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abcd Scilab Group Scilab Function abcd
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feedback - feedback operation
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Sl1,Sl2 : linear systems (syslin list) in state-space or transfer form,
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or ordinary gain matrices.
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Sl : linear system (syslin list) in state-space or transfer form
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The feedback operation is denoted by /. (slashdot). This command
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returns Sl=Sl1*(I+Sl2*Sl1)^-1, i.e the (negative) feedback of Sl1 and
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Sl2. Sl is the transfer v -> y for y = Sl1 u , u = v - Sl2 y.
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The result is the same as Sl=LFT([0,I;I,-Sl2],Sl1).
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Caution: do not use with decimal point (e.g. 1/.1 is ambiguous!)
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S1=ssrand(2,2,3);S2=ssrand(2,2,2);
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//Same operation by LFT:
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ss2tf(lft([zeros(2,2),eye(2,2);eye(2,2),-S2],S1))
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//Other approach: with constant feedback
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BigS=sysdiag(S1,S2); F=[zeros(2,2),eye(2,2);-eye(2,2),zeros(2,2)];
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W1=Bigclosed(1:2,1:2); //W1=W (in state-space).
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ss2tf(S1*inv(eye()+S2*S1))
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lft, sysdiag, augment, obscont