triplet_loss.py

class TripletLossLayer(Layer):
    """
        Layer object to minimise the triplet loss.
        Here we implement the Bayesian Personal Ranking triplet loss.
    """
    def __init__(self, **kwargs):
        super(TripletLossLayer, self).__init__(**kwargs)
    
    def bpr_triplet_loss(self, inputs):
        """
            Bayesian Personal Ranking triplet loss.
            We actually use log-loss for numerical purposes.
        """
        anchor, positive, negative = inputs
        p_dist = K.sum(anchor*positive, axis=-1, keepdims=True)
        n_dist = K.sum(anchor*negative, axis=-1, keepdims=True)
        return K.log(1.0 - K.sigmoid(p_dist - n_dist))
    
    def call(self, inputs):
        loss = self.bpr_triplet_loss(inputs)
        self.add_loss(loss)
        return loss