Re: [CHANGESET]: First attempt at a single precision type.

[Jaroslav Hajek]

On Mon, Apr 28, 2008 at 9:57 AM, David Bateman
<address@hidden> wrote:
> David Bateman wrote:
>  >
>  >> | I've assumed that the correct mixed double/single behavior is to promote
>  >> | the single type to double,
>  >>
>  >> Yeah, you would think that would be the way it should work, but of
>  >> course Matlab converts to single.
>  >>
>  >
>  > You're kidding.... That is just incorrect in terms of ensuring a
>  > consistent precision. I assume the reason they did this is to allow
>  > something like
>  >
>  > single_arg + function_that_returns_double_for_single_arg(single_arg)
>  >
>  > to return single. This allows some functions not to be converted to
>  > handle singles and the majority of the calculation remaining in single
>  > precision. If this is the case there might be a difference between the
>  > treatment of operators and functions. For example, what about a mix of
>  > single/double arguments to a function like  filter or betainc for
>  > example, does it promote or demote the returned argument?
>  >
>
>  I thought about this further and it seems that matlab's behavior for
>  mixed operators is
>
>  double OP int -> int
>  single OP int   -> error
>  double OP single -> single
>
>  We can easily get this behavior but removing the numeric conversion
>  methods from the single classes and putting them in the double classes.
>  However I see no reason why "single OP int" should be an error, but if
>  the numeric conversion methods are removed from the single classes then
>  to ensure that it isn't an error we'd have to implement all of the mixed
>  single/int operators.. So perhaps complete matlab compatibility is teh
>  way to go here  :-)
>
>  I also tried the mixed types to some functions, such as
>
>  >> a = filter (single(1),[1,1], 1:5)
>
>  a =
>
>      1     1     2     2     3
>
>  >> whos a
>   Name      Size            Bytes  Class     Attributes
>
>   a         1x5                20  single
>
>  and it appears that matlab prefers to demote the types if possible. So
>  the behavior I currently implemented will need to be up dated.
>

I suggest to think twice, however. You've implemented the most
"normal" or "obvious" behaviour, IMHO. That single+double = single in
Matlab was a surprise for me. Is there anyone who considers the Matlab
behaviour as normal? I mean, I think that almost all other languages
or math systems do it the other way around - promote single to double.
Perhaps even Matlab users are unsatisfied with this behaviour (I think
I've never used single in Matlab, but if I did, certainly I'd have
been disappointed).
Octave has a chance here to go the right way from the beginning, if
this is the case.


-- 
RNDr. Jaroslav Hajek
computing expert
Aeronautical Research and Test Institute (VZLU)
Prague, Czech Republic
url: www.highegg.matfyz.cz