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[G,PV]=trfsd(th,nnu,w,nny)
TRFSD Computes a model's frequency function,along with its standard deviation G = trfsd(TH) or [G,NSP] = trfsd(TH) TH: A matrix defining a model, as described in HELP THETA G is returned as the transfer function estimate, and NSP (if specified) as the noise spectrum, corresponding to the model TH. These matrices contain also estimated standard deviations, calculated from the covariance matrix in TH, and are of the standard frequency function format (see HELP FREQFUNC).If TH describes a time series, G is returned as its spectrum. If the model TH has several inputs, G will be returned as the transfer functions of selected inputs # j1 j2 .. jk by G = trfsd(TH,[j1 j2 ... jk]) [default is all inputs]. The functions are computed at 128 equally spaced frequency-values between 0(excluded) and pi/T, where T is the sampling interval specified by TH. The func- tions can be computed at arbitrary frequencies w (a row vector, gene- rated e.g. by LOGSPACE) by G = th2ff(TH,ku,w). The transfer function can be plotted by BODEPLOT. bodeplot(trfsd(TH),sd) is a possible construction. If the model TH has several outputs, G will be returned as the frequency function at selected outputs ky (a row vector) by G=trf(TH,ku,w,ky); (Default is all outputs).
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function [G,PV]=trfsd(th,nnu,w,nny) % L. Ljung 7-7-87, 3-25-89 % Copyright (c) 1986-98 by The MathWorks, Inc. % $Revision: 2.3 $ $Date: 1997/12/02 03:42:41 $ T=gett(th); % *** Set up default values *** if nargin<4, nny=[];end if nargin<3, w=[];end if nargin<2 , nnu=[];end if T>0,wdef=pi*[1:128]/128/T; else wdef=logspace(log10(pi/abs(T)/100),log10(10*pi/abs(T)),128);end if isempty(w),w=wdef;end if length(w)==1, if w<0, w=wdef;end,end if isempty(nnu),nnu=1:th(1,3);end if nargout==1, G=th2ff(th,nnu,w,nny);else [G,PV]=th2ff(th,nnu,w,nny);end