# Torch CNN not training

I am completely new to CNN's, and I do not quite know how to design or use them efficiently. That being said, I am attempting to build a CNN that learns to play Pac-man with reinforcement learning. I have trained it for about 3 hours and have seen little to no improvement. My observation space is 3 channels * 15 * 19, and there are 5 actions. Here is my code, I am open to any and all suggestions. Thanks for all your help.

from minipacman import MiniPacman as pac
from torch import nn
import torch
import random
import torch.optim as optimal
import matplotlib.pyplot as plt
import numpy as np
import keyboard

loss_fn = nn.MSELoss()
epsilon = 1
env = pac("regular", 1000)
time = 0
action = random.randint(0, 4)
q = np.zeros(3)
alpha = 0.01
gamma = 0.9
tick = 0
decay = 0.9999

class Value_Approximator (nn.Module):
def __init__(self):
super(Value_Approximator, self).__init__()
# Convolution 1
self.cnn1 = nn.Conv2d(in_channels=3, out_channels=16, kernel_size=5, stride=1, padding=2)
self.relu1 = nn.ReLU()

# Max pool 1
self.maxpool1 = nn.MaxPool2d(kernel_size=2)

# Convolution 2
self.cnn2 = nn.Conv2d(in_channels=16, out_channels=32, kernel_size=5, stride=1, padding=2)
self.relu2 = nn.ReLU()

# Max pool 2
self.maxpool2 = nn.MaxPool2d(kernel_size=2)

self.fc1 = nn.Linear(384, 5)

def forward(self, x):
# Convolution 1
out = self.cnn1(x)
out = self.relu1(out)

# Max pool 1
out = self.maxpool1(out)

# Convolution 2
out = self.cnn2(out)
out = self.relu2(out)

# Max pool 2
out = self.maxpool2(out)

# Resize
# Original size: (100, 32, 7, 7)
# out.size(0): 100
# New out size: (100, 32*7*7)
out = out.view(out.size(0), -1)

out = self.fc1(out)

return out

approx = Value_Approximator()
optimizer = optimal.SGD(approx.parameters(), lr=alpha)

while time < 50000:
print("Time: "+str(time))
print("Epsilon: "+str(epsilon))
print()
time += 1
state = env.reset()
tick = 0

epsilon *= decay

if epsilon < 0.1:
epsilon = 0.1

while True:
tick += 1
state = np.expand_dims(state, 1)
state = state.reshape(1, 3, 15, 19)
q = approx.forward(torch.from_numpy(state))[0]

if random.uniform(0, 1) < epsilon:
action = env.action_space.sample()
else:
_, action = torch.max(q, -1)
action = action.item()
new_state, reward, terminal, _ = env.step(action)
show_state = new_state
new_state = np.expand_dims(new_state, 1)
new_state = state.reshape(1, 3, 15, 19)

q_new = approx.forward(torch.from_numpy(new_state).type(torch.FloatTensor))[0]  # " find Q (s', a') "
#  find optimal action Q value for next step
new_max, _ = torch.max(q_new, -1)
new_max = new_max.item()

q_target = q.clone()
q_target = Variable(q_target.data)

#  update target value function according to TD
q_target[action] = reward + torch.mul(new_max, gamma)  # " reward + gamma*(max(Q(s', a')) "

loss = loss_fn(q, q_target)  # " reward + gamma*(max(Q(s', a')) - Q(s, a)) "
# Update original policy according to Q_target ( supervised learning )
loss.backward()
optimizer.step()

#  Q and Q_target should converge
if time % 100 == 0:
state = torch.FloatTensor(show_state).permute(1, 2, 0).cpu().numpy()

plt.subplot(131)
plt.title("Imagined")
plt.imshow(state)
plt.subplot(132)
plt.title("Actual")
plt.imshow(state)
plt.show(block=False)
plt.pause(0.000001)

if keyboard.is_pressed('1'):
torch.save(approx.state_dict(), 'trained-10000.mdl')
if keyboard.is_pressed('9'):
torch.save(approx.state_dict(), 'trained-10000.mdl')

if terminal or tick > 100:
plt.close()
break

state = new_state

torch.save(approx.state_dict(), 'trained-10000.mdl')

• Are you implementing DQN algorithm? If yes, where did you study the algorithm from? Or did you wing it and implemented it like regular Q-learning with NN and hoped for the best. As far as I can see you didn't implement experience replay nor target network. You should read original DQN papers here and here , also there are numerous question asked about DQN on this site so you should dig through for more information. – Brale_ Aug 25 '19 at 9:59
• @Brale_ thanks for your reply! I implemented target network, and I’m pretty sure I did it right because it converges ok, and I didn’t think that experience replay was neccessary, is it? And I found a lot of solutions like making the network larger on here but none of them worked. I have also tried many different network configurations. – iamPres Aug 25 '19 at 13:22
• experience replay is a must have so you should implement that – Brale_ Aug 25 '19 at 14:02
• @Brale_ ok just to make sure if I wasn’t seeing any improvement whatsoever that could be attributed solely to not having experience replay? – iamPres Aug 25 '19 at 14:08
• not solely to that but a part of it yes – Brale_ Aug 25 '19 at 14:33