const std::string &fileName,

const MPI_Comm &mpiComm)

{

// Get the rank and size in the original communicator

int world_rank, world_size;

MPI_Comm_rank(mpiComm, &world_rank);

MPI_Comm_size(mpiComm, &world_size);

if (world_rank == 0)

{

std::ofstream file(fileName);

file << "";

file.close();

}

dftfe::Int color =

data.size() > 0 ?

1 :

MPI_UNDEFINED; // Determine color based on non-zero/zero data size

// Split the communicator based on the color and use the

// original rank for ordering

MPI_Comm nontrivialcomm;

MPI_Comm_split(mpiComm, color, world_rank, &nontrivialcomm);

if (nontrivialcomm != MPI_COMM_NULL)

{

int rank, size;

MPI_Comm_size(nontrivialcomm, &size);

MPI_Comm_rank(nontrivialcomm, &rank);

// create char array

const dftfe::uInt localSize = data.size();

const dftfe::Int charsPerDataElement =

data[0]->getNumberCharsPerCompositeData();

// FIXME Playing a dangerous game ... the +1 is for the trailing NULL

// in the sprintf

std::vector<char> dataTxt(localSize * charsPerDataElement + 1);

// auto dataTxt = new char[localSize*charsPerDataElement];

for (auto i = decltype(localSize){0}; i < localSize; ++i)

data[i]->getCharArray(&dataTxt[i * charsPerDataElement]);

// create data type

MPI_Datatype newType;

data[0]->getMPIDataType(&newType);

// create local array for set view

std::vector<dftfe::uInt> sizes(static_cast<dftfe::uInt>(size)),

offset(static_cast<dftfe::uInt>(size), 0);

MPI_Allgather(&localSize,

1,

dftfe::dataTypes::mpi_type_id(&localSize),

sizes.data(),

1,

dftfe::dataTypes::mpi_type_id(sizes.data()),

nontrivialcomm);

const auto globalSize = (std::accumulate(

sizes.begin(), sizes.end(), static_cast<dftfe::uInt>(0)));

for (dftfe::Int i = 1; i < size; ++i)

{

offset[i] = offset[i - 1] + sizes[i - 1];

}

int globalsizes[1] = {static_cast<int>(globalSize)};

int localsizes[1] = {static_cast<int>(localSize)};

int starts[1] = {static_cast<int>(offset[rank])};

int order = MPI_ORDER_C;

MPI_Datatype localarray;

MPI_Type_create_subarray(

1, globalsizes, localsizes, starts, order, newType, &localarray);

MPI_Type_commit(&localarray);

// open file and write

/* open the file, and set the view */

MPI_File file;

MPI_File_open(nontrivialcomm,

fileName.c_str(),

MPI_MODE_CREATE | MPI_MODE_WRONLY,

MPI_INFO_NULL,

&file);

MPI_File_set_view(

file, 0, MPI_CHAR, localarray, "native", MPI_INFO_NULL);

MPI_Status status;

MPI_File_write_all(file, &(dataTxt[0]), localSize, newType, &status);

MPI_File_close(&file);

MPI_Type_free(&localarray);

MPI_Type_free(&newType);

// delete [] dataTxt;

//

MPI_Comm_free(&nontrivialcomm);

}

return;