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Re: fix null assignment
From: |
Jaroslav Hajek |
Subject: |
Re: fix null assignment |
Date: |
Fri, 19 Sep 2008 09:07:53 +0200 |
On Fri, Sep 19, 2008 at 12:12 AM, John W. Eaton <address@hidden> wrote:
> On 18-Sep-2008, Jaroslav Hajek wrote:
>
> | Apparently, Matlab never changes lhs if the index set is empty, i.e.
> | it does not even reshape the matrix to row vector when you do A([]) =
> | [] for a matrix A. An updated changeset is attached. With this, only 2
> | tests are failing. These are caused by blkdiag relying on
> | Matlab-incompatible behaviour. The second changeset addresses this.
>
> Thanks, I applied both patches.
>
> Maybe the second change would not be needed if we only performed the
> empty-assignment-is-deletion operation for the specific literal "= []"
> syntax, and not for any 0x0 array assignment.
I see. So it was not a Matlab-incompatible behaviour after all. Maybe
we should revert the second patch once this works.
> As I recall, that's
> what Matlab does, but it might require some work to implement
> correctly in Octave. For example, should the special syntax be
> recognized directly in the parser, or should there be a special
> representation for [] so that it can be recognized in the interpreter?
>
It seems that there is a need to propagate the information (whether
this is a deletion statement) fairly deeply - thinking of things like
a(3).x.y(1:2,:) = []
that should work... this stuff is resolved by subsasgn, and creating
methods like subsnulasgn would probably mean a lot of duplication. It
seems better to make a special kind of object for the "genuine" empty
matrix that was not touched by expressions. I'm just not sure where to
put it.
> jwe
>
--
RNDr. Jaroslav Hajek
computing expert
Aeronautical Research and Test Institute (VZLU)
Prague, Czech Republic
url: www.highegg.matfyz.cz
- fix null assignment, Jaroslav Hajek, 2008/09/18
- fix null assignment, John W. Eaton, 2008/09/18
- Re: fix null assignment, Jaroslav Hajek, 2008/09/18
- Re: fix null assignment, Jaroslav Hajek, 2008/09/18
- Re: fix null assignment, John W. Eaton, 2008/09/18
- Re: fix null assignment,
Jaroslav Hajek <=
- Re: fix null assignment, John W. Eaton, 2008/09/19
- Re: fix null assignment, Jaroslav Hajek, 2008/09/19
- Re: fix null assignment, Jaroslav Hajek, 2008/09/19
- Re: fix null assignment, John W. Eaton, 2008/09/20
- Re: fix null assignment, John W. Eaton, 2008/09/20
- Re: fix null assignment, Jaroslav Hajek, 2008/09/22
- Re: fix null assignment, Jaroslav Hajek, 2008/09/22
- Re: fix null assignment, John W. Eaton, 2008/09/22
- Re: fix null assignment, Jaroslav Hajek, 2008/09/22
- Re: fix null assignment, John W. Eaton, 2008/09/22