Date: 2022-08-02T03:13:36+00:00

Actual source code: ex6.c

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

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

      7:     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
      8:     share/petsc/matlab/PetscBinaryRead() and share/petsc/matlab/PetscBinaryWrite() to read (or write) the vector into MATLAB.

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

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

     23:   PetscInitialize(&argc,&args,(char*)0,help);
     24:   MPI_Comm_size(PETSC_COMM_WORLD,&size);

     27:   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:   PetscMalloc1(m,&array);
     35:   for (i=0; i<m; i++) array[i] = i*10.0;

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

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

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

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

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

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

     63:   /* Read data into vector */
     64:   PetscBinaryRead(fd,&sz,1,NULL,PETSC_INT);

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

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

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

     81: /*TEST

     83:      test:

     85: TEST*/