IndexError: dimension specified as -2 but tensor has no dimensions

Hello. I am messing around with flow-based generative models, and decided to play around with a simple implementation of Invertible Convolutions. I tried adapting one from a time-series model, only to catch this error:

PS C:\Users\AyazA> & C:/Python37/python.exe c:/Users/AyazA/Desktop/RRF/
Traceback (most recent call last):
  File "c:/Users/AyazA/Desktop/RRF/", line 49, in <module>
    z, log = conv(x)
  File "C:\Python37\lib\site-packages\torch\nn\modules\", line 547, in __call__
    result = self.forward(*input, **kwargs)
  File "c:/Users/AyazA/Desktop/RRF/", line 43, in forward
    log_det_W = height * width * torch.logdet(W)
IndexError: dimension specified as -2 but tensor has no dimensions

Here is the code:

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

# From
class Invertible1x1Conv(nn.Module):
    The layer outputs both the convolution, and the log determinant
    of its weight matrix.  If reverse=True it does convolution with
    def __init__(self, c):
        super(Invertible1x1Conv, self).__init__()
        self.conv = nn.Conv2d(c, c, kernel_size=1, stride=1, padding=0,

        # Sample a random orthonormal matrix to initialize weights
        W = torch.qr(torch.FloatTensor(c, c).normal_())[0]
        # Ensure determinant is 1.0 not -1.0
        if torch.det(W) < 0:
            W[:,0] = -1*W[:,0]
        W = W.view(c, c, 1) = W

    def forward(self, z, reverse=False):
        # shape
        batch_size, channels, height, width = z.size()

        W = self.conv.weight.squeeze()

        if reverse:
            if not hasattr(self, 'W_inverse'):
                # Reverse computation
                W_inverse = W.float().inverse()
                W_inverse = Variable(W_inverse[..., None])
                if z.type() == 'torch.cuda.HalfTensor':
                    W_inverse = W_inverse.half()
                self.W_inverse = W_inverse
            z = F.conv2d(z, self.W_inverse, bias=None, stride=1, padding=0)
            return z
            # Forward computation
            log_det_W = height * width * torch.logdet(W)
            z = self.conv(z)
            return z, log_det_W

x = torch.rand([1, 1, 28, 28])
conv = Invertible1x1Conv(1)
z, log = conv(x)

This will remove all singleton dimensions. As you have 1 channel, you delete all of them from a (1, 1, 1, 1)-shaped-Tensor. You only want to delete the last two.
In general, I would recommend to furnish such code with comments or asserts on the expected shapes at each step. - The shape things are quite messy.

(The code also could use a PyTorch >= 0.4 migration, but that’s another story.)

Best regards