# Sensitivity
Whenever we introduce our reference input,
we should check the associated [Sensitivity Function](./../Formularies/CONTROL-FORMULARY.md/#sensitivity-function).

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As we can see, a reference put 
just after the output og $G_p(s)$
yealds a more robust system, overall.

# Augmented state
Each time we need to make the system 
faster, we need an `integrator`. 
In order to being able to place it, we just 
need to augment the state. By doing that 
we introduce some ***helping*** 
`state variables` and the rest is as it is.