[petsc-users] Read in sequential, solve in parallel

[Moinier, Pierre (UK)]

Dear Developers,
 
I have a Matrix and a Right Hand Side (RHS) in an ASCII format stored in
2 different files. I have written the code that reads the data and solve
the system in sequential. I would like to solve the same problem in
parallel. I read the FAQ section that says:
 
Never read or write in parallel an ASCII matrix file, instead for
reading: read in sequentially then save the matrix with the binary
viewer PetscBinaryViewerOpen() and load the matrix in parallel with
MatLoad().
 
So far, I did not manage to implement this. Could any one help me?
 
My matrix is in the Matrix Market format. I have put below my current
implementation.
 
Kind regards,
 
    -Pierre.
 
 
 
  PetscInitialize(&argc,&argv,(char *)0,help);
  ierr = MPI_Comm_size(PETSC_COMM_WORLD,&size);CHKERRQ(ierr);
  if (size != 1) SETERRQ(1,"This is a uniprocessor example only!");
 
  /* Read in matrix */
  ierr =
PetscOptionsGetString(PETSC_NULL,"-fin",filein,127,PETSC_NULL);CHKERRQ(i
err);
  ierr = PetscFOpen(PETSC_COMM_SELF,filein,"r",&file);CHKERRQ(ierr);
  
 
  /* find out size of sparse matrix .... */
  fgets(buf,PETSC_MAX_PATH_LEN-1,file);
  printf("%s",buf);
  fscanf(file,"%d %d %d\n",&M,&N,&nz);
 
  ierr = PetscPrintf(PETSC_COMM_SELF,"M: %d, N: %d, nz:
%d\n",M,N,nz);CHKERRQ(ierr);
 
  MatCreate(PETSC_COMM_WORLD,&A);
  MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,M,N);
  MatSetType(A,MATAIJ);
  MatSetUp(A);
 
  for (i=0; i<nz; i++){
    fscanf(file,"%d %d %le\n",&I,&J,(double*)&val);
    I = I-1; J = J-1;
    ierr = MatSetValues(A,1,&I,1,&J,&val,INSERT_VALUES);CHKERRQ(ierr);
  }
 
  ierr = MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
  ierr = MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
 
  if (file !=stdin) fclose(file);
  ierr = PetscPrintf(PETSC_COMM_SELF,"Reading matrix
completes.\n");CHKERRQ(ierr);


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