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Parameter Estimation Methods in Physiological Modeling: An ...

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Sensitivity Identifiability (cont’d)<br />

<br />

Sensitivity Identifiability (cont’d)<br />

Now, let !" = " # " 0 denote a small perturbation from ! 0<br />

. This gives<br />

rise to a small perturbation <strong>in</strong> the output<br />

!y = y(t,") # y(t," 0 ). Then,<br />

by the cha<strong>in</strong> rule for differentiation, we obta<strong>in</strong> the follow<strong>in</strong>g<br />

(approximate)) relationship<br />

!y = S!"<br />

A structure is then said to be sensitivity identifiable if the above<br />

equation can be solved uniquely for<br />

!" . This is the case if and only<br />

the<br />

rank(S) = p, or equivalently, if and only if det(S T S) ! 0 .<br />

GRAZ 2007<br />

It is clear that (local) output dist<strong>in</strong>guishability and sensitivity<br />

identifiability are equivalent concepts.<br />

#<br />

Comput<strong>in</strong>g the sensitivity function matrix S(t,!) =<br />

"y i(t,!) &<br />

% ?<br />

$ "!<br />

(<br />

j '

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