model.py

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

class ResidualBlock(nn.Module):
    def __init__(self, channels):
        super(ResidualBlock, self).__init__()
        self.conv1 = nn.Conv2d(channels, channels, kernel_size=3, padding=1, bias=False)
        self.bn1 = nn.BatchNorm2d(channels)
        self.conv2 = nn.Conv2d(channels, channels, kernel_size=3, padding=1, bias=False)
        self.bn2 = nn.BatchNorm2d(channels)

    def forward(self, x):
        residual = x
        out = F.relu(self.bn1(self.conv1(x)))
        out = self.bn2(self.conv2(out))
        out += residual
        out = F.relu(out)
        return out

class OthelloNet(nn.Module):
    def __init__(self, num_res_blocks=10, num_channels=256):
        super(OthelloNet, self).__init__()
        
        # Input: 3 channels (Player pieces, Opponent pieces, Legal moves/Constant plane)
        self.conv_input = nn.Conv2d(3, num_channels, kernel_size=3, padding=1, bias=False)
        self.bn_input = nn.BatchNorm2d(num_channels)
        
        # Residual Tower
        self.res_blocks = nn.ModuleList([
            ResidualBlock(num_channels) for _ in range(num_res_blocks)
        ])
        
        # Policy Head
        self.policy_conv = nn.Conv2d(num_channels, 2, kernel_size=1, bias=False)
        self.policy_bn = nn.BatchNorm2d(2)
        # 2 channels * 8 * 8 = 128
        self.policy_fc = nn.Linear(128, 65) # 64 squares + pass

        # Value Head
        self.value_conv = nn.Conv2d(num_channels, 1, kernel_size=1, bias=False)
        self.value_bn = nn.BatchNorm2d(1)
        # 1 channel * 8 * 8 = 64
        self.value_fc1 = nn.Linear(64, 256)
        self.value_fc2 = nn.Linear(256, 1)

    def forward(self, x):
        # Input Convolution
        x = F.relu(self.bn_input(self.conv_input(x)))
        
        # Residual Tower
        for block in self.res_blocks:
            x = block(x)
            
        # Policy Head
        p = F.relu(self.policy_bn(self.policy_conv(x)))
        p = p.view(p.size(0), -1) # Flatten
        p = self.policy_fc(p)
        # We return logits (unnormalized), let loss function handle softma separation
        # Or return log_softmax for NLLLoss if needed.
        # Often for alpha zero implementations, returning log_softmax for training stability is good
        # But here let's stick to returning raw logits (or log_softmax)
        # Let's return log_softmax as it is numerically stable for KLDivLoss
        p = F.log_softmax(p, dim=1)

        # Value Head
        v = F.relu(self.value_bn(self.value_conv(x)))
        v = v.view(v.size(0), -1) # Flatten
        v = F.relu(self.value_fc1(v))
        v = torch.tanh(self.value_fc2(v))

        return p, v