AssertionError: Torch not compiled with CUDA enabled
From https://pytorch.org/

to install pytorch on MacOS the following is stated : 

conda install pytorch torchvision -c pytorch
# MacOS Binaries dont support CUDA, install from source if CUDA is needed


Why would want to install pytorch without cuda enabled ?

Reason I ask is I receive error : 


  --------------------------------------------------------------------------- AssertionError                            Traceback (most recent call
  last)  in ()
       78 #     predicted = outputs.data.max(1)[1]
       79 
  ---> 80     output = model(torch.tensor([[1,1]]).float().cuda())
       81     predicted = output.data.max(1)[1]
       82 
  
  ~/anaconda3/lib/python3.6/site-packages/torch/cuda/init.py in
  _lazy_init()
      159         raise RuntimeError(
      160             "Cannot re-initialize CUDA in forked subprocess. " + msg)
  --> 161     _check_driver()
      162     torch._C._cuda_init()
      163     _cudart = _load_cudart()
  
  ~/anaconda3/lib/python3.6/site-packages/torch/cuda/init.py in
  _check_driver()
       73 def _check_driver():
       74     if not hasattr(torch._C, '_cuda_isDriverSufficient'):
  ---> 75         raise AssertionError("Torch not compiled with CUDA enabled")
       76     if not torch._C._cuda_isDriverSufficient():
       77         if torch._C._cuda_getDriverVersion() == 0:
  
  AssertionError: Torch not compiled with CUDA enabled


when attempting to execute code : 

x = torch.tensor([[0,0] , [0,1] , [1,0]]).float()
print(x)

y = torch.tensor([0,1,1]).long()
print(y)

my_train = data_utils.TensorDataset(x, y)
my_train_loader = data_utils.DataLoader(my_train, batch_size=2, shuffle=True)

# Device configuration
device = 'cpu'
print(device)

# Hyper-parameters 
input_size = 2
hidden_size = 100
num_classes = 2


learning_rate = 0.001

train_dataset = my_train

train_loader = my_train_loader

pred = []


for i in range(0 , model_iters) : 
    # Fully connected neural network with one hidden layer
    class NeuralNet(nn.Module):
        def __init__(self, input_size, hidden_size, num_classes):
            super(NeuralNet, self).__init__()
            self.fc1 = nn.Linear(input_size, hidden_size) 
            self.relu = nn.ReLU()
            self.fc2 = nn.Linear(hidden_size, num_classes)  

        def forward(self, x):
            out = self.fc1(x)
            out = self.relu(out)
            out = self.fc2(out)
            return out

    model = NeuralNet(input_size, hidden_size, num_classes).to(device)

    # Loss and optimizer
    criterion = nn.CrossEntropyLoss()
    optimizer = torch.optim.Adam(model.parameters(), lr=learning_rate)  

    # Train the model
    total_step = len(train_loader)
    for epoch in range(num_epochs):
        for i, (images, labels) in enumerate(train_loader):  
            # Move tensors to the configured device
            images = images.reshape(-1, 2).to(device)
            labels = labels.to(device)

            # Forward pass
            outputs = model(images)
            loss = criterion(outputs, labels)

            # Backward and optimize
            optimizer.zero_grad()
            loss.backward()
            optimizer.step()
{:.4f}'.format(epoch+1, num_epochs, i+1, total_step, loss.item()))

    output = model(torch.tensor([[1,1]]).float().cuda())


To fix this error I need to install pytorch from source with cuda already installed ?

To summarize and expand on the comments:


CUDA is an Nvidia proprietary (apparently unlicensed) technology to allow general computing on GPU processors.
Very few Macbook Pro's have an Nvidia CUDA-capable GPU. Take a look here to see whether your MBP has an Nvidia GPU.  Then, look at the table here to see if that GPU supports CUDA
Same story for iMac, iMac Pro and Mac Pro.
Therefore, PyTorch is installed without CUDA support by default on MacOS


This PyTorch github issue mentions that very few Macs have Nvidia processors: https://github.com/pytorch/pytorch/issues/30664

IF your Mac does have a CUDA-capable GPU, then to use CUDA commands on MacOS you'll need to recompile pytorch from source with correct command line options. 
