[Chanegset]: Re: cat does not convert sparse matrices?

[John W. Eaton]

On 13-Sep-2008, David Bateman wrote:

| dbateman wrote:
| > In fact I think I see two bugs here
| > 
| > 
| > Francesco Potorti`-2 wrote:
| >> In Octave 3.0.1, I cannot catenate a full double matrix with a sparse
| >> logical matrix.  Is this normal or a bug?
| >>
| >> octave> a=zeros(3,3,0);
| >> octave> b1=zeros(3,3);
| >> octave> b2=sparse(1,1,true,3,3);
| >> octave> whos a b1 b2
| >>
| >> *** local user variables:
| >>
| >>   Prot Name        Size                     Bytes  Class
| >>   ==== ====        ====                     =====  ===== 
| >>    rwd a           3x3x0                        0  double
| >>    rwd b1          3x3                         72  double
| >>    rwd b2          3x3                         21  logical
| >>
| >> Total is 10 elements using 93 bytes
| >>
| >> octave> size(cat(3,a,b1))
| >> ans =
| >>
| >>    3   3   1
| >>
| > 
| > Trailing singleton dimensions should be dropped, So I suspect there is a
| > function call missing in the cat function that should do this.
| > 
| 
| The attached patch addresses this, but
| 
| > 
| > 
| >> octave> size(cat(3,a,b2))
| >> error: invalid conversion of NDArray to Matrix
| >> error: range error for insert
| >> error: evaluating argument list element number 1
| >>
| > 
| > The sparse logical matrix should be promoted to a sparse matrix and the
| > concatenation allowed. Ok, I'll look at this wen I'm on a development
| > machine.
| 
| It seems I missed the point you made by this one.. Sparse logical 
| matrices are promoted to sparse double matrices before concatenation 
| with another double matrix. The issue above is that a 3x3x0 is an 
| NDArray and the Sparse matrix type only supports 2D arrays and so the 
| conversion of the 3x3x0 array to a sparse matrices prior to the 
| concatenation fails. It would be interesting to know what matlab does in 
| this case, as I suspect it fails as well. If it doesn't then I suppose 
| we need to special case for this.
| 
| In fact we used to special case for all empty matrices in data.cc 
| (do_cat) and just drop them from the concatenation. However, something 
| like "cat(1,[],single([]))" must return a single precision empty matrix 
| and so even empty matrices play their part in selecting the type of the 
| returned matrix. So care would have to be taken if we did allow this not 
| to cause other issues.

I applied this changeset.

Thanks,

jwe