README

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About
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`tric` is a distributed-memory triangle counting code that assumes a 1-D vertex-based 
distribution of a graph. The concept is quite simple, and the main idea is to consider
all combinations of consecutive edges and check whether they are triangles. For high-degree
graphs, this design can result in significant memory increase.

Papers:

[1] Ghosh S. Improved Distributed-memory Triangle Counting by Exploiting the Graph Structure. 
In 2022 IEEE High Performance Extreme Computing Conference (HPEC) 2022 Sep 19 (pp. 1-6). IEEE.

[2] Ghosh S, Halappanavar M. TriC: Distributed-memory Triangle Counting by Exploiting the 
Graph Structure. In 2020 IEEE High Performance Extreme Computing Conference (HPEC) 2020 
Sep 22 (pp. 1-6). IEEE.

Please contact the following for any queries or support:

Sayan Ghosh, PNNL (sg0 at pnnl dot gov)

Please '*' this repository if you find it useful.

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Compile
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tric is a C++ header-only library and requires an MPI implementation. It uses MPI Send/Recv and 
collectives, and may also use derived-types based on the version used. Please update the Makefile 
with compiler flags and use a C++11 compliant compiler of your choice. Invoke `make clean; make` 
after setting paths to MPI for generating the binary. Use `mpirun` or `mpiexec` or `srun` to 
execute the code with specific runtime arguments mentioned in the next section.

Pass -DPRINT_DIST_STATS while building for printing distributed graph characteristics.

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Execution options
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E.g.: 
mpiexec -n 2 bin/./tric -f karate.bin 
mpiexec -n 2 bin/./neve -n 100 -t 0
mpiexec -n 2 bin/./neve -p 2 -n 100

Possible options (can be combined):

1.  -f <bin-file>   : Specify input binary file after this argument. 
2.  -b              : Only valid for real-world inputs. Attempts to distribute approximately 
                      equal number of edges among processes. Irregular number of vertices
                      owned by a particular process. Increases the distributed graph creation
                      time due to serial overheads, but may improve overall execution time.
3.  -n <vertices>   : Only valid for synthetically generated inputs. Pass total number of 
                      vertices of the generated graph.
4.  -l              : Use distributed LCG for randomly choosing edges. If this option 
                      is not used, we will use C++ random number generator (using 
                      std::default_random_engine).
5.  -p <percent>    : Only valid for synthetically generated inputs. Specify percent of overall 
                      edges to be randomly generated between processes.
6.  -r <nranks>     : This is used to control the number of aggregators in MPI I/O and is
                      meaningful when an input binary graph file is passed with option "-f".
                      naggr := (nranks > 1) ? (nprocs/nranks) : nranks;
7.  -s <size>       : Buffer size, only relevant when -DAGGR_<> is passed for aggregate-buffered 
                      triangle counting. Default buffer size can be set by updating DEFAULT_BUF_SIZE. 

Please try the default version (no need to pass any macro in the Makefile) or the aggregate-buffered
versions, this is a growing codebase and there are versions that are under development. If you want
to consider a version which uses conditional computation to avoid double or triple counting, then select
-DAGGR_BUFR_INRECV.