GAN does not learn when using symmetric outputs from generator to disciminator
I'm currently trying to implement the paper Generative modeling for protein structures and I have succesfully been able to train a model following Pytorch's DCGAN Tutorial which has a similar model structure to the paper. The two implementations differ when it comes to output of the generator.
In the tutorial's model, the generator simply passes a normal output matrix to the discriminator. This works fine when I implement the paper's model (ommiting the symmetry and clamping) but the paper specifies:

During training, we enforce that G(z) be
positive by clamping output values above zero and symmetric


when I put this into my training loop I receive a loss graph that indicates that the generator isn't learning.
Here is my training loop:
# Training Loop
# Lists to keep track of progress
img_list = []
G_losses = []
D_losses = []
iters = 0

print(&quot;Starting Training Loop...&quot;)
# For each epoch
for epoch in range(num_epochs):
    # For each batch in the dataloader
    for i, data in enumerate(dataloader, 0):
        ############################
        # (1) Update D network: maximize log(D(x)) + log(1 - D(G(z)))
        ###########################
        ## Train with all-real batch
        netD.zero_grad()
        # Format batch
        # Unsqueezed dim one to convert [128, 64, 64] to [128, 1, 64, 64] to conform to D architecture 
        real_cpu = (data.unsqueeze(dim=1).type(torch.FloatTensor)).to(device)
        b_size = real_cpu.size(0)
        label = torch.full((b_size,), real_label, device=device)
        # Forward pass real batch through D
        output = netD(real_cpu).view(-1)
        # Calculate loss on all-real batch
        errD_real = criterion(output, label)
        # Calculate gradients for D in backward pass
        errD_real.backward()
        D_x = output.mean().item()

        ## Train with all-fake batch
        # Generate batch of latent vectors
        noise = torch.randn(b_size, nz, 1, 1, device=device)
        # Generate fake image batch with G
        fake = netG(noise)
        label.fill_(fake_label)
        # Make Symmetric
        sym_fake = (fake.detach().clamp(min=0) + fake.detach().clamp(min=0).permute(0, 1, 3, 2)) / 2
        # Classify all fake batch with D
        output = netD(sym_fake).view(-1)
        # Calculate D's loss on the all-fake batch
        errD_fake = criterion(output, label)
        # Calculate the gradients for this batch
        errD_fake.backward()
        D_G_z1 = output.mean().item()
        # Add the gradients from the all-real and all-fake batches
        errD = errD_real + errD_fake
        # Update D
        optimizerD.step()
        #adjust_optim(optimizerD, iters)
        ############################
        # (2) Update G network: maximize log(D(G(z)))
        ###########################
        netG.zero_grad()
        label.fill_(real_label)  # fake labels are real for generator cost
        # Since we just updated D, perform another forward pass of all-fake batch through D
        output = netD(fake.detach()).view(-1)
        # Calculate G's loss based on this output
        errG = criterion(output, label)
        # Calculate gradients for G
        errG.backward()
        D_G_z2 = output.mean().item()
        # Update G
        optimizerG.step()
        adjust_optim(optimizerG, iters)

        # Output training stats
        if i % 50 == 0:
            print('[%d/%d][%d/%d]\tLoss_D: %.4f\tLoss_G: %.4f\tD(x): %.4f\tD(G(z)): %.4f / %.4f'
                  % (epoch, num_epochs, i, len(dataloader),
                     errD.item(), errG.item(), D_x, D_G_z1, D_G_z2))

        # Save Losses for plotting later
        G_losses.append(errG.item())
        D_losses.append(errD.item())

        # Check how the generator is doing by saving G's output on fixed_noise
        if (iters % 500 == 0) or ((epoch == num_epochs-1) and (i == len(dataloader)-1)):
            with torch.no_grad():
                fake = netG(fixed_noise).detach().cpu()
            img_list.append(vutils.make_grid(fake, padding=2, normalize=True))

        iters += 1

Here is the training loss.

Here is my expected loss.

I make the output symmetric with the following line
sym_fake = (fake.detach().clamp(min=0) + fake.detach().clamp(min=0).permute(0, 1, 3, 2)) / 2

and I pass it to the discriminator on the lines that call sym_fake
Question
Is my implementation in pytorch wrong or is there something I'm missing? I don't understand why the paper makes the matrix symmetric and clamps if the network is capable of generating images without the need for symmetry and clamping.

It could be because after the criterion for netG obtains an output that was detached from the parameters of netG thus the optimizer is not / can't be updating the parameters for netG.
