diff --git a/pyFTS/common/Membership.py b/pyFTS/common/Membership.py
index 4960dea..79c00a3 100644
--- a/pyFTS/common/Membership.py
+++ b/pyFTS/common/Membership.py
@@ -52,12 +52,23 @@ def gaussmf(x, parameters):
     :return: the membership value of x given the parameters
     """
     return math.exp((-(x - parameters[0])**2)/(2 * parameters[1]**2))
-    #return math.exp(-0.5 * ((x - parameters[0]) / parameters[1]) ** 2)
 
 
 def bellmf(x, parameters):
+    """
+    Bell shaped membership function
+    :param x:
+    :param parameters:
+    :return:
+    """
     return 1 / (1 + abs((x - parameters[2]) / parameters[0]) ** (2 * parameters[1]))
 
 
 def sigmf(x, parameters):
+    """
+    Sigmoid / Logistic membership function
+    :param x:
+    :param parameters: an list with 2 real values (smoothness and midpoint)
+    :return:
+    """
     return 1 / (1 + math.exp(-parameters[0] * (x - parameters[1])))
diff --git a/pyFTS/common/NonStationary.py b/pyFTS/common/NonStationary.py
index 3e5e21b..8eccb43 100644
--- a/pyFTS/common/NonStationary.py
+++ b/pyFTS/common/NonStationary.py
@@ -3,6 +3,76 @@ from pyFTS import *
 from pyFTS.common import FuzzySet, Membership
 
 
+class NonStationaryMembershipFunction(object):
+    def __init__(self, name, mf, parameters, **kwargs):
+        self.mf = mf
+        self.parameters = parameters
+        self.location = kwargs.get("location", None)
+        self.location_params = kwargs.get("location_params", None)
+        self.width = kwargs.get("width", None)
+        self.width_params = kwargs.get("width_params", None)
+        self.noise = kwargs.get("noise", None)
+        self.noise_params = kwargs.get("noise_params", None)
+
+    def perform_location(self, t, param):
+        if self.location is None:
+            return param
+
+        inc = self.location(t, self.location_params)
+
+        if self.mf == Membership.gaussmf:
+            #changes only the mean parameter
+            return [param[0] + inc, param[1]]
+        elif self.mf == Membership.sigmf:
+            #changes only the midpoint parameter
+            return [param[0], param[1] + inc]
+        elif self.mf == Membership.bellmf:
+            return [param[0], param[1], param[2] + inc]
+        else:
+            #translate all parameters
+            return [k + inc for k in param]
+
+    def perform_width(self, t, param):
+        if self.width is None:
+            return param
+
+        inc = self.width(t, self.width_params)
+
+        if self.mf == Membership.gaussmf:
+            #changes only the variance parameter
+            return [param[0], param[1] + inc]
+        elif self.mf == Membership.sigmf:
+            #changes only the smooth parameter
+            return [param[0] + inc, param[1]]
+        elif self.mf == Membership.trimf:
+            return [param[0] + inc, param[1], param[2] - inc]
+        elif self.mf == Membership.trapmf:
+            l = (param[3]-param[0])
+            rab = (param[1] - param[0]) / l
+            rcd = (param[3] - param[2]) / l
+            return [param[0] + inc, param[1] + inc*rab, param[2] - inc*rcd, param[3] - inc]
+        else:
+            return param
+
+    def membership(self, x, t):
+        """
+        Calculate the membership value of a given input
+        :param x: input value
+        :return: membership value of x at this fuzzy set
+        """
+
+        param = self.parameters
+        param = self.perform_location(t, param)
+        param = self.perform_width(t, param)
+
+        tmp = self.mf(x, param)
+
+        if self.noise is not None:
+            tmp += self.noise(t, self.noise_params)
+
+        return tmp
+
+
 class NonStationaryFuzzySet(FuzzySet.FuzzySet):
     """
     Non Stationary Fuzzy Sets
@@ -11,28 +81,12 @@ class NonStationaryFuzzySet(FuzzySet.FuzzySet):
     IEEE Transactions on Fuzzy Systems, v. 16, n. 4, p. 1072-1086, 2008.
     """
 
-    def __init__(self, name, mf, parameters):
+    def __init__(self, name, mf, **kwargs):
         """
         Constructor
         :param name: Fuzzy Set name
-        :param mf: Membership Function
-        :param pf: Pertubation Function
-        :param parameters: initial parameters of the membership function
-        :param pf_parameters: parameters of the membership pertubation function
+        :param mf: NonStationary Membership Function
         """
-        super(FuzzySet, self).__init__(order=1, name=name, **kwargs)
-        self.name = name
-        self.mf = mf
-        self.parameters = parameters
-        self.pf = []
-        self.pf_parameters = []
+        super(FuzzySet, self).__init__(name=name, mf=mf, parameters=None, centroid=None)
+        
 
-    def appendPertubation(self, pf, pf_parameters):
-        """
-        Append a pertubation function to the non-stationary fuzzy set
-        :param pf:
-        :param pf_parameters:
-        :return:
-        """
-        self.pf.append(pf)
-        self.pf_parameters.append(pf_parameters)