import tensorflow as tf

        ha = tf.matmul(varphis, param_eta * tf.matmul(Kt, prec) + Wsa) + wa

        # hss(s): eta * (\varphi(s)^T * K^T * \Sigma^{-1} * K * \varphi(s))
        varphisKt = tf.matmul(varphis, Kt)
        hss = param_eta * tf.reduce_sum(tf.matmul(varphisKt, prec) * varphisKt, axis=1)

        Haa = param_eta * prec + Waa
        # Haa = 0.5 * (Haa + TT.transpose(Haa))
