Solution for hw3 added

hw3/solution/Makefile

+CXX=mpicxx  #h5pcc
+CXXFLAGS = -Wpedantic -Wall -Wextra -std=c++11 -lstdc++ -g -O3 -fopenmp 
+
+all: main
+%.o: %.cpp
+	$(CXX) -c -o $@ $< $(CXXFLAGS)
+clean:
+	rm -rf *.o *.xmf *h5 *txt main
+main: main.o auxiliary.o wave.o
+	$(CXX) $(CXXFLAGS)-I. -o main $^
+
+run_mpi:
+	make clean ; make ; mpirun -n 64 ./main 512 4 0.25
+
+run_hybrid_v1:
+	export OMP_NUM_THREADS=8 ; make clean ; make ; mpirun -n 8 --map-by ppr:3:node ./main 512 2 0.25
+
+run_hybrid_v2:
+	export OMP_NUM_THREADS=8 ; make clean ; make ; mpirun -n 8 --map-by ppr:2:node ./main 512 2 0.25
+
+develop:
+	export OMP_NUM_THREADS=8 ; make clean ; make ; mpirun -n 8 ./main 256 2 0.1
+
+
+.PHONY: all clean run_mpi run_hybrid_v1 run_hybrid_v2 develop

hw3/solution/auxiliary.cpp

+#include "wave.h"
+
+WaveEquation::WaveEquation(int a_N, int a_procs_per_dim) {
+  MPI_Comm_size(MPI_COMM_WORLD, &size);
+  procs_per_dim = a_procs_per_dim;
+  Ntot = a_N;
+  h = L / a_N;
+  N = a_N / procs_per_dim;
+
+  // the chosen numerical method is stable if  dt <= h/sqrt(3)
+  dt = h / sqrt(3.0);
+  aux = dt * dt / h / h;
+
+  nthreads = omp_get_max_threads();
+  threads_per_dim = pow(nthreads, 1. / 3.);
+
+  assert(N % threads_per_dim == 0);
+
+  FindCoordinates();
+
+  origin[0] = coords[0] * N * h;
+  origin[1] = coords[1] * N * h;
+  origin[2] = coords[2] * N * h;
+  u = new double[(N + 2) * (N + 2) * (N + 2)];
+
+  u_old = new double[(N + 2) * (N + 2) * (N + 2)];
+  u_new = new double[(N + 2) * (N + 2) * (N + 2)];
+
+  pack = new double *[6 * threads_per_dim * threads_per_dim];
+  unpack = new double *[6 * threads_per_dim * threads_per_dim];
+
+#pragma omp parallel
+  {
+    int tid = omp_get_thread_num();
+    int ti0, ti1, ti2;
+    thread_coordinates(tid, threads_per_dim, ti0, ti1, ti2);
+
+    int nloc = N / threads_per_dim;
+
+    int i0_min = ti0 * nloc;
+    int i1_min = ti1 * nloc;
+    int i2_min = ti2 * nloc;
+
+    for (int i0 = i0_min; i0 < i0_min + nloc; i0++) {
+      double x0 = origin[0] + i0 * h + 0.5 * h;
+      for (int i1 = i1_min; i1 < i1_min + nloc; i1++) {
+        double x1 = origin[1] + i1 * h + 0.5 * h;
+        for (int i2 = i2_min; i2 < i2_min + nloc; i2++) {
+          double x2 = origin[2] + i2 * h + 0.5 * h;
+          int m = (i0 + 1) * (N + 2) * (N + 2) + (i1 + 1) * (N + 2) + (i2 + 1);
+          u[m] = Initial_Condition(x0, x1, x2);
+          u_new[m] = u[m];
+          u_old[m] = u[m];
+          // assuming that u_old = u is equivalent to du/dt(t=0) = 0
+        }
+      }
+    }
+  }
+}
+
+WaveEquation::~WaveEquation() {
+  delete[] u;
+  delete[] u_old;
+  delete[] u_new;
+}
+
+void WaveEquation::FindCoordinates() {
+  int p = procs_per_dim;
+
+  cart_comm = MPI_COMM_WORLD;
+  MPI_Comm_rank(cart_comm, &rank);
+
+  coords[0] = rank / (p * p);
+
+  coords[1] = (rank - coords[0] * (p * p)) / p;
+
+  coords[2] = (rank - coords[0] * (p * p) - coords[1] * p) % p;
+
+  int coor_0_plus = (coords[0] + 1 + p) % p;
+  int coor_1_plus = (coords[1] + 1 + p) % p;
+  int coor_2_plus = (coords[2] + 1 + p) % p;
+
+  int coor_0_minus = (coords[0] - 1 + p) % p;
+  int coor_1_minus = (coords[1] - 1 + p) % p;
+  int coor_2_minus = (coords[2] - 1 + p) % p;
+
+  rank_plus[0] = (p * p) * coor_0_plus + coords[1] * p + coords[2];
+  rank_plus[1] = coords[0] * p * p + p * coor_1_plus + coords[2];
+  rank_plus[2] = coords[0] * p * p + coords[1] * p + coor_2_plus;
+
+  rank_minus[0] = (p * p) * coor_0_minus + coords[1] * p + coords[2];
+  rank_minus[1] = coords[0] * p * p + p * coor_1_minus + coords[2];
+  rank_minus[2] = coords[0] * p * p + coords[1] * p + coor_2_minus;
+}
+
+void WaveEquation::pack_face(double *pack, int array_of_sizes[3],
+                             int array_of_subsizes[3], int array_of_starts[3]) {
+  int p0 = array_of_subsizes[0];
+  int p1 = array_of_subsizes[1];
+  int p2 = array_of_subsizes[2];
+
+  int n1 = array_of_sizes[1];
+  int n2 = array_of_sizes[2];
+
+  for (int i0 = array_of_starts[0]; i0 < array_of_starts[0] + p0; i0++)
+    for (int i1 = array_of_starts[1]; i1 < array_of_starts[1] + p1; i1++)
+      for (int i2 = array_of_starts[2]; i2 < array_of_starts[2] + p2; i2++) {
+        int i = (i0 - array_of_starts[0]) * p1 * p2 +
+                (i1 - array_of_starts[1]) * p2 + (i2 - array_of_starts[2]);
+
+        pack[i] = *(u + i0 * n1 * n2 + i1 * n2 + i2);
+      }
+}
+
+void WaveEquation::unpack_face(double *pack, int array_of_sizes[3],
+                               int array_of_subsizes[3],
+                               int array_of_starts[3]) {
+  int p0 = array_of_subsizes[0];
+  int p1 = array_of_subsizes[1];
+  int p2 = array_of_subsizes[2];
+
+  int n1 = array_of_sizes[1];
+  int n2 = array_of_sizes[2];
+
+  for (int i0 = array_of_starts[0]; i0 < array_of_starts[0] + p0; i0++)
+    for (int i1 = array_of_starts[1]; i1 < array_of_starts[1] + p1; i1++)
+      for (int i2 = array_of_starts[2]; i2 < array_of_starts[2] + p2; i2++) {
+        int i = (i0 - array_of_starts[0]) * p1 * p2 +
+                (i1 - array_of_starts[1]) * p2 + (i2 - array_of_starts[2]);
+
+        *(u + i0 * n1 * n2 + i1 * n2 + i2) = pack[i];
+      }
+}
+
+void WaveEquation::thread_coordinates(int tid, int threads_per_dim, int &ti0,
+                                      int &ti1, int &ti2) {
+  ti0 = tid / (threads_per_dim * threads_per_dim);
+  ti1 = (tid - ti0 * threads_per_dim * threads_per_dim) / threads_per_dim;
+  ti2 = tid - ti0 * threads_per_dim * threads_per_dim - ti1 * threads_per_dim;
+  assert(tid ==
+         ti0 * threads_per_dim * threads_per_dim + ti1 * threads_per_dim + ti2);
+}
+
+double WaveEquation::Initial_Condition(double x0, double x1, double x2) {
+  double r = (x0 - 0.5) * (x0 - 0.5) + (x1 - 0.5) * (x1 - 0.5) +
+             (x2 - 0.5) * (x2 - 0.5);
+  return exp(-r / 0.1);
+}
+
+// do not change this function
+void WaveEquation::Print(int kt = 0) {
+#ifdef USE_HDF5
+
+  std::string name = "Wave__" + std::to_string(kt);
+  if (rank == 0) {
+    FILE *xmf = 0;
+    xmf = fopen((name + ".xmf").c_str(), "w");
+
+    std::stringstream s_head;
+
+    s_head << "<?xml version=\"1.0\" ?>\n";
+    s_head << "<!DOCTYPE Xdmf SYSTEM \"Xdmf.dtd\" []>\n";
+    s_head << "<Xdmf Version=\"2.0\">\n";
+    s_head << " <Domain>\n";
+
+    s_head << "     <Time Value=\"" << std::setprecision(10) << std::setw(10)
+           << t << "\"/>\n\n";
+
+    fprintf(xmf, (s_head.str()).c_str());
+
+    std::stringstream s;
+    s << "   <Grid GridType=\"Uniform\">\n";
+    s << "     <Topology TopologyType=\"3DCoRectMesh\" Dimensions=\" "
+      << Ntot + 1 << " " << Ntot + 1 << " " << Ntot + 1 << "\"/>\n\n";
+    s << "       <Geometry GeometryType=\"ORIGIN_DXDYDZ\">\n";
+    s << "          <DataItem Dimensions=\"3\" NumberType=\"Double\" "
+         "Precision=\"8\" Format=\"XML\">\n";
+    s << "                 " << 0 << " " << 0 << " " << 0 << "\n";
+    s << "          </DataItem>\n";
+    s << "          <DataItem Dimensions=\"3\" NumberType=\"Double\" "
+         "Precision=\"8\" Format=\"XML\">\n";
+    s << "                 " << std::setprecision(10) << std::setw(15) << h
+      << " " << std::setw(15) << h << " " << std::setw(15) << h << "\n";
+    s << "          </DataItem>\n";
+    s << "     </Geometry>\n\n";
+
+    s << "     <Attribute Name=\"data\" AttributeType=\" "
+      << "Scalar"
+      << "\" Center=\"Cell\">\n";
+    s << "       <DataItem Dimensions=\" " << Ntot << " " << Ntot << " " << Ntot
+      << " " << std::setw(10) << 1 << "\" NumberType=\"Float\" Precision=\" "
+      << sizeof(double) << "\" Format=\"HDF\">\n";
+    std::stringstream name_ss;
+    name_ss << "data"; // << std::setfill('0') << std::setw(10) << mm ;
+    std::string tmp = name_ss.str();
+    s << "        " << (name + ".h5").c_str() << ":/" << tmp << "\n";
+    s << "       </DataItem>\n";
+    s << "     </Attribute>\n";
+
+    s << "   </Grid>\n";
+
+    std::string st = s.str();
+
+    fprintf(xmf, st.c_str());
+
+    std::stringstream s_tail;
+    s_tail << " </Domain>\n";
+    s_tail << "</Xdmf>\n";
+
+    fprintf(xmf, (s_tail.str()).c_str());
+    fclose(xmf);
+  }
+
+  hid_t file_id, dataset_id, fspace_id, fapl_id, mspace_id;
+
+  H5open();
+  fapl_id = H5Pcreate(H5P_FILE_ACCESS);
+
+  H5Pset_fapl_mpio(fapl_id, cart_comm, MPI_INFO_NULL);
+
+  file_id =
+      H5Fcreate((name + ".h5").c_str(), H5F_ACC_TRUNC, H5P_DEFAULT, fapl_id);
+
+  H5Pclose(fapl_id);
+
+  double *array_all = new double[N * N * N];
+
+  hsize_t count[4] = {static_cast<unsigned int>(N),
+                      static_cast<unsigned int>(N),
+                      static_cast<unsigned int>(N), 1};
+  hsize_t dims[4] = {static_cast<unsigned int>(Ntot),
+                     static_cast<unsigned int>(Ntot),
+                     static_cast<unsigned int>(Ntot), 1};
+  hsize_t offset[4] = {static_cast<unsigned int>(coords[0] * N),
+                       static_cast<unsigned int>(coords[1] * N),
+                       static_cast<unsigned int>(coords[2] * N), 0};
+
+  for (int i0 = 1; i0 <= N; i0++) {
+    for (int i1 = 1; i1 <= N; i1++) {
+      for (int i2 = 1; i2 <= N; i2++) {
+        array_all[(i2 - 1) + (i1 - 1) * N + (i0 - 1) * N * N] =
+            u[i2 + i1 * (N + 2) + i0 * (N + 2) * (N + 2)];
+      }
+    }
+  }
+  fapl_id = H5Pcreate(H5P_DATASET_XFER);
+  H5Pset_dxpl_mpio(fapl_id, H5FD_MPIO_COLLECTIVE);
+  fspace_id = H5Screate_simple(4, dims, NULL);
+
+  dataset_id = H5Dcreate(file_id, "data", H5T_NATIVE_DOUBLE, fspace_id,
+                         H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT);
+  fspace_id = H5Dget_space(dataset_id);
+
+  H5Sselect_hyperslab(fspace_id, H5S_SELECT_SET, offset, NULL, count, NULL);
+
+  mspace_id = H5Screate_simple(4, count, NULL);
+
+  H5Dwrite(dataset_id, H5T_NATIVE_DOUBLE, mspace_id, fspace_id, fapl_id,
+           array_all);
+
+  H5Sclose(mspace_id);
+  H5Sclose(fspace_id);
+  H5Dclose(dataset_id);
+  H5Pclose(fapl_id);
+  H5Fclose(file_id);
+  H5close();
+
+  delete[] array_all;
+#else
+
+  std::string name = "Wave__" + std::to_string(kt) + ".txt";
+  MPI_File file;
+  MPI_File_open(cart_comm, name.c_str(), MPI_MODE_RDWR | MPI_MODE_CREATE,
+                MPI_INFO_NULL, &file);
+
+  std::stringstream ss;
+
+  for (int i0 = 0; i0 < N; i0++) {
+    double x0 = origin[0] + i0 * h + 0.5 * h;
+    for (int i1 = 0; i1 < N; i1++) {
+      double x1 = origin[1] + i1 * h + 0.5 * h;
+      for (int i2 = 0; i2 < N; i2++) {
+        double x2 = origin[2] + i2 * h + 0.5 * h;
+        ss << x0 << " " << x1 << " " << x2 << " "
+           << u[(i2 + 1) + (i1 + 1) * (N + 2) + (i0 + 1) * (N + 2) * (N + 2)]
+           << "\n";
+      }
+    }
+  }
+
+  std::string asciiData = ss.str();
+
+  MPI_Offset my_length = asciiData.size() * sizeof(char);
+
+  MPI_Offset offset;
+  MPI_Exscan(&my_length, &offset, 1, MPI_OFFSET, MPI_SUM, cart_comm);
+
+  MPI_File_write_at_all(file, offset, asciiData.data(), asciiData.size(),
+                        MPI_CHAR, MPI_STATUS_IGNORE);
+  MPI_File_close(&file);
+
+#endif
+}
+
+// do not change this function
+void WaveEquation::UpdateGridPoint(int i0, int i1, int i2) {
+  int m = i0 * (N + 2) * (N + 2) + i1 * (N + 2) + i2;
+  int ip1 = (i0 + 1) * (N + 2) * (N + 2) + (i1) * (N + 2) + (i2);
+  int im1 = (i0 - 1) * (N + 2) * (N + 2) + (i1) * (N + 2) + (i2);
+  int jp1 = (i0) * (N + 2) * (N + 2) + (i1 + 1) * (N + 2) + (i2);
+  int jm1 = (i0) * (N + 2) * (N + 2) + (i1 - 1) * (N + 2) + (i2);
+  int kp1 = (i0) * (N + 2) * (N + 2) + (i1) * (N + 2) + (i2 + 1);
+  int km1 = (i0) * (N + 2) * (N + 2) + (i1) * (N + 2) + (i2 - 1);
+  u_new[m] =
+      2.0 * u[m] - u_old[m] +
+      aux * (u[ip1] + u[im1] + u[jp1] + u[jm1] + u[kp1] + u[km1] - 6.0 * u[m]);
+}
\ No newline at end of file

hw3/solution/main.cpp

+#include "wave.h"
+
+int main(int argc, char **argv) {
+  int provided;
+  MPI_Init_thread(&argc, &argv, MPI_THREAD_MULTIPLE, &provided);
+
+  int rank, size;
+  MPI_Comm_rank(MPI_COMM_WORLD, &rank);
+  MPI_Comm_size(MPI_COMM_WORLD, &size);
+
+  if (argc != 4) {
+    if (rank == 0) {
+      std::cout << " Incorrect number of inputs. Run as:\n";
+      std::cout << " mpirun -n x ./main N y t \n";
+      std::cout << " where \n";
+      std::cout << " N= number of grid points per direction\n";
+      std::cout << " y= number of ranks per direction (=(x)^(1/3))\n";
+      std::cout << " t= final time of simulation \n";
+      std::cout << " Aborting...\n";
+    }
+    int err = 1;
+    MPI_Abort(MPI_COMM_WORLD, err);
+  }
+
+  int points = std::stoi(argv[1]);
+  int procs_per_dim = std::stoi(argv[2]);
+  double t_end = std::stof(argv[3]);
+
+  if (size != procs_per_dim * procs_per_dim * procs_per_dim) {
+    if (rank == 0)
+      std::cout << " Incorrect number of ranks per direction. Aborting... \n";
+    int err = 2;
+    MPI_Abort(MPI_COMM_WORLD, err);
+  }
+
+  if (points % procs_per_dim != 0) {
+    if (rank == 0)
+      std::cout << " Grid points per direction must be divisible by the number "
+                   "of ranks per direction. Aborting... \n";
+    int err = 3;
+    MPI_Abort(MPI_COMM_WORLD, err);
+  }
+
+  int nthreads = omp_get_max_threads();
+  int threads_per_dim = pow(nthreads, 1.0 / 3.0) + 0.5;
+  if (nthreads != threads_per_dim * threads_per_dim * threads_per_dim) {
+    if (rank == 0)
+      std::cout
+          << " Number of OPENMP threads must be a cubic number. Aborting... \n";
+    int err = 4;
+    MPI_Abort(MPI_COMM_WORLD, err);
+  }
+
+  WaveEquation Simulation(points, procs_per_dim);
+
+  Simulation.run(t_end);
+
+  MPI_Finalize();
+  return 0;
+}

hw3/solution/wave.cpp

+#include "wave.h"
+
+/*
+Solution notes
+
+Each thread is associated with a set of thread coordinates (t0,t1,t2) and the number of threads
+per direction is p (so the total number of threads is p^3).
+
+A thread lies at the boundary of a process if ti=0 and/or if ti=p-1, for i=0,1,2.
+
+Threads at the boundary are associated with a unique send/pack id and a unique receive/unpack id.
+Those ids are used to properly pack/unpack data and to match message tags when sending/receiving.
+
+
+
+Each MPI process is assigned a cubic part of the domain. Thus, there are 6 faces where data needs 
+to be exchanged. Each face has p^2 threads. This means that there are 6p^2 send/pack ids and 
+6p^2 unpack/receive ids.
+
+Logically, those ids correspond to a 3-dimensional array, with sizes [6][p][p]. They are stored in
+1-dimensional arrays, so that 
+[i][j][k] = i * p^2 + j * p + k 
+i=0,1,...,5
+j=0,1,...,p-1
+k=0,1,...,p-1  
+
+
+In the present solution, send ids correspond to receive ids as follows
+
+send_id[0][j][k] = receive_id[1][j][k]
+send_id[1][j][k] = receive_id[0][j][k]
+send_id[2][j][k] = receive_id[3][j][k]
+send_id[3][j][k] = receive_id[2][j][k]
+send_id[4][j][k] = receive_id[5][j][k]
+send_id[5][j][k] = receive_id[4][j][k]
+for all j,k=0,...,p-1
+
+*/
+
+
+
+void WaveEquation::pack_all() {
+  int array_of_sizes[3] = {N + 2, N + 2, N + 2};
+  int nloc = N / threads_per_dim;
+  int p = threads_per_dim;
+  int tid = omp_get_thread_num();
+  int t0, t1, t2;
+  thread_coordinates(tid, threads_per_dim, t0, t1, t2);
+
+  if (t0 == p - 1) {
+    int pid = 0 * p * p + t1 * p + t2;
+    int array_of_subsizes[3] = {1, nloc, nloc};
+    int array_of_starts[3] = {N, 1 + t1 * nloc, 1 + t2 * nloc};
+    pack_face(pack[pid], array_of_sizes, array_of_subsizes, array_of_starts);
+  }
+  if (t0 == 0) {
+    int pid = 1 * p * p + t1 * p + t2;
+    int array_of_subsizes[3] = {1, nloc, nloc};
+    int array_of_starts[3] = {1, 1 + t1 * nloc, 1 + t2 * nloc};
+    pack_face(pack[pid], array_of_sizes, array_of_subsizes, array_of_starts);
+  }
+
+  if (t1 == p - 1) {
+    int pid = 2 * p * p + t0 * p + t2;
+    int array_of_subsizes[3] = {nloc, 1, nloc};
+    int array_of_starts[3] = {1 + t0 * nloc, N, 1 + t2 * nloc};
+    pack_face(pack[pid], array_of_sizes, array_of_subsizes, array_of_starts);
+  }
+  if (t1 == 0) {
+    int pid = 3 * p * p + t0 * p + t2;
+    int array_of_subsizes[3] = {nloc, 1, nloc};
+    int array_of_starts[3] = {1 + t0 * nloc, 1, 1 + t2 * nloc};
+    pack_face(pack[pid], array_of_sizes, array_of_subsizes, array_of_starts);
+  }
+  if (t2 == p - 1) {
+    int pid = 4 * p * p + t0 * p + t1;
+    int array_of_subsizes[3] = {nloc, nloc, 1};
+    int array_of_starts[3] = {1 + t0 * nloc, 1 + t1 * nloc, N};
+    pack_face(pack[pid], array_of_sizes, array_of_subsizes, array_of_starts);
+  }
+  if (t2 == 0) {
+    int pid = 5 * p * p + t0 * p + t1;
+    int array_of_subsizes[3] = {nloc, nloc, 1};
+    int array_of_starts[3] = {1 + t0 * nloc, 1 + t1 * nloc, 1};
+    pack_face(pack[pid], array_of_sizes, array_of_subsizes, array_of_starts);
+  }
+}
+
+void WaveEquation::unpack_all() {
+  int array_of_sizes[3] = {N + 2, N + 2, N + 2};
+  int nloc = N / threads_per_dim;
+  int p = threads_per_dim;
+  int tid = omp_get_thread_num();
+  int t0, t1, t2;
+  thread_coordinates(tid, threads_per_dim, t0, t1, t2);
+
+  if (t0 == 0) {
+    int pid = 0 * p * p + t1 * p + t2;
+    int array_of_subsizes[3] = {1, nloc, nloc};
+    int array_of_starts[3] = {0, 1 + t1 * nloc, 1 + t2 * nloc};
+    unpack_face(unpack[pid], array_of_sizes, array_of_subsizes,array_of_starts);
+  }
+  if (t0 == p - 1) {
+    int pid = 1 * p * p + t1 * p + t2;
+    int array_of_subsizes[3] = {1, nloc, nloc};
+    int array_of_starts[3] = {N + 1, 1 + t1 * nloc, 1 + t2 * nloc};
+    unpack_face(unpack[pid], array_of_sizes, array_of_subsizes,array_of_starts);
+  }
+  if (t1 == 0) {
+    int pid = 2 * p * p + t0 * p + t2;
+    int array_of_subsizes[3] = {nloc, 1, nloc};
+    int array_of_starts[3] = {1 + t0 * nloc, 0, 1 + t2 * nloc};
+    unpack_face(unpack[pid], array_of_sizes, array_of_subsizes,array_of_starts);
+  }
+  if (t1 == p - 1) {
+    int pid = 3 * p * p + t0 * p + t2;
+    int array_of_subsizes[3] = {nloc, 1, nloc};
+    int array_of_starts[3] = {1 + t0 * nloc, N + 1, 1 + t2 * nloc};
+    unpack_face(unpack[pid], array_of_sizes, array_of_subsizes,array_of_starts);
+  }
+  if (t2 == 0) {
+    int pid = 4 * p * p + t0 * p + t1;
+    int array_of_subsizes[3] = {nloc, nloc, 1};
+    int array_of_starts[3] = {1 + t0 * nloc, 1 + t1 * nloc, 0};
+    unpack_face(unpack[pid], array_of_sizes, array_of_subsizes,array_of_starts);
+  }
+  if (t2 == p - 1) {
+    int pid = 5 * p * p + t0 * p + t1;
+    int array_of_subsizes[3] = {nloc, nloc, 1};
+    int array_of_starts[3] = {1 + t0 * nloc, 1 + t1 * nloc, N + 1};
+    unpack_face(unpack[pid], array_of_sizes, array_of_subsizes,array_of_starts);
+  }
+}
+
+void WaveEquation::run(double t_end) {
+  t = 0;
+
+  //as described above, we need 6p^2 packs and 6p^2 unpacks
+  int n = N * N / threads_per_dim / threads_per_dim;
+  for (int i = 0; i < 6 * threads_per_dim * threads_per_dim; i++) {
+    pack[i] = new double[n];
+    unpack[i] = new double[n];
+  }
+
+  double total_time = 0;
+
+  int count = 0;
+  MPI_Barrier(cart_comm);
+  double t0 = MPI_Wtime();
+
+
+//the only parallel region used startas here
+#pragma omp parallel
+  {
+
+    int nloc = N / threads_per_dim;
+    int p = threads_per_dim;
+    int tid = omp_get_thread_num();
+    int t0, t1, t2;
+    thread_coordinates(tid, threads_per_dim, t0, t1, t2);
+    int pid;
+
+    //each thread finds the loop ranges it need only once, before starting the time iterations
+    int i0_min = t0 * nloc;
+    int i1_min = t1 * nloc;
+    int i2_min = t2 * nloc;
+    int i0_max = i0_min + nloc;
+    int i1_max = i1_min + nloc;
+