2: static char help[] = "Saves 4by4 block matrix.\n\n";

 4:  #include petscmat.h

  8: int main(int argc,char **args)
  9: {
 10:   Mat            A;
 11:   PetscInt       i,j;
 13:   PetscMPIInt    size;
 14:   PetscViewer    fd;
 15:   PetscScalar    values[16],one = 1.0;
 16:   Vec            x;

 18:   PetscInitialize(&argc,&args,(char *)0,help);
 19:   MPI_Comm_size(PETSC_COMM_WORLD,&size);
 20:   if (size > 1) SETERRQ(1,"Can only run on one processor");

 22:   /* 
 23:      Open binary file.  Note that we use FILE_MODE_WRITE to indicate
 24:      writing to this file.
 25:   */
 26:   PetscViewerBinaryOpen(PETSC_COMM_WORLD,"4by4",FILE_MODE_WRITE,&fd);

 28:   MatCreateSeqBAIJ(PETSC_COMM_WORLD,4,12,12,0,0,&A);

 30:   for (i=0; i<16; i++) values[i] = i; for (i=0; i<4; i++) values[4*i+i] += 5;
 31:   i = 0; j = 0;
 32:   MatSetValuesBlocked(A,1,&i,1,&j,values,INSERT_VALUES);
 33:   for (i=0; i<16; i++) values[i] = i;
 34:   i = 0; j = 2;
 35:   MatSetValuesBlocked(A,1,&i,1,&j,values,INSERT_VALUES);
 36:   for (i=0; i<16; i++) values[i] = i;
 37:   i = 1; j = 0;
 38:   MatSetValuesBlocked(A,1,&i,1,&j,values,INSERT_VALUES);
 39:   for (i=0; i<16; i++) values[i] = i;for (i=0; i<4; i++) values[4*i+i] += 6;
 40:   i = 1; j = 1;
 41:   MatSetValuesBlocked(A,1,&i,1,&j,values,INSERT_VALUES);
 42:   for (i=0; i<16; i++) values[i] = i;
 43:   i = 2; j = 0;
 44:   MatSetValuesBlocked(A,1,&i,1,&j,values,INSERT_VALUES);
 45:   for (i=0; i<16; i++) values[i] = i;for (i=0; i<4; i++) values[4*i+i] += 7;
 46:   i = 2; j = 2;
 47:   MatSetValuesBlocked(A,1,&i,1,&j,values,INSERT_VALUES);

 49:   MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);
 50:   MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);
 51:   MatView(A,fd);
 52:   MatDestroy(A);

 54:   VecCreateSeq(PETSC_COMM_WORLD,12,&x);
 55:   VecSet(x,one);
 56:   VecView(x,fd);
 57:   VecDestroy(x);

 59:   PetscViewerDestroy(fd);
 60:   PetscFinalize();
 61:   return 0;
 62: }