@Override
public void invoke(InputStream[] fis, OutputStream[] fos, String[] args) {
/** inputs: none. */
/** args: (int) number of samples, (int) initial offset. */
int numSamples = Integer.parseInt(args[0]);
int offset = Integer.parseInt(args[1]);
final HaltonSequence haltonsequence = new HaltonSequence(offset);
long numInside = 0L;
long numOutside = 0L;
for (long i = 0; i < numSamples; ++i) {
// generate points in a unit square
final double[] point = haltonsequence.nextPoint();
// count points inside/outside of the inscribed circle of the square
final double x = point[0] - 0.5;
final double y = point[1] - 0.5;
if (x * x + y * y > 0.25) {
numOutside++;
} else {
numInside++;
}
}
/** output: single file containing (long) numInside, (long) numOutside. */
try {
DataOutputStream out = new DataOutputStream(fos[0]);
out.writeLong(numInside);
out.writeLong(numOutside);
out.close();
} catch (IOException ioe) {
throw new RuntimeException(ioe);
}
}
/**
* Map method.
*
* @param offset samples starting from the (offset+1)th sample.
* @param size the number of samples for this map
* @param out output {ture->numInside, false->numOutside}
* @param reporter
*/
public void map(
LongWritable offset,
LongWritable size,
OutputCollector<BooleanWritable, LongWritable> out,
Reporter reporter)
throws IOException {
final HaltonSequence haltonsequence = new HaltonSequence(offset.get());
long numInside = 0L;
long numOutside = 0L;
for (long i = 0; i < size.get(); ) {
// generate points in a unit square
final double[] point = haltonsequence.nextPoint();
// count points inside/outside of the inscribed circle of the square
final double x = point[0] - 0.5;
final double y = point[1] - 0.5;
if (x * x + y * y > 0.25) {
numOutside++;
} else {
numInside++;
}
// report status
i++;
if (i % 1000 == 0) {
reporter.setStatus("Generated " + i + " samples.");
}
}
// output map results
out.collect(new BooleanWritable(true), new LongWritable(numInside));
out.collect(new BooleanWritable(false), new LongWritable(numOutside));
}
