Feasible or not...?
> Date: 04 Aug 2011 13:07:06 +0100
> From: "N.M. Maclaren" <nmm1@xxxxxxxxx>
> To: Dan Zuras Intervals <intervals08@xxxxxxxxxxxxxx>
> Cc: stds-1788@xxxxxxxxxxxxxxxxx
> Subject: Re: Determinism is hard & not the only thing on our plate...
>
> On Aug 4 2011, Dan Zuras Intervals wrote:
> >
> > Nick, I don't want to go tit for tat with you in an open
> > forum in the hope that one of us will change our mind.
> > That does nobody any good & pisses off our readers.
> >
> > Determinism is hard. You have to pay a price for it.
> > Things can be done to mediate the problem of parallelism
> > but it is true that performance is part of the cost.
> >
> > This does not mean we should not offer our users the means
> > to compute deterministically. We should. We should also
> > offer them other things.
>
> It is clear that we are still not communicating. I am asserting not
> just that it is hard and conflicts with performance, but that it is
> actually infeasible. Some of the infeasibilities that I am claiming
> are mathematical or are statements about what language standards say,
> and therefore subject to proof or disproof. In those cases, there
> are two possibilities:
>
> I am wrong, and therefore my statements can be disproved. In this
> case, I should be corrected, and then I should just shut up.
>
> I am right, and therefore you are proposing an infeasible project.
> In this case, following the path you propose will lead to 1788 failing,
> whether or not it is completed.
>
>
> Regards,
> Nick Maclaren.
In its full generality, including on-the-fly heterogeneous
parallelism, you are no doubt correct that it is infeasible.
But you must admit that there are contexts in which it IS
feasible. Whether or not Arnold would use it in that case.
All I propose is some statement of the form "It shall be
possible to deterministically evaluate an interval
expression" & not much more. How this is made to be
possible we can leave up to the implementers.
Together with statements like "It shall be possible to
parallelize the crap out of things" & "It shall be possible
to use (1) algebraic identities, (2) numeric tricks, & (3)
algorithmic improvements to tighten results" we have said
all we need to say to give the users the necessary
capabilities.
It doesn't mean we're done.
We still have to put reasonable limits on how loose a
parallel expression can get & when it is safe to change
what is written to something else.
But its a start.
Do you really think I am proposing a failing course of
action?
I don't.
But it is up to you (collectively) to decide that.
Yours,
Dan