Specifications

modred
16-143
The last three diagonal entries of the balanced grammians are small, so
eliminate the last three states with
modred using both matched DC gain and
direct deletion methods.
hmdc = modred(hb,2:4,'mdc')
hdel = modred(hb,2:4,'del')
Both hmdc and hdel are first-order models. Compare their Bode responses
against that of the original model .
bode(h,'-',hmdc,'x',hdel,'*')
The reduced-order model hdel is clearly a better frequency-domain
approximation of . Now compare the step responses.
hs
()
hs
()