ch4_1i.m

这是书籍:Matlab控制系统与应用的源码,

%       This demo describes the group of RECURSIVE (ON-LINE)
%       algorithms.  The recursive M-files include: RPEM, RPLR,
%       RARMAX, RARX, ROE, and RBJ.   These algorithms implement
%       all the recursive algorithms described in Chapter 11 of
%       Ljung(1987).
%
%       RPEM is the general Recursive Prediction Error Algorithm
%       for arbitrary multiple-input-single-output models
%       (the same models as PEM works for).
%
%       PRLR is the general Recursive PseudoLinear Regression method
%       for the same family of models.
%
%       RARX is a more efficient version of RPEM (and RPLR) for the
%       ARX-case.
%
%       ROE, RARMAX and RBJ are more efficient versions of RPEM for
%       the OE, ARMAX, and BJ cases (compare these functions to the
%       off-line methods).

%       ADAPTATION MECHANISMS:  Each of the algorithms implement the
%       four most common adaptation principles:
%
%       KALMAN FILTER approach: The true parameters are supposed to
%       vary like a random walk with incremental covariance matrix
%       R1.
%
%       FORGETTING FACTOR approach: Old measurements are discounted
%       exponentially. The base of the decay is the forgetting factor
%       lambda.
%
%       GRADIENT method: The update step is taken as a gradient step
%       of length gamma (th_new=th_old + gamma*psi*epsilon).
%
%       NORMALIZED GRADIENT method: As above, but gamma is replaced by
%       gamma/(psi'*psi). The Gradient methods are also
%       known as LMS (least mean squares) for the ARX case.


%  Let's pick a model and generate some input-output data:
u = sign(randn(50,1)); e = 0.2*randn(50,1);
th0 = idpoly([1 -1.5 0.7],[0 1 0.5],[1 -1 0.2]);
y = sim(th0,[u e]); z = iddata(y,u);

figure, plot(z)  % Press a key to see data.

%       First we build an Output-Error model of the data we just
%       plotted.  Use a second order model with one delay, and apply
%       the forgetting factor algorithm with lambda = 0.98:
thm1 = roe(z,[2 2 1],'ff',0.98);  % It may take a while ....

%       The four parameters can now be plotted as functions of time.
figure, plot(thm1), title('Estimated parameters')% Press a key to see plot.

%       The true values are as follows: (Press a key for plot)
 hold on, plot(ones(50,1)*[1 0.5 -1.5 0.7]), 
title('Estimated parameters and true values')

hold off

%       Now let's try a second order ARMAX model, using the RPLR
%       approach (i.e ELS) with Kalman filter adaptation, assuming
%       a parameter variance of 0.001:
thm2 = rplr(z,[2 2 2 0 0 1],'kf',0.001*eye(6));


figure,plot(thm2), title('Estimated parameters')
axis([0 50 -2 2])

% The true values are as follows: (Press any key for plot)
 hold on, plot(ones(50,1)*[-1.5 0.7 1 0.5 -1 0.2]),
title('Estimated parameters and true values')
hold off

%       So far we have assumed that all data are available at once.
%       We are thus studying the variability of the system rather
%       than doing real on-line calculations. The algorithms are
%       also prepared for such applications, but they must then
%       store more update information. The conceptual update then
%       becomes:
%  1. Wait for measurements y and u.
%  2. Update: [th,yh,p,phi] = rarx([y u],[na nb nk],'ff',0.98,th',p,phi)
%  3. Use th for whatever on-line application required.
%  4. Go to 1.
%       Thus the previous estimate th is fed back into the algorithm
%       along with the previous value of the "P-matrix" and the data
%       vector phi.
%       We now do an example of this where we plot just the current
%       value of th. The code is as follows:

       figure,
     [th,yh,p,phi] = rarx(z(1,:),[2 2 1],'ff',0.98);
     for k = 2:50
          [th,yh,p,phi] = rarx(z(k,:),[2 2 1],'ff',0.98,th',p,phi);
          plot(k,th(1),'*',k,th(2),'+',k,th(3),'o',k,th(4),'*'),hold on
     end
hold off

%   SEGMENTATION OF DATA
%
%   The command SEGMENT segments data that are generated from
%   systems that may undergo abrupt changes. Typical applications
%   for data segmentation are segmentation of speech signals (each
%   segment corresponds to a phonem), failure detection (the segments
%   correspond to operation with and without failures) and estimating
%   different working modes of a system.  We shall study a system
%   whose time delay changes from two to one.
load iddemo6m.mat
z = iddata(z(:,1),z(:,2));
%       First, take a look at the data:
figure, idplot(z)  % Press any key for plot.

%       The change takes place at sample number 20, but this is not
%       so easy to see.
%
%       We would like to estimate the system as an ARX-structure model
%       with one a-parameter, two b-parameters and one delay:
%       y(t) + a*y(t-1) = b1*u(t-1) + b2*u(t-2)
%       The information to be given is the data, the model orders
%       and a guess of the variance (r2) of the noise that affects
%       the system. If this is entirely unknown, it can be estimated
%       automatically. Here we set it to 0.1:
nn = [1 2 1];
[seg,v,tvmod] = segment(z,nn,0.1);



%       Let's take a look at the segmented model. Blue(yellow) line
%       is for the a-parameter. Green(magneta) is for b1 and Red(cyan)
%       for the parameter b2.
figure,plot(seg)    % Press any key for plot.
hold on

%       We see clearly the jump around sample number 19. b1 goes from
%       0 to 1 and b2 vice versa, which shows the change of the
%       delay. The true values can also be shown:
 plot(pars)   % Press any key for plot.
hold off


%       The method for segmentation is based on AFMM (adaptive
%       forgetting through multiple models), Andersson, Int. J.
%       Control Nov 1985.  A multi-model approach is used in a first
%       step to track the time varying system. The resulting tracking
%       model could be of interest in its own right, and are given by
%       the third output argument of SEGMENT (tvmod in our case). They
%       look as follows:
figure, plot(tvmod)   % Press any key for plot.

%       The SEGMENT M-file is thus an alternative to the recursive
%       algorithms RPEM, RARX etc for tracking time varying systems.
%       It is particularly suited for systems that may change rapidly.
%       From the tracking model, SEGMENT estimates the time points when
%       jumps have occurred, and constructs the segmented model by a
%       smoothing procedure over the tracking model.
%       The two most important "knobs" for the algorithm are r2, as
%       mentioned before, and the guessed probability of jumps, q, the
%       fourth input argument to SEGMENT.  The smaller r2 and the larger
%       q, the more willing SEGMENT will be to indicate segmentation
%       points. In an off line situation, the user will have to try a
%       couple of choices (r2 is usually more sensitive than q). The
%       second output argument to SEGMENT, v, is the loss function for
%       the segmented model (i.e. the estimated prediction error variance
%       for the segmented model). A goal will be to minimize this value.


%       OBJECT DETECTION IN LASER RANGE DATA
%
%       The reflected signal from a laser (or radar) beam contains
%       information about the distance to the reflecting object. The
%       signals can be quite noisy.  The presence of objects affects
%       both the distance information and the correlation between
%       neighbouring points. (A smooth object increases the
%       correlation between nearby points.)
%
%       In the following we study some quite noisy laser range data.
%       They are obtained by one horizontal sweep, like one line on
%       a TV-screen. The value is the distance to the reflecting object.
%       We happen to know that an object of interest hides between
%       sample numbers 17 and 48.
figure, plot(hline)  % Press any key for plot.

%       The eye is not good at detecting the object. We shall use
%       "segment".  First we detrend and normalize the data to a
%       variance about one. (This is not necessary, but it means that
%       the default choices in the algorithm are better tuned.)
hline = dtrend(hline)/200;

%       We shall now build a model of the kind:
%
%          y(t) + a y(t-1) = b
%
%       The coefficient 'a' will pick up correlation information.  The
%       value 'b' takes up the possible changes in level. We thus
%       introduce a fake input of all ones:
[m,n]=size(hline);
zline = [hline ones(m,n)];
s = segment(zline,[1 1 1],0.2);

figure
subplot(211),plot(hline),title('LASER RANGE DATA')
subplot(212),plot(s)
title('SEGMENTED MODELS, blue/solid: correlation, green/dashed: distance')

%       The segmentation has thus been quite successful.
%       SEGMENT is capable of handling multi-input systems, and of using
%       ARMAX models for the added noise.  We can try this on the test
%       data iddata1.mat (which contains no jumps):
load iddata1.mat
s = segment(z1(1:100),[2 2 2 1],1);
figure, subplot(111),plot(s),hold on% Press any key for plot.

%       Compare this with the true values:
plot([ ones(100,1)*[-1.5 0.7],ones(100,1)*[1 0.5],ones(100,1)*[-1 0.2]])
hold off

%       SEGMENT thus correctly finds that no jumps have occurred, and
%       also gives good estimates of the parameters.