model.py

import torch
import torch.nn as nn
import torch.nn.functional as F

class QNetwork(nn.Module):
    """Actor (Policy) Model."""
    net_type = 'qnetwork'

    def __init__(self, state_size, action_size, seed, fc1_units=128, fc2_units=64):
        """Initialize parameters and build model.
        Params
        ======
            state_size (int): Dimension of each state
            action_size (int): Dimension of each action
            seed (int): Random seed
            fc1_units (int): Number of nodes in first hidden layer
            fc2_units (int): Number of nodes in second hidden layer
        """
        super(QNetwork, self).__init__()
        
        self.state_size = state_size
        self.action_size = action_size   
        self.seed = torch.manual_seed(seed)

        self.fc1 = nn.Linear(state_size, fc1_units)
        self.fc2 = nn.Linear(fc1_units, fc2_units)
        self.fc3 = nn.Linear(fc2_units, action_size)

    def forward(self, state):
        """Build a network that maps state -> action values."""
        x = F.relu(self.fc1(state))
        x = F.relu(self.fc2(x))
        return self.fc3(x)
    
class DuelingQNetwork(nn.Module):
    net_type = 'dueling_qnetwork'

    def __init__(self, state_size, action_size, seed, fc1_units=128, fc2_units=64):
        """Initialize parameters and build model.
        Params
        ======
            state_size (int): Dimension of each state
            action_size (int): Dimension of each action
            seed (int): Random seed
            fc1_units (int): Number of nodes in first hidden layer
            fc2_units (int): Number of nodes in second hidden layer
        """
        super(DuelingQNetwork, self).__init__()
        
        self.state_size = state_size
        self.action_size = action_size
        self.seed = torch.manual_seed(seed)

        self.fc1 = nn.Linear(state_size, fc1_units)
        
        self.fc2_adv = nn.Linear(fc1_units, fc2_units)
        self.fc2_val = nn.Linear(fc1_units, fc2_units)
        
        self.fc3_adv = nn.Linear(fc2_units, action_size)
        self.fc3_val = nn.Linear(fc2_units, 1)

    def forward(self, state):
        """Build a network that maps state -> action values."""
        x = F.relu(self.fc1(state))
        
        adv = F.relu(self.fc2_adv(x))
        val = F.relu(self.fc2_val(x))
        
        adv = self.fc3_adv(adv)
        val = self.fc3_val(val)
        
        return val + adv - adv.mean()