def update_actor()

in drqv2.py [0:0]


    def update_actor(self, obs, step):
        metrics = dict()

        stddev = utils.schedule(self.stddev_schedule, step)
        dist = self.actor(obs, stddev)
        action = dist.sample(clip=self.stddev_clip)
        log_prob = dist.log_prob(action).sum(-1, keepdim=True)
        Q1, Q2 = self.critic(obs, action)
        Q = torch.min(Q1, Q2)

        actor_loss = -Q.mean()

        # optimize actor
        self.actor_opt.zero_grad(set_to_none=True)
        actor_loss.backward()
        self.actor_opt.step()

        if self.use_tb:
            metrics['actor_loss'] = actor_loss.item()
            metrics['actor_logprob'] = log_prob.mean().item()
            metrics['actor_ent'] = dist.entropy().sum(dim=-1).mean().item()

        return metrics