def save(self, doc):
        if doc.id:
            return self.update(doc)
        else:
            return self.insert(doc)
def gradients(self, d_grads, g_grads):
      if self.d_grads is None:
          self.d_grads = [torch.zeros_like(_g) for _g in d_grads]
          self.g_grads = [torch.zeros_like(_g) for _g in g_grads]