Re: diagonal matrices specializations

[John W. Eaton]

On  4-Dec-2008, Jaroslav Hajek wrote:

| OK, I've pushed the patches.
| 
| Rationale: as in the first mail.
| 
| Summary of changes:
| 
| Rectangular diagonal matrices are now special objects.
| 
| [...]
| 
| i.e. a 38x, resp. 100x speed-up (will increase with n).
| 
| TODO:
| 1. special printing/saving of diagonal & permutation matrices
| 2. make "balance" benefit from the changes
| 3. I'm sure there's a lot of stuff I forgot.
| 4. Sparse code is mostly untouched. When dealing with diagonal &
| permutation matrices as sparse, the performance hit is much smaller
| (not by an order, but a constant factor). As I don't work with sparse
| matrices much, I'd appreciate advice about what interactions would be
| beneficial to implement (e.g., diagonal-sparse multiplication etc).

I think this is a good change and the performance improvements are
impressive.  However, I see the following problem:

  octave:1> x = diag ([1,2,3,4]);
  octave:2> save foo.dat x
  octave:3> load foo.dat
  error: octave_base_value::load_ascii(): wrong type argument `diagonal matrix'
  error: load: trouble reading ascii file `foo.dat'
  error: load: reading file foo.dat

Until this is fixed, I can't make a new snapshot, because this
represents a regression from previous versions and will likely be
noticed immediately by more than a few people who try to use the new
snapshot...

jwe