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

[David Bateman]

Jaroslav Hajek wrote:
> 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.
>
>   

I implemented most of this over the weekend with a few nights last week
and didn't have access to matlab to test its behavior, and did what I
thought was the obvious thing to do.. I'd be happy to keep it the way it
is as then we also get "single OP int" operators defined for nothing.
The reasoning for the matlab way of doing it is that if the user chose a
single precision type for one variable in an expression its because they
think they don't need the precision, and the matlab behavior allows
single precision to be kept in an expression even if some of the
underlying code hasn't been converted to accept single precision
arguments... I see some sense with this behavior in terms of what the
user would want, as they have to explicitly call "single" on an argument
to get it to be single precision in the first place, though I completely
agree its the wrong thing to do in terms of precision...

Another things I did which promotes to double that matlab demote is
something like

a = zeros (1, 5, 'single');
a(1) = 1;

we need to be consistent there as well. I'm happy to go either way, but
looking through the matlab news groups, in fact it seems that most of
their users are happy with the current behavior. See

http://groups.google.com/group/comp.soft-sys.matlab/browse_thread/thread/ed16a8f1bda1893f/0b001535bc8c23de?lnk=gst&q=single+precision+promotion#0b001535bc8c23de

for example. And in fact the behavior of

A(idx) = object

is documented as "object" is always promoted to the type of A. Thus

a = zeros(1,5)
a(1) = single(1)

should have "a" as double and

a = zeros (1, 5, 'single');
a(1) = 1;

should have "a" as single, which is even less consistent with the
behavior I expected, as I would have though that "a" should either be
promoted to double or demoted to a "single" for consistency with the
other operations..

So what should we do? Do promotion of "single" to "double" for all mixed
operations as I currently implemented it? Change only the subsasgn
operator for consistency with matlab? Or go the whole way and duplicate
matlab's behavior? I suspect we'll probably have to duplicate matlab's
behavior in something as basic as this otherwise we'll end up with a lot
of odd differences between the behavior of a script run in Matlab or in
Octave.. John whats your opinion?

Regards
David

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David Bateman                                address@hidden
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