21. The system of claim 16 , wherein the relevance function tuner is configured to initialize the one or more coefficients, to calculate a sum of query errors based on the query error for a plurality of queries, to calculate a gradient of the calculated sum of the query errors, and to modify the one or more coefficients in a negative direction of the calculated gradient.
21. The system of claim 16 , wherein the relevance function tuner is configured to initialize the one or more coefficients, to calculate a sum of query errors based on the query error for a plurality of queries, to calculate a gradient of the calculated sum of the query errors, and to modify the one or more coefficients in a negative direction of the calculated gradient. 23. The system of claim 21 , wherein the relevance function tuner is configured to calculate a regularized sum of query errors based on the query error for a plurality of queries to calculate the sum of query errors.