pvfmm-static-build/examples/src/example2.cpp

#include <mpi.h>
#include <omp.h>
#include <iostream>

#include <pvfmm.hpp>
#include <utils.hpp>

//Input function
void fn_input(double* coord, int n, double* out){
  double a=-160;
  for(int i=0;i<n;i++){
    double* c=&coord[i*3];
    double r_2=(c[0]-0.5)*(c[0]-0.5)+(c[1]-0.5)*(c[1]-0.5)+(c[2]-0.5)*(c[2]-0.5);
    out[i]=(2*a*r_2+3)*2*a*exp(a*r_2);
  }
}

//Analytical solution (Expected output)
void fn_output(double* coord, int n, double* out){
  double a=-160;
  for(int i=0;i<n;i++){
    double* c=&coord[i*3];
    double r_2=(c[0]-0.5)*(c[0]-0.5)+(c[1]-0.5)*(c[1]-0.5)+(c[2]-0.5)*(c[2]-0.5);
    out[i]=-exp(a*r_2);
  }
}

void fmm_test(size_t N, int mult_order, int cheb_deg, double tol, MPI_Comm comm){

  // Set kernel.
  const pvfmm::Kernel<double>& kernel_fn=pvfmm::laplace_potn_d;

  // Construct tree.
  size_t max_pts=100;
  std::vector<double> trg_coord=point_distrib<double>(RandUnif,N,comm);
  pvfmm::ChebFMM_Tree* tree=ChebFMM_CreateTree(cheb_deg, kernel_fn.ker_dim[0], fn_input,
                                              trg_coord, comm, tol, max_pts, pvfmm::FreeSpace);

  // Load matrices.
  pvfmm::ChebFMM matrices;
  matrices.Initialize(mult_order, cheb_deg, comm, &kernel_fn);

  // FMM Setup
  tree->SetupFMM(&matrices);

  // Run FMM
  std::vector<double> trg_value;
  size_t n_trg=trg_coord.size()/COORD_DIM;
  pvfmm::ChebFMM_Evaluate(tree, trg_value, n_trg);

  // Re-run FMM
  tree->ClearFMMData();
  pvfmm::ChebFMM_Evaluate(tree, trg_value, n_trg);

  {// Check error
    std::vector<double> trg_value_(n_trg*kernel_fn.ker_dim[1]);
    fn_output(&trg_coord[0],n_trg,&trg_value_[0]);
    double max_err=0;
    double max_err_glb=0;
    for(size_t i=0;i<n_trg;i++){
      if(fabs(trg_value_[i]-trg_value[i])>max_err)
        max_err=fabs(trg_value_[i]-trg_value[i]);
    }
    MPI_Reduce(&max_err, &max_err_glb, 1, MPI_DOUBLE, MPI_MAX, 0, comm);

    int rank;
    MPI_Comm_rank(comm, &rank);
    if(!rank) std::cout<<"Maximum Error:"<<max_err_glb<<'\n';
  }

  // Free memory
  delete tree;
}

int main(int argc, char **argv){
  MPI_Init(&argc, &argv);
  MPI_Comm comm=MPI_COMM_WORLD;

  // Read command line options.
  commandline_option_start(argc, argv, "\
  This example demonstrates solving a volume potential problem,\n\
with Laplace kernel, using the PvFMM library.\n");
  commandline_option_start(argc, argv);
  omp_set_num_threads( atoi(commandline_option(argc, argv,  "-omp",     "1", false, "-omp  <int> = (1)    : Number of OpenMP threads."          )));
  size_t   N=(size_t)strtod(commandline_option(argc, argv,    "-N",     "1",  true, "-N    <int>          : Number of target points."           ),NULL);
  int      m=       strtoul(commandline_option(argc, argv,    "-m",    "10", false, "-m    <int> = (10)   : Multipole order (+ve even integer)."),NULL,10);
  int      q=       strtoul(commandline_option(argc, argv,    "-q",    "14", false, "-q    <int> = (14)   : Chebyshev order (+ve integer)."     ),NULL,10);
  double tol=        strtod(commandline_option(argc, argv,  "-tol",  "1e-5", false, "-tol <real> = (1e-5) : Tolerance for adaptive refinement." ),NULL);
  commandline_option_end(argc, argv);
  pvfmm::Profile::Enable(true);

  // Run FMM with above options.
  fmm_test(N, m,q, tol, comm);

  //Output Profiling results.
  pvfmm::Profile::print(&comm);

  // Shut down MPI
  MPI_Finalize();
  return 0;
}