1: static char help[] = "Writes an array to a file, then reads an array from a file, then forms a vector.\n\n";

  3: /*
  4:     This uses the low level PetscBinaryWrite() and PetscBinaryRead() to access a binary file. It will not work in parallel!

  6:     We HIGHLY recommend using instead VecView() and VecLoad() to read and write Vectors in binary format (which also work in parallel). Then you can use
  7:     share/petsc/matlab/PetscBinaryRead() and share/petsc/matlab/PetscBinaryWrite() to read (or write) the vector into MATLAB.

  9:     Note this also works for matrices with MatView() and MatLoad().
 10: */
 11: #include <petscvec.h>

 13: int main(int argc, char **args)
 14: {
 15:   PetscMPIInt  size;
 16:   int          fd;
 17:   PetscInt     i, m = 10, sz;
 18:   PetscScalar *avec, *array;
 19:   Vec          vec;
 20:   PetscViewer  view_out, view_in;

 22:   PetscFunctionBeginUser;
 23:   PetscCall(PetscInitialize(&argc, &args, (char *)0, help));
 24:   PetscCallMPI(MPI_Comm_size(PETSC_COMM_WORLD, &size));
 25:   PetscCheck(size == 1, PETSC_COMM_WORLD, PETSC_ERR_WRONG_MPI_SIZE, "This is a uniprocessor example only!");

 27:   PetscCall(PetscOptionsGetInt(NULL, NULL, "-m", &m, NULL));

 29:   /* ---------------------------------------------------------------------- */
 30:   /*          PART 1: Write some data to a file in binary format            */
 31:   /* ---------------------------------------------------------------------- */

 33:   /* Allocate array and set values */
 34:   PetscCall(PetscMalloc1(m, &array));
 35:   for (i = 0; i < m; i++) array[i] = i * 10.0;

 37:   /* Open viewer for binary output */
 38:   PetscCall(PetscViewerBinaryOpen(PETSC_COMM_SELF, "input.dat", FILE_MODE_WRITE, &view_out));
 39:   PetscCall(PetscViewerBinaryGetDescriptor(view_out, &fd));

 41:   /* Write binary output */
 42:   PetscCall(PetscBinaryWrite(fd, &m, 1, PETSC_INT));
 43:   PetscCall(PetscBinaryWrite(fd, array, m, PETSC_SCALAR));

 45:   /* Destroy the output viewer and work array */
 46:   PetscCall(PetscViewerDestroy(&view_out));
 47:   PetscCall(PetscFree(array));

 49:   /* ---------------------------------------------------------------------- */
 50:   /*          PART 2: Read data from file and form a vector                 */
 51:   /* ---------------------------------------------------------------------- */

 53:   /* Open input binary viewer */
 54:   PetscCall(PetscViewerBinaryOpen(PETSC_COMM_SELF, "input.dat", FILE_MODE_READ, &view_in));
 55:   PetscCall(PetscViewerBinaryGetDescriptor(view_in, &fd));

 57:   /* Create vector and get pointer to data space */
 58:   PetscCall(VecCreate(PETSC_COMM_SELF, &vec));
 59:   PetscCall(VecSetSizes(vec, PETSC_DECIDE, m));
 60:   PetscCall(VecSetFromOptions(vec));
 61:   PetscCall(VecGetArray(vec, &avec));

 63:   /* Read data into vector */
 64:   PetscCall(PetscBinaryRead(fd, &sz, 1, NULL, PETSC_INT));
 65:   PetscCheck(sz > 0, PETSC_COMM_SELF, PETSC_ERR_FILE_UNEXPECTED, "Error: Must have array length > 0");

 67:   PetscCall(PetscPrintf(PETSC_COMM_SELF, "reading data in binary from input.dat, sz =%" PetscInt_FMT " ...\n", sz));
 68:   PetscCall(PetscBinaryRead(fd, avec, sz, NULL, PETSC_SCALAR));

 70:   /* View vector */
 71:   PetscCall(VecRestoreArray(vec, &avec));
 72:   PetscCall(VecView(vec, PETSC_VIEWER_STDOUT_SELF));

 74:   /* Free data structures */
 75:   PetscCall(VecDestroy(&vec));
 76:   PetscCall(PetscViewerDestroy(&view_in));
 77:   PetscCall(PetscFinalize());
 78:   return 0;
 79: }

 81: /*TEST

 83:      test:

 85: TEST*/