在matlab中像buttord,butter,pburg这些函数是已经定义好的吗?可以直...
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%PBURG
Power Spectral Density (PSD) estimate via Burg's method.
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Pxx = PBURG(X,ORDER) returns the PSD of a discrete-time signal vector X
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in the vector Pxx. Pxx is the distribution of power per unit frequency.
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The frequency is expressed in units of radians/sample. ORDER is the
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order of the autoregressive (AR) model used to produce the PSD. PBURG
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uses a default FFT length of 256 which determines the length of Pxx.
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For real signals, PBURG returns the one-sided PSD by default; for
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complex signals, it returns the two-sided PSD. Note that a one-sided
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PSD contains the total power of the input signal.
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Pxx = PBURG(X,ORDER,NFFT) specifies the FFT length used to calculate
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the PSD estimates. For real X, Pxx has length (NFFT/2+1) if NFFT is
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even, and (NFFT+1)/2 if NFFT is odd. For complex X, Pxx always has
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length NFFT. If empty, the default NFFT is 256.
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[Pxx,W] = PBURG(...) returns the vector of normalized angular
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frequencies, W, at which the PSD is estimated. W has units of
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radians/sample. For real signals, W spans the interval [0,Pi] when
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NFFT is even and [0,Pi) when NFFT is odd. For complex signals, W
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always spans the interval [0,2*Pi).
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[Pxx,F] = PBURG(...,Fs) specifies a sampling frequency Fs in Hz and
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returns the power spectral density in units of power per Hz. F is a
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vector of frequencies, in Hz, at which the PSD is estimated. For real
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signals, F spans the interval [0,Fs/2] when NFFT is even and [0,Fs/2)
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when NFFT is odd. For complex signals, F always spans the interval
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[0,Fs). If Fs is empty, [], the sampling frequency defaults to 1 Hz.
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[Pxx,W] = PBURG(...,'twosided') returns the PSD over the interval
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[0,2*Pi), and [Pxx,F] = PBURG(...,Fs,'twosided') returns the PSD over
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the interval [0,Fs). Note that 'onesided' may be optionally specified,
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but is only valid for real X. The string 'twosided' or 'onesided' may
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be placed in any position in the input argument list after ORDER.
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PBURG(...) with no output arguments plots the PSD estimate in dB per
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unit frequency in the current figure window.
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EXAMPLE:
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randn('state',1); x = randn(100,1);
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y = filter(1,[1 1/2 1/3 1/4 1/5],x); % Fourth order AR filter.
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pburg(y,4,[],1000);
% Uses the default NFFT of 256.
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See also PCOV, PMCOV, PYULEAR, PMTM, PMUSIC, PEIG, PWELCH, PERIODOGRAM,
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ARBURG, PRONY, SPECTRUM/BURG, DSPDATA/PSD.
% Author(s): R. Losada and P. Pacheco
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Copyright 1988-2004 The MathWorks, Inc.
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$Revision: 1.26.4.5 $ $Date: 2004/04/13 00:18:07 $
error(nargchk(2,5,nargin))
method = 'arburg';
[Pxx,freq,msg,units,Sxx,options] = arspectra(method,x,p,varargin{:});
error(msg);
if nargout==0,
freq = {freq};
if strcmpi(units,'Hz'),
freq = {freq{:},'Fs',options.Fs};
end
hpsd = dspdata.psd(Pxx,freq{:},'SpectrumType',options.range);
% Create a spectrum object to store in the PSD object's metadata.
hspec = spectrum.burg(p);
hpsd.Metadata.setsourcespectrum(hspec);
plot(hpsd);
else
% Assign output arguments.
varargout = {Pxx,freq,Sxx}; % Pxx=PSD, Sxx=PS
end
% [EOF] pburg.m
