Synchronization of the fractional order chaotic systems is extensively studied in recent years due to
its potential applications in many branches of science and engineering. The main problems in this field
are that the dynamics of the system in hand are often uncertain and are perturbed by external disturbances. Also the unknown nonlinear functions in the system dynamics are generally complicated and in
many practical applications we have measurement errors and unavailable states. In this paper, a novel
robust and asymptotically stable controller is proposed to synchronize uncertain fractional order chaotic
systems. Its design is based on linear matrix inequality (LMI) technique. Furthermore, an observer is
presented to estimate the unavailable states. A general type-2 fuzzy system (GT2FS) based on ˛-plane
representation with Gaussian secondary membership functions (MF) and type-2 non-singleton fuzzification is proposed to approximate the unknown complex nonlinear functions in the dynamics of system.
The input uncertainties associated with the observer error and the malfunctioning of the input devices
are modeled by intervaltype-2 fuzzy MFs instead of crisp numbers. To decrease the computational cost of
the GT2FS, a simple type-reduction method is proposed. The antecedent parameters of GT2FS are tuned
based on a modified form of social spider optimization (SSO) algorithm. The simulation examples show
that the proposed control scheme gives high performance in the presence of unknown functions, external disturbances and unavailable states. The performance of GT2FS with different ˛-levels and different
fuzzification methods are compared with type-1 and interval type-2 fuzzy systems in several examples