Should be either 'input' or 'output', which relates to the type of variable (stored on the existing fis structure) that the membership function will be added to.
varIndex
Should be an integer value representing the index value of the input or output variable that the membership function will be added to (base 1).
mfName
Membership function name to be declared, for example (Poor,Good)
mfType
Membership function type to be declared, for example (trimf, trapmf)
mfParams
The value of membership function.
Value
A fis structure with the new membership function added.