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+// Scilab ( http://www.scilab.org/ ) - This file is part of Scilab
+// Copyright (C) INRIA -
+//
+// This file must be used under the terms of the CeCILL.
+// This source file is licensed as described in the file COPYING, which
+// you should have received as part of this distribution. The terms
+// are also available at
+// http://www.cecill.info/licences/Licence_CeCILL_V2.1-en.txt
+
+function [K,X]=lqr(P12)
+ //lqr gain for full-state LQ problem
+ //(discrete or continuous)
+ // discrete continuous
+ // |I 0 0| | A 0 B | |I 0 0| | A 0 B |
+ // z|0 A' 0| - |-C'C I -S'| s |0 I 0| - |-C'C -A' -S' |
+ // |0 B' 0| | S 0 D'D| |0 0 0| | S -B' D'D|
+ if typeof(P12)<>"state-space" then
+ error(msprintf(gettext("%s: Wrong type for input argument #%d: Linear state space expected.\n"),"lqr",1))
+ end
+
+ [A,B2,C1,D12]=P12(2:5);
+ Q=C1'*C1;R=D12'*D12;S=D12'*C1;
+ [n,nu]=size(B2);
+ [ny,n]=size(C1);
+ if P12(7) == [] then
+ error(msprintf(gettext("%s: Wrong value for input argument #%d: Time domain must be ''c'' or ''d''.\n"),"lqr",1))
+ elseif P12(7) == "c"
+ Z=0*A;I=eye(A);O=zeros(n,nu);
+ bigE=[I,Z,O; ...
+ Z,I,O; ...
+ zeros(nu,2*n+nu)];
+
+ bigA=[A ,Z, B2; ...
+ -Q ,-A',-S'; ...
+ S ,B2', R];
+ Ri=inv(R);
+ Left=[I, Z, -B2*Ri;
+ Z, I, S'*Ri;
+ zeros(nu,2*n), Ri];
+ LA=Left*bigA;LE=Left*bigE;N=1:2*n;
+ //[wsmall,ks1]=schur(LA(N,N),LE(N,N),'c');
+ [wsmall,ks1]=schur(LA(N,N),"c");
+ if ks1<>n then
+ error(msprintf(gettext("%s: Stable subspace is too small.\n"),"lqr"));
+ end
+ X12=wsmall(1:n,1:n);phi12=wsmall(n+1:$,1:n);X=phi12/X12;
+ if rcond(X12)< 1.d-5 then
+ warning(msprintf(gettext("%s: Bad conditionning.\n"),"lqr"));
+ end
+ K=-Ri*(B2'*X+S);
+ return;
+ //////////////////////////////
+ // Other implementation ... //
+ //////////////////////////////
+ //[Q,Z,Qd,Zd,numbeps,numbeta]=kroneck(bigE,bigA);
+ //[w,ks]=schur(bigA,bigE,'c');
+ //if ks<>n then error('lqr: stable subspace too small!');end
+ //ws=w(:,1:n);
+ //X12=ws(1:n,:);
+ //phi12=ws(n+1:2*n,:);
+ //u12=ws(2*n+1:2*n+nu,:);
+ //if rcond(X12)< 1.d-5 then warning('lqr: bad conditionning!');end
+ //K=u12/X12;
+ //X=phi12/X12;
+ //return
+ elseif P12(7) == "d" | type(P12(7))==1
+ I=eye(A);Z=0*I;
+ Q=C1'*C1;R=D12'*D12;S=D12'*C1;
+ bigE=[I,Z,0*B2; ...
+ Z,A',0*B2; ...
+ 0*B2',-B2',0*B2'*B2];
+
+ bigA=[A,Z, B2; ...
+ -Q ,I, -S'; ...
+ S, 0*B2', R];
+
+ Ri=inv(R);
+
+ Left=[I, Z, -B2*Ri; ...
+ Z, I, S'*Ri; ...
+ zeros(nu,2*n), Ri];
+ LA=Left*bigA;LE=Left*bigE;N=1:2*n;
+ [wsmall,ks1]=schur(LA(N,N),LE(N,N),"d");
+ if ks1<>n then
+ error(msprintf(gettext("%s: Stable subspace is too small.\n"),"lqr"));
+ end
+ X12=wsmall(1:n,1:n);phi12=wsmall(n+1:$,1:n);X=phi12/X12;
+ if rcond(X12)< 1.d-5 then
+ warning(msprintf(gettext("%s: Bad conditionning.\n"),"lqr"));
+ end
+ K=-pinv(B2'*X*B2+R)*(B2'*X*A+S);
+ return
+ ////////////////////
+ // Other form ... //
+ ////////////////////
+ //[w,ks]=schur(bigA,bigE,'d');
+ //if ks<>n then error('lqr: stable subspace too small!');end
+ //ws=w(:,1:n);
+ //X12=ws(1:n,:);
+ //phi12=ws(n+1:2*n,:);
+ //u12=ws(2*n+1:2*n+nu,:);
+ //if rcond(X12)< 1.d-5 then warning('lqr: bad conditionning!');end
+ //K=u12/X12;
+ //X=phi12/X12;
+ //return
+ end
+
+endfunction