I have a code (from here) to classify the MINST digits. The code is working fine. Here they used CrossEntropyLoss
and Adam
optimizer.
The model code is given below
class CNN(nn.Module):
def __init__(self):
super(CNN, self).__init__()
self.conv1 = nn.Sequential(
nn.Conv2d(
in_channels=1,
out_channels=16,
kernel_size=5,
stride=1,
padding=2,
),
nn.ReLU(),
nn.MaxPool2d(kernel_size=2),
)
self.conv2 = nn.Sequential(
nn.Conv2d(16, 32, 5, 1, 2),
nn.ReLU(),
nn.MaxPool2d(2),
)
# fully connected layer, output 10 classes
self.out = nn.Linear(32 * 7 * 7, 10)
# self.softmax = torch.nn.Softmax(dim=1)
def forward(self, x):
x = self.conv1(x)
x = self.conv2(x)
# flatten the output of conv2 to (batch_size, 32 * 7 * 7)
x = x.view(x.size(0), -1)
output = self.out(x)
# output = self.softmax(output)
return output, x # return x for visualization
The shape of the `b_x` and `b_y` is
torch.Size([100, 1, 28, 28]) torch.Size([100])
Now, I wanted to get continuous value from the output layer. Say, I want the output as alike i.e, 1.0, 0.9, 8.6, 7.0, etc. If the value of the output layer is 1.0 and the label is 1 that means the prediction is perfect. Otherwise, not perfect. More simply, I want to think the MNIST digits as a regression problem.
So, I changed the loss function to MSELoss
and optimizer to SGD
(the rest of the code remains as the same as the website). But now, I am getting an error
/home/Opps_0/.local/lib/python3.8/site-packages/torch/nn/modules/loss.py:528: UserWarning: Using a target size (torch.Size([100])) that is different to the input size (torch.Size([100, 10])). This will likely lead to incorrect results due to broadcasting. Please ensure they have the same size.
return F.mse_loss(input, target, reduction=self.reduction)
Traceback (most recent call last):
File "/usr/lib/python3.8/runpy.py", line 194, in _run_module_as_main
return _run_code(code, main_globals, None,
File "/usr/lib/python3.8/runpy.py", line 87, in _run_code
exec(code, run_globals)
File "/home/Opps_0/Desktop/MNIST/src/train.py", line 60, in <module>
train(NB_EPOCS, model, loaders)
File "/home/Opps_0/Desktop/MNIST/src/train.py", line 45, in train
loss = criterion(output, b_y)
File "/home/Opps_0/.local/lib/python3.8/site-packages/torch/nn/modules/module.py", line 889, in _call_impl
result = self.forward(*input, **kwargs)
File "/home/Opps_0/.local/lib/python3.8/site-packages/torch/nn/modules/loss.py", line 528, in forward
return F.mse_loss(input, target, reduction=self.reduction)
File "/home/Opps_0/.local/lib/python3.8/site-packages/torch/nn/functional.py", line 2925, in mse_loss
expanded_input, expanded_target = torch.broadcast_tensors(input, target)
File "/home/Opps_0/.local/lib/python3.8/site-packages/torch/functional.py", line 74, in broadcast_tensors
return _VF.broadcast_tensors(tensors) # type: ignore
RuntimeError: The size of tensor a (10) must match the size of tensor b (100) at non-singleton dimension 1
Could you tell me what I have to change to get the continuous value for the output layer?
CodePudding user response:
Assuming your targets are shape as (batch_size,)
, something along the lines of:
>>> model = CNN()
>>> criterion = nn.MSELoss()
>>> output, _ = model(torch.rand(2, 1, 28, 28))
>>> b_y = torch.randint(0, 10, (2,))
tensor([1, 2, 6, 5, 7])
Loss computation with MSELoss
will result in:
>>> loss = criterion(output, b_y)
RuntimeError: The size of tensor
a
(10)
must match the size of tensorb
(2)
at non-singleton dimension1
.
This means the shape of your target b_y
is incorrect, it needs to match output
's shaped, i.e. it needs to be a two-dimensional tensor.
Since you are optimizing this task with a regression loss you could encode your target as a sparse vector also known as one-hot encoding. You can do so with ease using the builtin torch.nn.functional.one_hot
:
>>> ohe_target = torch.nn.functional.one_hot(b_y, num_classes=10)
tensor([[0, 1, 0, 0, 0, 0, 0, 0, 0, 0],
[0, 0, 1, 0, 0, 0, 0, 0, 0, 0],
[0, 0, 0, 0, 0, 0, 1, 0, 0, 0],
[0, 0, 0, 0, 0, 1, 0, 0, 0, 0],
[0, 0, 0, 0, 0, 0, 0, 1, 0, 0]])
Now you can compute the loss properly:
>>> criterion(output, ohe_target)
tensor(0.1169, grad_fn=<MseLossBackward>)