[Scilab-Dev] Input requested on a few behaviors for Scilab 6...

[Nicolas FEZANS]

Hi,

first on point 2)

A) [1 2 3] + 1 (as a scalar) makes mathematically no sense but can be
seen as some syntax sugar to avoid having users constantly writing
things like: "A+scalar*ones(size(A))"

B) [1 2 3] + [4 5] makes no sense and there is no clear way of
understanding what the user wanted to do and actually in most cases
this means that something went wrong earlier and that the matrices
being added do not have the dimension that the user thought that would
have at that stage. An error is certainly the right thing to do to
prevent the code from throwing an error much later and forcing the
user to search backwards.

C) [] + 1 = [] makes sense to me as an extension of rule A)

D) [2 1 -3] + [] is to my mind as wrong than B) and should not be allowed


then on point 3)

I agree with Serge: the sooner you get a feedback about an error the
better. This even brings me to ask why not throwing a real error
instead of falling back to %nan?
I think the first thing to consider is that the sign of the step
always need to match the sign of the difference end-start. If not that
is clearly an error. %inf and %nan are also errors when talking about
such ranges.

Bringing answer like %nan or [] is such cases usually only make the
program blow up some time later and that is not helpful. If someone
really wants to make something very special, then he should be forced
to specify it in his code, but the default behavior should (to my
mind) be as safe, straightforward, and self-explaining as possible.

I would however expect [1:0:1] to be [1] since this makes sense and
could easily happen when computing bounds like this:
"start:stepSize:start+NBsteps*stepSize" when NBsteps is set to 0 (I
agree that this is not very elegant but it is very readable for a
human being)

If we would decide that [1:0:1] = [1] is OK, that would open the
question of making a similar exception for %inf:0:%inf and for
-%inf:0:-%inf . My opinion is however that with %inf or -%inf that
would still be an error.


Regards
Nicolas

On Fri, Oct 2, 2015 at 12:36 AM, Samuel Gougeon <sgougeon at free.fr> wrote:
> Le 01/10/2015 18:37, François Granade a écrit :
>>
>> .../...
>>
>> 2. Make operations with the empty matrix more consistent
>> -----------
>>
>> In particular, change:
>>
>> 1 + []
>>
>> to return [] in 6.0, instead of 1 in 5.5.2; and same for 1 - []. This
>> would be more consistent with other operations ( 1*[], 1.^[] ...).
>>
>> More generally:
>>
>> A + []
>>
>> would return [] for A of any Scilab basic type; same for other binary
>> numerical operators.
>
> .
> Here is a debatable question: Are you considering this rule only whether A
> is scalar: 1 + [] == []
> or as well whether A is a vector or matrix: [2  1 -3] + [] == []
> ? This discussion started @ http://bugzilla.scilab.org/12661
> It looks to be a hard one.
>
>
>
> _______________________________________________
> dev mailing list
> dev at lists.scilab.org
> http://lists.scilab.org/mailman/listinfo/dev