The output y is obtained by applying a factor in the interval [0,1] to the maximum output u_max (the ceiling). It effectively calculates a smooth minimum with regard to the inputs u and u_max:
The following graph shows the results for u_max =
1.0 and k ∈ {10,5,3,2}:
When the intended output u is a small fraction of
the maximum output u_max (ceiling) the actual output
y will be equal to the intended output. As
u approaches the ceiling the limitations will have a
gradual effect so that less than the intended output is returned.
Eventually the output will be identical to the maximum value.
u : u_max is used as
input to the smooth minimum; John Sterman [3,
pp. 711-713] uses the ratio u_max : u
instead.