Systems, methods, and apparatus are provided for determining relevance of documents to queries. An optimized relevance function is configured to determine a relevance value of documents of a first type that are linked to documents of a second type. The relevance function is optimized to satisfy certain criteria. According to one criterion, a relevance value produced by the optimized relevance function, when invoked for documents of the first type, should have a locally maximal degree of fit to the results of the existing relevance function for the sample training documents of the second type. An assessed degree of fit of a document can be increased or decreased to arrive at an optimized relevance function that ranks the documents of the first type in a desired position relative to documents of the second type in search results. The degree of fit can be assessed by a user-provided objective function.