ReLU6

f(x)=min(max(0,x),6)f(x) = \rm {min}(\rm {max}(0, x), 6)

f(x)={0x<0 or x>61otherwisef^{\prime}(x) = \begin{cases} 0 & x < 0 \text{ or } x > 6 \\ 1 & \text{otherwise}\end{cases}