Combining TF-IDF Text Retrieval with an Inverted Index over Symbol Pairs in Math Expressions: The Tangent Math Search Engine at NTCIR 2014

We report on the system design and NTCIR-Math-2 task results for the Tangent math-aware search engine. Tangent uses a federated search over two indices: 1) a TF-IDF tex-tual search engine (Lucene), and 2) a query-by-expression engine. Query-by-expression is performed using a bag-of-words approach where expressions are represented by pairs of symbols computed from symbol layout trees (e.g. as ex-pressed in LATEX or Presentation MathML). Extensions to support matrices and prefix subscripts and superscripts are described. Our system produced the highest highly + par-tially relevant Precision@5 result for the main text/math query task (92%), and the highest Top-1 specific-item recall for the Wikipedia query-by-expression subtask (68%). The current implementation is slow and produces large indices for large corpora, but we believe this can be ameliorated. Source code for our system is publicly available