Re: Importing a sparse matrix to Octave

[Chong Yidong]

"John W. Eaton" <address@hidden> writes:

> On 24-Jul-2009, Jaroslav Hajek wrote:
>
> | No, not yet. A futher requirement is that the row indices should be
> | sorted (for a certain column index).
>
> Is that necessary?  For example, loading
>
> # name: s
> # type: sparse matrix
> # nnz: 5
> # rows: 10
> # columns: 10
> 1 1 1
> 6 2 6
> 4 2 4
> 5 2 5
> 3 6 3
>
> appears to work.

No, Jaroslav's right.  If the indices are out of order, some kind of
corruption takes place that prevents some matrix operations.  With the
above file:

octave:1> load "foo.dat"
octave:2> [L,U] = splu(s)
error: SparseLU::SparseLU symbolic factorization failed
warning: Invalid matrix type

If I re-order the file as

# name: s
# type: sparse matrix
# nnz: 5
# rows: 10
# columns: 10
1 1 1
4 2 4
5 2 5
6 2 6
3 6 3

then the LU factorization proceeds without an error.