diff --git a/chapter4_reward/q1.md b/chapter4_reward/q1.md
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+# RND
+模型过小时，容易欠拟合，训练误差更大，而且奖励浮动范围大，但small比little的模型浮动更大，这就有点奇怪。模型过大时，容易过拟合，泛化能力弱，large和very_large模型曲线走势接近，完全拟合了训练数据包括噪声，收敛更慢。
+![q1](q1.png)
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diff --git a/chapter4_reward/q1.png b/chapter4_reward/q1.png
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diff --git a/chapter4_reward/q1.py b/chapter4_reward/q1.py
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+++ b/chapter4_reward/q1.py
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+# pip install minigrid
+from typing import Union, Tuple, Dict, List, Optional
+from multiprocessing import Process
+import multiprocessing as mp
+import random
+import numpy as np
+import torch
+import torch.nn as nn
+import torch.nn.functional as F
+import torch.optim as optim
+import minigrid
+import gymnasium as gym
+from torch.optim.lr_scheduler import ExponentialLR, MultiStepLR
+from tensorboardX import SummaryWriter
+from minigrid.wrappers import FlatObsWrapper
+
+random.seed(0)
+np.random.seed(0)
+torch.manual_seed(0)
+if torch.cuda.is_available():
+    device = torch.device("cuda:0")
+else:
+    device = torch.device("cpu")
+
+train_config = dict(
+    train_iter=1024,
+    train_data_count=128,
+    test_data_count=4096,
+)
+
+little_RND_net_config = dict(
+    exp_name="little_rnd_network",
+    observation_shape=2835,
+    hidden_size_list=[32, 16],
+    learning_rate=1e-3,
+    batch_size=64,
+    update_per_collect=100,
+    obs_norm=True,
+    obs_norm_clamp_min=-1,
+    obs_norm_clamp_max=1,
+    reward_mse_ratio=1e5,
+)
+
+small_RND_net_config = dict(
+    exp_name="small_rnd_network",
+    observation_shape=2835,
+    hidden_size_list=[64, 64],
+    learning_rate=1e-3,
+    batch_size=64,
+    update_per_collect=100,
+    obs_norm=True,
+    obs_norm_clamp_min=-1,
+    obs_norm_clamp_max=1,
+    reward_mse_ratio=1e5,
+)
+
+standard_RND_net_config = dict(
+    exp_name="standard_rnd_network",
+    observation_shape=2835,
+    hidden_size_list=[128, 64],
+    learning_rate=1e-3,
+    batch_size=64,
+    update_per_collect=100,
+    obs_norm=True,
+    obs_norm_clamp_min=-1,
+    obs_norm_clamp_max=1,
+    reward_mse_ratio=1e5,
+)
+
+large_RND_net_config = dict(
+    exp_name="large_RND_network",
+    observation_shape=2835,
+    hidden_size_list=[256, 256],
+    learning_rate=1e-3,
+    batch_size=64,
+    update_per_collect=100,
+    obs_norm=True,
+    obs_norm_clamp_min=-1,
+    obs_norm_clamp_max=1,
+    reward_mse_ratio=1e5,
+)
+
+very_large_RND_net_config = dict(
+    exp_name="very_large_RND_network",
+    observation_shape=2835,
+    hidden_size_list=[512, 512],
+    learning_rate=1e-3,
+    batch_size=64,
+    update_per_collect=100,
+    obs_norm=True,
+    obs_norm_clamp_min=-1,
+    obs_norm_clamp_max=1,
+    reward_mse_ratio=1e5,
+)
+
+class FCEncoder(nn.Module):
+    def __init__(
+            self,
+            obs_shape: int,
+            hidden_size_list,
+            activation: Optional[nn.Module] = nn.ReLU(),
+    ) -> None:
+        super(FCEncoder, self).__init__()
+        self.obs_shape = obs_shape
+        self.act = activation
+        self.init = nn.Linear(obs_shape, hidden_size_list[0])
+
+        layers = []
+        for i in range(len(hidden_size_list) - 1):
+            layers.append(nn.Linear(hidden_size_list[i], hidden_size_list[i + 1]))
+            layers.append(self.act)
+        self.main = nn.Sequential(*layers)
+
+    def forward(self, x: torch.Tensor) -> torch.Tensor:
+        x = self.act(self.init(x))
+        x = self.main(x)
+        return x
+
+class RndNetwork(nn.Module):
+    def __init__(self, obs_shape: Union[int, list], hidden_size_list: list) -> None:
+        super(RndNetwork, self).__init__()
+        self.target = FCEncoder(obs_shape, hidden_size_list)
+        self.predictor = FCEncoder(obs_shape, hidden_size_list)
+
+        for param in self.target.parameters():
+            param.requires_grad = False
+
+    def forward(self, obs: torch.Tensor) -> Tuple[torch.Tensor, torch.Tensor]:
+        predict_feature = self.predictor(obs)
+        with torch.no_grad():
+            target_feature = self.target(obs)
+        return predict_feature, target_feature
+
+class RunningMeanStd(object):
+    def __init__(self, epsilon=1e-4, shape=(), device=torch.device('cpu')):
+        self._epsilon = epsilon
+        self._shape = shape
+        self._device = device
+        self.reset()
+
+    def update(self, x):
+        batch_mean = np.mean(x, axis=0)
+        batch_var = np.var(x, axis=0)
+        batch_count = x.shape[0]
+
+        new_count = batch_count + self._count
+        mean_delta = batch_mean - self._mean
+        new_mean = self._mean + mean_delta * batch_count / new_count
+        # this method for calculating new variable might be numerically unstable
+        m_a = self._var * self._count
+        m_b = batch_var * batch_count
+        m2 = m_a + m_b + np.square(mean_delta) * self._count * batch_count / new_count
+        new_var = m2 / new_count
+        self._mean = new_mean
+        self._var = new_var
+        self._count = new_count
+
+    def reset(self):
+        if len(self._shape) > 0:
+            self._mean = np.zeros(self._shape, 'float32')
+            self._var = np.ones(self._shape, 'float32')
+        else:
+            self._mean, self._var = 0., 1.
+        self._count = self._epsilon
+
+    @property
+    def mean(self) -> np.ndarray:
+        if np.isscalar(self._mean):
+            return self._mean
+        else:
+            return torch.FloatTensor(self._mean).to(self._device)
+
+    @property
+    def std(self) -> np.ndarray:
+        std = np.sqrt(self._var + 1e-8)
+        if np.isscalar(std):
+            return std
+        else:
+            return torch.FloatTensor(std).to(self._device)
+
+class RndRewardModel():
+
+    def __init__(self, config) -> None:  # noqa
+        super(RndRewardModel, self).__init__()
+        self.cfg = config
+
+        self.tb_logger = SummaryWriter(config["exp_name"])
+        self.reward_model = RndNetwork(
+            obs_shape=config["observation_shape"], hidden_size_list=config["hidden_size_list"]
+        ).to(device)
+
+        self.opt = optim.Adam(self.reward_model.predictor.parameters(), config["learning_rate"])
+        self.scheduler = ExponentialLR(self.opt, gamma=0.997)
+
+        self.estimate_cnt_rnd = 0
+        if self.cfg["obs_norm"]:
+            self._running_mean_std_rnd_obs = RunningMeanStd(epsilon=1e-4, device=device)
+
+    def __del__(self):
+        self.tb_logger.flush()
+        self.tb_logger.close()
+
+    def train(self, data) -> None:
+        for _ in range(self.cfg["update_per_collect"]):
+            train_data: list = random.sample(data, self.cfg["batch_size"])
+            train_data: torch.Tensor = torch.stack(train_data).to(device)
+            if self.cfg["obs_norm"]:
+                # Note: observation normalization: transform obs to mean 0, std 1
+                self._running_mean_std_rnd_obs.update(train_data.cpu().numpy())
+                train_data = (train_data - self._running_mean_std_rnd_obs.mean) / self._running_mean_std_rnd_obs.std
+                train_data = torch.clamp(
+                    train_data, min=self.cfg["obs_norm_clamp_min"], max=self.cfg["obs_norm_clamp_max"]
+                )
+
+            predict_feature, target_feature = self.reward_model(train_data)
+            loss = F.mse_loss(predict_feature, target_feature.detach())
+            self.opt.zero_grad()
+            loss.backward()
+            self.opt.step()
+        self.scheduler.step()
+
+    def estimate(self, data: list) -> List[Dict]:
+        """
+        estimate the rnd intrinsic reward
+        """
+
+        obs = torch.stack(data).to(device)
+        if self.cfg["obs_norm"]:
+            # Note: observation normalization: transform obs to mean 0, std 1
+            obs = (obs - self._running_mean_std_rnd_obs.mean) / self._running_mean_std_rnd_obs.std
+            obs = torch.clamp(obs, min=self.cfg["obs_norm_clamp_min"], max=self.cfg["obs_norm_clamp_max"])
+
+        with torch.no_grad():
+            self.estimate_cnt_rnd += 1
+            predict_feature, target_feature = self.reward_model(obs)
+            mse = F.mse_loss(predict_feature, target_feature, reduction='none').mean(dim=1)
+            self.tb_logger.add_scalar('rnd_reward/mse', mse.cpu().numpy().mean(), self.estimate_cnt_rnd)
+
+            # Note: according to the min-max normalization, transform rnd reward to [0,1]
+            rnd_reward = mse * self.cfg["reward_mse_ratio"]  #(mse - mse.min()) / (mse.max() - mse.min() + 1e-11)
+
+            self.tb_logger.add_scalar('rnd_reward/rnd_reward_max', rnd_reward.max(), self.estimate_cnt_rnd)
+            self.tb_logger.add_scalar('rnd_reward/rnd_reward_mean', rnd_reward.mean(), self.estimate_cnt_rnd)
+            self.tb_logger.add_scalar('rnd_reward/rnd_reward_min', rnd_reward.min(), self.estimate_cnt_rnd)
+
+            rnd_reward = torch.chunk(rnd_reward, rnd_reward.shape[0], dim=0)
+
+def training(config, train_data, test_data):
+    rnd_reward_model = RndRewardModel(config=config)
+    for i in range(train_config["train_iter"]):
+        rnd_reward_model.train([torch.Tensor(item["last_observation"]) for item in train_data[i]])
+        rnd_reward_model.estimate([torch.Tensor(item["last_observation"]) for item in test_data])
+
+def main():
+    env = gym.make("MiniGrid-Empty-8x8-v0")
+    env_obs = FlatObsWrapper(env)
+
+    train_data = []
+    test_data = []
+
+    for i in range(train_config["train_iter"]):
+
+        train_data_per_iter = []
+
+        while len(train_data_per_iter) < train_config["train_data_count"]:
+            last_observation, _ = env_obs.reset()
+            terminated = False
+            while terminated != True and len(train_data_per_iter) < train_config["train_data_count"]:
+                action = env_obs.action_space.sample()
+                observation, reward, terminated, truncated, info = env_obs.step(action)
+                train_data_per_iter.append(
+                    {
+                        "last_observation": last_observation,
+                        "action": action,
+                        "reward": reward,
+                        "observation": observation
+                    }
+                )
+                last_observation = observation
+            env_obs.close()
+
+        train_data.append(train_data_per_iter)
+
+    while len(test_data) < train_config["test_data_count"]:
+        last_observation, _ = env_obs.reset()
+        terminated = False
+        while terminated != True and len(train_data_per_iter) < train_config["test_data_count"]:
+            action = env_obs.action_space.sample()
+            observation, reward, terminated, truncated, info = env_obs.step(action)
+            test_data.append(
+                {
+                    "last_observation": last_observation,
+                    "action": action,
+                    "reward": reward,
+                    "observation": observation
+                }
+            )
+            last_observation = observation
+        env_obs.close()
+
+    p0 = Process(target=training, args=(little_RND_net_config, train_data, test_data))
+    p0.start()
+
+    p1 = Process(target=training, args=(small_RND_net_config, train_data, test_data))
+    p1.start()
+
+    p2 = Process(target=training, args=(standard_RND_net_config, train_data, test_data))
+    p2.start()
+
+    p3 = Process(target=training, args=(large_RND_net_config, train_data, test_data))
+    p3.start()
+
+    p4 = Process(target=training, args=(very_large_RND_net_config, train_data, test_data))
+    p4.start()
+
+    p0.join()
+    p1.join()
+    p2.join()
+    p3.join()
+    p4.join()
+
+if __name__ == "__main__":
+    mp.set_start_method('spawn')
+    main()
diff --git a/chapter4_reward/q2.py b/chapter4_reward/q2.py
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+# Please install latest DI-engine's main branch first
+from ding.bonus import PPOF
+
+
+def acrobot():
+    # Please install acrobot env first, `pip3 install gym`
+    # You can refer to the env doc (https://di-engine-docs.readthedocs.io/zh_CN/latest/13_envs/acrobot_zh.html) for more details
+    agent = PPOF(env='acrobot', exp_name='./acrobot_demo')
+    agent.train(step=int(1e5))
+     # Classic RL interaction loop and save replay video
+    agent.deploy(enable_save_replay=True)
+
+
+def metadrive():
+    # Please install metadrive env first, `pip install metadrive-simulator`
+    # You can refer to the env doc (https://di-engine-docs.readthedocs.io/zh_CN/latest/13_envs/metadrive_zh.html) for more details
+    agent = PPOF(env='metadrive', exp_name='./metadrive_demo')
+    agent.train(step=int(1e6), context='spawn')
+     # Classic RL interaction loop and save replay video
+    agent.deploy(enable_save_replay=True)
+
+
+def minigrid_fourroom():
+    # Please install minigrid env first, `pip install gym-minigrid`
+    # Note: minigrid env doesn't support Windows platform
+    # You can refer to the env doc (https://di-engine-docs.readthedocs.io/zh_CN/latest/13_envs/minigrid_zh.html) for more details
+    agent = PPOF(env='minigrid_fourroom', exp_name='./minigrid_fourroom_demo')
+    agent.train(step=int(3e6))
+     # Classic RL interaction loop and save replay video
+    agent.deploy(enable_save_replay=True)
+
+
+if __name__ == "__main__":
+    # acrobot()
+    # metadrive()
+    minigrid_fourroom()
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