DICO, 'C' ) .OR. LSAME( DICO, 'D' ) ) ) THEN
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INFO = -1
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ELSE IF( .NOT. ( LSAME( JOB, 'B' ) .OR. LSAME( JOB, 'N' ) ) ) THEN
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INFO = -2
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ELSE IF( .NOT. ( LSAME( EQUIL, 'S' ) .OR.
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$ LSAME( EQUIL, 'N' ) ) ) THEN
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INFO = -3
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ELSE IF( .NOT. ( FIXORD .OR. LSAME( ORDSEL, 'A' ) ) ) THEN
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INFO = -4
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ELSE IF( N.LT.0 ) THEN
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INFO = -5
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ELSE IF( M.LT.0 ) THEN
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INFO = -6
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ELSE IF( P.LT.0 ) THEN
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INFO = -7
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ELSE IF( FIXORD .AND. ( NR.LT.0 .OR. NR.GT.N ) ) THEN
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INFO = -8
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ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
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INFO = -10
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ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
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INFO = -12
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ELSE IF( LDC.LT.MAX( 1, P ) ) THEN
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INFO = -14
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ELSE IF( LDWORK.LT.MAX( 1, N*( 2*N + MAX( N, M, P ) + 5 ) +
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$ ( N*( N + 1 ) )/2 ) ) THEN
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INFO = -19
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END IF
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C
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IF( INFO.NE.0 ) THEN
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C
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C Error return.
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C
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CALL XERBLA( 'AB09AD', -INFO )
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RETURN
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END IF
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C
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C Quick return if possible.
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C
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IF( MIN( N, M, P ).EQ.0 .OR. ( FIXORD .AND. NR.EQ.0 ) ) THEN
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NR = 0
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DWORK(1) = ONE
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RETURN
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END IF
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C
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C Allocate working storage.
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C
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NN = N*N
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KT = 1
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KR = KT + NN
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KI = KR + N
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KW = KI + N
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C
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IF( LSAME( EQUIL, 'S' ) ) THEN
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C
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C Scale simultaneously the matrices A, B and C:
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C A <- inv(D)*A*D, B <- inv(D)*B and C <- C*D, where D is a
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C diagonal matrix.
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C
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MAXRED = C100
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CALL TB01ID( 'A', N, M, P, MAXRED, A, LDA, B, LDB, C, LDC,
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$ DWORK, INFO )
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END IF
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C
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C Reduce A to the real Schur form using an orthogonal similarity
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C transformation A <- T'*A*T and apply the transformation to
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C B and C: B <- T'*B and C <- C*T.
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C
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CALL TB01WD( N, M, P, A, LDA, B, LDB, C, LDC, DWORK(KT), N,
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$ DWORK(KR), DWORK(KI), DWORK(KW), LDWORK-KW+1, IERR )
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IF( IERR.NE.0 ) THEN
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INFO = 1
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RETURN
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END IF
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C
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WRKOPT = DWORK(KW) + DBLE( KW-1 )
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KTI = KT + NN
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KW = KTI + NN
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C
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CALL AB09AX( DICO, JOB, ORDSEL, N, M, P, NR, A, LDA, B, LDB, C,
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$ LDC, HSV, DWORK(KT), N, DWORK(KTI), N, TOL, IWORK,
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$ DWORK(KW), LDWORK-KW+1, IWARN, IERR )
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C
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IF( IERR.NE.0 ) THEN
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INFO = IERR + 1
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RETURN
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END IF
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C
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DWORK(1) = MAX( WRKOPT, DWORK(KW) + DBLE( KW-1 ) )
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C
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RETURN
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C *** Last line of AB09AD ***
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END
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