nce_cost.py

import theano as T
def nce_binary_conditional_likelihood(p_unnormalized,y,y_flat,noise_samples,noise_dist,k):
    p_unnormalized_exp=T.exp(p_unnormalized)
    p_unnormalized_flat=p_unnormalized_exp.flatten()
    unnorm_y=p_unnormalized_flat[y_flat]
    noise_y=noise_dist[y]
    pos_cost=T.log(unnorm_y/(unnorm_y+k*noise_y))
    
    neg_cost=T.log(k*noise_dist/(p_unnormalized_exp+k*noise_dist))
    return -T.mean(pos_cost+ T.sum(neg_cost*noise_samples,axis=1),dtype=theano.config.floatX)