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[a,b,c,d,k,x0,da,db,dc,dd,dk,dx0]=th2ss(th)
TH2SS Transforms a model in THETA-format to state-space. [A,B,C,D,K,X0]=TH2SS(TH) TH: The model, defined in the THETA format (see also THETA). A,B,C,D,K,X0 : The matrices in the state-space description Xn = A X + B u + K e X0 initial value y = C X + D u + e Here Xn is the derivative of X or the next value of X, depending on whether TH is denoted as continuous or discrete time. With [A,B,C,D,K,X0,dA,dB,dC,dD,dK,dX0] = TH2SS(TH) also the standard deviations of the matrix elements are computed. See also TH2FF, TH2POLY, TH2TF and TH2ZP.
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function [a,b,c,d,k,x0,da,db,dc,dd,dk,dx0]=th2ss(th) % L. Ljung 10-2-90 % Copyright (c) 1986-98 by The MathWorks, Inc. % $Revision: 2.3 $ $Date: 1997/12/02 03:40:42 $ if nargin < 1 disp('Usage: [A,B,C,D,K,X0] = TH2SS(TH)') disp(' [A,B,C,D,K,X0,dA,dB,dC,dD,dK,dX0] = TH2SS(TH)') return end T=th(1,2); if isthss(th), if nargout<7, eval('[a,b,c,d,k,x0]=eta2ss(th);'), else eval('[a,b,c,d,k,x0,da,db,dc,dd,dk,dx0]=eta2ss(th);'),end,return,end [a,b,c,d,k,x0]=th2ssaux(th); if nargout>6, % This assumes that TH does not use both an A-polynomial and F/D polynomials [thpar,p]=th2par(th); thpar=thpar+sqrt(diag(p))'; th(3,1:length(thpar))=thpar; [a1,b1,c1,d1,k1,x01]=th2ssaux(th); da=abs(a-a1);db=abs(b-b1);dc=abs(c-c1);dd=abs(d-d1);dk=abs(k-k1); dx0=abs(x0-x01);end