static char help[] = "Reads a PETSc matrix and vector from a file; expands the matrix with the vector\n\n";

/*
  Include "petscmat.h" so that we can use matrices.
  automatically includes:
     petscsys.h       - base PETSc routines   petscvec.h    - vectors
     petscmat.h    - matrices
     petscis.h     - index sets            petscviewer.h - viewers
*/
#include <petscmat.h>

/*

   Adds a new column and row to the vector (the last) containing the vector
*/
PetscErrorCode PadMatrix(Mat A, Vec v, PetscScalar c, Mat *B)
{
  PetscInt           n, i, *cnt, *indices, nc;
  const PetscInt    *aj;
  const PetscScalar *vv, *aa;

  PetscFunctionBegin;
  PetscCall(MatGetSize(A, &n, NULL));
  PetscCall(VecGetArrayRead(v, &vv));
  PetscCall(PetscMalloc1(n, &indices));
  for (i = 0; i < n; i++) indices[i] = i;

  /* determine number of nonzeros per row in the new matrix */
  PetscCall(PetscMalloc1(n + 1, &cnt));
  for (i = 0; i < n; i++) {
    PetscCall(MatGetRow(A, i, &nc, NULL, NULL));
    cnt[i] = nc + (vv[i] != 0.0);
    PetscCall(MatRestoreRow(A, i, &nc, NULL, NULL));
  }
  cnt[n] = 1;
  for (i = 0; i < n; i++) cnt[n] += (vv[i] != 0.0);
  PetscCall(MatCreateSeqAIJ(PETSC_COMM_SELF, n + 1, n + 1, 0, cnt, B));
  PetscCall(MatSetOption(*B, MAT_IGNORE_ZERO_ENTRIES, PETSC_TRUE));

  /* copy over the matrix entries from the matrix and then the vector */
  for (i = 0; i < n; i++) {
    PetscCall(MatGetRow(A, i, &nc, &aj, &aa));
    PetscCall(MatSetValues(*B, 1, &i, nc, aj, aa, INSERT_VALUES));
    PetscCall(MatRestoreRow(A, i, &nc, &aj, &aa));
  }
  PetscCall(MatSetValues(*B, 1, &n, n, indices, vv, INSERT_VALUES));
  PetscCall(MatSetValues(*B, n, indices, 1, &n, vv, INSERT_VALUES));
  PetscCall(MatSetValues(*B, 1, &n, 1, &n, &c, INSERT_VALUES));

  PetscCall(MatAssemblyBegin(*B, MAT_FINAL_ASSEMBLY));
  PetscCall(MatAssemblyEnd(*B, MAT_FINAL_ASSEMBLY));
  PetscCall(VecRestoreArrayRead(v, &vv));
  PetscCall(PetscFree(cnt));
  PetscCall(PetscFree(indices));
  PetscFunctionReturn(PETSC_SUCCESS);
}

int main(int argc, char **args)
{
  Mat         A, B;
  PetscViewer fd;                       /* viewer */
  char        file[PETSC_MAX_PATH_LEN]; /* input file name */
  PetscBool   flg;
  Vec         v;

  PetscFunctionBeginUser;
  PetscCall(PetscInitialize(&argc, &args, NULL, help));
  /*
     Determine files from which we read the two linear systems
     (matrix and right-hand-side vector).
  */
  PetscCall(PetscOptionsGetString(NULL, NULL, "-f0", file, sizeof(file), &flg));
  PetscCheck(flg, PETSC_COMM_WORLD, PETSC_ERR_USER, "Must indicate binary file with the -f0 option");

  PetscCall(PetscViewerBinaryOpen(PETSC_COMM_WORLD, file, FILE_MODE_READ, &fd));

  PetscCall(MatCreate(PETSC_COMM_WORLD, &A));
  PetscCall(MatSetType(A, MATSEQAIJ));
  PetscCall(MatLoad(A, fd));
  PetscCall(VecCreate(PETSC_COMM_WORLD, &v));
  PetscCall(VecLoad(v, fd));
  PetscCall(MatView(A, PETSC_VIEWER_STDOUT_SELF));
  PetscCall(PadMatrix(A, v, 3.0, &B));
  PetscCall(MatView(B, PETSC_VIEWER_STDOUT_SELF));
  PetscCall(MatDestroy(&B));
  PetscCall(MatDestroy(&A));
  PetscCall(VecDestroy(&v));
  PetscCall(PetscViewerDestroy(&fd));

  PetscCall(PetscFinalize());
  return 0;
}

/*TEST

   test:
      args: -f0 ${wPETSC_DIR}/share/petsc/datafiles/matrices/ns-real-int32-float64
      requires: double !complex !defined(PETSC_USE_64BIT_INDICES)

TEST*/