Bug: optimizer got an empty parameter list

I am trying to build Logistic matrix factorization.When I run it,the error says that :optimizer got an empty parameter list.I am unfamiliar to PyTorch and I don’t know what causes the error.Can you give me some suggestions?Thank you!
this is my code

class LMF(nn.Module):
    def __init__(self, C, R_test , n_factor):
       :param C:
       :param R_test:
       :param n_factor:
       super(LMF, self).__init__()
       self.n_factor = n_factor
       self.C = torch.tensor(C)
       self.R = torch.tensor(R_test)
       self.n_user = C.shape[0]
       self.n_item = C.shape[1]
       self.X = torch.randn([self.n_user, self.n_factor], requires_grad=True)
       self.Y = torch.randn([self.n_item, self.n_factor], requires_grad=True)
       self.user_biases = torch.randn((self.n_user, 1), requires_grad=True)
       self.item_biases = torch.randn((self.n_item, 1), requires_grad=True)

    def forward(self):

        loss=self.C.dot(A) - (1+C).dot(torch.log((1+torch.exp(A))))
        return -loss

    def MPR(self):
        rank = 0.0
        R_sum = torch.sum(self.R)
        R_hat=torch.mm(self.X , self.Y.T)
        R_hat_rank = torch.argsort(torch.argsort(-R_hat, axis=1))
        A = R * (R_hat_rank / self.n_item)
        rank = torch.sum(A)/ R_sum
        return rank.item()

optimizer=torch.optim.Adam(params = model.parameters() , lr = learning_rate)

You should use torch.nn.Parameter or torch.nn.ParameterList to specify your parameters.

thank you for your help