Adds a dimension to class.
        
        :parameter name: dimension name
        :parameter value: dimension value

def create_Dim(self, name,value):
        '''
        Adds a dimension to class.
        
        :parameter name: dimension name
        :parameter value: dimension value
        '''
        if not self._dimensions.has_key(name) :
            self.message(3, 'Create dimension {0}:{1}'.format(name,value))
            self._dimensions[name]=value
            self._dimensions['_ndims']=len(self._dimensions) - 1
        else :
            self.message(3, 'Dimension {0} already exists'.format(name))