Re: Importing a sparse matrix to Octave

[John W. Eaton]

On 24-Jul-2009, Chong Yidong wrote:

| "John W. Eaton" <address@hidden> writes:
| 
| >   # name: s
| >   # type: sparse complex matrix
| >   # nnz: 70
| >   # rows: 10
| >   # columns: 10
| >   1 1 (0,1.145193428282681)
| >   2 1 (0,0.5663270399606521)
| >   3 1 (0,0.007270909230606313)
| >   4 1 (0,0.1480797228543177)
| >   5 1 (0,0.2478795113138578)
| >   ...
| >
| > The first column is the row index, the second is the column index, and
| > the third is the corresponding value (real,complex).  The number of
| > elements must match the value of NNZ.  To load this file into Octave,
| > use the load command.
| 
| Thanks.  However, this method doesn't seem to work properly:
| 
| # name: s
| # type: sparse complex matrix
| # nnz: 3
| # rows: 10
| # columns: 10
| 1 1 (0,1.14)
| 3 6 (0,0.56)
| 6 2 (0.1,0.0)
| 
| octave:1> load "foo.dat"
| octave:2> s
| s =
| 
| Compressed Column Sparse (rows = 10, cols = 10, nnz = 3)
| 
|   (1, 1) ->  0.00000 + 1.14000i
|   (3, 2) ->  0.00000 + 0.56000i
|   (6, 2) ->  0.10000 + 0.00000i
| 
| The second line seems to be assigned to the wrong entry.  Is this a bug?
| I'm using Octave 3.0.1, as distributed by Ubuntu.

Oops, there was one detail I wasn't aware of.  You must group the
elements by column.  So change your file to

  # name: s
  # type: sparse complex matrix
  # nnz: 3
  # rows: 10
  # columns: 10
  1 1 (0,1.14)
  6 2 (0.1,0.0)
  3 6 (0,0.56)

and I think it should work.

jwe