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u = idinput(N,type,band,levels,nosine)
IDINPUT Generates input signals for identification.
U = IDINPUT(N,TYPE,BAND,LEVELS)
U: The generated input signal, a column vector.
N: The length of the input.
TYPE: One of the following:
'RGS': Generates a Random, Gaussian Signal.
'RBS': Generates a Random, Binary Signal.
'PRBS': Generates a Pseudo-random, Binary Signal.
'SINE': Generates a sum-of-sinusoid signal.
Default: TYPE = 'RBS'.
BAND: A 2 by 1 row vector that defines the frequency band for the
input's frequency contents.
For the 'RS', 'RBS' and 'SINE' cases BAND = [LFR,HFR], where
LFR and HFR are the lower and upper limits of the passband,
expressed in fractions of the Nyquist frequency (thus always
numbers between 0 and 1).
For the 'PRBS' case BAND = [2LOGP,M], where the periodicity
of the generated signal is 2^2LOGP-1, and M is such that the
signal is constant over intervals of length 1/M. 2LOGP = 0,
gives the maximum length PRBS, corresponding to 2LOGP = 18.
Default: BAND =[0 1].
LEVELS = [MI, MA]: A 2 by 1 row vector, defining the input levels.
For 'RBS', 'PRBS', and 'SINE', the levels are adjusted so
that the input signal always is between MI and MA.
For the 'RS' case, MI is the signal's mean value minus one
standard deviation and MA is the signal's mean plus one standard
deviation.
Default LEVELS = [-1 1].
In the 'SINE' case a 5th input argument NUMBERS can be used,
U = IDINPUT(N,TYPE,BAND,LEVELS,NUMBERS)
where NUMBERS = [no_of_sinusoids, no_of_trials], meaning that
no_of_sinusoids are equally spread over the indicated BAND, trying
no_of_trials different, random, relative phases, until the lowest
amplitude signal is found. Default: NUMBERS = [10,10];
See also IDSIM, POLY2TH and MS2TH.
| This function calls | |
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function u = idinput(N,type,band,levels,nosine)
% L. Ljung 3-3-95
% Copyright (c) 1986-98 by The MathWorks, Inc.
% $Revision: 2.5 $ $Date: 1997/12/02 03:41:48 $
if nargin < 1
disp('Usage: U = IDINPUT(N);')
disp(' U = IDINPUT(N,TYPE,BAND,LEVELS,NUMBERS);')
disp(' with TYPE one of ''RGS'', ''RBS'', ''PRBS'', ''SINE''.')
return
end
if nargin < 5
nosine=[];
end
if nargin < 4
levels = [];
end
if nargin < 3
band = [];
end
if nargin < 2
type =[];
end
if isempty(nosine),nosine=[10,10];end
if isempty(levels),levels=[-1,1];end
if isempty(band),band=[0 1];end
if isempty(type),type='rbs';end
if band(2)<band(1)&~strcmp(lower(type),'prbs')
error('The first component of BAND must be less than the second one.')
end
if levels(2)<levels(1)
error('The first component of LEVELS must be less than the second one.')
end
if nosine(1)<1|nosine(2)<1
error('The number of sinusoids and the number of trials must be larger than 1.')
end
if ~isstr(type)
error('The argument TYPE must be one of ''rs'', ''rbs'', ''prbs'' or ''sine''.')
end
if strcmp(lower(type),'rs')|strcmp(lower(type),'rgs')
u=randn(N,1);
if ~all(band==[0 1]),u=idfilt(u,8,band);end
u=u-mean(u)+(levels(2)+levels(1))/2;
u=u/norm(u)*sqrt(N)*(levels(2)-levels(1))/2;
elseif strcmp(lower(type),'rbs')
u=randn(N,1);
if ~all(band==[0 1]),u=idfilt(u,8,band);end
u=sign(u);
u=(levels(2)-levels(1))*(u+1)/2+levels(1);
elseif strcmp(lower(type),'prbs')
if band(1)==0,n=18;else n=floor(band(1));end
if n<3|n>18,
error('The length of the PRBS sequence, BAND(1), must be between 3 and 18.')
return
end
fi=-ones(n,1);
M=floor(1/band(2));
if n==3
ind=[1,3];
elseif n==4
ind=[1,4];
elseif n==5
ind=[2,5];
elseif n==6
ind=[1,6];
elseif n==7
ind=[1,7];
elseif n==8
ind=[1,2,7,8];
elseif n==9
ind=[4,9];
elseif n==10
ind=[3,10];
elseif n==11
ind=[9,11];
elseif n==12
ind=[6,8,11,12];
elseif n==13
ind=[9,10,12,13];
elseif n==14
ind=[4,8,13,14];
elseif n==15
ind=[14,15];
elseif n==16
ind=[4,13,15,16];
elseif n==17
ind=[14,17];
elseif n==18
ind=[11,18];
end
for t=1:M:N
u(t:t+M-1,1)=ones(M,1)*fi(n);
fi=[prod(fi(ind));fi(1:n-1,1)];
end
u=(levels(2)-levels(1))*(u+1)/2+levels(1);
elseif strcmp(lower(type),'sine')
freqs=band(1)+(band(2)-band(1))/(nosine(1))*[1:nosine(1)];
freqs=pi*freqs;
numtrial=nosine(2);
for kn=1:numtrial
ut=zeros(N,1);
for ks=1:nosine(1)
ut=ut+cos([0:N-1]'*freqs(ks)+rand(1,1)*2*pi);
end
mm=max(ut);mn=min(ut);
if kn==1,u=ut;bestamp=mm-mn;end
if mm-mn<bestamp,u=ut;bestamp=mm-mn;end
end
u=(levels(2)-levels(1))*(u-mn)/(mm-mn)+levels(1);
else
error('The argument TYPE must be one of ''rgs'', ''rbs'', ''prbs'' or ''sine''.')
end