A bell shaped membership function is specified by three parameters $(a,b,c)$ as follows:
- $\dfrac{1}{1+\bigg(\dfrac{x-c}{a} \bigg)^b} \\$
- $\dfrac{1}{1+\bigg(\dfrac{x-c}{a} \bigg)^{2b}} \\$
- $1+\bigg(\dfrac{x-c}{a}\bigg)^b \\$
- $1+\bigg(\dfrac{x-c}{a} \bigg)^{2b}$