how do you access the nonzero elements in SeqAIJ matrices

[Ahmed El Zein]

I am working on a project where I would like to copy a sparse matrix in
CSR format. 

I have tried MatGetRow() which works OK but I would really like to get
pointers to the 3 arrays directly.

I also tried MatGetRowIJ() which allows me to get the i and j arrays but
I can't see how to access the nonzero elements.

and finally I attempted to access the arrays directly like this:
Mat_SeqAIJ  *a = (Mat_SeqAIJ*)A->data;
MatScalar *val = a->a;
PetscInt  *ptr = a->i;
PetscInt  *ind = a->j;

However when accessing directly I get different values for ptr and
SIGSEGV when accessing val or ind.

also I get a bogus number for a->nz (134630032 instead of 21)

Can someone please explain when I am doing wrong?

Ahmed