Re: About diagonal matrices

[John W. Eaton]

On 20-Feb-2009, dbateman wrote:

| I consider that the fact speye(3)/0 returns a full matrix a bug unless the
| sparse_auto_mutate function is set. In fact this behavior is a hang over
| from when sparse_auto_mutate(1) was not only the default but only behavior
| and certain narrowing could be donee in the operators themselves rather than
| the narrowing function of the octave_value. I pushed a patch..
| 
| 
| 
| octave:4> a = eye(3)/0
| a =
| 
|    Inf     0     0
|      0   Inf     0
|      0     0   Inf
| 
| octave:5> a = speye(3)/0
| warning: division by zero
| a =
| 
| Compressed Column Sparse (rows = 3, cols = 3, nnz = 3 [33%])
| )
| 
|   (1, 1) -> Inf
|   (2, 2) -> Inf
|   (3, 3) -> Inf
| 
| octave:14> full(a)/0
| warning: division by zero
| ans =
| 
|    Inf   NaN   NaN
|    NaN   Inf   NaN
|    NaN   NaN   Inf
| 
| and would expect the NaN fill in even for diagonal matrices as John
| suggested and so the NaN values. The current Octave behavior is
| mathematically wrong and saying thats the answer the user expected is no
| excuse. We should bring back the NaN fill-in.

With the current sources, which I think includes your patch, I now see

  octave:2> speye (3)/0
  warning: division by zero
  ans =

  Compressed Column Sparse (rows = 3, cols = 3, nnz = 3 [33%])
  )

    (1, 1) -> Inf
    (2, 2) -> Inf
    (3, 3) -> Inf

  octave:3> speye (3)*Inf
  ans =

  Compressed Column Sparse (rows = 3, cols = 3, nnz = 3 [33%])
  )

    (1, 1) -> Inf
    (2, 2) -> Inf
    (3, 3) -> Inf

  octave:4> speye (3)*NaN
  ans =

  Compressed Column Sparse (rows = 3, cols = 3, nnz = 3 [33%])
  )

    (1, 1) -> NaN
    (2, 2) -> NaN
    (3, 3) -> NaN


Is that the behavior you want?

jwe