how to get gradient of input xyz

[QtEngineer]

I wanted to get grad of input xyz，but function returned None，and requires_grad=True/certain_grad doesnot work.Is it because the input of network concate x and xyz?
def patch_network_forward(self, input,):
xyz = input[:, -original_coordinate_size:]
...,
for layer in range(0, self.num_layers - 1):
lin = getattr(self, "patch_lin" + str(layer))
if layer in self.latent_in:
x = torch.cat([x, input], 1)
elif layer != 0 and self.xyz_in_all:
x = torch.cat([x, xyz], 1)
x = lin(x)
if layer < self.num_layers - 2:
if (
self.norm_layers is not None
and layer in self.norm_layers
and not self.weight_norm
):
bn = getattr(self, "patch_bn" + str(layer))
x = bn(x)
#x = self.softplus(x)
x = self.relu(x)
#x = self.elu(x)
if self.dropout is not None and layer in self.dropout:
x = F.dropout(x, p=self.dropout_prob, training=self.training)