Torch sum a tensor along an axis

Question

How do I sum over the columns of a tensor?

torch.Size([10, 100])    --->    torch.Size([10])

Answer 1

The simplest and best solution is to use torch.sum().

To sum all elements of a tensor:

torch.sum(x) # gives back a scalar

To sum over all rows (i.e. for each column):

torch.sum(x, dim=0) # size = [ncol]

To sum over all columns (i.e. for each row):

torch.sum(x, dim=1) # size = [nrow]

It should be noted that the dimension summed over is eliminated from the resulting tensor.