▁very ▁wide ▁applic ability ▁in ▁rule - based ▁f uz zy ▁logic ▁systems ▁( F LS s ) ▁because ▁they ▁let ▁un cert aint ies ▁be ▁mode led ▁by ▁them ▁whereas ▁such ▁un cert aint ies ▁cannot ▁be ▁mode led ▁by ▁type - 1 ▁f uz zy ▁sets . ▁A ▁block ▁diagram ▁of ▁a ▁type - 2 ▁F LS ▁is ▁dep icted ▁in ▁Fig . ▁ 3 . ▁This ▁kind ▁of ▁F LS ▁is ▁used ▁in ▁f uz zy ▁logic ▁control , ▁f uz zy ▁logic ▁signal ▁processing , ▁rule - based ▁classification , ▁etc ., ▁and ▁is ▁sometimes ▁referred ▁to ▁as ▁a ▁function ▁approximation ▁application ▁of ▁f uz zy ▁sets , ▁because ▁the ▁F LS ▁is ▁designed ▁to ▁minim ize ▁an ▁error ▁function . ▁ ▁The ▁following ▁discuss ions , ▁about ▁the ▁four ▁components ▁in ▁the ▁Fig . ▁ 3 ▁rule - based ▁F LS , ▁are ▁given ▁for ▁an ▁interval ▁type - 2 ▁F LS , ▁because ▁to - date ▁they ▁are ▁the ▁most ▁popular ▁kind ▁of ▁type - 2 ▁F LS ; ▁however , ▁most ▁of ▁the ▁discuss ions ▁are ▁also ▁applicable ▁for ▁a ▁general ▁type - 2 ▁F LS . ▁ ▁R ules , ▁that ▁are ▁either ▁provided ▁by ▁subject ▁exper ts ▁or ▁are ▁extracted ▁from ▁numerical ▁data , ▁are ▁expressed ▁as ▁a ▁collection ▁of ▁IF - TH EN ▁statements , ▁e . g ., ▁ ▁IF ▁temperature ▁is ▁moder ate ▁and ▁pressure ▁is ▁high , ▁then ▁rotate ▁the ▁val ve ▁a ▁bit ▁to ▁the ▁right . ▁ ▁F