This is a reimplementation of the Generalized Compressed Suffix Array (GCSA), a BWT-based index for directed graphs. The implementation is based on the Succinct Data Structures Library 2.0 (SDSL). To compile, set SDSL_DIR in the Makefile to point to your SDSL directory. As the implementation uses C++11, OpenMP, and libstdc++ parallel mode, you need g++ 4.7 or newer to compile.
The old implementation indexed all paths in a directed acyclic graph, which had to be determinized before index construction. This implementation indexes paths of length up to 128 in any graph. The upper bound on path length should limit the combinatorial explosion often occurring in graphs containing regions with a lot of branching.
The input to index construction is a set of paths of length k in the input graph. The prefix-doubling algorithm transforms the input into an order-8k (order-2k, order-4k) pruned de Bruijn graph for paths in the input graph. A pruned de Bruijn graph differs from a de Bruijn graph in that its nodes may have shorter labels than the order of the graph, if the shorter labels uniquely determine the start nodes of the corresponding paths in the input graph. As such, pruned de Bruijn graphs are usually smaller than proper de Bruijn graphs.
At the moment, GCSA2 is being developed as a part of vg. The only implemented construction option is based on extracting k-mers from vg. Later, GCSA2 should become a more general graph indexing library.
See the wiki for further documentation.
The maximum resident size reported by getrusage() is in kilobytes in Linux and in bytes in OS X. By default, the implementation assumes Linux-like behavior. To get the correct memory usage reports in OS X, uncomment the line RUSAGE_FLAGS=-DRUSAGE_IN_BYTES in the makefile.
There are some verification/debugging options in build_gcsa. To enable them, uncomment the line VERIFY_FLAGS=-DVERIFY_CONSTRUCTION in the makefile and select the debugging options in build_gcsa.cpp.
Jouni Sirén, Niko Välimäki, and Veli Mäkinen: Indexing Graphs for Path Queries with Applications in Genome Research. IEEE/ACM Transactions on Computational Biology and Bioinformatics 11(2):375-388, 2014. DOI: 10.1109/TCBB.2013.2297101
Alexander Bowe, Taku Onodera, Kunihiko Sadakane, and Tetsuo Shibuya: Succinct de Bruijn Graphs. Proc. WABI 2012, Springer LNCS 7534, pp. 225-235, Ljubljana, Slovenia, September 10-12, 2012. DOI: 10.1007/978-3-642-33122-0_18
Jouni Sirén: Indexing Variation Graphs. arXiv:1604.06605, 2016.