def __getitem__(self, key):

        # self.lib.getHMatrix.restype=ctypes.POINTER(_C_HMatrix)
        # self.lib.getHMatrix.argtypes=[ctypes.POINTER(_C_MultiHMatrix), ctypes.c_int]
        # c_data_hmatrix = self.lib.getHMatrix(self.c_data,key)
        # return HMatrix(c_data_hmatrix,**self.params)
        return self.hmatrices[key]