Fastbook - GRU from Scratch

In chapter 12, we are asked to create a GRU (Gated Recurrent Unit) from scratch, and to compare our results to PyTorch’s implementation.

I have done so, but the accuracy of my version is significantly less than PyTorch’s:



Also, the validation loss stops improving much earlier, and the accuracy does not improve. I am convinced it is a problem with my own implementation, and I don’t know where I am making the error.

Here is the code for the module:

class GRUCell(Module):
    def __init__(self, ni, nh):
        super(GRUCell, self).__init__()
        self.reset_gate = nn.Linear(ni + nh, nh)
        self.update_gate = nn.Linear(ni + nh, nh)
        self.candidate = nn.Linear(ni + nh, nh)
    def forward(self, input, hidden):
        out_seq = []
        #we have an input tensor of shape n_hidden, sl, n_hidden
        for in_step in input.permute(1,0,2):
            combined =[in_step, hidden], dim = 1)
            reset_gate = torch.sigmoid(self.reset_gate(combined))
            update_gate = torch.sigmoid(self.update_gate(combined))
            combined_reset =[in_step, reset_gate * hidden], dim = 1)
            candidate_hidden = torch.tanh(self.candidate(combined_reset))
            new_hidden = (1 - update_gate) * hidden + update_gate * candidate_hidden
            hidden = new_hidden.clone().detach()

        #print(f'out_seq shape: {out_seq.shape}')
        #we have an output tensor of shape sl, n_hidden, n_hidden
        out_seq = torch.stack(out_seq, dim = 1)
        return out_seq

Here is a link to the full notebook on Kaggle, in case the issue exists elsewhere: GRU From the Basics

I am a beginner, so if anyone could offer any pointers, it would be much appreciated.