contrastive.py

class ContrastiveLoss(torch.nn.Module):
    """
    Contrastive loss function.
    Based on:
    """

    def __init__(self, margin=1.0):
        super(ContrastiveLoss, self).__init__()
        self.margin = margin

    def forward(self, x0, x1, y):
        # euclidian distance
        diff = x0 - x1
        dist_sq = torch.sum(torch.pow(diff, 2), 1)
        dist = torch.sqrt(dist_sq)

        mdist = self.margin - dist
        dist = torch.clamp(mdist, min=0.0)
        loss = y * dist_sq + (1 - y) * torch.pow(dist, 2)
        loss = torch.sum(loss) / 2.0 / x0.size()[0]
        return loss