Original serial code from https://www.olcf.ornl.gov/tutorials/monte-carlo-pi/
Modified and then parallelized by Yuwu Chen for LSU HPC training purpose only
1. On Queenbee2, intel-14.0.2 was used to compile serialpi.out; mvapich2-2.0/INTEL-14.0.2 was used to compile mpi_pi.out. 
2. On Supermike2, intel-18.0.0 was used to compile serialpi_mike.out; mvapich2-2.2/INTEL-18.0.0 was used to compile mpi_pi_mike.out. 
3. The source code (.c files) should be recompiled to generate a new .out executables if non-default mpi compiler is loaded (e.g. if the current loaded mpi compiler is openmpi, then mpi_pi.c should be recompiled by mpicc from openmpi to create a new executable)
4. To compile serialpi.c with gcc, use "-lm" (without quotes) option to link the math library
5. Codes in "userenv" are for demonstrating the part of "compiling and analyze codes on cluster", which is uaually not included in the training session due to the time limit. 

