"WARP loss for Pytorch. WSABIE"
Project description
WARPPytorch
An implementation of WARP loss which uses matrixes and stays on the GPU in PyTorch.
An implementation of WARP loss which uses matrixes and stays on the GPU in PyTorch.
This means instead of using a forloop to find the first offending negative sample that ranks above our positive, we compute all of them at once. Only later do we find which sample is the first offender, and compute the loss with respect to this sample.
The advantage is that it can use the speedups that comes with GPUusage.
When is WARP loss advantageous?
If you're ranking items or making models for recommendations, it's often advantageous to let your loss function directly optimize for this case. WARP loss looks at 1 explicit positive up against the implicit negative items that a user never sampled, and allows us to adjust weights of the network accordingly.
Install
pip install warp_loss
How to use
The loss function requires scores for both positive examples, and negative examples to be supplied, such as in the example below.
from torch import nn
import torch
class OurModel(nn.Module):
def __init__(self, num_labels, emb_dim=10):
super(OurModel, self).__init__()
self.emb = nn.Embedding(num_labels, emb_dim)
self.user_embs = nn.Embedding(1, emb_dim)
def forward(self, pos, neg):
batch_size = neg.size(0)
one_user_vector = self.user_embs(torch.zeros(1).long())
repeated_user_vector = one_user_vector.repeat((batch_size, 1)).view(batch_size, 1, 1)
pos_res = torch.bmm(self.emb(pos), repeated_user_vector).squeeze(2)
neg_res = torch.bmm(self.emb(neg), repeated_user_vector).squeeze(2)
return pos_res, neg_res
num_labels = 100
model = OurModel(num_labels)
pos_labels = torch.randint(high=num_labels, size=(3,1)) # our five labels
neg_labels = torch.randint(high=num_labels, size=(3,2)) # a few random negatives per positive
pos_res, neg_res = model(pos_labels, neg_labels)
print('Positive Labels:', pos_labels)
print('Negative Labels:', neg_labels)
print('Model positive scores:', pos_res)
print('Model negative scores:', neg_res)
loss = warp_loss(pos_res, neg_res, num_labels=num_labels, device=torch.device('cpu'))
print('Loss:', loss)
loss.backward()
Positive Labels: tensor([[65],
[94],
[21]])
Negative Labels: tensor([[ 8, 45],
[37, 93],
[88, 84]])
Model positive scores: tensor([[3.7806],
[1.9974],
[4.1741]], grad_fn=<SqueezeBackward1>)
Model negative scores: tensor([[1.5696, 4.4905],
[1.9300, 0.3826],
[ 2.4564, 2.1741]], grad_fn=<SqueezeBackward1>)
Loss: tensor(54.7226, grad_fn=<SumBackward0>)
print('We can also see that the gradient is only active for 2x the number of positive labels:', (model.emb.weight.grad.sum(1) != 0).sum().item())
print('Meaning we correctly discard the gradients for all other than the offending negative label.')
We can also see that the gradient is only active for 2x the number of positive labels: 6
Meaning we correctly discard the gradients for all other than the offending negative label.
Assumptions
The loss function assumes you have already sampled your negatives randomly.
As an example this could be done in your dataloader:
 Assume we have a total dataset of 100 items
 Select a positive sample with index 8
 Your negatives should be a random selection from 0100 excluding 8.
Ex input to loss function: model scores for pos: [8] neg: [88, 3, 99, 7]
Currently only tested on PyTorch v0.4
References
 WSABIE: Scaling Up To Large Vocabulary Image Annotation
 Intro to WARP loss  Automatic differentiation and PyTorch
 LightFM as a reference implementaiton
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