def read_memory(self):
        """
        This function read mean value of target`d`
        and input vector `x` from history
        """
        if self.mem_empty == True:
            if self.mem_idx == 0:
                m_x = np.zeros(self.n)
                m_d = 0
            else:
                m_x = np.mean(self.mem_x[:self.mem_idx+1], axis=0)
                m_d = np.mean(self.mem_d[:self.mem_idx])
        else:
            m_x = np.mean(self.mem_x, axis=0)
            m_d = np.mean(np.delete(self.mem_d, self.mem_idx))
        self.mem_idx += 1
        if self.mem_idx > len(self.mem_x)-1:
            self.mem_idx = 0
            self.mem_empty = False
        return m_d, m_x
This function read mean value of target`d`
        and input vector `x` from history