Getting Started

Prerequisites #

Ligra can be compiled with multiple backend compilers. We currently support

• g++ >= 4.8.0 with support for Cilk Plus
• Intel icpc compiler
• OpenMP

Organization #

Download the code if you have not already. The main directories are the apps directory, where we will program and compile applications, and the ligra directory, where the framework code lives.

$ cd ligra
$ ls -1
apps        # code for Ligra applications
inputs      # example graph inputs
LICENSE
ligra       # code for the Ligra framework
README.md
utils       # utilities for parsing different graph formats

Compilation #

Compilation is done from within the apps/ directory. Depending on the compiler you wish to use, you will need to set a different environment variable.

• g++ using Cilk Plus: define the environment variable CILK.
• icpc: define the environment variable MKLROOT and make sure CILK is not defined.
• OpenMP: define the environment variable OPENMP and make sure CILK and MKLROOT are not defined.

Using Cilk Plus seems to give the best parallel performance in our experience. To compile with g++ with no parallel support, make sure CILK, MKLROOT and OPENMP are not defined.

OpenMP on OSX #

On OSX, the g++ binary installed through commandline-tools should error out if you try to use OpenMP. If you encounter this error, you will need to install g++-4.8 or g++-4.9. You can easily do this by using homebrew as follows:

$ brew tap homebrew/versions
$ brew install gcc49

Finally, open up the Makefile and replace g++ with g++-4.9 (or g++-4.8). Your code should cleanly compile.

Example #

$ cd apps/
$ export CILK=1
$ make
ln -s ../ligra/encoder.C .
ln -s ../ligra/ligra.h .
...
g++ -fcilkplus -lcilkrts -O3 -DCILK   -o encoder encoder.C
g++ -fcilkplus -lcilkrts -O3 -DCILK   -o BFS BFS.C
...