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Stochastic attention-based models have been shown to improve computational efficiency at test time , but they remain difficult to train because of intractable posterior inference and high variance in the stochastic gradient estimates .
 computational efficiency, Stochastic attention-based models; intractable posterior inference, stochastic gradient estimates
Please list all entity pairs containing a certain relationship in the given options.Output format is "word1, word2; word3, word4". 
Option: conjunction, feature of, hyponym of, used for, part of, compare, evaluate for 
Text: {0} 
Answer:
 computational efficiency, Stochastic attention-based models; intractable posterior inference, stochastic gradient estimates