**Pi Estimator**
The value of PI can be calculated in a number of ways. Consider the following method of estimating PI

- Inscribe a circle in a square
- Randomly generate points in the square
- Determine the number of points in the square that are also in the circle
- Let r be the number of points in the circle divided by the number of points in the square
- PI ~ 4 r

Serial pseudo code for this procedure as below:

iterations = 10000
circle_count = 0
do j = 1,iterations
generate 2 random numbers between 0 and 1
xcoordinate = random1
ycoordinate = random2
if (xcoordinate, ycoordinate) inside circle
then circle_count = circle_count + 1
end do
PI = 4.0*circle_count/iterations

**The BSP implementation for Pi**
A distributed strategy in HAMA with

BSP programming model, is break the loop into portions that can be executed by the tasks.

- Each task executes locally its portion of the loop a number of times.
- One task acts as master and collects the results through the BSP communication interface.

public class PiEstimator {
private static String MASTER_TASK = "master.task.";
public static class MyEstimator extends BSP {
public static final Log LOG = LogFactory.getLog(MyEstimator.class);
private Configuration conf;
private String masterTask;
private static final int iterations = 10000;
@Override
public void bsp(BSPPeer bspPeer) throws IOException, KeeperException,
InterruptedException {
int in = 0, out = 0;
for (int i = 0; i < iterations; i++) {
double x = 2.0 * Math.random() - 1.0, y = 2.0 * Math.random() - 1.0;
if ((Math.sqrt(x * x + y * y) < 1.0)) {
in++;
} else {
out++;
}
}
byte[] tagName = Bytes.toBytes(getName().toString());
byte[] myData = Bytes.toBytes(4.0 * (double) in / (double) iterations);
BSPMessage estimate = new BSPMessage(tagName, myData);
bspPeer.send(bspPeer.getAddress(masterTask), estimate);
bspPeer.sync();
double pi = 0.0;
BSPMessage received;
while ((received = bspPeer.getCurrentMessage()) != null) {
LOG.info("Receives messages:" + Bytes.toDouble(received.getData()));
if(pi == 0.0) {
pi = Bytes.toDouble(received.getData());
} else {
pi = (pi + Bytes.toDouble(received.getData())) / 2;
}
}
if (pi != 0.0) {
LOG.info("\nEstimated value of PI is " + pi);
}
}
@Override
public Configuration getConf() {
return conf;
}
@Override
public void setConf(Configuration conf) {
this.conf = conf;
this.masterTask = conf.get(MASTER_TASK);
}
}
public static void main(String[] args) throws InterruptedException,
IOException {
// BSP job configuration
HamaConfiguration conf = new HamaConfiguration();
// Execute locally
// conf.set("bsp.master.address", "local");
BSPJob bsp = new BSPJob(conf, PiEstimator.class);
// Set the job name
bsp.setJobName("pi estimation example");
bsp.setBspClass(MyEstimator.class);
BSPJobClient jobClient = new BSPJobClient(conf);
ClusterStatus cluster = jobClient.getClusterStatus(true);
// Choose one as a master
for (String name : cluster.getActiveGroomNames()) {
conf.set(MASTER_TASK, name);
break;
}
BSPJobClient.runJob(bsp);
}
}