Understanding Linguistic Variable in Fuzzy Logic

One of the beauties of Fuzzy Logic is Linguistic Variable. Fuzzy Logic can define mathematical values in Linguistic variables with range of values. It is usually named as Membership Function. Based on the figure below, room_temperaturevariable has 4 membership functions i.e. low_temp,normal,raised_temperatureand strong_fever. 

Membership function low_temp(yellow color) has range of real temperature values 0 °C to 37 °C, normal (green color) has range of real temperature values 36 °C to 37.25 °C, and raised_temperature (blue color) has value range 37 °C to 39.25 °C. More detail about value range of all membership functions can be seen in the table below.

No	Membership Function	Color	Range of Real Temp. Values
1.	low_temp	Yellow	0 °C to 37 °C
2.	normal	Green	36 °C to 37.25 °C
3.	raised_temperature	Blue	37 °C to 39.25 °C
4.	strong_fever	Purple	37.5 °C to 43 °C

Each membership function has values which is overlapping each other in the border. It will make a changing of temperature from a membership function to other membership function can be controlled with very smooth. The moving of room_temperaturefrom raised_temperature to strong_feverwill be running very smooth. This is another beauty of Fuzzy Logic!

Source of  figures:

Industrial Application of Fuzzy Logic Control (slide presentations), Inform Software Corporation, 20001  Midwest Rd., Oak Brook, IL 60521, U. S. A.