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# Run this program using
#
# mpirun -np 2 ruby pi.rb numpoints
#
# where numpoints is an integer
#
# The program is based on an example from
# https://carpentries-incubator.github.io/hpc-intro/16-parallel/index.html
require "mpi"
if defined?(NumRu::NArray)
include NumRu
end
def inside_circle my_count
x = NArray.float(my_count).random
y = NArray.float(my_count).random
a = ((x**2 + y**2) < 1.0)
return a.count_true
end
MPI.Init
world = MPI::Comm::WORLD
size = world.size
rank = world.rank
def usage(rank)
if rank==0
print <<EOF
Usage: mpirun -np numproc ruby #$0 numpoints
numpoints must be an integer > 0
EOF
end
MPI.Finalize
exit -1
end
usage(rank) if ARGV.length != 1
usage(rank) if ( ( /^\d+$/ =~ ARGV[0] ) != 0)
n_samples = ARGV[0].to_i
usage(rank) unless n_samples > 0
my_samples = n_samples.div(size)
if ( n_samples % size > rank )
my_samples = my_samples + 1
end
my_count = NArray[0]
count = NArray[0]
my_count[0] = inside_circle my_samples
world.Reduce(my_count,count,MPI::Op::SUM,0)
if ( rank == 0 )
p "Pi is approximately " + ((count[0]*4.0)/(1.0*n_samples)).to_s
end
MPI.Finalize
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