Re: About diagonal matrices

[Jaroslav Hajek]

On Sat, Feb 21, 2009 at 10:41 PM, John W. Eaton <address@hidden> wrote:
> 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
>

Well, this is the "mathematically wrong" behavior David defined.
Still, this is the most reasonable one.

-- 
RNDr. Jaroslav Hajek
computing expert
Aeronautical Research and Test Institute (VZLU)
Prague, Czech Republic
url: www.highegg.matfyz.cz