exc1

lab10/computePi/computePi.cpp

@@ -0,0 +1,61 @@
+#include <chrono>
+#include <iostream>
+#include <iomanip>
+#include <mpi.h>
+#include <fstream>
+
+double computePartialSum(int64_t i0, int64_t i1, double step)
+{
+  // compute part of the integral
+  double sum = 0.0;
+  for (int64_t i = i0; i < i1; i++)
+  {
+    double x = (i + 0.5) * step;
+    sum += 4.0 / (1.0 + x * x);
+  }
+  return sum;
+}
+
+int main(int argc, char *argv[])
+{
+  auto start = std::chrono::system_clock::now();
+
+  MPI_Init(&argc, &argv);
+
+  int rank, numTasks;
+  MPI_Comm_size(MPI_COMM_WORLD, &numTasks);
+  MPI_Comm_rank(MPI_COMM_WORLD, &rank);
+
+  // roughly 1e11, but divisible through 2, 4, 6, 8, 12, 16, 18, ...
+  const int64_t numSteps = 1024LL * 1024 * 1024 * 9 * 9;
+
+  // compute boundaries
+  int64_t chunkSize = numSteps / numTasks;
+  int64_t i0 = rank * chunkSize;
+  int64_t i1 = (rank == numTasks - 1) ? numSteps : i0 + chunkSize;
+
+  double step = 1.0 / (double)numSteps;
+
+  // compute partial sum
+  double sum = computePartialSum(i0, i1, step);
+
+  double globalSum = 0.0;
+  MPI_Reduce(&sum, &globalSum, 1, MPI_DOUBLE, MPI_SUM, 0, MPI_COMM_WORLD);
+
+  if (rank == 0)
+  {
+    double pi = step * globalSum;
+    auto end = std::chrono::system_clock::now();
+
+    std::chrono::duration<double, std::milli> diff = end - start;
+
+    std::string filename = "results_reduce" + std::to_string(numTasks) + ".txt";
+    std::ofstream outFile(filename);
+    outFile << std::fixed << std::setprecision(16);
+    outFile << "π ≈ " << pi << ", Runtime: " << diff.count() << " ms, Tasks:  " << numTasks << ", Step: " << step << ", Sum: " << sum << std::endl;
+    outFile.close();
+  }
+
+  MPI_Finalize();
+  return 0;
+}