Authors:
Alessandro Chiuso,
Giorgio Picci,
Volume: 1, Page 1544 Paper number 201
Abstract:
There is experimental evidence that the standard subspace methods (e.g.
the N4SID method) perform poorly in certain conditions where the past
signals (past inputs and past outputs) and future input spaces are
nearly parallel. Based on an elementary numerical conditioning analysis,
this paper describes a class of (system-dependent) input signals (called
probing inputs) which lead to the worst possible conditioning of
the identification problem. Numerical results are included demonstrating
how these input signals may lead to a substantial deterioration of
performance of the algorithms in some experimental conditions.
Authors:
Albert Benveniste,
Michèle Basseville,
Laurent Mével,
Volume: 1, Page 1550 Paper number 202
Abstract:
We apply the general results of companion paper INV0401 in session
WeM06-1 on the relationship between identification and local tests,
to the estimation of convergence rates for MIMO system eigenstructure
identification using subspace algorithms. We provide a new and practical
estimator for such convergence rates.
Authors:
Tony van Gestel,
Johan A.K. Suykens,
Paul van Dooren,
Bart de Moor,
Volume: 1, Page 1555 Paper number 203
Abstract:
In subspace methods for linear system identification, the system matrices
are usually estimated by least squares, based on estimated Kalman filter
state sequences and the observed inputs and outputs. For an infinite
number of data points and a correct choice of the system order, this
least squares estimate of the system matrices is unbiased. However,
when using subspace identification on a finite number of data points,
the estimated model can become unstable, for a given deterministic
system which is known to be stable. In this paper, stability of the
estimated model is imposed by adding a regularization term to the least
squares cost function. The regularization term used here is the trace
of a matrix which involves the dynamical system matrix and a positive
(semi-)definite weighting matrix. The amount of regularization needed
can be determined by solving a generalized eigenvalue problem. It is
shown that the so-called data augmentation method proposed by Chui
and Maciejowski corresponds to adding regularization terms with specific
choices for the weighting matrix.
Authors:
Katrien de Cock,
Bart de Moor,
Volume: 1, Page 1561 Paper number 204
Abstract:
In this paper we define a notion of principal angles between two linear
autoregressive (AR) models by considering the principal angles between
the ranges of their infinite observability matrices. We show how a
recently defined metric for these models, which is based on their cepstra,
is related to the subspace angles between them. The definition of subspace
angles is also extended to the linear autoregressive-moving-average
(ARMA) model class.
Authors:
Vincent Verdult,
Michel Verhaegen,
Volume: 1, Page 1567 Paper number 205
Abstract:
The paper presents a subspace type of identification method for multivariable
linear parameter-varying systems in state space representation with
affine parameter dependence. It is shown that a major problem with
subspace methods for this kind of systems is the enormous dimensions
of the data matrices involved. To overcome the curse of dimensionality,
we suggest to use only the most dominant rows of the data matrices
in estimating the model. An efficient selection algorithm is discussed
that does not require the formation of the complete data matrices,
but can process them row by row.
Authors:
Huixin Chen,
Jan M. Maciejowski,
Volume: 1, Page 1573 Paper number 206
Abstract:
Several subspace algorithms for the identification of bilinear systems
have been proposed recently. A key practical problem with all of these
is the very large size of the data-based matrices which must be constructed
in order to `linearise' the problem and allow parameter estimation
essentially by regression. Favoreel et al (ACC 1997) proposed an algorithm
which gave unbiased results only if the measured input signal was white.
Favoreel and De Moor (MTNS 1998) suggested an alternative algorithm
for general input signals, but which gave biased estimates. Chen and
Maciejowski proposed algorithms for the deterministic (ACC 2000) and
deterministic-stochastic (SYSID 2000) cases which give asymptotically
unbiased estimates with general inputs, and for which the rate of reduction
of bias can be estimated. The computational complexity of these algorithms
was also significantly lower than the earlier ones, both because the
matrix dimensions were smaller, and because convergence to correct
estimates (with sample size) appears to be much faster. In this paper
we reduce the matrix dimensions further, by making different choices
of subspaces for the decomposition of input-output data. In fact we
propose two algorithms: an unbiased one for the case m>=n (m: number
of outputs, n:number of states), and an asymptotically unbiased one
for the case m
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