Re: command \

[David Bateman]

Christophe Prud'homme wrote:

> Hi Dave
>
> thank you so much for the detailed info !!
>
> basically we have the same functionalities except that :
>
> o octave (2.1.72, 2.9.4) does not support symbolic calculation
> o octave-2.1.72 is not interfaced with umfpack
>
>

octave-forge has a symbolic package that links to ginac/cln/gmp for
symbolic calculation. However, it doesn't handle matrices and so the
question of how the \ operator works doesn't arise.

The octave-forge sparse solver that can be used with 2.1.72 only uses
SuperLU for the solver.

> [ Wednesday 8 March 2006 15:17 ]
> | Hi Christophe,
> |
> | Your description below is pretty much the goal of the octave, though I
> | think Matlab also special cases at least three other matrices you don't
> | include, these being
> |
> | 1) If A is symbolic, matlab uses maple for symbolic factorization
> | 2) If A is sparse and diagonal (or permuted diagonal), the result is
> | just a scaled version of the input
> | 3) If A is dense Hessenberg matrix, reduce to upper triangular and
> solve.
> |
> | I haven't gotten to implementing the dense upper/lower triangular and
> | cholesky solvers yet (this is on my todo list for octave 3.0), but once
> | that is done the only missing things from matlab relative to octave
> will
> | be the symbolic and Hessenberg factorization. That is at the moment
> | dense matrix are only treated by LU or QR factorization. The current
> | situation for sparse matrices in the octave CVS tree is the following
>
> does that apply to some extent also for octave 2.9.4 or only to CVS ?
>
octave 2.9.4 is missing the sparse QR solvers and so is slightly more
limited than the CVS. So 2.9.4 only handles square non-singular
matrices. Note that the octave CVS also updated the diagonal, and
triangular solvers to handle non-square cases which is why there is no
step 0)
"0) If the matrix is not square go to step 8)".


Regards
David



-- 
David Bateman                                address@hidden
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