Solved by VirginieBfd in post #4 
              
              
                This solution looks correct. 
model = models.resnet101(pretrained=True)
num_ftrs = model.fc.in_features
model.fc = nn.Linear(num_ftrs, 1)

Ensure you change you use a loss made for regression problems such as torch.nn.MSELoss. 
You can use a network pre-trained on a classification problem and transf…